Physical Optics

Question 1

What is light

Answer 1

spatiotemporal electromagnetic wave

Question 2

Highest lowest frequency waves

Answer 2

Gamma, X-rays, UV, Visible, IR, microwaves, radar, TV waves

Question 3

UV absorbed by tears, aqueous, cornea,

Answer 3

UV-C and below

Question 4

UVA and UVB and the lens

Answer 4

Partially transmitted

Question 5

Aphakic patitents and UV

Answer 5

Higher risk of UV retinal damage

Question 6

A laser produces

Answer 6

highly intense, coherent beam of light. It results from a chain reaction of photon emissions.

Question 7

Population inversion

Answer 7

◦ We need to achieve a situation where the majority of atoms are in an excited state. This population inversion is achieved by adding energy to the system (called pumping)
‣ Could be in the form of UV light, chemical reactions, or any number of other sources

Question 8

Metastable states of laser

Answer 8

◦ Long lived intermediate energy states of the atoms

Question 9

Laser functioning

Answer 9

◦ 1. Pump atoms to higher energy state to achieve population inversion
◦ 2. Atoms will decay to the metastable energy states
◦ 3. Atoms will eventually decay to the ground state E0
◦ 4. A photon will be released during this decay process
◦ 5. The released photon stimulates the release of other photons (a process termed stimulated emission)

Question 10

confocal scanning laser tomography

Answer 10

Image retina

3D

Question 11

Scanning laser polarimetry

Answer 11

‣ GDx for glaucoma, polarimery to measure the RNFL thickness

Question 12

OCT

Answer 12

‣ Ultrasound bu tuning light rather than sound

‣ RNFL thickness

Question 13

ARgon laser

Answer 13

PRP
	◦ Neo and mac edema 
	◦ ALT
	◦ LPI
	◦ Treat retinal tears

Question 14

Excimer laser

Answer 14

◦ LASIK and PRK
◦ Measured IOP will decreases following LASIK (thinner cornea)
◦ LASIK: flap thickness, amount of residual stroma, and diameter and depth of ablation

Question 15

LASIK flap thickness, depth ablation

Answer 15

‣ Flap thickness: 160-250um
‣ Approximately 250um of central stroma hsould be conserved following LASIK
‣ The ablation depth per diopter for traditional LASIK
• 12u/1D=LASIK
• 15u/1D=wavefront + LASIK

Question 16

Nd:YAG

Answer 16

◦ PCO, SLT, LPI

Question 17

Helium neon laser

Answer 17

Illuminate the retina

Question 18

Krypton laser

Answer 18

Photocoagulation of the retina

Question 19

Speckle affect

Answer 19

• coherent light beam on a wall will appear to have speckles as a result of interference.

Question 20

Speckle effect: emmetrope

Answer 20

◦ When a patient is asked to move his or her head while observing the speckle effect, the speckles will appear stationary

SAME AS RET

Question 21

Speckle Effect for hyperope

Answer 21

◦ When a patient is asked to move his or her head while observing the speckle effect, the speckles will move along with head motion

SAME AS RET

Question 22

Speckle effect in myope

Answer 22

◦ When a patient is asked to move his or her head while observing the speckle effect, the speckles will move against head motion

SAME AS RET

Question 23

Diffraction

Answer 23

• bending of waves around obstacles 
• Diffraction and resolution ability 
	◦ Resolution is limited by diffraction
	◦ As light passes through a circular pattern it creates at Airy Disk. 
	◦ This is larger for smaller apertures
	◦ Two objects cannot be distinguishes when the two corresponding Airy’s disks overlap.
		‣ Rayleigh’s Criterion
• Estimating pinhole acuity
	◦ MAR=(2.33)/d

Question 24

Estimating pinhole acuity

Answer 24

MAR=2.33/d

Question 25

Thin films

Answer 25

• an anti reflective thin film can be used to created destructive interference between two reflecting light waves
• Reduce glare in sunglasses
• The minimum thickness providing destructive interference can be found from
d=wavelength/(4nf)
◦ D is the thickness, nf is the index of refraction of the film itself
◦ If wavelength is unspecified, use 555nm
• Minimum thickness version 2
OT=wavelength/4

• ideal thin film:
NF=square root n1n2

Question 26

Linearly polarizaed light

Answer 26

oscillations of the E vector (in time) all fall on a line. The magnitude of E is changing, but its direction is constant

Question 27

Circularly polarized light

Answer 27

oscillations of the E vector (in time) trace out a circle. The E vector is rotating, but its magnitude is constant. Mathematically, this is due to the addition of two linearpolarized waves of equal amplitude and aphase difference of pi/2

Question 28

Elliptically polarized light

Answer 28

different amplitudes and phase differential of pi/2

Question 29

Brewsters law

Answer 29

• some angle of incidence, the light ray reflected from the interface and the ray refracted are perpendicular:
Tan0B=n2/n1

• Polaroid sunglasses: Brewster’s law is directly applied in the design of Polaroid sunglasses, made to reduce glare arising from HORIZONTAL surfaces. They will not transmit the polarized light

Question 30

Rayleigh scattering

Answer 30

• particles causing Rayleigh are much smaller than the wavelength of light
• Underlies the reddish-orange colors seen during sunsets

Question 31

Tyndall scattering

Answer 31

• appearance of clouds