1. Working with lasers Includes IEC 60825-1:2014 & EN 207:2017
Background information
Basics of safety calculations
Laser-lab tour.
Laser safety course at the Optical Sciences group, by ing. F.B. Segerink, safety coordinator O.S. group. Mail at
This presentation is available from the O.S. website,
Goals: provide background information, present basics of safety calculations and procedures on how to work in the lab.
Photo: camera pointed towards the sun, showing a diffractive pattern (four red images of the sun) caused by light reflected from the ccd chip (pixel spacing 1.6 micron) interfering with a second reflection in the camera lens.
Safety standards are copyright protected and not available for free. The IEC :2014 document contains 105 pages and sets you back ~€ 300. EN 207:2017 sells for ~€ 115,- (28 pages). Both documents refer to multiple other documents.
IEC deals with the safety of laser products. IEC stands for International Electrotechnical Commission. Part 1 (of 14) deals with the equipment classification and requirements. Maximum Permissible Exposure (MPE) values, the basis for selecting a laser goggle, are therefore given in annex A, instead of the “core” document, which deals with the Accessible Emission Limits (AEL).
Laser goggles are not dealt with here, but in EN 207 (laser eye protectors) and EN 208 (alignment lasers). EN stands for: European Norm.
What’s new in IEC :2014, highlights:
Introduction of class 1C.
Eye loupe condition is removed.
Lasers for illumination purposes (projectors, car lights with blue lasers directing to conversion phosfor) are moved to IEC photo biological safety of lamps and lamp systems. Also LEDs have been deleted from the scope of this document. In IEC , a Risk Group is assigned.
New labels.
Rules for pulsed lasers were changed. In most cases the MPE/AEL increases (ultra short pulses). For micro/nano-second pulse sources however the MPE/AEL decreases.
A time dependent αmax was introduced (IEC :2014, p40).
What’s new in EN 207:2017, highlights:
The scale number is preceded by the letters LB in order to distinct between the old and the new standards.
Correction factor for multiple pulses N-1/4 is introduced.
The laser beam diameter for testing is set to 1 mm.
Increase in power density of M-type lasers in the wavelength range nm by a factor of 3.
EN 207:2017 refers to IEC :2007. This is remarkable because this document is superseded by IEC :2014.
New (from 2016) at the University of Twente: phasing in an e-learning course from the company Sentix Stralingszorg, Noorderstraat 388a, 9611 AW Sappemeer. After full implementation all people working with lasers must have completed this instruction.
The instruction consists of a syllabus (31 pages) and a powerpoint presentation (33 slides), which reviews and enhances the content of the syllabus. After completion of these two documents, a test must be passed, to obtain the qualification “laserwerker”.
The e-leaning course aims at a broad audience. The first 15 pages of the syllabus contain background information on lasers and laser-light properties. Chapter 3 explains the laser classification system. Chapter 4 presents information about riscs related to eye and skin, mainly as function of wavelength. The remaining chapters explain the safety goggles markings, briefly mention the legislation and finishes with a general work-instruction on how to work safely with lasers.
The course does not deal with safety calculations. The underlying documents NEN-EN-IEC :2014 and NEN EN 207:2017 are mentioned but not made available, probably because these are not for free and copyrighted. Furthermore the readability of these documents is rather limited, probably due to the formal character. (NEN = Nederlandse Norm).
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2. Challenge: check your goggles
Challenge/homework for the audience: check the calculation of your goggle requirements.
This is the “experts” work.
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3. Laser vs extended source
<1.5 mrad
(0.086 °)
In the case of a well collimated beam, the retinal image is assumed to be a diffraction-limited spot of around 10 μm to 20 μm diameter.
Lasers are supposed to emit below 1.5 mrad (since the eye focusus down to 10 to 20 micron).
The increase in irradiance [W/m2] from the cornea to the retina is approximately the ratio of the pupil area to that of the retinal image. This increase arises because the light which has entered the pupil is focused to a "point" on the retina. The pupil is a variable aperture but the diameter may be as large as 7 mm when maximally dilated in the young eye. The retinal image corresponding to such a pupil may be between 10 μm and 20 μm in diameter. With intra-ocular scattering and corneal aberrations considered, the increase in irradiance between the cornea and the retina is of the order of 2*105.
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4. The sun is the brightest source
(AM-1)
Seen from an evolutionary point of view.
The sun is a kind of reference regarding the (upper) capabilities of the eye.
Solar irradiance spectrum above atmosphere and at sea level, AM-1 spectrum, perpendicular to the Earth’s surface (AM = Air Mass). Note that the extraterrestrial solar spectral irradiance = 1367 W/m2, corresponding to a black body spectrum for T = 5777 K.
From Wikipedia:
Sunlight in space at the top of Earth's atmosphere (see solar constant) is composed of about 50% infrared light, 40% visible light, and 10% ultraviolet light, for a total intensity of about 1400 W/m2 in vacuum.
At ground level sunlight is 44% visible light, 3% ultraviolet (with the sun at its zenith), and the remainder infrared. Thus, the atmosphere blocks about 77% of the Sun's UV, almost entirely in the shorter UV wavelengths, when the Sun is highest in the sky (zenith). Of the ultraviolet radiation that reaches the Earth's surface, more than 95% is the longer wavelengths of UVA, with the small remainder UVB. There is essentially no UVC. The fraction of UVB which remains in UV radiation after passing through the atmosphere is heavily dependent on cloud cover and atmospheric conditions. Thick clouds block UVB effectively; but in "partly cloudy" days, patches of blue sky showing between clouds are also sources of (scattered) UVA and UVB, which are produced by Rayleigh scattering in the same way as the visible blue light from those parts of the sky.
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5. Eye “reference” values:
Sunlight: 1000 W/m2 (= 1 mW/mm2)
Pupil range Ø: 3-7 mm (7-38 mm2)
Optical power received by the eye: 7-38 mW
Eye blink reflex: 0.25 sec. (only applicable in the visible area)
Divergence = 9.3 mrad (0.53 degrees) (For classifying the sun according to the laser classification scheme, see notes.)
These values are kind of a reference for the Maximum Permissable Exposure values.
NOTE: the sun emits under 0.53 degrees or 9.3 mrad. This angle is called the angular subtense α.
Lasers are supposed to emit below 1.5 mrad (the eye focusus down to 10 to 20 micron).
Classifying the sun.
IEC :2014 strongly suggests that the sun should be included for classification (p25, section 4.3.b, “radiation of multiple wavelengths”).
The sun is not a point source and therefore the exposure limit is (according to IEC :2014) increased by the spot size dependence C6, which is for an intermediate source α/αmin = 9.3/1.5 = 6.2.
This means that the sun is to be accessed as an extended multi wavelength source: 38 mW (open pupil, all wavelengths) / 6.2 = 6.1 mW. From 700 nm to 1050 nm a factor C4 (wavelength dependence of epithelium absorbtion) adds from 1 to 5 to the AEL, remaining at 5 from 1050 nm to 1400 nm, relaxing the AEL (Accessible Emission Limit) a bit, say below 5 mW, so remaining at the upper side of class 3R, fortunately just outside the requirements of class 3B, where interlock, key switch and proper labeling are required!
A more accurate result can be obtained from table A4, p65.
For sunlight, three wavelength ranges are relevant.
400 nm – 700 nm, MPE = 7*10-4*t0.75*C6 J.
700 nm – 1050 nm, MPE = 7*10-4*t0.75*C4*C6 J.
1050 nm – 1400 nm, MPE = 3.5*10-3*t0.75*C6*C7 J.
Based on the solar spectrum at sea level, the optical power received by the eye can be obtained.
400 nm – 700 nm, 14.8 mW, yielding in 0.25 s an energy of 3.7 mJ.
700 nm – 1050 nm, 9.3 mW, yielding 2.3 mJ.
1050 nm – 1400 nm, 2.4 mW, yielding 0.6 mJ.
C6 = 6.2 (see above),
C4 = *(λ-700) = nm, rising to 1050 nm. Assume an average value of C4 = 2.5.
C7 = *(λ-1150) = 1150 nm, rising to 1200 nm, rising further according the formula C7 = *(λ-1250) from 1200 nm to 1400 nm, rising rapidly yielding a value at 1300 nm of 108. Assume a worst case value of C7 = 1, because there is not much power in the wavelength range 1150 nm – 1400 nm, see above.
Now we can calculate the MPE’s, using the eye blink reflex of 0.25 s:
400 nm – 700 nm, MPE = 7*10-4* *6.2 = 1.5 mJ.
700 nm – 1050 nm, MPE = 7*10-4* *2.5*6.2 = 3.8 mJ.
1050 nm – 1400 nm, MPE = 3.5*10-3* *6.2*1 = 7.7 mJ
Adding the relative MPE ratio’s (in the three wavelength-bands calculated above) of sunlight radiation (mJ)/MPE (mJ), we obtain the attenuation needed for eye-safety:
3.7/1.5 (400 nm – 700 nm) + 2.3/3.8 (700 nm – 1050 nm) + 0.6/7.7 (1050 nm – 1400 nm) = = 3.2.
Note that table A4 does not account for wavelengths below 400 nm. From the solar spectrum at sea level, it shows that in the wavelength range 300 nm – 400 nm, 0.95 mW can be received by the eye (at the cornea). According to table 1, p25, this UV part is not additive on the eye with the nm part. Nevertheless adding the 0.95 mW to the 14.8 mW (to be on the safe side) gives mW, corresponding to 3.9 mJ in 0.25 seconds (instead of 3.7). Therefore the relative MPE ratio in the visible will rise marginally from 3.7/1.5 to 3.9/1.5, so from 2.5 to 2.6.
This completes the MPE calculation to a total number of 3.3.
As this number is less than 5 (and more than 1), the sun is to be rated Class 3R.
In this calculation, photochemical effects (in the UVA and UVB region) are not included.
As photochemical damage accumulates, be ware looking into the sun!
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6. The human eye (simplified)
