Diffraction 1 (10-11) Flashcards
A diffraction grating made of _______slits
‘circular
• An optical device that blocks alternate zones is called
a
‘Zone Plate’
A diffraction grating that creates inwardly bending
‘spherical’ diffracted wave forms a ._______
‘point image’
For a ___________source of light incident on a zone plate:
• Central order (0th) goes through
• First order (1st) forms point image at___
.
• Second order forms point image at ____
• Third order forms point image at _____
monochromatic
straight.
f2
f2/2.
f2/3
___________ blocks wave that contribute to
destructive interference at the diffraction maximum,
making the image formation much__________
Fresnel zone plate
‘dimmer’.
Phase Plate:
Instead of blocking these waves, they are phase shifted
by _______
Then, the phase shifted waves would be________with the axial wave, and would contribute to the
_________ interference at the diffraction maximum,
making the image much________
180°.
in phase
constructive
‘brighter’.
Ways to make ‘Phase Plate’ by adjusting -
- No. of _______
- Depth of the____ d)
- Refractive ______μ)
- __________
grooves
groove (
Index (
Wavelength(λ)
A zone plate with kinoform shaped grooves
is referred to as a _______
diffractive lens.
: A single
refractive lens with a
phase plate imbedded on
one side of its surfaces.
Hybrid lens
A Fresnel lens with equal zone widths. A Fresnel
lens is always a ______lens.
mono-focal
Diffractive Lens Design Details:
Local grating ______determines ray direction (add power).
Spacing gets progressively smaller from____ to its
______.
spacing
center to its edge.
Diffractive Lens Design Details:
Local Step______determines ‘diffraction efficiency’ of light.
[determines how much light put into the add portion]
height
Allocation of energy into each diffraction order
When m= ____focal length of 0th order is infinite (zero
power).
The base power of the lens provides all the power at
this order. At this power, ______ vision is corrected.
When m=_____ energy is distributed to the 1
st order.
=0,
distant
=1,
Unwanted patterns onto the retina
which affect the visual performance by
obscuring relevant retinal image.
Dysphotopsia
Bright artifacts onto the retina.
Ex. Arcs, rings, streaks, halos & glare
Positive Dysphotopsia:
Blockage of light onto the retina.
Ex. Shadows, dark spots.
Negative Dysphotopsia:
Fresnel’s lens increases the luminosity of the
lighthouse lamp by a factor of ______
4.
\_\_\_\_\_\_\_\_Lighhouse in Waimanalu, Hawaii. The lighthouse has a hyper-radiant Fresnel lens with a 1.3-m focal length, one of the largest in the world.
Makapuu
Delivers color by absorption at
certain wavelength and reflects at
others)
chemistry
and pigment coloration
Delivers color due to Interference,
diffraction & Scattering.
physics and structural patteren
A component found on the insect
exoskeletons. RI, n = 1.53 – 1.56.
chitin
_______________causes ‘iridescence’ color.
Overlap of several orders of diffraction
• Strength of the Iridescence depends on the__________ and ___________
‘groove density’ and
the ‘surface quality’.
0th order is very _____
3rd-8th order is ______
intense
iridescence
Holography:
Developed by__________ in 1948. Had to wait until the invention of Lasers (Coherent source) to record a hologram. In _______received Noble prize in physics
Dennis Gabor
1971
Requirements of Holography :
_______ Light
Maintain ‘_______ of 2 waves
constant all through out
Extremely complicated ______________
Coherent
phase relationship’
Interference
Unlike conventional imaging, in_________imaging ‘Light from each point on the object will reach all points on the film’
holographic
holography: _________causes Interference pattern to
be formed producing an image with 3D
information.
Phase-difference
Requires a_________Source to view the holographic image recording
Coherent
__________ in 1969 invented ‘rainbow’ hologram
– a second generation holography.
Stephen Benton
________ viewed – You will see ‘3D image’
_________viewed – You will see ‘different colors’
Types of Holograms: ____________
Real Image formed (m=+1) are not normal viewed
Virtual Image formed (m=-1) behind the film are viewed
Horizontally
Vertically
Transmission and Reflection
For the eye, only a section passes through the pupil; the iris is an obstruction that diffracts the light. This
diffraction blurs the image. For a system limited only by diffraction (no optical aberrations), the image radius for a
point object =__________
1.22 λ f/d meters.
Pupil size controls impact of ___________ and ___________on retinal image quality (emmetrope)
ocular aberrations
diffraction
collagen:
A fibril spacing (d) ______than the wavelength of light (λ) will make
the fibrils transparent as light passes through undeviated.
smaller
If d < λ then θ > 90 deg for all m > 0.
Therefore, no diffraction orders exist except _____
Under this condition, the fibrils diffract no light
and appear transparent.
m = 0.
WHAT IS THIS TALKING ABOUT?
Light entering the eye is diffracted by small
particles in the eye.
Each particle causes a circular diffraction
pattern on the retina tens of degrees across.
Interference of overlapping diffraction
patterns for white light is easily observed by
viewing a small, bright, white light source.
We perceive a very fine pattern of
innumerable needles of light, fanning out
from the point object over several degrees.
The
ciliary corona
is an entoptic diffraction phenomeno
