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27 Cards in this Set

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  • Back
  • 3rd side (hint)
What does laser stand for?
Light Amplification by the Stimulated Emission of Radiation
EM Radition and Matter - What Einstein Learned
What are the 4 concepts that emerged with his work?
Spontaneous Emission
Stimulated Emission
Population Inversion
picture yourself like the sponge. you're absorbing water (energy) and dripping them back out spontaneously when there's too much. but when you're stimulated by squeezing, you get even more water out. If you're to be drived, then somebody will pop you into the hanger and invert you.
Radiation and Matter - What Einsteined Learned
Concept of Absorption
- atom receive photons with the right energy
- atom uses the energy and its electron jump to higher energy states
Radiation and Matter - What Einsteined Learned
Concept of Spontaneous Emission
- electron drop spontaneously from the unstable higher energy level to a lower orbit or ground state
- photon is emitted in a random direction
- one atom/molecular can produce multiple wavelengths
- disco, get high
- dance is random
- you can dance with many people
Radiation and Matter - What Einsteined Learned
Concept of Stimulated Emission
- requires external energy
- the excited atom is stimated by a photon to drop to a lower energy state
- atom relaese a photon identical to the photon hitting it (same energy, wavelength, direction, phase and polarization)
- initiates cascade 1-->2-->4 etc like a light amplifier
ppls who are shy in the disco needs some alcohol to get warmed up (external energy). When they're excited they release the same amount of highs as the amt of EtOH intake. The aloohol surely plays an cascade effect on everyone.
Radiation and Matter - What Einsteined Learned
Concept of Population Inversion, metastable state
- stimulated emission must out-rival absorption and spontaneous emission for LASER
- population inversion when there's more atoms in a higher energy, excited state than at a lower energy/ground state
- achieve metastable state when excited e's take longer to spontaneously decay, which means P(causing stimulated emission) is greater
Components of a Laser
1. Pump
2. Laser medium
3. Resonator
Component of Laser - Pump
What it is
What does it do
- laser's external energy source
- create population inversion
- types: *electrical, *optical, chemical, thermal
Electrical pump vs. optical pump
- type of laser
- mechanism
electrical pump:
- strong electrical current passed through the gas in gas lasers
optical pump
-used in liquid and solid state lasers
- interse flash of light (white or light from another laser) is directed into laser medium
The laser medium
What it is
AKA amplifying medium or lasing material (ex. YAG)
- determines wavelength of laser radiation emitted
- type: gas, liquid or solid
what it is
set up and mechanism
AKA resonant cavity or optical cavity
- the chamber that holds the laser medium
- laser medium between two aligned parallel mirrors
- one mirror reflects 100% of the light
- one mirror partially reflect some incident light and transmit the remainder
Types of Lasers
1. Solid Sate
2. Semiconductor/Diode
3. Liquid/tunable dye
4. Gas Lasers
4 types
Type of laser - solid state
a. type of medium
b. set up
a. transparent solid crystal
- crystal forms the resonator
- ends are polished to act as mirrors
- optical pump is a light wrappened around the crystal
a. type of medium
b. set up
c. ex.
- solid crystallin substance with enhnaced conductive rpoperties
- doped with taraces of impurities that enhanced the crystal's conductive properties
- hardy, compact and relatively inexpensive
ex. LEDs, transistors and other electronic components
Liquid/Tunable dye
a. type of medium
b. set up
a. organic dye in liquid solution or suspension
- potential output includes the entire visible spectrum
b. specific wavelenth can be tuned
cost effective bc multiple lasers are not required
Gas Lasers
a. type of medium
b. set up
c. ex.
a. single element gases or compounds
- pump is an electric current that passes through
- excrimer laser in LASIK and PRK
Production of Laser Light
Mirror 1= total reflect
Mirror 2= partial reflect
Atoms in laser in the resoonator are in ground state
1. External energy (light/e) is pumped into the laser medium
2. Population inversion when atoms raised to excited state
3. Initially, spontaneous emission giving off photons randomly and are lost
4. Some along cavity's optical axis perp. to mirror = seed photons
5. Seed photons hit atoms in metastable state and stimulated emisstion starts cascade
6. build up of coherent photons in the cavity
4. some hit partially reflecting mirror --> transmitted as laser beams
5. remaining oscillates back and forth to continue cascade and stimulated emission
What is the first medical use of laser?
- ophthalmologist first to use it surgically to repair a retinal detachment
Why lasers over surgical blades?
- cleaner incisions
- dry (bloodless) field of surgery
- less postop pain
- better sterility
- clear field of view
- can perform microsurgery
- minimally invasive
- can be computer controlled
Examples of Diagnostic Ophthalmic Uses of Lasers
1. Laser Interferometry
- VA with media opacities
- diffraction patterns projected onto the macula
2. Confocal Scanning Laser Ophthalmoscopy = Retinal Tomography
- high resolution digital colour images of the retina --> ON and macular disease
ex. HRT
3. Scanning laser polarimetry
- measures retinal NFL thickenss for detection of glaucoma
- phase shift of IR laser proportional to thickness
ex. the GDx NFL analyzer
4. Optical coherence tomography
- high resoltion, corss sections of retina
- analogous to B-scan (but light wave intd of sound)
Examples of Therapeutic Use of Lasers
1. Refractive surgery
2. Glaucoma surgery (TM meshwork increase outflow)
3. Retinal surgery (seal leaky vessles and repair holes/tears)
5 unique characteristics of laser light
- monochromatic
- coherent
- collimated
- intense
- easily focused
Characteristic of Laser Light
- single wavelength - pure in colour
- no loss of brightness bc no filtering
- wavelength determins how laser light interacts with human tissue
- piment molecules absorb laser --> rhodopsin, melanin, Hb, xanthophyll
Characteristic of Laser Light
each photon in laser light is identical in phase, wavelength, polarization adn energy and direction
- no reduction in light intensity
- neccessary for small, intense spot of light in therapeutic laser procedures
Characteristic of Laser Light
- extremely narrow beams with minimal spread
- can travel long d w/o divergence
resonator's mirror concave --> increases collim by narrowing reflected light
- also affected by distance between mirrors
Characteristic of Laser Light
- lower power lasers hundrens times brighter than sunlight
- high intensities by focuign light on small area and devlivering energy in pulses
- no cancelling of light due to incoherent photons
Characteristic of Laser Light
- lens + collimate => small diam spot sizes
- able to focus to wavelenth of the light
- when lens are used, place target at focal point where laser energy is the greatest