Laser safety Paul van Kampen 02/02/11

Almost all you need to know about laser safety Beware of electrical safety Dont expose your eyes or skin Minimise the number of shiny surfaces Wear goggles Beware of water leaks Use warning signs Use interlocks

Types of laser Continuous wave (cw) or pulsed Power Wavelength Visible/invisible Effect on skin, cornea, retina

Laser classification What is it based on? Maximum Permissible Exposure (MPE) 10% of dose that has 50% chance of doing damage Depends on wavelength, body part, cw or pulsed Visible-IR range, cornea, cw: 1 mW cm 2 Example: class 1 or class I laser limit Fully dilated pupil: diameter 7 mm, area 0.39 cm 2 Maximum permissible power: 0.39 mW

Laser classification (old) Class I: safe (UNFOCUSSED!) Class II: safe - your aversion to bright light will protect you Class IIIA: cw: 1-5 mW, safe unless you look at it, or its reflection, directly Class IIIB: cw mW, pulsed <10 J/cm 2, sometimes diffuse reflection hazard Class IV: cw >500 mW, pulsed >10 J/cm 2, diffuse reflection, fire, skin hazard

More data become available

More data become available

Laser classification (new) Class 1(M): safe (UNFOCUSSED!) <0.4 mW Class 2(M): safe - your aversion to bright light will protect you. <1 mW Class 3R: cw: 1-5 mW, safe unless you look at it, or its reflection, directly. Low risk Class 3B: cw mW, (<300 mW visible), pulsed <10 J/cm 2, diffuse reflection OK Class 4: cw >500 mW, pulsed >10 J/cm 2, diffuse reflection, fire, skin hazard, interlock required

UV lasers Excimer lasers: gas premix typically contains 0.1 percent of fluorine/chlorine ArF, KrCl, KrF: UV-C radiation Eye: snowblindness Skin: sunburn, skin cancer XeCl: UV-B radiation Eye: snowblindness Skin: skin aging, increased pigmentation XeF, Nd:YAG tripled: UV-A radiation Eye: cataracts Skin: skin burn, pigment darkening

Germicidal lamps 15 W UV-C lamp 254 nm, cylindrical, 30 cm tall 40% efficient in UV-C so 6 W of UV-C light Model: every ring 1 cm high centred on lamp transmits a total of 200 mW outward Irradiance of 30/r mW/cm 2 at r cm from lamp Skin/eye MPE = 3 mJ/cm 2, cumulative so MPE = 3/t mW/cm 2 for exposure of t seconds For every second of exposure, you must be about 10 cm from the lamp Place lamp in enclosed reflective chamber WEAR GOGGLES & DONT EXPOSE SKIN

Germicidal lamps (2) What about cooling tube made of Pyrex? Transmits ~80% in UV- C range (Some sources give cut-off as 300 nm) Almost no protection Perhaps not surprising – the lamp kills bacteria in 5 seconds!

Visible/IR lasers CW/pulsed: protect your eyes blue-green worse than red-infrared dont shoot at your skin Dye lasers: dyes are carcinogens CO 2 lasers: fire hazard

Good lab design Often a competition between hazards: Water Electrical Trip Laser radiation Scatter Direct exposure Good management is mostly common sense e.g., dont forget to remove your watch!

A laser lab (1) Data: Vacuum chamber Pulsed IR class IV laser Target 10 cm behind glass Target 1.5 m above floor Lens: F.L. 20 cm Lens holder: aluminium Can you do better?

A laser lab (2) Beam height: Unsafe for people >5 ft If you cant adjust target, move beam out of the way Door: Dont shoot laser in that direction! Make sure the system is interlocked – door open, laser off

A laser lab (3) Lens: Beware of scatter Each surface reflects 4% as a mirror (back into laser!) AR coating Turn lens around You may hit lens holder Spray paint black Window: 4% reflection focused on lens

A laser lab (4) Adaptability Cant easily adjust beam Tripping: Water/electrical leads all over the floor Invisibility Can you mount a collinear visible alignment laser?

A laser lab (5) Possible solution: Collinear weak visible laser Shorter FL lens Turn lens or beam dump Piped beam Mirrors allow manipulation Laser against wall Beware of pushing against piping Curtain/screen near door curtain/ screen