Abstract

A digital phase measuring interferometer with a frequency-modulated laser diode using the integrated-bucket technique is described. The injection current is continuously changed to introduce a time-varying phase difference between the two beams of an unbalanced Twyman-Green interferometer. The intensity of the interference patterns is integrated with a CCD array sensor for intervals of one-quarter period of the fringe. Using the intensity data a microcomputer calculates the phase to be detected. Some experimental results with the interferometer are presented; the rms repeatability obtained was λ/80.

© 1988 Optical Society of America

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References

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  1. J. H. Bruning, D. R. Herriott, J. E. Gallagher, D. P. Rosenfeld, A. D. White, D. J. Brangaccio, “Digital Wavefront Measuring Interferometer for Testing Optical Surfaces and Lenses,” Appl. Opt. 13, 2693 (1974).
    [CrossRef] [PubMed]
  2. J. C. Wyant, “Use of an ac Heterodyne Lateral Shear Interferometer with Real-Time Wavefront Correction Systems,” Appl. Opt. 14, 2622 (1975).
    [CrossRef] [PubMed]
  3. K. D. Stumpf, “Real Time Interferometer,” Opt. Eng. 18, 648 (1979).
    [CrossRef]
  4. K. Tatsuno, Y. Tsunoda, “Diode Laser Direct Modulation Heterodyne Interferometer,” Appl. Opt. 26, 37 (1987).
    [CrossRef] [PubMed]
  5. Y. Ishii, J. Chen, K. Murata, “Digital Phase-Measuring Interferometry with a Tunable Laser Diode,” Opt. Lett. 12, 233 (1987).
    [CrossRef] [PubMed]
  6. K. Creath, “Interferometric Investigation of a Diode Laser Source,” Appl. Opt. 24, 1291 (1985).
    [CrossRef] [PubMed]
  7. C. J. Morgan, “Least-Squares Estimation in Phase-Measurement Interferometry,” Opt. Lett. 7, 368 (1982).
    [CrossRef] [PubMed]
  8. M. Yonemura, “Wavelength-Change Characteristics of Semiconductor Lasers and Their Application to Holographic Contouring,” Opt. Lett. 10, 1 (1985).
    [CrossRef] [PubMed]
  9. K. N. Prettyjohns, “Charge coupled device image acquisition for digital phase measurement interferometry,” Opt. Eng. 23, 371 (1984).

1987

1985

1984

K. N. Prettyjohns, “Charge coupled device image acquisition for digital phase measurement interferometry,” Opt. Eng. 23, 371 (1984).

1982

1979

K. D. Stumpf, “Real Time Interferometer,” Opt. Eng. 18, 648 (1979).
[CrossRef]

1975

1974

Brangaccio, D. J.

Bruning, J. H.

Chen, J.

Creath, K.

Gallagher, J. E.

Herriott, D. R.

Ishii, Y.

Morgan, C. J.

Murata, K.

Prettyjohns, K. N.

K. N. Prettyjohns, “Charge coupled device image acquisition for digital phase measurement interferometry,” Opt. Eng. 23, 371 (1984).

Rosenfeld, D. P.

Stumpf, K. D.

K. D. Stumpf, “Real Time Interferometer,” Opt. Eng. 18, 648 (1979).
[CrossRef]

Tatsuno, K.

Tsunoda, Y.

White, A. D.

Wyant, J. C.

Yonemura, M.

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Figures (8)

Fig. 1
Fig. 1

Experimental setup for measuring phase and wavelength change of the LD by varying the injection current with a heterodyne interferometer.

Fig. 2
Fig. 2

Dependence of the wavelength change on temperature for the laser diode.

Fig. 3
Fig. 3

Peak wavelength of the LD used in the experiment as a function of injection current.

Fig. 4
Fig. 4

Interference signals (lower traces) introduced by 100-Hz triangular modulation current (upper traces) which is varied from 60 to 70 mA. The optical path differences are l1 and l2, respectively.

Fig. 5
Fig. 5

Timing diagram for the data acquisition scheme with the integrated-bucket technique: (a) and (b), field-shift pulses; (c) trigger signal; (d) the triangular modulation injection current; (e), (g), and (f) illustrate that only the even field can be frozen.

Fig. 6
Fig. 6

Oscillograph showing the even field-shift pulse ϕυ1 and the triangular injection current.

Fig. 7
Fig. 7

Experimental result of the spherical aberration of a test lens.

Fig. 8
Fig. 8

Three-dimensional plot of the phase distribution of an evaporated thin film.

Equations (7)

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Δ Φ 1 = 2 π l 1 Δ λ λ 0 2 , Δ Φ 2 = 2 π l 2 Δ λ λ 0 2 ,
Δ λ = ( m 2 m 1 ) λ 0 2 l 2 l 1 ,
I ( x , y , l ) = a ( x , y ) + b ( x , y ) cos { 2 π λ [ 2 w ( x , y ) + l ] } ,
Φ 0 + Δ Φ = 2 π λ 0 ( 2 w + l ) ( 2 π l Δ λ λ 0 2 + 2 π 2 w Δ λ λ 0 2 ) .
I ( x , y , t ) = a ( x , y ) + b ( x , y ) cos [ Φ 0 ( x , y ) ν t ] ,
A ( x , y ) = π 2 a ( x , y ) + 2 b ( x , y ) cos [ Φ 0 ( x , y ) ] , B ( x , y ) = π 2 a ( x , y ) + 2 b ( x , y ) sin [ Φ 0 ( x , y ) ] , C ( x , y ) = π 2 a ( x , y ) 2 b ( x , y ) cos [ Φ 0 ( x , y ) ] , D ( x , y ) = π 2 a ( x , y ) 2 b ( x , y ) sin [ Φ 0 ( x , y ) ] ,
Φ 0 ( x , y ) = 2 π λ 0 [ 2 w ( x , y ) + l ] = tan 1 B D A C .

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