Physical Optics Midterm 2

What is diffraction?

light waves bending around an object

What does the degree of diffraction (spreading of the wave) depend on?

ratio of the wavelength to size of opening

What affect does a small opening and long wavelength have on diffraction?

diffraction is more visible

What is Huygen's Principle?

Every point on a wave front is a source of secondary waves

According to Huygens' principle, continuing wavefronts...

are given by the envelop of secondary waves

What is the Huygens-Fresnel principle ?

wider slit=N point sources

Each part of a slit acts as what

point source

What is the central maximum with diffraction?

Constructive interference when all waves are 100% in phase

What is Fraunhofer diffraction also called?

far field diffraction

What is Fraunhofer diffraction/far field diffraction?

distant screen AND distance light source are not sensitive to distance changes

What happens to diffraction when moving the screen distance in Fraunhofer/far field diffraction?

only the diffraction size changes, not the shape

What is Fresnel diffraction also called?

near field diffraction

What is fresnel/near field diffraction?

near screen OR near light source make the diffraction sensitive to distance changes

What happens to diffraction when moving the screen distance in fresnel/near field diffraction?

both diffraction size and shape changes

The minimums of single-slit diffraction radian comparison to central maximum

always have less radians than central maximum

What is the equation for angular location of single-slit diffraction? (with small angle approximation?)

ø=mwavelength/d

What is d in angular location of single-slit diffraction equation?

d= size of slit

What happens to the ø if you increase the size of the slit?

smaller ø

What happens to the ø if you decrease the size of the slit?

larger ø

What is ø in angular location of single slit diffraction equation?

angle of location of dark fringe

What is m in angular location of single slit diffraction equation?

order of dark fringe

What is the equation for linear location of single slit diffraction? (with small angle approximation?)

x=tø

What is t in linear location of single slit diffraction?

distance of slit to diffraction

What is x in the linear location of single slit diffraction?

distance between fringe and the central maximum

What is the angular radius of Airy's disk?

angular location of 1st minimum

What is the equation for Airy's Disk?

ø=1.22 wavelength/d

What is d in the Airy's Disk equation?

diameter of the aperture

What is the Rayleigh criterion?

Resolution limit between two points occurs when the max of one diffraction pattern lies on the 1st minimum of other diffraction pattern.

How to find the resolvable angle?

ømin=1.22 wavelength/d

What is the criteria for a resolvable angle (distinguishable)?

ø of 2nd diffraction pattern >/= ømin

What is the criteria for a nonresolvable angle?

ø of 2nd diffraction pattern< ømin

How to calculate angle in minutes of arc to snellen acuity?

20/(20 x ø [in minutes of arc])

How do you convert radians to arc minutes?

radians x 57.3 x 60

What happens to image quality if the pupil size is too large?

image is degraded due to aberrations

What happens to image quality if the pupil is too small

image is degraded due to diffraction

Why does a myope with no higher order aberrations see best with a smaller pupil?

it makes a smaller circle of least confusion

If a patient looks through a pinhole and sees no improvement in acuity, what is likely the cause of their poor acuity?

pathology

If a patient looks through a pinhole and sees improvement in acuity, what is likely the cause of their poor acuity?

optical causes (refractive error)

What are zone plates?

Circular Diffraction gratings used to focus light by diffraction

How many point images does an amplitude zone plate form?

3

How many point images does a phase zone plate form?

2

What are the advantages to a phase zone plate?

All light is transmitted, compared to only 50% with amplitude zone plate. Therefore the image is brighter

light an be focused at 2 points instead of 3

What is a speckle pattern?

interference pattern formed on the retina

What is the movement of the speckle pattern of a myope who is moving their head?

against motion

What is the movement of a speckle pattern of a myope when the surface is moving?

with motion

What is the movement of the speckle pattern of a hyperope who is moving their head?

with motion

What is the movement of a speckle pattern of a hyperope when the surface is moving?

against motion

How does the speckle pattern move for an emmetrope who is moving their head?

no movement

How does the speckle pattern move for an emmetrope looking at a moving surface?

no movement

How does the motion of a speckle pattern change with decrease ametropia?

the lower the ametropia, the slower the perceived motion

Scattering can be?

coherent or incoherent

What defines small particle scattering

d << wavelength

What is the process of small particle scattering?

re-radiation

How does wavelength affect small particle scattering?

