OL 11

Question 1

what does the beam splitter do in the Michelson interferometer?

Answer 1

splits light into 2 beams

Question 2

what is the property of the two beams after the beam splitter does its job?

Answer 2

both beams have the same amplitude, frequency and wavelength.

Question 3

whats the difference in the beams produced by the beam splitter?

Answer 3

path length (distance the beam travels from the source to the detector)

Question 4

what are the measurements in the Michelson interferometer based on?

Answer 4

1. the appearance of the interference pattern
2. the number of times the interference pattern changes from constructive to destructive interference when adjusting the mirror.

Question 5

when two light beams in the michelson interferometer are brought together, what is the resultant amplitude dependant on?

Answer 5

the resultant amplitude is dependant on the phase difference (phase shift) between the 2 beams

Question 6

in the Michelson interferometer a _______ beam of light is split into ____ these beams travel a certain ________ before each is being brought back together. The ______ _____. -_______ depends on the ____ difference between the ____ beams and builds the basis of _____/______ measurements

Answer 6

coherent
2
distances
resultant
light
intensity 
path 
2
length / depth

Question 7

what part of the Michelson interferometer is able to move? and effects of this?

Answer 7

the mirror

is able to move back and forth,
the combined light beams are able to move in and out of phase as
the phase shift varies continuously

Question 8

how long is phase of light in- interference in ophthalmic imaging- predictable and unpredictable?

Answer 8

phase of light is predictable for a finite length of time

phase of light is unpredictable for longer periods of time

Question 9

in ophthalmic imaging, interference is produced using what kind of light source?

Answer 9

low coherence light sources

Question 10

what is the coherence length calculation?

Answer 10

L= (wavelength)^2 divided by n (triangle wavelength)

n= refractive index of medium
wavelength squared= is the central wavelength of the source
triangle wavelength= spectral width of source

Question 11

what are the advantages of low coherent light sources?

Answer 11

• creation of a fringe pattern which is useful to assess structures
• less powerful light source with respect to intensity and possible harm to ocular structures

Question 12

what does low coherence imply?

Answer 12

implies that is not a single wavelength but a range of wavelengths but not from a whole spectrum

Question 13

what does the spacing of the fringe pattern provide?

Answer 13

gives position of the tissue layers in depth

Question 14

what happens when you move the reference mirror back and forth in ophthalmic imaging

Answer 14

3 interference fringe patterns will be created

Question 15

what kind of light source is used in OCT?

Answer 15

near infrared

Question 16

most tissues are partially transparent to what in ophthalmic imaging/ OCT?

Answer 16

most tissues are partially transparent to near infrared light

Question 17

what happens to the light in OCT? what does this enable?

Answer 17

some light is scattered back to the detector but some will be transmitted to deeper layers before it is reflected

-this transmission allows us to get a depth profile of the tissues assessed

Question 18

what is the wavelength is long in ophthalmic imaging, what des it enable?

Answer 18

longer the wavelength the greater the tissue penetration

Question 19

describe the mirror used in time domain OCT system?

Answer 19

moveable mirror

Question 20

describe the light source used in time domain OCT system?

Answer 20

low coherence near infrared light

produced using a superluminescent diode

Question 21

what happens to the measurement beam in time domain oct system?

Answer 21

the measurement beam is reflected or back scattered from the object ( e.g retina)

with different delay times (which are dependant on the optical properties of the ocular tissue)

Question 22

how is the axial profile of reflectivity versus depth obtained in Time domain OCT?

Answer 22

by movement of the reference mirror

which changes the path length in the reference arm

Question 23

how can the depth of the tissue be determined in Time domain OCT?

Answer 23

for each point on the retina,

magnitude of intensity of resulting interference fringes,

is recorded for each position of reference mirror and computer processing…. which determines the depth of tissue.

Question 24

what is the axial and transverse resolution of time domain OCT?

Answer 24

Axial = 10-15 microns 
transverse= 15 microns

Question 25

what kind of reference mirror does the Fourier domain OCT system use?

Answer 25

the reference mirror is stationary

Question 26

how does a Fourier domain OCT compare to a time domain OCT?

Answer 26

scan is much faster (20 to 40 times) and more detailed information is acquired.