A parallel beam (typically from a laser) can be focused with a very high power density. If an increase of 2*105 is assumed, 50 W/m2 (= 1.9 mW/open pupil) on the cornea becomes 107 W/m2 on the retina! (IEC :2014, p90).
Damage can be very local, anywhere on the retina and might not be noticed until you search for blind spots!
A transient increase of only 10°C can destroy retinal photoreceptor cells.
Note that this is a simplified image. It does however explain the danger of a parallel beam!
In case of a well-collimated beam, the hazard is virtually independent of the distance between the source of radiation and the eye, because the retinal image is assumed to be a diffraction-limited spot of around 10 μm to 20 μm diameter. In this case, assuming thermal equilibrium, the retinal zone of hazard is determined by the limiting angular subtense αmin, which generally corresponds to a retinal spot of approximately 25 μm in diameter.
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7. Luminosity function of the eye
Intensity
400 nm
700 nm
DEMO TIME: show laserpointers < 5 mW, blue 453 nm, red 637 nm and green 512 nm.
NOTE: green is far better visible and therefore to be preferred for demo purposes considering eye safety.
Green curve: rods, for low light levels.
Black curve: cones, for everyday light levels.
Photopic (daylight vision, black) and scotopic (night vision, green) luminosity functions. The photopic includes the CIE 1931 standard (solid), the Judd-Vos 1978 modified data (dashed), and the Sharpe, Stockman, Jagla & Jägle 2005 data (dotted).
Note that the UV-side of the spectrum in practice does not look black, but due to fluorescence more or less blue-ish.
Wavelength [nm]
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8. Wavelength (λ) and impact
UV-C
UV-B
UV-A
sea level
Data for this graph is taken from a table originating from IEC 62471: This document is not available for free, but the Indian government approved this document suitable for publication as an Indian standard without deviations, named IS 16108: This “Indian” document is available for the general public for free.
From Wikipedia: Actinism is the property of solar radiation that leads to the production of photochemical and photobiological effects.
German Standard :
UV-C: 100 nm – 280 nm, photon energy 4.43 – 12.4 eV
UV-B: 280 nm – 315 nm, photon energy 3.94 – 4.43 eV
UV-A: 315 nm – 380 nm, photon energy 3.10 – 3.94 eV
Note the logarithmic scale in the spectral efficacy.
Also note that there is concern about the “blue light hazard”, see the Wikipedia item below:
Blue-light hazard is defined as the potential for a photochemical-induced retinal injury resulting from electromagnetic radiation exposure at wavelengths primarily between 400 and 500 nm. This injury has not been shown to occur in humans, only inconclusively in some rodent, primate, and in vitro (“outside the body”) studies.
Note from the creator of this sheet: The IEC 62471: 2006 standard lists a blue light hazard curve, which I do not consider useful for this presentation.
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9. Wavelength (λ) and impact
Source: LaserVision, manual laser safety.
UV: mostly chemical damage (accumulates!), from there, more and more thermal damage. Above 1400 nm, too much attenuation to reach the retina.
Wavelength range (CIE) Pathological effect on eye and skin
180 nm–280 nm (UV-C) eye: photokeratitis (inflammation of the cornea, equivalent to sunburn)
skin: erythema (sunburn), accelerated skin ageing process and increased pigmentation
280 nm – 315 nm (UV-B) same as UV-C
315 nm – 400 nm (UV-A) eye: photochemical cataract (clouding of the eye lens)
skin: pigment darkening, photosensitive reactions and skin burn
400 nm – 780 nm (visible) eye: photochemical damage to the retina, retinal burn
skin: same as UV-A
780 nm – 1400 nm (IR-A) eye: cataract, retinal burn
skin: skin burn
1.4 μm – 3.0 μm (IR-B) eye: aquaous flare (protein in the aquaous humour), cataract, corneal burn
skin: same as IR-A
3.0 μm – 1 mm (IR-C) eye: corneal burn
skin: same as IR-A and IR-B
IEC :2014 deals with wavelengths from 180 nm to 1 mm.
CIE = Commission Internationale de l’Eclairage
International Commission on Illumination
Internationale Beleuchtungskommission
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10. Exposure duration and impact
Short pulse
5 μs - sub ns,
thermo-mechanical
CW,
thermal
<10 ps
non linear effects
photo: laser induced self focusing
Most of the light in the visible is absorbed by the pigmented epithelium, underneath the retina.
In long-pulse or CW lasers, the persistence of the thermal front gives rise to a progressively enlarging lesion.
In short-pulse lasers, the high power density gives rise to explosive rupture of cells and damage by physical displacement.
Photograph on the right shows laser induced self focusing. Photo from the Laser Plasma Group, Max-Planck-Institut für Quantenoptik. The damage mechanism for sub 100 fs pulsed lasers is believed to be a plasma channel created by a low-density plasma, see: Clarence P. Cain et. Al, Sub-50-fs laser retinal damage thresholds in primate eyes with group velocity dispersion, self-focusing and low-density plasmas, Graefe’s Arch Clin Exp Ophthalmol (2005) 243:101–112
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11. Laser Class IEC 60825-1:2014 (simplified)
Class 1: always safe
1C: laser only active when in contact with skin
1M: always safe without focusing
Class 2: safe, due to the blink reflex, < 1mW, nm M: safe, without focusing
Class 3R: low risk of injury, restricted beam viewing, < 5mW B: direct exposure = eye hazard, <0.5W
Class 4: ALL OTHER LASERS Reflection from a matted surface up to a few watts is allowed.
DEMO TIME: crank up the power of the RED laser ~1 mW...(potmeter below “mark” = treshold), ~5mW...(potmeter just above treshold), 277 mW (potmeter at max) and (optional) pop a balloon.
The classification scheme is based on the ability of lasers to produce eye-damage to exposed people.
Classifying and providing all relevant safety information is the responsibility of the manufacturer.
Class 1: this includes high power lasers with an enclosure.
Class 1M: the total power that can pass through the pupil of the eye is within class 1. The accommodation range of the eye is assumed to be variable from 100 mm to infinity. Class 1M ranges from nm to 4000 nm, where most optical materials transmit.
New: Class 1C laser product: any laser product which is designed explicitly for contact application to the skin or non-ocular tissue and that:
– during operation ocular hazard is prevented by engineering means, i.e. the accessible emission is stopped or reduced to below the AEL of Class 1 when the laser/applicator is removed from contact with the skin or non-ocular tissue,
– during operation and when in contact with skin or non-ocular tissue, irradiance or radiant exposure levels may exceed the skin MPE as necessary for the intended treatment procedure, and
– the laser product complies with applicable vertical standards. (Vertical standards apply to specific products or product groups.)
Class 2: Power <= 1 mW, CW, 400 – 700 nm. Intentional suppression of the blink reflex could lead to eye injury. Many laser pointers and measuring instruments are class 2.
Class 2M applies to lasers with a large beam diameter or large divergenge.
Class 3R: < 5 mW in the visible range (5 times class 2 and 5 times class 1 outside the visible range). Low risk of injury. Even if injury occurs, most people will fully recover their vision.
Note that a laserpointer of class 3R, accidentally pointed at an audience, is in fact a scanned beam, which reduces the risc somewhat. Suppose a 5 mW pointer sweeps at a speed of 1 m/s over a fully opened pupil (7 mm diameter). The MPE is given in table A3, p64: MPE = 7*10-4*t0.75. Filling in t = 7 ms: MPE = 7*10-4*(7*10-3)0.75 = 1.7*10-5 J. In 7 ms this corresponds to 1.7*10-5/7*10-3 = 2.4 mW! So a 2.4 mW pointer could be considered safe. To obtain a MPE of 5 mW, an exposure time can be calculated from 5*10-3*t = 7*10-4*t0.75, which gives t = 0.38 ms, which in turn is obtained at a speed of 7*10-3/0.38*10-3 = 18 m/s. So a 5 mW laserpointer is not intrinsically safe, exceeding the safe limit by a factor of 5/2.4 = 2.1 (assuming a sweep speed of 1 m/s).
Class 3B: <0.5 W CW in the range 315 nm – far infrared. Class-3B lasers must be equipped with a key switch and a safety interlock. Class 3B: Diffuse reflections are not harmful. When tightly focused, a balloon can be popped or a fire ignited. Class 4: Contains a very large group of lasers.
A class 4 laser up to a few watts, viewed from a matted surface is irritating but usually not harmful to the eye.
Quiz time:
“C” stands for “contact”, in some interpretations for “conditional”.
“M” stands for “magnifying”.
“R” stands for “reduced” or “relaxed”, with regard to the safety requirements.
“B” has a historical origin as Class 3A existed in the past (IEC :1993).
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12. Laser class Laser Safety, ANP, 2-11-2017. Source: Wikipedia.
The maximal allowed CW-powers for the laser classes 1, 2, 3R and 3B according to the (outdated) standard EN :2007. Note that these values hold only for static, point-like laser sources (i.e. collimated or weakly divergent laser beams).
This graph is to illustrate that the classification of lasers is slightly more complicated as mentioned in the “Classification” sheet.
Note that class 2 is limited to the visible range: 400 nm – 700 nm.
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13. Not always a laser….. Less Risk More Risk Warm White ExemptUV
Vis.
UV spot curing,
10 W/cm2
200 nm
800 nm
Less Risk
Warm White
Neutral White
Cool White
Blue
Royal Blue
Exempt
RG-1
RG-2
RG-3
Eye safety is generally associated with lasers. However it’s not all about lasers, when it comes to eye-safety. The LED torch in the photograph is rated class 2. In the 2014 version of IEC , a laser classification is no longer necessary, see below. Remote controls operate around 900 nm, probably class 2M.
From fall 2008, leds and LED lumieres are no longer covered by IEC 60825, because they are not coherent light sources.
Instead, the IEC standard "Photobiological safety of lamps and lamp systems“ is used with testing method ANSI/IESNA RP-27.
