Part 9 Phase Shifting Interferometry

Part 9

Phase Shifting Interferometry

?? Classical

Classical Interferogram

Interferogram

Analysis

Analysis

?? Phase

Phase Shifting

Shifting Advantages

Advantages

?? Phase

Phase Shifters

Shifters

?? Algorithms

Algorithms

?? Removing

Removing Phase

Phase Ambiguities

Ambiguities

?? Error

Error Sources

Sources

Optics 505 - James C. Wyant

Part 9 Page 1 of 36

Classical Analysis of Interferograms

Surface Error =

(¦Ë/2) (?/S)

? Classical Analysis

? Measure positions of fringe

centers.

? Deviations from straightness and

equal spacing gives aberration.

Optics 505 - James C. Wyant

Part 9 Page 2 of 36

Optics 505 - James C. Wyant

Page 1

Computer Analysis of

Interferograms

Largest

Largest Problem

Problem

Getting

Getting interferogram

interferogram data

data into

into

computer

computer

Solutions

Solutions

??Graphics

GraphicsTablet

Tablet

??Scanner

Scanner

?? CCD

CCD Camera

Camera

??Phase-Shifting

Phase-ShiftingInterferometry

Interferometry

Optics 505 - James C. Wyant

Part 9 Page 3 of 36

Advantages of Phase-Shifting

Interferometry

??High

High measurement

measurement accuracy

accuracy (>1/1000

(>1/1000

fringe,

fringe

following

only

1/10

fringe, fringe following only 1/10

fringe)

fringe)

??Rapid

Rapid measurement

measurement

??Good

Good results

resultswith

with low

low contrast

contrast fringes

fringes

??Results

Resultsindependent

independent of

of intensity

intensity

variations

across

pupil

variations across pupil

??Phase

Phase obtained

obtained at

at fixed

fixed grid

gridof

of points

points

??Easy

Easy to

to use

usewith

with large

large solid-state

solid-state

detector

arrays

detector arrays

Optics 505 - James C. Wyant

Part 9 Page 4 of 36

Optics 505 - James C. Wyant

Page 2

Phase-Shifting Interferometry

TEST

1) MODULATE PHASE

SOURCE

2) RECORD MIN 3 FRAMES

REF

3) CALCULATE OPD

INTERFEROGRAM

0¡ã

90¡ã

180¡ã

A

B

C

OPD = ¦Ë TAN-1 C - B

2¦Ð

A-B

[

Optics 505 - James C. Wyant

]

Part 9 Page 5 of 36

Phase Shifting - Moving Mirror

Move ¦Ë/8

¦Ð/2

Phase

Shift

PZT

Pushing

Mirror

Optics 505 - James C. Wyant

Part 9 Page 6 of 36

Optics 505 - James C. Wyant

Page 3

Phase Shifting - Diffraction Grating

Diffraction

Grating

+1 Order

¦Ð/2

Phase

Shift

Move 1/4

Period

Optics 505 - James C. Wyant

Part 9 Page 7 of 36

Phase Shifting - Bragg Cell

Bragg

Cell

fo

fo+f

+1 Order

fo

0 Order

Frequency

f

Optics 505 - James C. Wyant

Part 9 Page 8 of 36

Optics 505 - James C. Wyant

Page 4

Phase Shifting - Tilted Glass Plate

¦Ð/2

Phase

Shift

Optics 505 - James C. Wyant

Part 9 Page 9 of 36

Phase Shifting - Rotating Half-Wave

Plate

Circularly

Polarized

Light

Half-Wave Plate

45¡ã Rotation

¦Ð/2

Phase

Shift

Optics 505 - James C. Wyant

Part 9 Page 10 of 36

Optics 505 - James C. Wyant

Page 5

 ................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download