Physical Optics Flashcards
Diffraction
-Types
Bending of waves around obstacles, limits resolution
Component of pinhole acuity
Fraunhofer: far field diffraction
Fresnel: near field diffraction
Airy’s Disk
Best focused spot of light a circular aperture can make
Sine grating
Larger Disk = Smaller aperture
Rayleigh’s Criteria
Minimum resolvable distinction b/t two Airy disks
sin r = 1.22 (wavelength) / diameter (Circular Aperture)
sin r = (wavelength) / diameter (Single Slit)
Equation estimating pinhole acuity
MAR = 2.33 / pinhole diameter (in mm)
-Uses Rayleigh’s criterion
Principle of an AR coating
Provides destructive interference via a film with an n more than air but less than the lens behind it
Minimum thickness for an AR film
d (thickness) = wavelength / 4n(film)
Optical thickness = d x n(film) may be given
Use 555nm if wavelength is not given
Ideal AR film material
n(film) = SQrt of n(media) x n(lens)
Rayleigh Scattering
Gives red/orange colors during sunset and blue color to sky
Wavelength DEpendent
Intensity = 1 / Wavelength^4
Tyndall Scattering
Gives white appearance of clouds
Occurs when light passes through a suspension causing scattering of shorter wavelengths more than longer ones
Wavelength DEpendent
Polarized Light (3 ways)
Oscillations of E vector
Linear: Magnitude changing, constant direction
Circular: Magnitude constant
Elliptically: Magnitude changing
Brewster’s Law and use
At some angle at an interface, the light reflected is perpendicular to the light refracted
tan0 = n2/n1
Applied to polaroid sunglasses to reduce horizontal glare
Intensity of light transmitted through a polarizer
Unpolarized light use I = 1/2 (I of incident light)
Polarized light use I = (I of incident light) (cos angle b/t)^2
-MALUS Law (simplified to 1/2 (incident light) if angle is 45)
UV-ABC wavelengths
UV-A: 400-315 (transmission by lens decreases with age)
UV-B: 315-280
UV-C: 280-100
Population Inversion
Majority of atoms in excited state, achieved by pumping energy into the system
-Initiates photon chain reaction in lasers
Stimulated Emmision
A released photon from an atom falling to an intermediate (metastable) state causes release of other photons
Confocal Scanning Laser Tomography (CSLT)
3-dimensional photographs of the optic nerve and surrounding retina
-images retinal surface
Heidelberg Retinal Tomograph
Scanning Laser Polarimetry (SLP)
Measures RNFL thickness by measuring change in polarization
GDxVCC
Optical Coherence Tomography
Measures RNFL thickness via temporal delay
Speckle Effect
If you shine a coherent beam on a wall, it appears to have speckles due to interference with other beams.
If you move your head the speckles move too
Hyperope: with motion
Myope: against motion
Argon Laser Applications
PRP!!
ALT, LPI, retinal tears
Excimer Laser Application
LASIK and PRK (photoablation)
-IOP lowers
LASIK Ablation depth
250 microns of stroma need to be preserved
12 microns per diopter (from Munnerlyns equation 1/3diameter^2)
40% larger ablation depth for wavefront guided LASIK (15 microns)
-USE 15
Nd YAG Applications
YPC for PCO
LPI
SLT (q switched)
Helium Neon Laser Applications
retinal illumination
