Abstract

As a means of modulating lasers, acousto-optical cells are a relatively simple and generally satisfactory solution. When used in the zero-order mode to modulate the undiffracted light, they do suffer from the disadvantage that the maximum contrast between the on and off states is typically 10 to 1. This cannot be improved by increasing cell length because it orginates from rediffraction of once-diffracted light. By spatial filtering the light between passes through multiple cells, or alternatively, multiple passes through a single cell, this contrast can be improved by removing the once-diffracted orders before they can be rediffracted into the zero-order beam. Experimentally we have demonstrated an improvement of a factor of 10 in contrast by using two cells, each of which by itself produces only a 10 to 1 contrast. In addition to using filters consisting of stops and apertures, it is possible to achieve similar results with polarization filters. Multiple applications of this filtering improve contrast as the power of the contrast of a given step, thus contrast of modulation in zero order can be improved to any desired degree.

© 1977 Optical Society of America

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References

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  1. See Proceedings of OSA/IEEE Conference on Laser and Electro-Optical Systems, San Diego, Calif.May 1976, Session WD, for a description of some of these.
  2. I. C. Chang, “Acoustooptic Devices and Applications,“ IEEE Trans. Sonics Ultrasonics SU23, 2–22 (1976).
    [Crossref]
  3. J. M. Hammer and D. J. Channin, “Simple Acoustic Grating Modulators,” Appl. Opt. 11, 2203–9 (1972).
    [Crossref] [PubMed]
  4. F. H. Sanders, “Intensity Measurements in Diffraction of Light by Ultrasonic Waves,” Can. J. Res. 14, 158–71 (1936).
    [Crossref]
  5. R. Bär, “Über Versuche zur Theorie von Raman and Nagendra Nath über die Beugung des Lichtes an Ultraschallwellen,“ Helv. Phys. Acta. 9, 215–284 (1936).
  6. W. R. Klein and B. D. Cook, “Unified Approach to Ultrasonic Light Diffraction,“ IEEE Trans. Sonics Ultrasonics SU14123–134 (1967).
    [Crossref]
  7. R. W. Damon, W. T. Malony, and D. H. McMahon, “Interaction of Light with Ultrasound: Phenomena and Applications,” in Physical Acoustics VII, edited by Mason (Academic, New York, 1970), pp. 273–366.
  8. C. V. Raman and N. S. Nagendra Nath, Proc. Indian Acad. Sci. 2A, 406–412, 413–420, (1935);Proc. Indian Acad. Sci. 3, 75–84, 119–125, 459–465 (1936).
  9. L. E. Hargrove, E. A. Hiedemann, and M. Mertens, “Diffraction of Light by Two Spatially Separated Parallel Ultrasonic Waves of Different Frequency,” Z. Phys. 167, 323–336 (1962).
  10. M. V. Berry, The Diffraction of Light by Ultrasound (Academic, London, 1966).
  11. R. S. Chu and T. Tamir, “Bragg diffraction of Gaussian beams by periodically modulated media,” J. Opt. Soc. Am. 66, 220–226 (1976).
    [Crossref]
  12. Schott Optical Glass, Inc., Duryea, Penn. 18642.
  13. M. Eschler and F. Weidinger, “Acousto-optic Properties of Dense Flint Glasses,” J. Appl. Phys. 46, 66–70 (1975).
    [Crossref]

1976 (2)

I. C. Chang, “Acoustooptic Devices and Applications,“ IEEE Trans. Sonics Ultrasonics SU23, 2–22 (1976).
[Crossref]

R. S. Chu and T. Tamir, “Bragg diffraction of Gaussian beams by periodically modulated media,” J. Opt. Soc. Am. 66, 220–226 (1976).
[Crossref]

1975 (1)

M. Eschler and F. Weidinger, “Acousto-optic Properties of Dense Flint Glasses,” J. Appl. Phys. 46, 66–70 (1975).
[Crossref]

1972 (1)

1967 (1)

W. R. Klein and B. D. Cook, “Unified Approach to Ultrasonic Light Diffraction,“ IEEE Trans. Sonics Ultrasonics SU14123–134 (1967).
[Crossref]

1962 (1)

L. E. Hargrove, E. A. Hiedemann, and M. Mertens, “Diffraction of Light by Two Spatially Separated Parallel Ultrasonic Waves of Different Frequency,” Z. Phys. 167, 323–336 (1962).