Also some extended laser sources are dealt with by this standard (see 4.4, p29, :2014), resulting in a laser classification as well as a Risk Group classification.
This standard specifies 4 risk groups:
risk group risk Definition
exempt None No photobiological hazard
RG-1 Low risk No photobiological hazard under normal behavioral limitation
RG-2 Moderate risk Does not pose a hazard due to aversion response to bright light or thermal discomfort
RG-3 High risk Hazardous even for momentary exposure
The safety of LED’s may slip our attention. The very powerful LED type CBT-140 (shown in this sheet) can be driven up to 28 A. Assuming 10% efficiency, from an electrical (input) power of ~100 W, 10 W optical output is expected, with a typical spectrum of a white light LED (peaking in the blue region) and a circular emitting area of only 14 mm2.
The datasheet however makes only one comment on the safety, on page 10: “Note 8: Caution must be taken not to stare at the light emitted from these LEDs. Under special circumstances, the high intensity could damage the eye.”
More Risk
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14. Not always a laser….. Laser Safety, ANP, 2-11-2017.
Many types of solar barbeques are available today.
Three thousand years ago the Chinese discovered how to make concave reflectors to turn sunlight into fire. Many centuries later, around the 5th century BC, the Greeks independently developed such solar devices. Both used them to kindle wood for cooking.
If you try this at home, you might consider safety.
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15. Warning symbols (new) Mainly symbol labels, tekst is optional.
The labels were changed to symbol labels to reduce the burden for manufacturers regarding multiple language labels for products. Text however is optional.
Some Class 1 lasers are exempt from labeling. If not: Each Class 1M laser product shall have affixed an explanatory label bearing the words:
LASER RADIATION
DO NOT EXPOSE USERS OF TELESCOPIC OPTICS
CLASS 1M LASER PRODUCT
Instead of the above labels on the product, at the discretion of the manufacturer, the same statements may be included in the information for the user.
class C explanatory label:
FOLLOW INSTRUCTIONS
CLASS 1C LASER PRODUCT
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16. Warning symbols (new) Mainly symbol labels, tekst is optional.
Class 2 explanatory label:
LASER RADIATION
DO NOT STARE INTO BEAM
CLASS 2 LASER PRODUCT
Class 2M explanatory label:
DO NOT STARE INTO BEAM OR EXPOSE USERS OF TELESCOPIC OPTICS
CLASS 2M LASER PRODUCT
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17. Warning symbols (new) Laser Safety, ANP, 2-11-2017.
For classifying the sun, see sheet 5 “eye reference values”.
Explanatory label Class 3R:
LASER RADIATION
AVOID DIRECT EYE EXPOSURE
CLASS 3R LASER PRODUCT
Explanatory label Class 3B:
WARNING – LASER RADIATION
AVOID EXPOSURE TO BEAM
CLASS 3B LASER PRODUCT
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18. More warning signal examples
Also instead of
can be used
Explanatory label: Class 4:
DANGER - LASER RADIATION
AVOID EYE OR SKIN EXPOSURE TO
DIRECT OR SCATTERED RADIATION
CLASS 4 LASER PRODUCT
Label for laser aperture
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19. On the safe side Laser Safety, ANP, 2-11-2017.
According to IEC :2014, p56, a panel permitting access to the source (window, in case of the sun) must be labelled:
CAUTION – Class 3R LASER RADIATION WHEN OPEN, AVOID DIRECT EYE EXPOSURE, if the accessible radiation does not exceed the AEL for Class 3R.
The warning might include: “VISIBLE AND INVISIBLE LASER RADIATION”.
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20. Maximum Permissible Exposure
Typically set at 10% of the dose creating damage with a probability of 50%, worst case conditions.
Basis for selecting laser goggles.
MPE values are to be used as guides, as there is no exact line between safe and dangerous.
The MPE curves give the quantitative answer to laser safety.
MPE is measured at the cornea of the human eye or at the skin, for a given wavelength and exposure time.
The MPE values should be used as guides in the control of exposures, for the safe design of a product and as basis for providing user information and should not be regarded as precisely defined dividing lines between safe and dangerous levels. In any case, exposure to laser radiation should be as low as possible.
Exposures from multiple wavelengths can be additive or not additive for both ocular and skin exposure, depending on the wavelength, IEC :2014, table 1, p25.
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21. MPE values IEC 60825-1:2014 Wave-length Exposure time
Note that there are more tables:
Table A2, MPE at the cornea for extended sources.
For convenience (no new or extra information):
Table A3, MPE expressed as power or energy through a 7 mm aperture (more simple calculation).
Table A4, MPE for extended sources, expressed as power or energy through a 7 mm aperture (more simple calculation).
Table A5, MPE of the skin to laser radiation.
Note 1: The MPE values are listed in the appendix of IEC :2014 because this document deals primarily with equipment classification and requirements.
Note 2: These tables are too detailed to discuss during the talk. They merely illustrate the complexity of the laser goggles calculation.
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22. Correction factors IEC 60825-1:2014
parameter
spectral region
C1: thermal hazard, 180 – 400 nm
T1: time breakpoint, the time T1 applies for small sources and is the critical exposure time below which the retinal thermal exposure limit (EL) is lower than the photochemical EL. In other words: t<=T1 = thermal hazard, t >T1 = photochemical hazard.
C2: photochemical hazard
T2: time breakpoint “eye movement vs immobilized eye”, which decreases retinal exposure. Note that T2 is small for small sources (10 s for α<=1.5 mrad) and gets bigger for larger sources (100 s for α>100 mrad).
C3: wavelength dependent photochemical induced damage to the retina
C4: wavelength dependence of pigment ephithelium absorbtion, between 700 – 1400 nm.
C5: multiple pulse reduction factor (based on thermal conductivity), for pulses < 0.25 sec.
C6: angular subtense factor for extended sources, only for thermal limits
C7: increased damping in the pre-retinal ocular media between 700 and 1400 nm (retina may be protected, anterior parts of the eye may not, so dual limit/skin MPE must be applied). C7 = 1 between 700 nm and 1150 nm.
α = angular subtense of the apparent source (figure 2, p43, IEC :2014)
γ = angle of acceptance (figure 2, p43, IEC :2014)
Small source: α <= 1.5 mrad
Extended source: 1.5 <= α < 100 mrad, above 100 mrad: large source. Note that αmax is time dependent, p40, IEC :2014.
T: exposure time of a train of pulses
t: time duration of a single laser pulse
Ti: times below which pulse groups are summed, table 2, p28 of IEC :2014.
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23. Eye protection terminology
Examples of EN 207 specifications
10600 D LB3 + IR LB4
1064 DI LB8 + R LB9
633 D LB4 + IR LB5
X S
EN 207 is the European norm for laser safety eyewear. It deals with absorbtion (OD) AND power density. The complete test schedule is given in EN 207:2017, table 3, p10.
The standard defines laser working modes (D, I, R, M) and scale numbers (LB1, LB2, …, LB10).
According to EN 207:2017, the safety glasses should be able to withstand a continuous wave laser for 5 seconds or at least 50 pulses (select the worst case) in case of a pulsed laser.
Non linear physical interaction processes of the light and the material of the goggle can result in a momentary increase of the spectral transmission when the goggle is irradiated with short, high energy pulses
(see photograph in sheet 10, “Exposure duration and impact”)
In the new example, the scale number is preceeded by the letters LB instead of L, in order to distinct between the old and the new standards.
: Wavelength range for which the eye-protector gives protection.
D,R: Test condition, see next slide “EN 207 laser working modes”.
LB8: Scale number. Attenuation = 10LB.
X: Manufacturer’s identification mark, for instance: CE10 ZZ for European certificate, 2010, granted by bureau “ZZ”.
S: Mechanical strength symbol.
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24. EN 207 laser working modes
EN 207 specifies four laser working modes: Working mode Letter Pulse length Continuous mode D > 0.25 s Pulsed mode I >1 μs s Giant pulsed mode R 1 ns - 1 μs Modelocked M < 1 ns
The pulse duration ranges are characteristic values of typical lasers.
Quiz:
D = Dauerstrichbetrieb
I = Impulsbetrieb
R = Riesenimpulsbetrieb
M = Modengekoppelt (“release all stored energy in the shortest possible time”)
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25. EN 207 scale numbers Range LB1-LB10, LBn means that OD > n; n=0: no protection.
Source: Wikipedia & EN 207:2017.
EN 207 uses simplified limits which either agree or are conservative compared with MPE.
The scale numbers range from LB1 to LB10, where the number is a lower limit for the optical density, i.e. LBn means that OD>n, or T < 10− n, where T is the transmittance.
The minimum scale number for a given laser depends on the working mode and the wavelength as shown in the slide.
From the scale it can be inferred that the power densities that correspond to n = 0 are considered safe without protective eyewear.
The safety glasses should be able to withstand a continuous wave laser for 5 seconds, or 50 pulses in case of a pulsed laser (select the worst case).
NOTE: the pulse repetition rate is NOT a parameter in this calculation!
For modulated lasers and finite size sources, the examples in this presentation refer to IEC :2014. EN 207:2017 however refers to the outdated version IEC :2007.
Notes:
goggles can be dimensioned to attenuate a laser in the visible area such that alignment is possible within eye safety margins.
There is commercial software available to calculate protection levels (I guess because of the relative complexity).
New in EN 207:2017: Increase in power density of M-type lasers in the wavelength range nm by a factor of 3.
Laser Safety, ANP,

