Diffraction 1 (7-9)

Question 1

Diffraction is a change in ________NOT due to _________or________.

Answer 1

direction of propagation of light

reflection or refraction.

Question 2

Snells law?

Answer 2

reflection or refraction.

Question 3

Can we use Snell’s law to predict diffraction?

Answer 3

If rays travel in straight lines, then the shadow pattern should have sharp edges,
but they don’t! Blurring of the edges is a sign of diffraction at work.

Question 4

Phenomenon of diffraction -

Answer 4

The deviation from rectilinear propagation
that occurs when light advances beyond an
obstruction

Question 5

THE HUYGENS PRINCIPLE.

Answer 5

All points on a wavefront can be considered as point sources for the production of spherical secondary
wavelets, and at any later time the new wavefront position is the envelope (or surface of tangency) to these
secondary wavelets.”

Question 6

Single-Slit Diffraction

Answer 6

Wavelength of source equal to or larger than width of the slit (λ > a), forms diffraction pattern.

Question 7

Fresnel (Near field) Diffraction

Answer 7

In the Fresnel diffraction, the source of light and the
screen are at a finite distance from the diffraction
aperture.

Question 8

Fraunhofer (Far-field) Diffraction

Answer 8

In the Frauhofer diffraction, the source of light and the
screen are at a infinite distance from the diffraction
aperture.

Question 9

Fresnel Diffraction or Fraunhofer Diffraction?

‘Near-field diffraction’

Answer 9

Fresnel

Question 10

Fresnel Diffraction or Fraunhofer Diffraction?

Finite distance (slit to screen)

Answer 10

Fresnel

Question 11

Fresnel Diffraction or Fraunhofer Diffraction?

Plane wave

Answer 11

Fraunhofer

Question 12

Fresnel Diffraction or Fraunhofer Diffraction?

‘Far-field diffraction’

Answer 12

Fraunhofer

Question 13

Fresnel Diffraction or Fraunhofer Diffraction?

Difficult to observe & calculate

Answer 13

Fresnel

Question 14

Fresnel Diffraction or Fraunhofer Diffraction?

Infinite distance (slit to screen)

Answer 14

Fraunhofer

Question 15

Fresnel Diffraction or Fraunhofer Diffraction?

Converging or Diverging wave

Answer 15

Fresnel

Question 16

Fresnel Diffraction or Fraunhofer Diffraction?

Diffraction patterns vary with distance
Slit to screen

Answer 16

Fresnel

Question 17

Fresnel Diffraction or Fraunhofer Diffraction?

Easy to observe & calculate

Answer 17

Fraunhofer

Question 18

Fresnel Diffraction or Fraunhofer Diffraction?

Insensitive to distance changes
(maintains same angular relationship

Answer 18

Fraunhofer

Question 19

Fresnel Diffraction or Fraunhofer Diffraction?

Poisson spot – Bright in the center of a
shadow (Argo spot or Fresnel’s bright spot)
Ex. Floaters in eye

Answer 19

Fresnel

Question 20

Combined effect of 2-slits and single-slit interference

Answer 20

With 2-slits, not only you will see diffraction patterns due to individual single-slits
but also interference patterns due to the waves coming from different slits.

Question 21

Rayleigh’s criterion states :

Answer 21

that the two point resolution limit occurs when the first minimum (the boundary of
Airy’s disk) of one diffraction pattern coincides with the center maximum of the other diffraction limited pattern.

Question 22

The diffraction pattern formed on a distant screen resulting from a uniformlyilluminated
circular aperture has a bright region in the center, known as _____________

Answer 22

Airy’s disk.

Question 23

The central disk plus the surrounding series of concentric bright rings is called the _________

Answer 23

Airy

pattern.

Question 24

Diffraction places a limit on the ability of the system to form ________

Answer 24

good quality images

Question 25

Diffraction is limited by

2 things:

Answer 25

a. Diffraction effects (small aperture)

b. All aberrations (large aperture)

Question 26

Optical systems that are “perfect” (correct focus, aberrations
sufficiently corrected) are referred to as :

Answer 26

diffraction limited systems

Question 27

Snellen acuity is equal to the reciprocal of the. (Keating 506)

Answer 27

minimum

resolvable angular detail (expressed in minutes)

Question 28

Resolution Efficiency is:

Answer 28

a subjective method of
determining image quality of an optics (IOL,
contact lens, spectacles, or any single optics).
Still considered as the industry ‘gold standard’
for image quality

Question 29

To remove the rings around the central maximum and concentrate energy in the central maximum is

Answer 29

‘Apodization.’

Question 30

At the center of the
apodized circular pupil,
the intensity
transmission is :.

Answer 30

100%

Question 31

At a distance (h = wo
)
from the center, the
transmission drops by:

Answer 31

13.5%.

Question 32

For a clear circular aperture, Airy’s
disk contains ____ of the intensity
(light) in the diffraction pattern.

Answer 32

84%

Question 33

In the Gaussian diffraction pattern,
_____of the intensity is inside the
circle described by h = w(z).

Answer 33

86%

Question 34

Stile Crawford Effect

Answer 34

The Luminous efficiency of rays entering at the center of
the eye pupil is greater than the luminous efficiency of the
rays entering through the edge of the pupil.t

Question 35

Stiles – Crawford apodization influences:

Answer 35

the visual acuity*

and visual performances+ of the human eye

Question 36

Transmission grating

\:Acts as a \_\_\_\_ splitter
- Less sensitive to \_\_\_\_\_
- Less sensitive to 
\_\_\_\_\_\_\_\_\_\_\_
- Efficiency reduces with higher \_\_\_\_\_\_\_\_\_\_\_

Answer 36

beam

polarization

alignment

wavelength

Question 37

A diffraction grating consists of many slits with a very

____ slit separations.

Answer 37

small

Question 38

Blazed Grating

Answer 38

A diffraction grating that is designed to channel light
away from the central maximum (0th order) into 1st or
2
nd order maximums.

Question 39

Blazing angle:

Answer 39

Angle at which the efficiency is maximum.