Dronka's Review - Martin Flashcards
(46 cards)
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