26. Example 1, Q
A laser operates at 1064 nm and has a pulse duration of 10 ns, 103 J/m². You have goggles that are specified as DIR 1064 LB5
Do these goggles offer suitable protection for this particular laser?
Source: Wikipedia, updated to EN 207:2017.
Note that the pulse repetition rate is not mentioned here.
So this applies for ONE pulse.
Laser Safety, ANP,

27. Example 1, A 1064nm/10ns/ 103 J/m² DIR 1064 LB5 ?? The pulse duration
indicates that we should
look at the R specification,
with scale number n=5,
which gives an upper
limit of 5*102 J/m²,
which means that these
goggles do not offer
suitable protection for
this particular laser.
Source: Wikipedia, updated to EN 207:2017.
Let’s recalculate using IEC :2014. Using table A1, p62, the MPE is on the border of two wavelength categories. The lower category extends to 1050 nm, calculating the MPE from 2*10-3*C4 J/m2, with C4 = 5, yielding a MPE of 10-2 J/m2. The higher wavelength category (from 1050 nm to 1400 nm) calculates the MPE using 2*10-2*C7 J/m2. With C7 = 1, this results in MPE = 2*10-2 J/m2, so twice as high.
The required attenuation is (lower wavelength range) log(103 J/m2 / 10-2 J/m2) = 5.0, or (higher wavelength range) log(103 J/m2 / 2*10-2 J/m2) = 4.7, so the LB5 rated goggle is (just) within specs.
Laser Safety, ANP,