1936 (2)

F. H. Sanders, “Intensity Measurements in Diffraction of Light by Ultrasonic Waves,” Can. J. Res. 14, 158–71 (1936).
[Crossref]

R. Bär, “Über Versuche zur Theorie von Raman and Nagendra Nath über die Beugung des Lichtes an Ultraschallwellen,“ Helv. Phys. Acta. 9, 215–284 (1936).

1935 (1)

C. V. Raman and N. S. Nagendra Nath, Proc. Indian Acad. Sci. 2A, 406–412, 413–420, (1935);Proc. Indian Acad. Sci. 3, 75–84, 119–125, 459–465 (1936).

Bär, R.

R. Bär, “Über Versuche zur Theorie von Raman and Nagendra Nath über die Beugung des Lichtes an Ultraschallwellen,“ Helv. Phys. Acta. 9, 215–284 (1936).

Berry, M. V.

M. V. Berry, The Diffraction of Light by Ultrasound (Academic, London, 1966).

Chang, I. C.

I. C. Chang, “Acoustooptic Devices and Applications,“ IEEE Trans. Sonics Ultrasonics SU23, 2–22 (1976).
[Crossref]

Channin, D. J.

Chu, R. S.

Cook, B. D.

W. R. Klein and B. D. Cook, “Unified Approach to Ultrasonic Light Diffraction,“ IEEE Trans. Sonics Ultrasonics SU14123–134 (1967).
[Crossref]

Damon, R. W.

R. W. Damon, W. T. Malony, and D. H. McMahon, “Interaction of Light with Ultrasound: Phenomena and Applications,” in Physical Acoustics VII, edited by Mason (Academic, New York, 1970), pp. 273–366.

Eschler, M.

M. Eschler and F. Weidinger, “Acousto-optic Properties of Dense Flint Glasses,” J. Appl. Phys. 46, 66–70 (1975).
[Crossref]

Hammer, J. M.

Hargrove, L. E.

L. E. Hargrove, E. A. Hiedemann, and M. Mertens, “Diffraction of Light by Two Spatially Separated Parallel Ultrasonic Waves of Different Frequency,” Z. Phys. 167, 323–336 (1962).

Hiedemann, E. A.

L. E. Hargrove, E. A. Hiedemann, and M. Mertens, “Diffraction of Light by Two Spatially Separated Parallel Ultrasonic Waves of Different Frequency,” Z. Phys. 167, 323–336 (1962).

Klein, W. R.

W. R. Klein and B. D. Cook, “Unified Approach to Ultrasonic Light Diffraction,“ IEEE Trans. Sonics Ultrasonics SU14123–134 (1967).
[Crossref]

Malony, W. T.

R. W. Damon, W. T. Malony, and D. H. McMahon, “Interaction of Light with Ultrasound: Phenomena and Applications,” in Physical Acoustics VII, edited by Mason (Academic, New York, 1970), pp. 273–366.

McMahon, D. H.

R. W. Damon, W. T. Malony, and D. H. McMahon, “Interaction of Light with Ultrasound: Phenomena and Applications,” in Physical Acoustics VII, edited by Mason (Academic, New York, 1970), pp. 273–366.

Mertens, M.

L. E. Hargrove, E. A. Hiedemann, and M. Mertens, “Diffraction of Light by Two Spatially Separated Parallel Ultrasonic Waves of Different Frequency,” Z. Phys. 167, 323–336 (1962).

Nagendra Nath, N. S.

C. V. Raman and N. S. Nagendra Nath, Proc. Indian Acad. Sci. 2A, 406–412, 413–420, (1935);Proc. Indian Acad. Sci. 3, 75–84, 119–125, 459–465 (1936).

Raman, C. V.

C. V. Raman and N. S. Nagendra Nath, Proc. Indian Acad. Sci. 2A, 406–412, 413–420, (1935);Proc. Indian Acad. Sci. 3, 75–84, 119–125, 459–465 (1936).

Sanders, F. H.

