Abstract

An improved photoelastic modulator (PEM) employing two piezoelectric transducers and incorporating a new ir zinc selenide (ZnSe) optical element is described. The 0.64-cm thick PEM is capable of obtaining quarter-wave retardation from 0.55 μm to 13.0 μm. Previously no single, high quality, low static strain PEM element existed for this wavelength range. We have also constructed other PEM’s using optical elements composed of fused quartz, calcium fluoride, and KRS-5. The important optical and mechanical properties are measured and compared.

© 1976 Optical Society of America

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References

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  1. M. Billardon, J. Badoz, C. R. Acad. Sci, Ser. B 262, 1672 (1966).
  2. L. F. Mollenauer, D. Downie, H. Engstrom, W. B. Grant, Appl. Opt. 8, 661 (1969).
    [CrossRef] [PubMed]
  3. J. C. Kemp, J. Opt. Soc. Am. 59, 950 (1969).
  4. S. N. Jasperson, S. E. Schnatterly, Rev. Sci. Instrum. 40, 761 (1969).
    [CrossRef]
  5. In practice, we found that the destruction of the optical elements always preceded that of the quartz transducers.
  6. I. Chabay, E. C. Hsu, G. Holzwartz, Chem. Phys. Lett. 15, 211 (1972).
    [CrossRef]
  7. We will use two criteria to describe the modulator’s performances. The quarter-wave retardation condition implies that the modulator’s peak relative retardation is π/2 between the Mx and My axes, while the J1 equals maximum condition implies that the relative peak retardation is 1.832 and that circular dichroism signals are maximized.
  8. G. A. Osborne, J. C. Cheng, P. J. Stephens, Rev. Sci. Instrum. 44, 10 (1973).
    [CrossRef]
  9. The frequency constants are slightly width and thickness dependent. Therefore, for best results, direct frequency measurements of both the optical element and transducers are recommended. The resonance frequency of the complete three-component bar is approximately 0.03% lower than the average individual component frequencies, due to the addition of glue between the drivers and the optical element.
  10. The transmission ranges quoted are always smaller than the ranges obtained at 69% transmission values. We have noted that for wavelengths where some absorption does occur, the PEM produces artifact signals at high CD sensitivities; therefore, those regions are excluded from the λT values.
  11. The piezoelectric quartz transducers are electrically polarized; the electrodes with the same polarization should be driven together.
  12. J. C. Cheng, L. A. Nafie, P. J. Stephens, to be published in J. Opt. Soc. Am.65, 1031 (1975).
    [CrossRef]
  13. W. A. Shurcliff, Polarized Light (Harvard U. P., Cambridge, Mass., 1962).
  14. T. C. McGill (private communication).

1973 (1)

G. A. Osborne, J. C. Cheng, P. J. Stephens, Rev. Sci. Instrum. 44, 10 (1973).
[CrossRef]

1972 (1)

I. Chabay, E. C. Hsu, G. Holzwartz, Chem. Phys. Lett. 15, 211 (1972).
[CrossRef]

1969 (3)

1966 (1)

M. Billardon, J. Badoz, C. R. Acad. Sci, Ser. B 262, 1672 (1966).

Badoz, J.

M. Billardon, J. Badoz, C. R. Acad. Sci, Ser. B 262, 1672 (1966).

Billardon, M.

M. Billardon, J. Badoz, C. R. Acad. Sci, Ser. B 262, 1672 (1966).

Chabay, I.

I. Chabay, E. C. Hsu, G. Holzwartz, Chem. Phys. Lett. 15, 211 (1972).
[CrossRef]

Cheng, J. C.

G. A. Osborne, J. C. Cheng, P. J. Stephens, Rev. Sci. Instrum. 44, 10 (1973).
[CrossRef]

J. C. Cheng, L. A. Nafie, P. J. Stephens, to be published in J. Opt. Soc. Am.65, 1031 (1975).
[CrossRef]

Downie, D.

Engstrom, H.

Grant, W. B.

Holzwartz, G.

I. Chabay, E. C. Hsu, G. Holzwartz, Chem. Phys. Lett. 15, 211 (1972).
[CrossRef]

Hsu, E. C.

I. Chabay, E. C. Hsu, G. Holzwartz, Chem. Phys. Lett. 15, 211 (1972).
[CrossRef]

Jasperson, S. N.

S. N. Jasperson, S. E. Schnatterly, Rev. Sci. Instrum. 40, 761 (1969).
[CrossRef]

Kemp, J. C.

McGill, T. C.

T. C. McGill (private communication).

Mollenauer, L. F.

Nafie, L. A.

J. C. Cheng, L. A. Nafie, P. J. Stephens, to be published in J. Opt. Soc. Am.65, 1031 (1975).
[CrossRef]

Osborne, G. A.

G. A. Osborne, J. C. Cheng, P. J. Stephens, Rev. Sci. Instrum. 44, 10 (1973).
[CrossRef]

Schnatterly, S. E.

S. N. Jasperson, S. E. Schnatterly, Rev. Sci. Instrum. 40, 761 (1969).
[CrossRef]

Shurcliff, W. A.

W. A. Shurcliff, Polarized Light (Harvard U. P., Cambridge, Mass., 1962).

Stephens, P. J.

