Dronka's Review - Martin Flashcards
What does LASER stand for
Light Amplification Stimulated Emission of Radiation
Blackbody radiation
- what
- ideal blackbody cavity
- low vs high temps
Material that absorbs most of the incident light
The spectrum is independent of the specific absorbing material
Low = radiation is IR - feel but can’t see heat High = emittence in incr, moving toward higher freq/shorter wavelengths
Characteristic properties of photons
- in the interaction of radiation with matter, radiation behaves like __ called __
- photon movement
- photon mass
Particles = photons
Always moving at speed of light in vacuum
- attempt to stop = absorption
- travel in straight line
Zero rest mass, but never occur at rest
Electron volt (eV) -what
Energy carried by a single photon
-the amount of energy that an e- gains while moving thru a potential difference of 1V
Bohr Atom Model
- electrons that orbit the atomic nucleus
- electron jumping
Exist only in discrete energy levels
Emit a photon -> lower level
Absorb a photon -> higher level
Spontaneous Emission
- an e- stays in an excited state for __ then jumps to a __, emitting a photon in the process
- an atom will absorb only photons whose energy __ and will release __
<8-10 seconds, lower level
Absorb: is the exact amount needed to raise by 1 level
Release: that same wavelength of energy as a photon
Stimulated Emission
- if a photon of the precise wavelength passes an e- in an elevated energy level of equal gain in energy, that e- will __
- for each that enters
Emit a photon of that same wavelength, direction, phase, coherence, and polarization
2 will leave = amplification
Fluorescent Colors
- why they stand out
- the energy that drives the fluorescent radiation comes from __
The luminous flux emitted at the fluorescent wavelengths by a fluorescent substance»_space;> luminous flux incident at those wavelengths
An incident higher frequency (shorter wavelength) radiation (UV)
Phosphorescence
-what is it
When a metastable with a long lifetime is populated by incident radiation, the material may continue to glow/emit radiation long after the source is removed
Fluorescence vs Phosphorescence
-difference
Matter of time
Fluorescent Dye
- ODs use
- when is it absorbed
- peak excitation and emission
Sodium fluorescein
Intact corneas do not absorb
Damage membranes absorb
Excitation = ~400nm Emission = 522nm
Population Inversion
- electrons of lower levels __
- electrons of higher levels __
- amplification occurs when
Absorb
Emit
More are at evelated than lower state
Pumping
- why
- how
Energy must be added to the system to allow e- to be in elevated orbits
Optical, e- emission, chemical reaction, explostive device, electrical
Uses metastable excited state (live very long time)
Cavity Oscillator
- where/what
- why
- how
Optical cavity
2 parallel mirrors w/ optical coating -> feedback loop with active medium b/w the mirrors
Builds up strength of avalanche
Stimulated emission causes causes amplification of signal within the optical resonator
Continuous Wave vs Long Pulse
-3 characteristics for each
CW:
- emitted continuously
- requires continuous pumping (electrical current, light source)
- thermal effects
LP:
- pulsed on order of miliseconds
- pumping typically by xenon flash lamp
- thermal effects
Q-switching
- what it is
- OD example
- duration
- intensity
Short-pulsed laser
Nd:YAG
Nanosecond duration
High power intensity
Q-switching
- modulator
- energy release
- formation
- effect
- pigmentation
Shutter or light modulator
Energy builds, then released in sudden burst
Plasma formation
Photodisruptive effect
Less affected by pigmentation
Modes
- single/fundamental
- multimode
Gaussian = smallest spot size
- achieves highest power density
- posterior capsulotomy
Non-Gaussian = larger cross sectional power output
- 2+ spots
- vitreolysis
Laser Light Characteristics (3)
Coherent
Monochromatic
Collimated
Therapeutic Lasers (7)
Ion gas Solid state (Nd:YAG) Diode CO2 Excimer Dye Femtosecond
Energy
- define
- units
- SLT