28. Example 2, Q
A laser operates at 780 nm, is continuous wave with a power density of P = 500 W/m².
Does a D 780 LB2 rated goggle offer suitable protection for this particular laser?
Source: Wikipedia, updated to EN 207:2017.
Laser Safety, ANP,

29. Example 2, A
780nm CW, P=500W/m2
D 780 LB2 ??
You need a D protection level of log(500)-1 = 1.69, rounded up to 2. In other words, the safety goggles should be at least D 780 LB2.
Source: Wikipedia, updated to EN 207:2017.
Following IEC :2014, table A3, p64, the MPE at CW 780 nm = 3.9*10-4C4C7 W, fully open pupil. C4 = ( ) = 1.45, C7 = 1, so the MPE at 780 nm = 3.9*10-4 *1.45 = 0.57 mW.
An area of 0.39 cm2 receives from an irradiance of 500 W/m2 a power of 500 * 0.39 *10-4 = 19.5 mW.
The attenuation needed = 19.5 / 0.57 = 34.5 times or, in OD’s: log(34.5) = 1.55.
Note that the same result can be obtained in a somewhat simpler way from table A1, p62. The MPE is given by 10*C4*C7 W/m2. Filling in C4 = 1.45 and C7 = 1, the MPE = 14.5 W/m2, yielding a required attenuation of 500/14.5 = 34.5 times or, in OD’s: log(34.5) = 1.55
Notes:
Although the MPE is specified as power or energy per unit surface, it is based on the power or energy that can pass through a fully open pupil (7 mm diameter,  cm2) for visible and near-infrared wavelengths. This is relevant for laser beams that have a cross-section smaller than 7 mm.
Laser goggles are tested with a beam diameter of 1 mm, d63 value, meaning 63% of the laser power/energy.
Laser Safety, ANP,

30. Case: lidar system FaunaPhotonics, 2016. Laser Safety, ANP, 2-11-2017.
Copyright FaunaPhotonics, 2016.
FaunaPhotonics, 2016.
Laser Safety, ANP,

31. Case: lidar system 808 nm diode laser
3 Watt CW (used with 3 kHz amplitude modulation giving 1.5 W output)
Aperture diameter 120 mm
Laser Safety, ANP,

32. Case: lidar system
Method 1: using the (latest) tables in IEC :2014: MPE = 10*C4*C7 W/m2, with C4 = ( ) = 1.6, and C7 = 1. So the MPE = 16 W/m2. So allowed = Telescope area * MPE = π*(0.06)2 *16 = 181 mW
Method 2: using the formulas in EN 207. According to EN 207, no protection is needed when log(P)-1=0, so P=10 W/m2, so for our telescope 10*π*(0.06)2 = 113 mW.
C4: wavelength dependence of pigment ephithelium absorbtion, between 700 – 1400 nm.
C7: increased damping in the pre-retinal ocular media between 700 and 1400 nm (retina may be protected, anterior parts of the eye may not, so dual limit eye/skin MPE must be applied). C7 = 1 between 700 nm and 1150 nm.
Method 1 uses table A1, p62 in IEC :2014.
In general, the formulas given in IEC :2014 are updated to the latest knowledge, take all available parameters into account and therefore will give the most accurate result.
The formulas in EN 207 take less parameters into account than IEC :2014, which generally results is a more restrictive use (higher protection level needed).
Note that the safety of the lidar-system can also be provided by placing the source outside human accessibility, for instance on a windmill axis.
Laser Safety, ANP,

33. Goggles, summary Consult the laser manufacturer
Consider the Visible Light Transmittance
Consider comfort
Keep the goggles in good shape, damaged goggles must be replaced (not repaired)
Selecting or dimensioning lasergoggles in compliance with EN 207 can be difficult.
From IEC :2014, 8.1f, p59, : Manufacturers of laser products shall provide: Where appropriate, information for the selection of eye protection. This shall include the required optical density and wavelength range as well as irradiance or radiation exposure levels that might be incident on the surface of the eye protection equipment, so that resistance levels can be determined.
Laser Safety, ANP,

34. Sheets from the ICFO institute, Barcelona, Spain.
Isolate the laser activity.
Lasers should only be used in well-defined “Designated Laser Areas” (DLAs), separated from the rest of the world by opaque barriers (such as partitions, curtains, or walls). Signs should indicate when the laser is active, to prevent an unknowing person from entering a hazardous area. A laser beam should never be allowed to leave the DLA, for example through a door or window. Interlocks or additional barriers may be necessary to prevent this.
Laser Safety, ANP,

35. Laser Safety, ANP, 2-11-2017. Terminate beams.
Any beam, whether a main beam or a reflection, should be terminated (directed into an opaque object capable of absorbing the beam’s power).
Note that, as in the illustration, it is possible for a beam to injure someone who is not close by. In fact, if the beams in use are roughly horizontal, it is more likely for a beam to reach eye height far from the table than close to it. This is a good argument for using a skirt around the table. It is also a good reason for paying attention to laser safety, not just on your optical table, but on the tables of others.
Laser Safety, ANP,

36. Laser Safety, ANP, 2-11-2017. Beam enclosures.
Beams should be confined to an optical table, for example by putting an opaque “skirt” around the border of the table, as in the lower picture. High power beams should be completely enclosed unless it is absolutely necessary to have access to them.
Laser Safety, ANP,

37. Laser Safety, ANP, 2-11-2017. Mounts.
All optical components should be rigidly fixed to the table.
Laser Safety, ANP,

38. Laser Safety, ANP, 2-11-2017. Shutters.
Every laser should have an easy-to-use shutter. This should be used to block the beam whenever any uncontrolled change is made, such as inserting or removing an optical element or flipping a flippable mirror. It is generally good practice to leave the shutter closed whenever the beam is not in use.
Laser Safety, ANP,

39. Laser Safety, ANP, 2-11-2017. Beam path design.
It is good practice to keep all beams in a horizontal plane close to the surface of the table. Upwardly directed beams are far more hazardous than horizontal ones, simply because the user’s head is normally above the table. Also, one should not put one’s head at beam height. When it is necessary to use an upwardly-directed beam, for example in a periscope, it is good practice to put a beam block above the periscope to prevent any stray upward beams from reaching the user.
Alignment aids.
Alignment with full power is usually not necessary, or necessary only in the final stages of alignment. Consider using an attenuator to reduce the power of the laser, or using a different laser to perform the alignment. In the case where a visible laser can be substituted for an invisible one, this is often both safer and faster.
Laser Safety, ANP,

40. Avoid beams at head height (and heads at beam height).
Computers should either by separated from the optical table by partitions, or placed so that they can be used while standing.
Laser Safety, ANP,

41. Laser Safety, ANP, 2-11-2017. Secondary beams.
Reflections from uncoated surfaces will sometimes carry 10% to 20% of the power of the beam. Anti-reflection coated surfaces typically reflect about 1% (per surface). Thus from a high power main beam, one can unintentionally split off dozens of dangerous, moderate-power beams. Block these.
Laser Safety, ANP,

42. Laser Safety, ANP, 2-11-2017. Hazard reduction.
Consider safety in designing experiments.
By the way, the picture above is an example of very bad practice: dangling wires near the beam, unenclosed high-power beam, exposure to electrical hazards within the open laser, and a defeated interlock (that’s what the wires are doing).
Laser Safety, ANP,

43. Laser Safety, ANP, 2-11-2017. Errant reflections.
Generally, putting anything into a high-power beam is potentially hazardous. Almost any surface, even a piece of paper, will have both a specular and a diffuse reflection. The specular component is stronger at grazing incidence and can be hazardous. Of course, watches, rings, and any other reflective objects should not be worn while working with beams.
Laser Safety, ANP,