G. A. Osborne, J. C. Cheng, P. J. Stephens, Rev. Sci. Instrum. 44, 10 (1973).
[CrossRef]

J. C. Cheng, L. A. Nafie, P. J. Stephens, to be published in J. Opt. Soc. Am.65, 1031 (1975).
[CrossRef]

Appl. Opt. (1)

C. R. Acad. Sci, Ser. B (1)

M. Billardon, J. Badoz, C. R. Acad. Sci, Ser. B 262, 1672 (1966).

Chem. Phys. Lett. (1)

I. Chabay, E. C. Hsu, G. Holzwartz, Chem. Phys. Lett. 15, 211 (1972).
[CrossRef]

J. Opt. Soc. Am. (1)

Rev. Sci. Instrum. (2)

S. N. Jasperson, S. E. Schnatterly, Rev. Sci. Instrum. 40, 761 (1969).
[CrossRef]

G. A. Osborne, J. C. Cheng, P. J. Stephens, Rev. Sci. Instrum. 44, 10 (1973).
[CrossRef]

Other (8)

The frequency constants are slightly width and thickness dependent. Therefore, for best results, direct frequency measurements of both the optical element and transducers are recommended. The resonance frequency of the complete three-component bar is approximately 0.03% lower than the average individual component frequencies, due to the addition of glue between the drivers and the optical element.

The transmission ranges quoted are always smaller than the ranges obtained at 69% transmission values. We have noted that for wavelengths where some absorption does occur, the PEM produces artifact signals at high CD sensitivities; therefore, those regions are excluded from the λT values.

The piezoelectric quartz transducers are electrically polarized; the electrodes with the same polarization should be driven together.

J. C. Cheng, L. A. Nafie, P. J. Stephens, to be published in J. Opt. Soc. Am.65, 1031 (1975).
[CrossRef]

W. A. Shurcliff, Polarized Light (Harvard U. P., Cambridge, Mass., 1962).

T. C. McGill (private communication).

In practice, we found that the destruction of the optical elements always preceded that of the quartz transducers.

We will use two criteria to describe the modulator’s performances. The quarter-wave retardation condition implies that the modulator’s peak relative retardation is π/2 between the Mx and My axes, while the J1 equals maximum condition implies that the relative peak retardation is 1.832 and that circular dichroism signals are maximized.

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Figures (4)

Fig. 1
Fig. 1

Three-component photoelastic modular bar design incorporating piezoelectric trancducers on each end of the optical element. The pulse signs on the electrical polarization of the piezoelectric drivers. The stress (—) and strain (- - -) are shown as a function of the position along the bar. The two component design can be obtained by removing one of the drivers.

Fig. 2
Fig. 2

Experimental ac peak-to-peak voltage vs wavelength data on modulators in order to maintain the J1 equal maximum retardation (α0 = 1.832) condition. Results for the 0.64-cm thick, quartz driven, three-component design employing optical elements consisting of CaF2, SiO2, and ZnSe are labeled (a), (b), and (d), respectively. The identical ZnSe element employed in (d) but now using the two-component design is labeled (c). The PZT driven 1.06-cm thick KRS-5 PEM, employing the two-component design, is labeled (e).

Fig. 3
Fig. 3

Setup used to measure the longitudinal frequencies of an optical element. The two piezoelectric transducers (PZT-4) act, respectively, as an acoustic transmitter and receiver.

Fig. 4
Fig. 4

Optical arrangement and axis orientations used to measure the modulator’s retardation as a function of wavelength. Light propagates down the Z axis; P1, P2 are the transmission axes of the calcite polarizers; Mx, My are the dynamically induced birefringent axes of the modulator M; and Bx, By are the static birefringent axes of the waveplate B. The same arrangement is used when measuring the static strain birefringence in the modulator element. For this case, the waveplate B is assumed to be internal to the modulator’s optical element rather than an actual external device.

Tables (2)

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Table I Optical and Mechanical Properties of the PEM Optical Elements

Tables Icon

Table II Mechanical Properties of the Piezoelectric Transducers

Equations (16)

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I = ( I 0 / 2 ) [ 1 - cos ( α m + α B ) ] ,
α m = α m 0 sin ( ω m t ) ,
I ( ω m ) = I 0 J 1 ( α m 0 ) sin ( ω m t ) ,
λ = λ { α m 0 [ a t J 1 ( α m 0 ) = 0 ] α m 0 [ a t J 1 ( α m 0 ) = max ] } 2.09 · λ .
FM = Δ λ Δ V Q ,
Q = f Δ f | - 3 dB .
[ d M ˜ ( z ) ] / d z = - i A ˜ ( z ) M ˜ ( z ) ,
A ˜ ( Z ) = ( sin 2 θ B d α B d z - sin θ B cos θ B d α B d z - sin θ B cos θ B d α B d z d α m d z + cos 2 θ B d α B d z ) .
α m 0 α B
M ˜ ( L ) = { 1 0 0 exp [ - i ( α m + α B cos 2 θ B ) ] }
α m α B ,
M ˜ ( L ) = { 1 0 0 exp [ - i ( α m + α B ) ] }
α B = α B cos 2 θ B .
R = I ( ω m ) I ( 2 ω m ) = J 1 ( α m 0 ) sin ( α B ) J 2 ( α m 0 ) cos ( α B ) .
λ Q W = 2 λ π · tan - 1 [ J 2 ( α m 0 ) J 1 ( α m 0 ) · R ] .
E ( λ ) = 100 { J 1 [ ( π / 2 ) · ( λ Q / λ ) ] J 1 ( π / 2 ) } .

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