- YAG CAP
- LPI
Transferred to an object to perform work/heat an object
Joules
- 1 joule = 1 watt-second
- 1 mJ = 1 mW-second
SLT = 0.8-1.2 mJ
YAG CAP = 1.3-1.8 mJ
LPI = 3-6 mJ
Power Density
- define
- units
- PD and area, pulse, energy
Transfer of an amount of energy per unit time to a given volume of matter
Watt/cm^3
Higher PD = smaller area, shorter pulse, higher energy
Photochemical Effects
-describe photoradiation
Absorption of light triggers chemical rxn
E.g. radiation therapy in target tissue for cancer tx
Photochemical Effects
-describe photoablation
Single UV photon breaks chemical bond
High irradiance + short exposure = clean cut (-) collateral
Predictable depth = layer by layer removal
Photochemical Effects
- describe
- list both
<320nm (short wavelength)
Low-mod irradiance
~1ms exposure
Photoradiation
Photoablation
Photothermal Effects
- describe
- list both
Longer wavelength
Low-mod irrandiance
~1ms exposure
Photocoagulation
Photovaporization
Photothermal Effects
-describe photocoagulation
Incr 10-20 C, overcomes van der Waals -> coagulation
Thermal energy proportional to (irradiance * exposure time)
Higher irradiance needed for immediate effect
Collateral damage
- heat spread
- scattered light
Photothermal Effects
-describe photovaporization
Higher irradiance than coag
Boiling point of water -> explosion -> tissue rips
Cauterization often follows
Photodisruptive Effects
-describe secondary/photomechanical
Longer wavelength
Higher irradiance
~20ns exposure
Very high irradiance (via Q-switching or mode-lock) + small spot size = ionize material by releasing bound e-
Free e- plasma expands rapidly -> shock wave -> rips tissue
Most photocoagulation laser systems have __ control setting
Power
- change power
- Argon
Most photodisruptive lasers have __ setting since duration is fixed
Energy
- change energy
- Nd:YAG 1064nm
Pigment Dependent Lasers (2)
Argon
Diode
Pigment Independent Lasers (3)
Nd:YAG 1064
Femtosecond
Excimer
Nd:YAG
- nm
- state, level
- pulse
- what type of effect/disruption
1064nm
Solid state (level 4)
Q-switch
Continuous or short-pulsed
Photodisruption
Frequency-doubled YAG (FD:YAG)
- nm
- pulses
- FD
- what type of effect/disruption
532nm
Frequency-doubling and Q-switched
FD = potassium-titanyl-phosphate-crystal
Photocoagulation/sublethal photostimulation pigment dependent
-less intense than argon
Wavelengths -ultraviolet —A —B —C -visible -infrared —near/A —far/B,C
In order: 200-280 UVC 280-315 UVB 315-400 UVA 400-780 visible 780-1400 near infrared/IRA 1400-3000 far infrared/IRB 3-1000 micrometers far infrared/IRC
Light Absorbtion in Eye
- ultraviolet (<400 nm)
- visible (400-700)
- near IR (700-1400)
- far IR (1400+)
Cornea
Retina
Retina
Cornea
Tissue variables
- melanin
- hemoglobin
- xanthophyll
Melanin
- absorbs across entire visible spectrum
- aborbs IR less effectively
Hemoglobin
- absorbs green/blue very well
- scatters red
Xanthophyll
- absorbs blue well
- use red/IR for macula (will cause immediate scarring)
LASIK
-myopia vs hyperopia
M: remove center, make flatter
H: remove peripheral, make steeper
ANSI Standards -class 1
Very low power (<0.5 microW)
No eye/skin hazard from full-day exposure
No label required
Lasers inside CD/DVD players
ANSI Standards -class 2
Low power (<1 mW) No eye hazard from short time period Basic laser pointers, surveying land
ANSI Standards
- class 3A
- class 3B
3A: visible beam, power <5mW
-damage on accidental exposure through optical iad
More powerful laser pointers
3B
- eye and skin hazard
- viewed only thru diffuse reflection from distance
ANSI Standards -class 4
Eye and skin hazard from intrabeam and diffuse reflection
Fire hazard
What ANSI class is an Nd:YAG 532nm (FD)
3B
What ANSI class is an Nd:YAG 1064
4
Laser Safety
- governing bodies, professional organizations (3)
- administrative controls
- practice guidelines
- protective equipment (3)
ANSI, FDA, OSHA
Laser safety officer
American Society for Laser Medicine and Surgery (ASLMS)
Warning signs, skin protection, smoke evacuation