44. Laser Safety, ANP, 2-11-2017. Laser protective eyewear.
Of course, eyewear does not work if you do not wear it!
Protective eyewear is the best defence against laser hazards, but it is the last line of defence, and it is not perfect. Engineering and administrative measures (enclosures, alignment aids, limited access, etc.) are the primary defence, and must not rely on protective eyewear. In short, your experiment should not be sending beams toward anyone’s eyes, and no one’s eyes should be unprotected. This double layer of protection is necessary to ensure against failures, either of the engineering/administrative controls, or of the eyewear.
Laser Safety, ANP,

45. Top 14 of laser related injuries Rockwell Laser Industries
Unanticipated eye exposure during alignment.
Misaligned optics and upwardly directed beams.
Available laser eye protection was not used.
Equipment malfunction.
Improper method of handling high voltage.
Intentional exposure of unprotected persons.
Operators unfamiliar with laser equipment.
No protection provided for associated hazards.
Improper restoration of equipment following servicing.
Incorrect eyewear selection and/or eyewear failure.
Accidental eye/skin exposure during normal use.
Inhalation of laser-generated fume or viewing of secondary radiation (UV, blue light).
Laser ignition of fires.
Photochemical eye or skin exposure.
Rockwell Laser Industries, 395 reported incidents between 1964 and 1998.
An extensive database is given at
Open beam alignment work, which incorporates the first three items in the list, is undoubtedly the most hazardous single laser activity.
Visible and near-infrared laser injuries account for more than 80% of all the reported incidents.
The main lesson from these statistics is to pay attention to alignment procedures. Visible lasers offer maximum temptation to remove eyewear, and we strongly recommend that LSOs ensure that effective beam visualization hardware is made available (e.g. cameras, scintillation screens) to reduce the temptation for eyewear removal during open-beam Class 3B or 4 visible laser work.
Laser Safety, ANP,

46. Laser accidents are: - High impact - Low probability
Injuries: An August 2004 article in the Archives of Ophthalmology states “It is estimated that fewer than 15 retinal injuries worldwide each year are caused by industrial and military lasers.
Photo from article: Assessment of Alleged Retinal Laser Injuries, Martin A. Mainster, PhD, MD; Bruce E. Stuck, MS; Jeremiah Brown, Jr, MD, MS, Arch Ophthalmol. 2004;122: The photograph shows a severe accidental laser injury from viewing into a laser range finder (deliberately, despite laser safety training).
The following notes are purely informative.
(opthalmology = “oogheelkunde”)
Lasers from:
Industrial and military lasers
Injuries: An August 2004 article in the Archives of Ophthalmology states “It is estimated that fewer than 15 retinal injuries worldwide each year are caused by industrial and military lasers.” The article gives footnoted references for the statement, which appears on page Similarly, a July 2012 paper in PLoS ONE states that “a review of military and civilian data sources in 1997 estimated that 220 confirmed laser eye injuries have occurred between 1964 and 1996; ”this is an average of 6.9 injuries per year.” A laser safety expert told LaserPointerSafety.com “I think this number has increased significantly since Iraq and Afghanistan,” apparently due to injuries suffered by military personnel in a war zone. It is not known how many were caused within a military’s own laser usage (accidents) and how many were caused by enemy forces (deliberate actions by hostile persons). Laser pointers and handheld lasers used by the general public
Deaths: None Injuries from momentary (accidental/unwanted) exposures: According to the U.S. Food and Drug Administration (FDA), as of April 2012 the FDA has never received a report of eye injury from momentary exposures to laser pointers of Class 2 and 3R power (e.g., below 5 milliwatts). Injuries from deliberately-caused exposures: Most proven or credible reports of laser eye injuries to the general public are self-inflicted -- often by youths who do not realize (or care about) the consequences. FDA has heard of injuries caused when a person intentionally stared into the beam for a prolonged period of time. Injuries from Class 4 consumer lasers: There have been no reported injuries from commercially manufactured Class 4 consumer lasers (over 500 milliwatts of visible light), as of April This includes the Wicked Lasers Spyder III Arctic “1 watt” laser which first came out in August 2010, as well as similar high-power Class 4 lasers sold by other companies such as DinoDirect.com. There have been two reports of injuries from homemade or hobbyist kit Class 4 lasers, the results are minor injury and more severe. Injury reports and claims: There are only a few reports per year in the media or medical journals where a member of the general public is actually injured, or claims to be injured, by another person misusing a pointer or handheld laser. For laser injury reports from LaserPointerSafety.com, see these links: aviation-related injury reports, non-aviation reports, other reports. For a sample of emergency room reports from the U.S. Consumer Product Safety Commission, see the U.S. CPSC laser page. Data from New Zealand’s national insurance system show that over the period 2000 to 2013, there was an average of 8.9 claims for laser eye or skin injuries each year. The average claim amount was NZD $93.63 (USD $61.42), which a representative said “would suggest the injuries were not significant.” The data includes all New Zealand laser injury claims, whether verified or not, from all sources including lasers used in industry and laboratories. Detailed statistics and analysis are in this article. Injury severity: If there is an injury, most often these are small spots in the periphery of vision. Often these heal or the brain “fills in” the spot so the person normally does not notice it. We are not aware of any near-total or total blindness in an eye caused by laser pointers or handheld lasers. (Of course, a future injury could occur in the central vision optic nerve and this would be likely to cause near-total or total blindness.) Other pointer and handheld laser concerns Low potential for eye injuries to pilots - Permanent retinal damage from lasers aimed at aircraft is not a major concern of laser and aviation experts. While a laser-caused eye injury is theoretically possible, experts consider this highly unlikely thanks to various factors including relatively low laser powers and the relative motions of the handheld laser, aircraft, pilot’s head and pilot’s eyes. Helicopter pilots flying “low and slow” would be at greatest risk from any possible eye injury.
Distraction/flashblinding of pilots - This is a significant concern for aviation. FAA incident reports have risen from 384 in 2006 to roughly 3,500 in 2011 and 2012.
Distraction/flashblinding of automobiles - This does not seem to be a significant problem. Motorist incidents are reported from time to time; one expert said he hears of “several media reports per year”. We have been unable to find any reports of deaths, injuries or property damage attributed to laser pointer misuse against motorists (compare to roughly 65,000,000 automobile accidents in the U.S., in the past 10 years). Some persons have said that perhaps there have been fatal accidents caused by aiming a laser at a car (thus there would be no report); however, the fact that we cannot find reports of less-than-fatal accidents causing injuries or property damage makes this unlikely.
Misuse at concerts and sporting events - Distraction or disruption of the event is the major concern. Eye damage is unlikely to occur due to various factors including the illuminated person moving and closing their eyes. There are perhaps 1-2 news accounts of “laser louts” each month. Anecdotally, these incidents seem to be more prevalent outside the U.S. and often are soccer (football) related.
Misuse and annoyance of the general public - This does not seem to be a problem, except in a few resort towns during the summer season where laser pointers are widely sold. (See these stories about Ocean City NJ and Ocean City MD) For example, Ocean City MD reported that sales of 30,000 laser pointers in the first half of 2010 led to “Star Wars” on the boardwalk. Some resort towns such as Myrtle Beach SC have restricted sales and/or possession of laser pointers due to annoyance, and concerns over more serious misuse such as injury potential and aircraft dazzling.
Laser light shows
Deaths: None Injuries: About 5 worldwide in over 30 years. Since laser shows began in the mid-1970s, an estimated 110,000,000 persons have been exposed to 11,000,000,000 pulses of continuous-wave laser light in their eyes. These 11 billion exposures resulted in about 5 proven or suspected injuries, worldwide, in 30+ years of laser shows. Distraction/flashblinding of pilots: None. Specifically, the International Laser Display Association is not aware of any incidents linked to FDA-reviewed (“varianced”) outdoor laser shows since about the year While it is possible that illegally produced shows have illuminated pilots, ILDA is not aware of any of these incidents either in the past decade. (From about 1994 to 2000, outdoor laser light shows were a concern because the effect on pilot vision was not well understood. ILDA worked with SAE G10T to help develop FAA’s current guidelines and regulations.) For more information on the safety of outdoor shows, see the ILDA page. Source for injury statistics:”Scanning Audiences at Laser Shows”, which gathered injury reports from a private study, from Internet searches, and from the Rockwell Laser Industries incident database. Note: The above statistics on laser light shows are for continuous-wave (CW) laser light, which is the only type that should be used for audience-scanning shows. There have been three incidents where pulsed lasers were erroneously used and a total of 50 injuries occurred. Because pulsed lasers should NEVER be used for audience-scanning, only CW lasers are considered for laser light show injury statistics.
Laser Safety, ANP,

47. Key to safety: multiple lines of defense.
(lasers are not devine)
Key to safety: multiple lines of defense.
Applies in general!
Laser Safety, ANP,

48. Thank you! Laser Safety, ANP, 2-11-2017.
Photo: demonstration of a home built laser projection system in the meeting room of the Optical Sciences group, CR 4.446, October 2014.
Note that a “hidden” case is presented in sheet 5, Eye “reference” values: “Classifying the sun”.
Laser Safety, ANP,

49. Extra sheets
Most safety calculations are to be found here, in view of the limited time allowed for the presentation.
Furthermore, some background sheets are put here.
Laser Safety, ANP,

50. Case: pulsed line laser
Lasers with
Line optics
Wind 0 – 60 m/s
Object
under
test
Photo by Elise Leusink, 2016, taken at the large wind tunnel located in the Westhorst, Engineering Fluid Dynamics group.
The area between the lasers and the test object is considered not accessible.
Laser Safety, ANP,

