Laser Basic Science (M) Flashcards
What class of laser is considered safe under all conditions?
class 1
What type of light (UV, visible, infra red, etc) is produced by the Excimer ArF laser? 1. What type of damage does it cause? 2. What is it usually used for? 3
- UV
- photoablation
- LASIK, PRK
What happens when the exposure time is greater than the thermal relaxation time?
heat conducted to adjacent tissue
What are excited electrons with relatively long decay times? 1. What does this provide? 2
- metastable state
2. inc likelihood of being stimulated before spontaneous emission
What is a laser pointers MPE?
1mW
What happens when the exposure time is less than the thermal relaxation time?
no heat conducted to adjacent tissue
What is it called when photons from the laser are absorbed by ocular tissue molecules (pigment dependent) to destroy the tissue?
photothermal (photocoagulative)
What is the range of wavelengths absorbed by the retina?
400 to 1400nm
What defines a lasers wavelength?
laser medium
What does doubling the diameter of the laser spot do to the fluence or irradiance?
reduces by a factor of 4
Is a pulsed laser listed in watts or Joules?
Joules
What type of light (UV, visible, infra red, etc) is produced by the Nd YAG laser? 1. Is it Q switched or CW? 2. What is it usually used for? 3
- infra red
- can be either
- PI, capsulotomies
What are the three types of excitation mechanisms for lasers?
- electrical
- optical
- chemical
What type of light (UV, visible, infra red, etc) is produced by the CO2 laser? 1. What type of damage does it cause? 2
- infra red
2. photovaporization
Is a continuous wave laser listed in watts or Joules? 1. What are the different types? 2
- watts
2. Ar, Kr, HeNe, diode lasers, CO2
What class of laser is capable of hazardous exposure if used with an optical device?
class 1M and 2M
What is the temperature change that can lead to denaturation and coagulation during photocoagulation?
10 to 20degC
What class of laser may be hazardous under some direct and specular reflection viewing conditions but is not a fire hazard?
class 3 (3R needs focused eye, 3B does not)
What is the distance in which the irradiance of the beam is greater than the MPE?
Nominal hazard zone (NHZ)
What type of transverse electromagnetic mode (TEM) do all the lasers we use have?
fundamental mode (single beam, TEM00)
What type of light (UV, visible, infra red, etc) is produced by the Intralase (femtosecond) diode pumped solid state (DPSS) laser? 1. What is it used for? 2
- infra red
2. LASIK, cataract surgery, corneal transplant
What is the range of wavelengths absorbed by the cornea?
180 to 315nm and over 1400nm
What does LASER stand for?
Light Amplification by Stimulated Emission of Radiation
What is the maximum irradiance or radiant exposure that may be incident upon the eye without causing biological damage? 1. What is the buffer zone of this? 2
- maximum permissible exposure (MPE)
2. 1 log unit
What is the photochemical reaction that is like 11-cis to all-trans in photoreceptors?
photoinduced isomerization
What temperature is used in photovaporization?
temp to get water in cell 100degC
What is the photochemical reaction that is the linking of two equal monomers to make the molecule nonfunctional?
dimerization
What type of light (UV, visible, infra red, etc) is produced by the Excimer XeCl laser? 1. What is it usually used for? 2.
- UV
2. LASIK, PRK
What type of light (UV, visible, infra red, etc) is produced by the Argon laser? 1. What type of damage does it cause? 2. What is it usually used for? 3
- visible (blue)
- photocoagulative
- SLT
What are the characteristics of all of the light made by LASERs?
- monochromatic
- coherent
- collimated
What is it called when a photosensitive drug is selectively absorbed by a lesion and a laser with a wavelength that is maximally absorbed by the drug is used to activate the drug (destroy the tissue)? 1. Example? 2
- PDT (photoradiation)
2. Verteporfin (anti-VEGF)
What is the tissue damage type that creates tissue fragments which escape at supersonic velocities (result in a laser plume) and increase tissue volume?
photoablation (photochemical and photodisruptive)
What type of light (UV, visible, infra red, etc) is produced by the HeNe laser? 1. What is it used for? 2
- visible (multiple colors)
2. aiming (red)
What is the range of wavelengths absorbed by the lens?
315 to 390nm
What does a Q-switched laser do?
has shutter between mirror and medium to build up energy and deliver more in small amount of time (smaller amount of time means more power)
What are some of the characteristics of a photodisruptive damage?
- shielding occurs (absorption by plasma)
- pressure wave (pop sound)
- cavitation (vapor bubble expands)
- photospallation (fracture tissue)
What is it called when more electrons are in the higher energy state than in the ground state?
population inversion
What is the photochemical reaction that is the splitting of molecules into free radicals?
photodissociation
What class of laser is a hazard to the eye or skin from the direct beam and pose as a diffuse reflection or fire hazard?
class 4
What is the power density of a laser called?
irradiance (W/cm^2)
What type of light (UV, visible, infra red, etc) is produced by the Nd YAG doubled laser? 1. Is it Q switched or CW? 2. What is it usually used for? 3
- visible (green)
- either
- SLT
What is the damage type that is pigment independent and delivers a lot of energy in a short duration with minimal collateral damage?
photodisruption
What type of light (UV, visible, infra red, etc) is produced by the Krypton lasers?
visible (multiple colors)
What is the energy density of a laser called?
fluence (J/cm^2)
