Lasers

Question 1

LASER

Answer 1

Light amplification stimulated emission radiation

Question 2

Coherance

Answer 2

Collimated light that is the same phase, same wavelength and traveling in the same direction.

Question 3

laser output can be described in 3 ways

Answer 3

Pulse duration (pulse vs continuous)

Irridance = incident laser power per unit area 
irradiance = power/ area (watts/cm^2) Decrease area or spot, then you increase the irradiance. 

Wavelength. Determines how effectively light is captured by the tissue target (absorption) and how well light penetrates overlying media to reach a tissue target (transmission= passing through)

Question 4

Ophthalmic laser wavelengths

Answer 4

UV: 100-380 nm
Visible: 380-760 nm
IR: 760 nm to 1mm

Question 5

2 ANSI requirements for lasers

Answer 5

Ansi Z136.1 safe use of lasers. More useful in general sense.

Ansi Z136.3 safe use of lasers in health care facilities.

Question 6

Laser eye hazards

Answer 6

1. Direct intrabeam viewing. Laser beam from source to eye unobstructed.
2. Specular reflection. Mirror like. (angle of incidence is between the normal and the beam)
3. Diffuse beam. Change of the partial direction of the beam when it is reflected by a surface or medium. Ex: fog, rain, dust getting in the way.

Question 7

Older laser classification

Answer 7

Class I: No eye hazard, no warning label. Outputs up to 0.4mW.

Class II: Low power, low risk. Natural avoidance by blinking (aversion response in 0.25sec). No warning label. Outputs up to 1mW of visible radiation. Only visible light!! Ex: old laser pointers.

Class IIIa: Eye safe when viewed directly. Retinal damage if viewed with binoculars. Required caution label. Outputs up to 5mW of visible radiation.

Class IIIb: Moderate power/risk. Retinal damage in less than 0.25sec. Aversion response cannot keep you safe- we don’t blink fast enough. Caution label required. Up to 500mW of power. Military range finder.

Class IV: High power/high risk. Causes retinal damage and can cause a fire. Outputs over 500mW. YAG and retinal coagulator. Danger label require.d

Question 8

Newer/reviesed standards. What changed?
ANSI adopted from EIC (european) in 2007
ANSI z136.1/IEC

Answer 8

Hazard class based on capability of the laser to injur a person. Based on man output. 
Require warning labels on laser equipment. Additional triangular warning for class 2 and higher.

Question 9

Warning label for ANSI Z136.1 should includee what 5 things

Answer 9

1. Class of laser
2. Emitted wavelength
3. Pulse duration if appropriate
4. Max output power
5. Precautionary statement for users. “Do not stare”

Question 10

ANSI z136.1 2007 classes

Answer 10

Class 1: Exempt from control measures. Safe.

Class 1M: Safe under normal use EXCEPT when you use a magnifier. “Laser radiation, do not view directly with optical instruments. Class 1M product” Otherwise, safe and exempt from control measures,

Class 2: Safe assuming blink response. Emits visual spectrum only. Exempt from control measures.

Class 2M: Safe assuming blink response and not viewed through optical instrument.

Class 3R (replaces 3A) Potential hazard, but low change. Laser eye protection not usually required, warning recommended. “caution”

Class 3B: Protective eyewear required.Warning sign required.

Class 4: Most dangerous. Eye damage from direct, specular or diffuse viewing. can also severely burn skin. Control measures and eye protection required. Danger or warning sign.

Question 11

How could lasers in low classes still cause damage

Answer 11

They demonstrate coherence. Human eyes act as imaging system. Exposure can be 100,000x greater at retina than K.

Question 12

What is YAG laser used for?

Answer 12

Used in post cataract care. Tx Posterior capsular opacification.

If the laser is focused on the retina and not the back of the lens, will get a scorched appearance. Eventually got back to 20/20 but prob not a very crisp view.

Question 13

Laser protection by engineering, admin, and PPE

Answer 13

Engineer: Control measures designed or incorporated into the laser or laser system. Locks, timers. First line defense.

Admin controls- training, safety approvals, laser safety officers. 2nd line of defense.

Personal protective equipment control measure: eye protection, protective clothing, last line of defense. last line of defense.

Question 14

Laser eye protection

Answer 14

Blocking the power of the wavelengths from the laser. Works similar to notch filters.
There is not a generic pair, it must be selected specifically for the laser and the wavelength it emits.

Question 15

Optical density=

Answer 15

Log 10 (opacity)

Therefore OD of 3 means you are dampening the wavelength by 10^3.

Question 16

For laser glasses, an optical density of __ is the minimum.

Answer 16

5. dampening the wavelength by 10^5

Question 17

VLT

Answer 17

Visible light transmission. The higher the VLT, the lighter the tint in the lens. More light transmitting through.

Question 18

YAG laser wavelength

Answer 18

1064nm

Question 19

Laser pointers cannot exceed class ___ limits these days per ANSI standards

Answer 19

3R.

405-445 violet
520-532 is green- more dangerous than red. Retinal pigments absorb green differently.
630-670 is red

Question 20

Maximum permissible exposure (MPE)

Answer 20

The level of laser radiation to which an unprotected person may be exposed without adverse biological changes.

Question 21

Limiting aperture (LA)

Answer 21

The circle diameter over which exposure is averaged for purpose of hazard eval and classification.

Question 22

Accessible emission limit (AEL)

Answer 22

The max radiation energy level permitted within a particular laser hazard class.

AEL= MPE x area of LA

Question 23

MPE assumptions

Answer 23

Eye is perfectly refracted for the wavelength
pupil size is 7mm
Aversion is 0.25 sec

Question 24

Laser pointer study by robertson

Answer 24

Class 3A laser with exposures at 1, 5, and 15 mins.

Conclusion- risk to human eye with class 3A laser having 1, 2, and 5mW is negligible.