51. Case: pulsed line laser
Power: 1 W
λ = 450 nm
Pulse width = 10 μs μs
Optics: line generator, resulting in a line of length 1 m, width 5 mm, assuming uniform illumination.
Laser safety calculation blue semiconductor laser with line optics.
Power: 1 W
λ = 450 nm
pulsewidth = 10 μs – 100 μs
Repetition rate: 10 Hz or lower.
Optics: line generator, resulting in a line of length 1 m, width 5 mm (assuming uniform illumination)
Calculation, assuming that the generated laser-line is accessible from a linewidth of 1 m:
According to the EN 207 scale numbers, see Wikipedia we can select the proper formula to calculate the minimum protection level.
The laser is used in pulsed mode, range 315 – 1400 nm. So the minimum protection level is to be calculated from the formula log(E/5) + 3, E = energy density in J/m2.
In order to calculate E we start with the power density P [W/m2]. An open pupil is assumed 7 mm in diameter. From the laser with line optics it will receive an optical power of 7mm/1000mm*1000mW = 7 mW. Power density = 7 mW/surface pupil = 7 mW/0.39 cm2 = 18 mW/cm2 or 180 W/m2.
Energy density = power density * pulse duration. As the pulse duration can vary (~10 – 100 μs), we can calculate the pulse duration where no protection level is needed, meaning log(E/5) + 3 = 0, or E = J/m2. So J/m2 = 180 W/m2 * pulse duration, yielding a maximum pulse length of 0.005/180 = 28 μs.
Note, that at a repetition rate of 10 Hz, two pulses will be viewed, due to the eye blink reflex. Multiple pulses are accounted for by the pulse additivity factor C5, which is in this case 1 (IEC :2014, p28), so this does not change pulse length.
Note that looking directly into the laser in the beam forming area (between laser and line optics at 1 m output) is dangerous and must be prevented. Restricting this area is necessary. If that’s not possible, the minimum protection level is to be calculated from log(P)-1. This is the worst case and highly unlikely scenario where all optical power enters the eye and the pulse length is set to infinite (continuous mode, single fault condition). So 1 W/0.39 cm2 (open pupil) = 2.6 W/cm2 or 2.6*104 W/m2. Minimum protection needed = log(2.6*104) -1 = 3.4. Rounding upwards, L4 protection is needed at 450 nm to be always safe.
Let’s also do the calculations using the formulas of IEC :2014, table A1 p62.
MPE for timescales < 5 μs = 2*10-3 J/m2. At P = 180 W/m2, the MPE limit would be reached when P*t = MPE limit, so 180 * t = 2*10-3, yielding t = 11 μs. So below 5 μs no protection is needed.
Above 5 μs the MPE = 18*t0.75 J/m2. The time where we hit this limit can be calculated from the equation 18*t0.75 = 180*t, yielding t = 100 μs, so more relaxed than the 28 μs according to EN 207. Correcting for 2 pulses makes no difference, as the pulse additivity factor C5 in this case = 1 (see above).
In the worst case scenario, where all power hits the cornea, the eye blink reflex sets the time window to 0.25 s. The MPE = 18* J/m2 = 6.4 J/m2 = 6.4/0.25 = 25 W/m2. The full laser power density is 2.6*104 W/m2, so the OD needed is log(2.6*104/25) = 3.0, so fortunately not to be rounded up to 4, but 3 as calculated, also a bit more relaxed compared to the EN 207 calculation (O.D 3.4, see above).
Laser Safety, ANP,

52. Case: pulsed line laser
λ = 450 nm, pulsed, μs
From EN 207 we need to
calculate log(E/5)+3.
In order to calculate E we start with the power density P [W/m2].
An open pupil of 7 mm diam. receives 7 mW from the projected line (1 m width, 1 W).
Power density = 7 mW per surface pupil = 7 mW/0.39 cm2 = 18 mW/cm2 or 180 W/m2.
Note: The EN 207 calculations are simplified compared to In general, simplified calculations give more restrictive results.
Laser Safety, ANP,

53. Case: pulsed line laser
Power density = 180 W/m2
Energy density = power density * pulse duration.
As the pulse duration can vary (~ μs), we can calculate the pulse duration where no protection level is needed, meaning log(E/5)+3 = 0, or E = J/m2.
So = 180*pulse duration, yielding a maximum pulse length of 0.005/180 = 28 μs.
C5 = 1, so for 2 pulses (10 Hz): 28*C5 = 28 μs.
For longer pulses the level values must be rounded upwards, so in that case OD1 is required. (For IEC :2014 calculations, see notes.)
Note that the IEC :2014 document gives a more relaxed longer pulse limit of 100 μs (one pulse).
Laser Safety, ANP,

54. Case: pulsed line laser
Remarks:
Note that looking directly into the laser in the beam forming area (between laser and line optics at 1 m output) is dangerous and must be prevented. Restricting this area is necessary.
If that’s not possible, the minimum protection level is to be calculated from log(P)-1. This is the worst case and highly unlikely scenario where all optical power enters the eye and the pulse length is set to infinite (continuous mode).
So 1 W/0.39 cm2 (open pupil) = 2.6 W/cm2 or 2.6*104 W/m2. Minimum protection needed = log(2.6*104)-1 = 3.4. Rounding upwards, LB4 protection is needed at 450 nm to be always safe.
Note that the IEC :2014 document gives a more relaxed OD of 3.0, so not to be rounded up.
Laser Safety, ANP,

55. Case: PIV system 150 mJ/pulse, 8 ns/40 Hz/532 nm
The Particle Image Velocimetry system uses 2 YAG lasers to acquire 2 time correlated images.
Laser Safety, ANP,

56. Case 1: NO line optics mounted.
Case: PIV system
Peak power = 0.15 J/(8*10-9 s) = 18*106 W.
Energy density = 0.15 J/0.39 cm2 (open pupil) = 0.38 J/cm2 = 38*102 J/m2 
Case 1: NO line optics mounted.
From IEC :2014, MPE one pulse = 2*10-3 J/m2.
In 0.25 sec., 10 pulses are emitted, but C5 = 1.0,
so the MPE is not to be lowered.
OD needed = log(38*102 J/m2 /1.0*2*10-3 J/m2 ) = 6.3.
Safety calculation PIV system using a YAG-laser
Wavelength λ = 532 nm, Peak energy = 150 mJ, pulse duration = 8 ns, rep. rate ~40 Hz.
Peak power = 0.15 J/(8*10-9) = 18*106 W.
Energy density = 0.15 J/0.39 cm2 (open pupil) = 0.38 J/cm2 = 38*102 J/m2
Case 1: NO line optics mounted.
According to IEC :2014, the Maximum Permissible Exposure (MPE) for one pulse = 2*10-3 J/m2 (table A.1, p62). Correction factor for the number of pulses expected in one exposure (10 pulses) = C5 = 1 (p28), so the MPE remains 2*10-3 J/m2.
Attenuation needed = 38*102 J/m2 / 2.0*10-3 J/m2 = 19*105 times = OD 6.3.
Case 2: line optics mounted, 12 degrees, specular reflection at 3 m distance.
The beam diverts to a line of width 0.64 m (3* tan12°). An open pupil receives 7 mm of this beam, which is 7/640 of the total power, approximately 1 percent, lowering the required optical density with 2 OD’s, so OD 4.3 is calculated, which is officially to be rounded to 5.
Case 2, according to the formulas of EN 207, corrected for multiple pulses (10 pulses in 0.25 sec.) with a factor 1.0, see above.
The total energy density of 10 pulses ( 2 YAG lasers, estimated ~20 pulses sec. each) is 1.0 * 38*102 J/m2 = 38*102 J/m2. In case of line optics, 12°, this reduces to 7/640 * 38*102 J/m2= 42 J/m2.
Minimum protection level = log(E/5)+3 = log(42/5)+3 = = 3.9, to be rounded to 4.
Conclusion:
Wearing goggles during building the setup with full laser power is mandatory. OD 6 is the minimum attenuation needed when using (almost) full laser power.
Recommended alignment procedure:
For setting up the system, do NOT use full laser power, but just enough to see the light-sheet. This way, the goggles are not needed, so alignments are easy.
For measuring with full power, goggles are needed again, but because of the line-optics OD4 should suffice, provided that the light sheet is shielded from direct viewing.
General info/tips:
PIV supplier: LaVision.
Particle source: DEHS fluid, 0.5 – 5 μm particle-size, data DESH.pdf.
Check at the manufacturers data sheet if any pump power (at 1064 nm) is present in the output. This should not be the case
Laser Safety, ANP,

57. Case 2: line optics mounted
Case: PIV system
Case 2: line optics mounted
Line optics: 12°, reflective surface at 3 m, linewidth = 0.64 m. An open pupil receives 7 mm of this beam, so 7/640 of the total power, ~1%, lowering the required optical density with 2 OD’s, so OD 4.3.
Calculation using EN 207, corrected for 10 pulses C5 = 1.0: energy density E = 1.0*38*102*7/640 = 42 J/m2. Minimum protection level = log(E/5)+3 = = 3.9.
Conclusions: align with lowest laser power. Use OD4 at full power, provided that the light sheet is shielded from direct viewing.
In this case, a cilindrical lens determines the “width” of the light-sheet to 12°.
Laser Safety, ANP,

58. Case: pulsed diode laser
Peak power 70 W
λ peak = 905 nm
Duty cycle = 0.1 %
Application: Range finding, …
Type: SPL-LL90-3, price per 27 may 2015: € per piece, 2 pieces, RS-Components.
In combination with fast pulse electronics, sub 10 ns pulses can be obtained.
Laser Safety, ANP,

59. Case: pulsed diode laser, precautions
From the datasheet:
“Depending on the mode of operation, these devices emit highly concentrated non visible infrared light which can be hazardous to the human eye. Products which incorporate these devices have to follow the safety precautions given in IEC "Safety of laser products". “
So lets calculate ourselves what laser goggles we need
From EN :2014 p8: Laser products that are sold to other manufacturers for use as components of any system for subsequent sale are not subject to IEC , since the final product will itself be subject to this standard.
Laser Safety, ANP,

