Lab 4 Laser - Institutt for elektronikk og telekommunikasjon - NTNU

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1.1 Laser safety 4 welders, movie projectors, searchlights and special tv photo lamps. Living tissues can be damaged when they absorb light because of excessive (even explosive!) heating or by photochemical changes. Examples of heat damage include skin burned by concentrated sunlight or laser emission, and retina lesions caused by laser beams. Examples of photochemical damage includes sunburn and cataracts caused by excessive exposure to ultraviolet light from the sun or from arc welders. When you look at a strong halogen bulb you feel that it is strong light and that you should not continue looking at it (you would see green spots for a couple of days if you continued long enough). The laser light is more concentrated and has a typical spot diameter of 300µm which, when it gets focused, makes a spot that is 10µm on your retina. Let’s now compare the light intensity of a 5mW laser-pointer to the intensity from the image of the sun focused on your retina. Sun retina intensity = Power Spot size = 3 · 10−3 W π(75 · 10 −6 = 180 kW/m2 ) 2 Laser retina intensity = Power Spot size = 5 · 10−3 W π(5 · 10 −6 = 63.6 MW/m2 ) 2 In other words: the laser retina intensity is 350 times the sun retina intensity. It is not recommended to stare at the sun, and with these calculations, I’d suggest that you don’t even think of staring into the laser light. It will burn your retina rather quickly. During this lab exercise you will handle a laser tube which is capable of delivering up to 5mW of coherent light at wavelengths around 632nm(red). It is dangerous to look into the laser beam so do not do that. You shall also wear welding glasses when working with the laser. This is to be sure that no one gets black spots on their retina due to focused laser light.
1.1 Laser safety 5 Class Power Hazards Precautions Examples I ≤ 4µW None none, ”exempt” UPC Scanners II > 4µW ≤ 1mW Retina damage Laserpointers, small HeNe lasers IIIa > 1mW ≤ 10mW possible after 10 seconds or more of steady direct viewing Retina damage possible in 0.25 seconds IIIb > 10mW Retina damage ≤ 0.5W likely in 0.1 seconds. IV > 0.5W Severe eye or skin damage from direct exposure. Eye damage likely from indirect exposure. Can ignite flammable materials Labelling and warnings do not stare into beam Trained operators attached beam stop warninglamp contain beams Key switch interlock connector eye protection trained personnel only emission delay intracavity shutter door interlock contain all reflections HeNe and semicounductor laserpointers Semiconductor Dye Cutters, welders laser shows pulsed lasers argon lasers Table 1.1: Summary of ANSI and CDRH Laser Classes (see Winburn 1990, Ch. 6) 1.1.3 Rules of thumb when working with lasers The following rules of thumb will prevent accidents that can damage vision. If in doubt of the safety of any situation, seek the advise of the lab instructor. 1. Know the appropriate laser Class(see table 1.1) and necessary precautions. 2. Do not look into a laser beam under any circumstances! 3. Control and confine all laser beams. 4. Use beam stops and carefully plan the placement and movement of optical elements. 5. Beware of stray reflections from the many surfaces the beams might encounter. 6. Confine the beams to the horizontal plane just above the table. 7. Keep your eyes above the level of the laser beams. (see rule 7)
Page 1 and 2: From pink light to red LASER Lab ex
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Page 13: Bibliography [Duc04] Stephen Duchar

Lab 4 Laser - Institutt for elektronikk og telekommunikasjon - NTNU

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