實驗 4 :光的折射、偏振、干涉和繞射 Lab.4 - Refraction, Polarization, Interference and Diffraction of Light To observe the various phenomena of light To study some important foudatmental optical principles. A. Refraction Index of Prism (三稜鏡的折射率) B. Polarization of Light (光的偏振) C. Thin-Film Interference of Air Wedge (空氣楔的薄膜干涉) D. Multi-reflective Interference in Glass (玻璃片內多次反射的干涉) E. Diffraction of Light (光的繞射)

一、雷射使用的基本安全規則 雷射光很容易對視網膜造成永久性的傷害，切記絕對不可將雷射光直接對著自己或他人的眼睛射照。 雷射光經光滑表面反射得的雷射光也可能會對眼睛造成嚴重的傷害，所以雷用使用操作時也要隨時留意，避免經雷射的反射光照射到自己或他人的頭部。 高功率的雷射光，縱使不是經光滑表面反射，而是經過一般粗糙的表面散射後，仍極有可能對人的眼睛、甚或人體造成不小的傷害。所以，高功率雷射更要嚴格遵守使用雷射的相關安全規範。 雷射的內部通常含有高壓電源裝置，特別是高功率雷射，故未經允許不可隨意開啟儀器外殼，以免發生高壓觸電的危險。 雷射電源線的插頭必須是含有地線的安全插頭，且必須插到接有地線的電源插座上。以防萬一雷射內部漏電，電流可經由接地線快速流通到地下，才不致傷害人體。

二、雷射危險度分級與防範對策 Ref: http://www.phys.ncyu.edu.tw/~ygwu/lasar_safety.doc 雷射危險度的分類 雷射處理上的安全對策 雷射對眼睛的傷害 雷射光對皮膚的傷害

I. Laser Safety Rulers Class 1 Lasers A warning sign indicating the laser classification should be placed in a visible location on the laser. Class 2 Lasers Do not stare at the laser or permit any person to stare at the laser beam. Do not point the laser at a person's eye.

Class 3 Lasers Never aim a laser beam at a person's eye. Use proper safety eyewear if there is a chance that the beam or hazardous specular reflection will expose the eyes. Only experienced personnel should be permitted to operate the laser. Never leave an operable laser unattended if there is a chance that an unauthorized person may attempt to use it. A key switch should be used. A warning light or buzzer should indicate when the laser is operating. Enclose as much of the beam path as possible. Avoid placing the unprotected eye along or near the beam axis as attempted in some alignment procedures since the chance of hazardous specular reflection is greatest in this area. Terminate the primary and secondary beams if possible at the end of their useful paths. Use beam shutters and output filters to reduce the beam power to less hazardous levels when the full output power is not required. Make sure that any spectators are not potentially exposed to a hazardous condition. Attempt to keep laser beam paths above or below either sitting or standing position eye level. Operate the laser only in a well-controlled area. That is, in a closed room with no windows and controlled access. Label lasers with appropriate Class III danger statements and placard hazardous areas with danger signs. Mount the laser on a firm support to assure that the beam travels along the intended path. Assure that individuals do not look directly into a laser beam with optical instruments unless a adequate protective filter is present. Eliminate unnecessary specular (mirror-like) surfaces from the vicinity of the laser beam path.

Class 4 Lasers Enclose the entire laser beam path if at all possible. If this is done, the laser device could be considered to be a less hazardous classification. Confine indoor laser operation to a light-tight room with interlocked entrances to assure that the laser cannot emit when a door is open. Insure that all personnel wear adequate eye protection, and if the laser beam irradiance represents a serious skin or fire hazard that a suitable shield is present between the laser beam and the any persons in the room. Use remote firing and video monitoring or remote viewing through a laser safety shield where feasible. Use beam traverse and elevation stops on outdoor laser devices to assure that the beam cannot intercept occupied areas or intercept aircraft. Use beam shutters and laser output filters to reduce the laser beam irradiance to less hazardous levels whenever the full beam power is not required. Assure that the laser device has a key-switch master interlock to permit only authorized personnel to operate the laser. Install appropriate signs and labels on entrances, switches and anywhere an unauthorized person might mistakenly activate the laser. Remember that optical pump systems may be hazardous to view and that once optical pumping systems for pulsed lasers are charged, they can spontaneously discharged, causing the laser to fire unexpectedly. Use dark, absorbing diffuse, fire-resistant targets and backstops where feasible.

Refraction Index of Triangular Prism (三稜鏡的折射率) Object: To measure the refraction index of prism. Principle: referred from http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html, “Light and Vision”, in web site “HyperPhysics”, hosted by the department of Physics and Astronomy, Georgia State University, GA, US A-1 Refraction of Light Refraction is the bending of a wave when it enters a medium where it's speed is different. The refraction of light when it passes from a fast medium to a slow medium bends the light ray toward the normal to the boundary between the two media. The amount of bending depends on the indices of refraction of the two media and is described quantitatively by Snell's Law. -be responsible for image formation by lenses and the eye.

Refraction of Light & Index of Refraction

Snell’s Law Total Internal Reflection

Refraction of Prism

Angle of Minimum Deviation of Prism --Provides a good way to measure the index of refraction of a material.

Applications of Prism A refracting prism is a convenient geometry to illustrate dispersion and The use of the angle of minimum deviation provides a good way to measure the index of refraction of a material. Reflecting prisms are used for erecting or otherwise changing the orientation of an image. Making use of total internal reflection instead of refraction.

Experimental Procedures Let laser beam horizontally incident to the wall or a white paper which has a distance of about 0.5 m far away. To mark the position of laser beam. Settle the triangular prism on the optical platform with the U-shaped support device and angular scale disc. To adjust the proper position of prism to locate the path of laser beam. Rotate the prism slowly and observe the deviation path of the refracted laser beam by prism. To mark the beam position when the angle of deviation through a prism is minimum. Prisms are typically characterized by their angle of minimum deviation d. This minimum deviation is achieved by adjusting the incident angle until the ray passes through the prism parallel to the bottom of the prism.

Experimental Procedures To measure the distance of the both positions marked by step (1) and (3), and the distance between the prism and the screen of laser spot. To calculate the angle of minimum deviation, , for the prism based on the formula above. Change the incident angle of laser into the prism and repeat the procedures (2) to (4), to get the other the angle of minimum deviation, . To measure the apex angle of the prism . To determine the refraction index of the prism.

B. Polarization of Light (光的偏振)