60. Case: pulsed diode laser, safety
Calculation according to EN 207 (for IEC : 2014, see notes)
Rep. rate = 30 kHz, Pulse duration = 30 ns
Peak power = 70 W, Wavelength = 905 nm
Energy of one pulse = 30*10-9 s * 70 W = 2.1*10-6 J
Assume all power enters the eye, the energy density = 2.1*10-6 / 0.39 cm2 = 5.4*10-6 J/cm2 = 5.4*10-2 J/m2 (= E).
A thermal correction factor C5 applies for N pulses.
C5 = 0.2, for timebase 100 sec, t > Ti, α > αmax, N > 625.
Minimum protection level = log(1/C5*E/5) +3 =
log(1/0.2*5.4*10-2 / 5)+3 = = 1.7, so OD 2 (rounded up).
Check with DC calculation (see notes)!
Exposure time is 100 sec., according to IEC : 2014, p27.
Safety calculation pulse laser SPL-LL90-3
Rep. rate = 30 kHz
Pulse duration = 30 ns
Peak power = 70 W
Wavelength = 905 nm
Pulsed laser calculation strategy: calculate both the average power AND the single pulse reduced by C5, as the most restrictive case is hard to predict.
Energy of one pulse = 30*10-9 s x 70 W = 2.1*10-6 J.
Assume all power enters the eye, the energy density E = 2.1*10-6/0.39 cm2 = 5.4*10-6 J/cm2 = 5.4*10-2 J/m2.
Thermal correction factor C5 in 100 sec. = 5*N-0.25 = 5*(30*103*100)-0.25 = (p28, t < Ti, N > 625), to be set to the minimum of 0.4.
Attenuation needed according to the formulas in EN 207= log(C5 * E/5) +3 = log(1/0.4*5.4*10-2 / 5)+3 = = 1.5.
Let’s also do the calculations using the formulas of IEC :2014, table A1 p62 (assuming collimating optics).
C4 is the wavelength dependence of pigment ephithelium absorbtion, between 700 – 1400 nm.
According to the tables in IEC :2014, the MPE is exceeded by (MPE of 1 pulse) * C5 /(2*10-3*C4) J/m2 = 5.4*10-2 J/m2 * 1/0.4 / (2*10-3 * ( ))J/m2 = 27. So the optical density needed is log(27) = 1.4, which also results in (rounded upwards) OD 2.
For DC calculation, average power = Peak power x duty cycle = 70 W x 30 ns x pulses/second = 63 mW. Assume all power enters the eye, power density = 0.063/0.39 cm2 = 0.16 W/cm2 = 1600 W/m2. Attenuation needed = log(P)-1 = log(1600)-1 = 3.2–1 = 2.2.
Again, let’s also do the calculations using the formulas of IEC :2014, table A1 p62.
C7 corrects for the wavelength dependence of the transmittance of the pre-retinal ocular media, defined for 700 nm to 1400 nm.
MPE = 10*C4*C7 W/m2, with C4 = ( ) = 2.6, and C7 = 1. So the MPE = 26 W/m2. Thus, the protection factor required (for DC calculation) is log(1600 W/m2/26 W/m2) = 1.8, so OD2 (rounded upwards) is required, more relaxed again as calculated above according to EN 207.
Conclusion: as all IEC calculations result in less than OD2, OD2 is required.
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61. Case: Fianium SC400-4 What goggles to buy ???? 400 2400
The white light Fianium laser is hard to evaluate (and to design goggles for) because of it’s
Wide spectral bandwidth (400 nm 2450 nm)
Short pulse width (100 fs)
High peak power (17 kW)
400
2400
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62. Case: Fianium SC400-4 Pulse width: 6 ps
Spectral range: 400 nm – 2450 nm
Total (average) power: > 4 W
Rep. Rate: 40 MHz
Beam diameter at 633 nm: 1.5 mm
Peak power = 17 kW
Peak Energy = 100 nJ
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63. Case: Fianium SC400-4 MPE formulas are λ-dependent
Calculate energy density for open pupil area: E = 100*10-9 / 0.39 = 25*10-8 J/cm2 = 2.5*10-3 J/m2 .
In 0.25 s, 10*106 pulses occur, sum to 5*10-6 s (200 pulses),
thermal correction factor C5 = 2.5 (IEC :2014, p28) OD value = log(E/1.5)+4 = log(2.5*200*2.5*10-3/1.5)+4 = 3.9.
DC calculation: log(P)-1 = log(4/0.39*104)-1 = = 4.0 (For λ-dependent IEC :2014 calculations, see notes.)
400
2400
Energy density of Fianium for open pupil area = 100*10-9 J / 0.39 cm2 = 2.5*10-7 J/cm2 or 2.5*10-3 J/m2, 2.5 times more than allowed for ONE pulse, IEC :2014 table A1, p62, giving a value of 10-3 J/m2 for λ between 400 nm and 1050 nm.
Let’s assume you need to take into account the number of pulses occurring during 0.25 s (= eye blink reflex). According to IEC :2014, table 2 p28, pulse groups have to be summed to 5*10-6 s (Ti), so 5*10-6*40*106 = 200 pulses. This results in a number of pulses of 0.25*40*106/200 = 50*103 pulses. According to p28, “for a time base <= 0.25 s, C5 = 1.0” and from 0.25 s C5 = 5*N-0.25 = 5*(50*103)-0.25 = 0.33, which is converted to the minimum value of 0.4. Let’s take the latter more restrictive value of 0.4.
In this case, the attenuation needed, according to the formula in EN 207, taking multiple pulses into account, would be log(E/1.5)+4 = log(1/0.4*200*2.5*10-3/1.5)+4 = = 3.9, so OD 4 would suffice. This accounts for the spectrum from 315 to 1400 nm according to EN 207, but the document uses an increased Ti from 1050 to 1400 nm (13 μs vs. 5 μs) so combining EN 207 with multiple pulse rules from cannot be done. A higher Ti increases the attenuation needed, but a decrease is expected from the fact that the Fianium emits about a quarter of it’s power above 1400 nm.
Note that we have multiplied the MPE of one pulse with 200, because 200 pulses had to be added to fill the summing interval of 5*10-6 s, see IEC :2014 p28.
Let’s also do the calculation according to the (latest) tables in IEC :2014. Note that we have to sum 200 pulses to obtain the time window of 5*10-6 s (see above). From table A1, p62, the MPE of one pulse from 400 nm to 1050 nm = 10-3 J/m2. Simplifying the calculation to this wavelength range, the MPE is exceeded by (MPE of 1 pulse)*C5 /10-3 J/m2 = 200*2.5*10-3 J/m2 * 1/0.4/10-3 J/m2 = Note again that we have multiplied the MPE of one pulse with 200, because 200 pulses had to be added to fill the summing interval of 5*10-6 s. So the required optical density is log(1250) = 3.1, which results in (rounded upwards) OD 4.
A more precise calculation deals with 6 wavelength regions, over which the energy of one pulse (2.5*10-3 J/m2) has to be divided. Hereby the energy in the peak ( nm) is handled as a seperate wavelength region. From the laser output, the MPE ratio’s can thus be calculated and summed. Taking the log of this sum will then give the required OD value.
MPE formulas according to IEC :2014:
nm: 1*10-3 J/m2 (one pulse)
nm, 1*10-3*C7 J/m2, C7 = *(λ-1150) = 1 from nm, rising to 1200 nm
nm, 1*10-3*C7 J/m2, C7 = *(λ-1250) , so rising rapidly with wavelength
nm, 1012 W/m2, 1500–1800 nm, 1013 W/m2, nm, 1012 W/m2
Power from Fianium power spectral density graph:
nm: 1000 mW, 25%, nm: 265 mW, 6.6%, nm, 375 mW, 9.4%, nm, 670 mW, 16.8%, nm, 290 mW, 7.2%, nm, 600 mW, 15%, nm, 800 mW, 20%.
MPE calculations:
nm, MPE ratio = 25% of 1250 (number by which the MPE is exceeded, see above) = 313
nm, C7 = 1, MPE ratio = 6.6% of 1250 = 83
nm, C7 = 1 up to 1150 nm, 245 mW (from Fianium power density spectrum) = 6.1% = MPE ratio of 76. C7,1200 = *( ) = 8. Taking a value of C7 = 4 in the λ-range nm, the remaining ( ) = 130 mW adds only 130/4/4000 = 0.8% = 10.
nm, C7 rises from 8 at 1200 nm to C7,1400 = *(λ-1250) = 106. Retinal eye safety limits are quite relaxed here. Assuming an average value for C7 of 10 in this wavelength range, the MPE ratio = 670/10/4000 = 1.7% of 1250 = 21.
nm, the laser emits 290 mW (= 7.2%). Power density (peak) = 17 kW/0.39 cm2 = 0.45*109 W/m2. As this is several orders of magnitude lower than the MPE (1012 W/m2), this wavelength region does not contribute to retinal eye damage.
nm (MPE = 1013 W/m2), as well as nm (MPE = 1012 W/m2): similar to nm: no contribution to retinal eye damage.
Adding all MPE ratio’s yields 503. OD needed = log(503) = 2.7, which is to be rounded to 3.
According to table 2, p28, the pulse summing interval from 1050 nm to 1400 nm has to be increased from 5*10-6 s to 13*10-6 s, so summing 13*10-6*40*106 = 520 pulses. This would increase the required OD value from log(1250) to log(520*2.5*10-3*1/0.4/10-3) = log(3250) about a factor of 3250/1250 = 2.6 on a linear scale. So we should increase the contributions from 1050 to 1400 nm, which results in a total MPE ratio of *( ) = 693, resulting in an OD value of log(693) = 2.8, only marginally different from 2.7 (without taking the longer summing interval into account).
For DC calculation, 4W/0.39 cm2 = 10 W/cm2. Log(P)-1 = log(10*104)–1 = = 4.0, so OD 4 is needed!
Let’s redo the DC calculation according to IEC :2014, see table A3, p64.
MPE = 7*10-4*t0.75 J, filling in t = 0.25 s (eye blink reflex), MPE = 2.5*10-4 J, resulting in an OD value of log(4 W*0.25 s / 2.5*10-4 J) = 3.6 so 4, rounded upwards.
Conclusions:
OD 4 is fine.
For high pulse rates, the DC calculation is most restrictive!
Note: According to the whitepaper of Schulmeister version 1c , on the new edition of the international laser product safety standard IEC , the single pulse limit equals the DC limit at 13 kHz below 1050 nm and 5 kHz between 1050 and 1400 nm. For higher pulse rates the DC calculation is most restrictive!
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64. Case: Fianium SC400-4 Transmitted: ~7 mW , still not safe.
I doubt the VLT of 10%, considering the OD1+ being the lowest attenuation.
Advantage: relatively safe, but still questionable in the regions nm (OD1+) and nm (OD2+).
Disadvantages: High price and low VLT. Additional environmental lighting is required!
Transmitted: ~7 mW , still not safe.
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65. Case: Fianium SC400-4 2. LaserVision T1L01, VLT = 30%, € 860.-
From 1400 nm to 2400 nm: ~OD4.
Better VLT than the Fianium goggles but therefore also more transmissive.
Also expensive.
Transmitted: 60 mW , OD still needed = 2.2
Conclusion: not safe.
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66. Case: Fianium SC400-4 3. Thorlabs LG2, VLT = 19%, € 156.-
VLT value (19%) in between the Fianium goggles (10%) and the Laservision T1LO1 (30%), fairly high transmittive power.
Not expensive.
Transmitted (vis): 105 mW , OD still needed 2.4
Conclusion: not safe.
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67. Case: Fianium SC400-4 100% protection Laser Safety, ANP, 2-11-2017.
In case of a 4 W white light Fianium laser, there is no 100% protection.
100% protection
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68. (il)legal? purchases… Dutch legislation (updated 1 april 2013)
Laserpointer: no selling of class 3R, 3B and 4.
Lasergadget: no selling of class 2, 2M, 3R, 3B and 4.
Definitions, according to “informatieblad 26”, 4 september 2006:
Laserpointer: modern version of a pointer, usually a red diode laser.
Lasergadget: a laser pointer with keychain, pen, knife, or other fancy attribute, that may fall into the hands of children.
Intentional suppression of the blink reflex can lead to eye injury.
NOTE: green laserpointers based on frequency doubling (emitting at 532 nm) may also emit the pump frequency (typ. 808 nm) and the 1064 nm.
Notes: selling classes are not changed in 2013, compared to 2006.
The NVWA (Nederlandse Voedsel en Waren Autoriteit) does not play a role on possession and use of laserproducts by individuals.
According to the WWM (Wet Wapens en Munitie), the police can act against carrying and or the use of lasers only in case of reasonable suspicion of hurting or threatening people.
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69. (This sheet is taken out of the presentation, because laser goggles are dealt with in previous sheets.)
Laser protective eyewear.
Proper eyewear is extremely important. Every laser user must wear adequate protective eyewear when they are working in the laboratory. The laboratory must provide eyewear which is appropriate to the lasers in use and clearly marked. Visitors to the laboratories must also be provided with proper eyewear. If this can not be done, the lasers must be turned off or completely blocked.
Laser eyewear is made of plastic or glass filters and protects against certain wavelengths. In general, different types of lasers (different wavelengths, different powers or different pulse durations) can require different protection. Choosing eyewear that conforms with European and international regulations can be complicated, and some eyewear companies have provided software to simplify the choice. We recommend the EYEPRO software from LaserVision, which can be found on the ICFO intranet. A full description of the regulations is provided in European standards EN 207 and EN 208.
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70. Distribution of rods and cones
This graph is added to illustate the simplification made in the human eye drawing.
Graph from “Webvision, the organization of the Retina and Visual System, Photoreceptors by Helga Kolb”.
Note the cone-peak in the fovea ( fovea = the pit in the macula lutea, caused by the absence of blood vessels in favour of the cone density)
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71. Types of photoreceptors
This graph is added to illustate the simplification often made in describing the spectral sensitivity of the eye.
Humans are trichromats. (the image is typical for primates).
Dotted line: rods, straight lines: cones.
Rods are used for low light level detection. They are capable of detecting single photons.
As a disadvantage, their response to light compared to cones is much slower. A delay of 100 ms is observed, so no sporting events like baseball in low light conditions.
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72. Good practice in beampath design
High-intensity beams that can cause fire or skin damage (mainly from class 4 and ultraviolet lasers) and that are not frequently modified should be guided through tubes.
Using tubes gives a passive, very effective, always working increase of safety!
Note the matte black finish of most components.
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73. Good practice in beampath design
Avoid upwards directed beams. If not possible, put a warning sign and shielding in place.
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74. Enclosure, black cloth curtain
Measurement with Shimadzu photospectrometer, max. range = OD 4.
Below 400 nm the Shimadzu is accurate up to 3.5 OD, due to scattering of the (single) grating.
Be sure that the applied curtain cannot catch fire.
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75. Enclosure, black plastic curtain
Measurement with Shimadzu photospectrometer, max. range = OD 4.
Below 400 nm the Shimadzu is accurate up to 3.5 OD, due to scattering of the (single) grating.
Be sure that the applied curtain cannot catch fire.
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76. MPE in W/cm2 (2007) “sun” Laser Safety, ANP, 2-11-2017.
These MPE curves are dated (2007), do not include extended sources nor modulated lasers, and introduce reading errors. Therefore these graph are moved to the “extra sheets” section.
Source: Wikipedia.
The MPE is calculated at the cornea at fully open pupil (0.38 cm2).
MPE as power density versus exposure time for various wavelengths.
The sunlight power density line is drawn as a dotted line. Exposure time not applicable of course. Furthermore, the sun is an “extended source”. Therefore the MPE is to be calculated from the total power reduced by C6, α/αmin = 9.3/1.5 = 6.2, see sheet 5, “eye reference values”.
Created by Han-Kwang based on the IEC , Edition formulas. Power density versus exposure time. Plot is based on Table A1 "Maximum permissible exposure limit for C6 equals 1 at the cornea" in IEC , Edition
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77. MPE in J/cm2 (2007) Laser Safety, ANP, 2-11-2017. Source: Wikipedia.
Maximum permissible exposure (MPE) at the cornea for a collimated laser beam according to IEC :2007, as energy density versus exposure time for various wavelengths.
(MPE representation comes in different flavors.) ONLY UPDATED UNTIL 2007!
If you want to reproduce this graph, read the following explanation, copied from Wikipedia.
The graph above shows the maximum permissible exposure (MPE) to light from lasers, as joules for a given exposure time. This is most suitable for use with pulsed lasers; for continuous-wave lasers, see File:IEC60825 MPE W s.png. See also File:IEC60825 MPE J nm.png for detailed wavelength dependence. Plots are based on Table A1 "Maximum permissible exposure limit for C6 equals 1 at the cornea" in IEC , Edition The vertical axis is the total energy which a person may be exposed to, per square cm. This is not the same as the power which a person can be exposed to. To determine the power a person can be exposed to, the energy must be divided by the time. In other words, if a lower powered laser is used, a person can be exposed for a longer period of time, before accumulating the same energy level. As an example, a 5 mW laser puts out 5 mJ (5*10-3 Joules) of energy per second. If the spread of the laser beam is 1 cm2, this point can be found by looking at the right column (labeled 1 second), and going up to the point J/cm2. This is therefore the maximum exposure for 1 second of light at nm. On the other hand, if the laser beam width was only half that diameter, the energy per square centimeter would be 4 times as great, or 20 mJ (0.020 J/cm2) in 1 second. To find the maximum exposure to this power level, the following procedure can be used: Begin at the point of exposure for 1 second (0.02 J/cm2 for our example). Move 1 line to the left (0.01 seconds), and 2 lines down ( J/cm2, or 2*10-4). This is exposure to the same power level, but for 1/100th of the time, and therefore 1/100th of the energy. Draw a line through these 2 points. This line indicates the maximum time a person can be exposed to that power level of laser, at that width. This line will intersect the green line (400 to 700 nm) at approximately 1*10-4 seconds. It will intersect the 800 nm line at about seconds, and the 1064 nm line at about 0.1 seconds. It is important to remember that to use this graph, the power of the laser, the beam width (beam area) of the laser, and the wavelength of the laser must be known. Visible lasers all fall into the nm range, which has the lowest level of acceptable MPE. In other words, we can be most easily injured by light at these levels. Summary Created by Han-Kwang based on IEC formulas. Energy versus exposure time.
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78. MPE in J/cm2(2007) Laser Safety, ANP, 2-11-2017. Source: Wikipedia.
MPE as energy density versus wavelength for various exposure times (pulse durations). ONLY UPDATED UNTIL 2007!
Created by Han-Kwang based on IEC formulas. Energy versus wavelength. See also File:IEC60825 MPE J s.png and File:IEC60825 MPE W s.png. Plot is based on Table A.1 "Maximum permissible exposure limit for C6 equals 1 at the cornea" in IEC , Edition Note that the MPE does not depend on wavelength in the range 2.9 to 10 micrometers. Hence, for 10 micrometer wavelength, one can read the value at 3 micrometers.
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