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Flashcards in Diffractive Optics And Iridescence Deck (33):
1

An optical device that blocks alternate zones is called a ___________

Zone plate

2

A diffraction grating that creates inwardly bending spherical diffracted wave forms a _________

Point image

3

The focal length of the plate is give by...

F2=r^2/mlambda

4

Fresnel zone plate blocks wave that contribute to destructive interference at the diffraction maximum, making the image formation much ________

Dimmer

5

Instead of blocking these waves, they are ________________.

Phase shifted by 180

6

After phase shift of 180, the phase shifted waves would be ___________ with the axial wave, and would contribute to the constructive interference at the diffraction maximum, making the image much _________.

What is this called?

-in phase
-brighter

Phase plate or phase reversal zone plate

7

A zone plate with kinoform shaped grooves is referred to as a ______________

Diffractive lens

8

What is the benefit of the kenoform shaped grooves on an ophthalmic diffractive lens?

It makes it much thinner

9

A single refractive lens with a phase plate embedded on one side of its surfaces

Hybrid lens
Multifocal

10

The original bulk of the dashed lens is reduced, leaving a thin lens whose surface slopes match the original lens. This example has __________

Equal step heights

11

A Fresnel lens with ______________. A fresnel lens is always a mono-focal lens.

Equal zone widths

12

What does the power in the M=0 come from?

The base curve power

13

1st order in contact lens

Near vision

14

0th order in contact lens

Distance vision

15

Local grating _________ determines ray direction (add power). Spacing gets progressively smaller from center to its edge

Spacing

16

Local step _____ determines "diffraction efficiency" of light. (Determines how much light put into the add portion)

Height

17

Allocation of energy into each diffraction order

Diffraction efficiency

18

When m=0, focal length of _________ is infinite (zero power)

0th order

19

What is the diffraction efficiency for multifocal

About 80%
40% from 0th order
40% from +1 order

20

Efficiency for trifocals

Divide 80% by 3

21

Expected VA for multifocal

Near: 20/40
Distance: 20/20

Cant get 20/20 all around

22

Unwanted patterns onto the retina which affect the visual performance by obscuring relevant retinal image

Dysphotopsia

23

What are the two types of dysphotopsia

Positive and negative

24

Positive dysphotopsia

Bright artifacts onto the retina
Ex. Arcs, rings, streaks, halos, and glares

25

Negative dysphotopsia

Blockage of light onto the retina
Ex. Shadows, dark spots

26

Fresenel's lens increases the luminosity of the lighthouse lamp by a factor of _____

4

27

The smaller fresnel lens orders, the 4th though the 6th orders, were often situated where?

Lakes and harbors

28

Biological color effects: physics

-structural pattern
-delivers color due to interference, diffraction and scattering

29

Natural diffraction grating on a component found on the insect exoskeleton

Chitin

30

Mollusk outer surface of shell

-fine scale grooves
-3.4 micrometer
-296 grooves/mm
-parallels grooves, smooth and even
-diffraction color is strong

31

Inner surface of mollusk shell

-widely separated
-11.5micometers
-87 grooves/mm
-very rough
-diffraction color is weak

32

Iridescence in shell

Higher orders (3-8) get overlapped
-this causes iridescence
-depend son groove density and surface quality

33

Pearl

Layer structure diffuses the light and causes less to the iridescence but contribute to the body color of the shell