Is=1/wavelength^4

How does d affect small particle scattering?

Is=volume^2

aka d^6

What is an example of small particle scattering?

d >> wavelength

What is the process for large particle scattering?

refraction, reflection, diffraction

How does wavelength affect large particle scattering?

it doesn't

How does d affect large particle scattering?

Is = area

aka d^2

Small and large particle scattering are what kinds of scattering?

incoherent

What are refractive waves?

scatter waves in a constructive interference direction

What does reflective light come from?

the scattering within a half wavelength zone or surface

Why do you get low scattering with coherent particles?

they cause destructive interference

When do you get coherent scattering?

When particles are much closer together than coherent wave of light

polarization of an electromagnetic wave is the

orientation of its electric field

What does linear polarization mean?

electric field is in a singular direction

What does circular + elliptical polarization mean?

electric field rotates as the wave travels

Polarization direction is always?

perpendicular to direction of light propagation

Unpolarized light has what polarization direction?

variable, rapidly changing direction

When is reflected light linearly polarized?

when it is incident on Brewsters angle

What is Brewster's angle?

This is the angle at which reflected light is linearly polarized

What is the orientation of the reflected + refracted ray at Brewsters angle?

reflected ray is 90º to refracted ray

How/what direction is light polarized from a waters surface at Brewsters angle?

horizontally

Polarizing specs with a vertical transmission axis only lets it what type of light? What light does it block?

only lets in vertical light, blocks horizontal light

What can be used to block light reflected from waters surface at brewsters angle?

polarizing specs with a vertical transmission axis

When is scattered light linearly polarized?

when the scattered light is 90º to the incident unpolarized light

What do you get when you add vertically polarized light + horizontally polarized light that are in phase or 180º out of phase?

linearly polarized light (diagonal direction)

Polarization direction is always compared to what?

direction of light propagation

If light is circularly polarized to the left, what direction is that?

counter clockwise

If two linearly polarized light waves are added 90º out of phase, what do you get?

circularly polarized light

What is the polarization state looking at?

When the vertical component is retarded compared to the horizontal component

Circular polarization phase retardation? phase difference?

phase retardation of either 90º or 270º

phase difference of 90º

Linear polarization phase retardation? phase difference?

phase retardation of 0º, 180º, or 360º

phase difference of 0 (in phase) or 180º

Elliptical polarization phase retardation?

Any phase retardation that isn't 0, 90, 180, or 270

Amount of phase retardation of a retardation plate is dependent on?

thickness of material

wavelength of material

What does a quarterwave plate do?

90º phase retardation

What does a halfwave plate do?

180º phase retardation

If light input to a quarterwave plate is linearly polarized, what is the output light polarization?

circularly polarized

If light input to a halfwave plate is linearly polarized, what is the output light polarization?

linearly polarized in opposite direction

If input into a quarterwave plate is circularly polarized, what is the output light polarization?

linearly polarized

If light input into a Halfwave plate is circularly polarized, what is the output light polarization?

circularly polarized in the opposite direction

If input into a quarterwave plate is unpolarized, what is the output light polarization?

unpolarized

If light input into a halfwave plate is unpolarized, what is the output light polarization?

unpolarized

What is an extraordinary ray?

ray that changes speed in crystal depending on propagation direction

What is an ordinary ray?

ray that is the same speed in every direction crystal

How are extraordinary and ordinary waves organized?

Linearly polarized 90º from eachother

When comparing two different light waves in a crystal, what is different between them?

speed, wavelength, and index of refraction