F. H. Sanders, “Intensity Measurements in Diffraction of Light by Ultrasonic Waves,” Can. J. Res. 14, 158–71 (1936).
[Crossref]

Tamir, T.

Weidinger, F.

M. Eschler and F. Weidinger, “Acousto-optic Properties of Dense Flint Glasses,” J. Appl. Phys. 46, 66–70 (1975).
[Crossref]

Appl. Opt. (1)

Can. J. Res. (1)

F. H. Sanders, “Intensity Measurements in Diffraction of Light by Ultrasonic Waves,” Can. J. Res. 14, 158–71 (1936).
[Crossref]

Helv. Phys. Acta. (1)

R. Bär, “Über Versuche zur Theorie von Raman and Nagendra Nath über die Beugung des Lichtes an Ultraschallwellen,“ Helv. Phys. Acta. 9, 215–284 (1936).

IEEE Trans. Sonics Ultrasonics (2)

W. R. Klein and B. D. Cook, “Unified Approach to Ultrasonic Light Diffraction,“ IEEE Trans. Sonics Ultrasonics SU14123–134 (1967).
[Crossref]

I. C. Chang, “Acoustooptic Devices and Applications,“ IEEE Trans. Sonics Ultrasonics SU23, 2–22 (1976).
[Crossref]

J. Appl. Phys. (1)

M. Eschler and F. Weidinger, “Acousto-optic Properties of Dense Flint Glasses,” J. Appl. Phys. 46, 66–70 (1975).
[Crossref]

J. Opt. Soc. Am. (1)

Proc. Indian Acad. Sci. (1)

C. V. Raman and N. S. Nagendra Nath, Proc. Indian Acad. Sci. 2A, 406–412, 413–420, (1935);Proc. Indian Acad. Sci. 3, 75–84, 119–125, 459–465 (1936).

Z. Phys. (1)

L. E. Hargrove, E. A. Hiedemann, and M. Mertens, “Diffraction of Light by Two Spatially Separated Parallel Ultrasonic Waves of Different Frequency,” Z. Phys. 167, 323–336 (1962).

Other (4)

M. V. Berry, The Diffraction of Light by Ultrasound (Academic, London, 1966).

See Proceedings of OSA/IEEE Conference on Laser and Electro-Optical Systems, San Diego, Calif.May 1976, Session WD, for a description of some of these.

R. W. Damon, W. T. Malony, and D. H. McMahon, “Interaction of Light with Ultrasound: Phenomena and Applications,” in Physical Acoustics VII, edited by Mason (Academic, New York, 1970), pp. 273–366.

Schott Optical Glass, Inc., Duryea, Penn. 18642.

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Figures (6)

FIG. 1
FIG. 1

Influence of on-to-off contrast on the amount of light which is modulated in a stroboscopic application. If the duty cycle is 10% and the contrast is only 10 to 1, then as much light appears between the pulses as is contained within the pulses.

FIG. 2
FIG. 2

Acousto-optical diffraction geometry. A sound wave of acoustic wavelength Λ diffracts incident light into various orders determined by the ratio of the sound to acoustic wavelengths.

FIG. 3
FIG. 3

General variation of the intensity of the undiffracted light passing through an acoustic cell as a function of the exciting power. The solid curve is the theoretical result which goes to zero for certain values of the power. Actual experiments show the result given by the dashed line, namely a finite amount of light is left, even at the position of the minima.

FIG. 4
FIG. 4

Schematic of the experimental apparatus for spatial filtering the light between two cells to improve contrast. In these experiments the cells are placed about 1m apart in order to allow the higher orders sufficient room to separate from the zero order.

FIG. 5
FIG. 5

Polarization filtering between the acoustic cells allows a shorter overall length to the experiment.

FIG. 6
FIG. 6

Comparison of acoustic diffraction out of the zero order for two cells, both with and without spatial filtering as a function of acoustic diffraction produced by one cell alone.

Tables (1)

Tables Icon

TABLE I Diffraction efficiency of two cells.

Equations (6)

Equations on this page are rendered with MathJax. Learn more.

sin θ n = n λ / Λ
I n = I J n 2 ( x ) ,
x = 2 π Δ n L / λ .
Q = 2 π λ L / Λ 2
Q = Q x / n 2 .
F = f ( 1 f ) + f ,