June 2009

Blinded by the Light Review Questions and Problems

  1. Which of the following is NOT a property of laser light?
  2. Coherence
  3. Low divergence
  4. Monochromatic
  5. Dispersive
  1. Which structure of the eye is most affected by VISIBLE light?
  1. Cornea
  2. Retina
  3. Lens
  4. Zonnules
  1. Which class of laser is generally exempt from radiation hazard controls during operation? (This also applies to a laser system with this classification.)
  2. I
  3. II
  4. IIIa
  5. IIIb
  6. IV
  1. Which class of lasers are hazardous to view under any condition (including diffuse reflection)?
  2. I
  3. II
  4. IIIa
  5. IIIb
  1. IV
  1. Which class of laser includes most common laser pointers?
  2. I
  3. II
  4. IIIa
  5. IIIb
  6. IV
  1. Which class of laser is associated with skin and fire hazards?
  2. I
  3. II
  4. IIIa
  5. IIIb
  6. IV
  1. Which class of laser included most supermarket scanners?
  2. I
  3. II
  4. IIIa
  5. IIIb
  6. IV
  1. What length of time is called the “human aversion reaction time”?
  2. 10 seconds
  3. A quarter second
  4. 3000 seconds
  5. 8 hours
  1. Intrabeam viewing means
  2. Staring at the beam from the side
  3. Staring at diffuse reflection of the beam
  4. Opening the laser and staring at the side of the tube
  5. Looking directly into the beam
  1. The MPE is
  2. The maximum permitted wavelength for a viewing situation
  3. The maximum level of laser exposure that will not have a hazardous effect
  4. The minimum distance from a laser where the laser presents a hazard
  5. The maximum radiation allowed from a laser
  1. What are the units of irradiance?
  2. Joule/m
  3. Watt
  4. W/cm2
  5. None of the above
  1. The Nominal Hazard Zone is defined as
  2. The space within which the level of direct, scattered or reflected laser radiation exceeds the MPE
  3. The distance where the laser’s divergence becomes twice the normal
  4. The space where it’s OK to stand and view the laser
  5. The immediate area around a laser
  1. Which of the following is not a consideration when purchasing laser safety eyewear?
  2. Wavelength
  3. Laser power
  4. Optical density
  5. Fashionable frames
  1. What does LASER stand for?
  1. What is an "LSO"?
  1. Consider a pupil opening 7 mm in diameter. What is the maximum green laser pointer power allowed for a 0.25 second intrabeam exposure?
  1. A 5 mW red laser pointer has a full angle divergence of 1.5 mR. Find the beam diameter and irradiance 10 m away and 100 m away from the laser. Does irradiance exceed the MPE?
  1. If the laser in problem #19 is directed at a glass windshield 10 meters away. How much light is transmitted through the windshield if the index of refraction of the glass is 1.5? Ignore absorption. Hint: there are two air-glass interfaces. Is the MPE exceeded?

Blinded by the Light Review Questions and Problems

Answers

NOTE: The (older) ANSI classifications and (harmonized) IEC classifications are:

ANSI / IEC
I / 1, 1M (M indicates viewing with optical aids such as magnifiers)
IIa, II / 2, 2M
IIIa / 3R
IIIb / 3bIV
IV / 4
  1. d
  2. b
  3. a
  4. e
  5. c
  6. e
  7. b
  8. b
  9. d
  10. b
  11. c
  12. a
  13. d
  14. Light Amplification (by) Stimulated Emission (of) Radiation
  15. Laser Safety Officer, the person responsible for safe use of lasers at institutions. LSOs are required at institutions with Class 3B lasers and above.
  16. From the MPE table in LIGHT-Introduction to Optics and Photonics (p. 9)
    MPE = 2.5 W/cm2 for visible wavelengths for 0.25 s exposure.

So, MPE = 2.5 W/cm2 = Irradiance = P/A = P/ (0.35 cm)2

P ~ 0.96 mW

  1. At 10 m, d=10m (1.5mR) =1.5 cm and irradiance= P/A= =0.005W/()(0.75 cm)2=2.8 mW/cm2

At 100 m, d = 15 cm, irradiance = 28 W/cm2. MPE is exceeded at 10 m but not at 100 m.

  1. 4% is reflected at each surface, so 96% is transmitted.

Transmitted irradiance = (.96)(.96)(2.8 mW/cm2) = 2.6 mW/cm2. MPE is still exceeded.