Abstract

We investigate thermally induced nonlinear optical effects on a CO2 laser beam that passes through an isotropic liquid crystal film. We evaluate the thermal nonlinear coefficient of the refractive index at a wavelength of 10.6 µm by means of a thermographic technique combined with an optical method based upon the measurement of the self-defocusing effect caused by the heating of the liquid crystal induced by the laser beam. The novelty of our work is the application of thermography in order to measure the temperature field on the liquid crystal film caused by the partial absorption of the laser radiation by the liquid crystal. These measurements provide a precise evaluation of the thermal diffusion length of the liquid crystal under investigation. Moreover, thermography results in a straightforward experimental technique that can be used to investigate the thermal properties of a wide class of other fluids.

© 2002 Optical Society of America

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References

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  1. S. T. Wu, R. J. Cox, “Optical and electro-optic properties of cyanotolanes and cyanostilbenes: potential infrared liquid crystals,” J. Appl. Phys. 64, 821–826 (1988).
    [CrossRef]
  2. P. Jagemalm, D. S. Hermann, L. Komitov, “Opto-thermal reorientation in nematics with two-fold degenerate alignment,” Liq. Cryst. 24, 335–340 (1998).
    [CrossRef]
  3. A. E. Siegman, Lasers (University Science, Mill Valley, Calif., 1986).
  4. I. C. Khoo, S. T. Wu, Optics and Nonlinear Optics of Liquid Crystals (World Scientific, Singapore, 1993).
  5. W. K. Bajdecki, L. Calero, R. Meucci, “Nonlinear infrared optical measurements of elastic constants in nematic liquid crystal,” Opt. Commun. 176, 473–477 (2000).
    [CrossRef]
  6. A. S. Zolot’ko, V. F. Kitaeva, N. Kroo, N. N. Sobolev, L. Chillag, “The effect of an optical field on the nematic phase of the liquid crystal OCBP,” JETP Lett. 32, 158–162 (1980).
  7. F. Simoni, Nonlinear Optical Properties of Liquid Crystals and Polymer Dispersed Liquid Crystals (World Scientific, Singapore, 1997).
  8. S. D. Durbin, S. M. Arakelian, Y. R. Shen, “Laser-induced diffraction rings from a nematic-liquid crystal film,” Opt. Lett. 6, 411–413 (1981).
    [PubMed]
  9. E. Santamato, Y. R. Shen, “Field-curvature effect on the diffraction ring pattern of a laser beam dressed by spatial self-phase modulation in a nematic film,” Opt. Lett. 9, 564–566 (1984).
    [CrossRef] [PubMed]
  10. I. C. Khoo, J. Y. Hou, T. H. Liu, P. Y. Yan, R. R. Michael, G. M. Finn, “Transverse self-phase modulation and bistability in the transmission of a laser beam through a nonlinear thin film,” J. Opt. Soc. Am. B 4, 886–891 (1987).
    [CrossRef]
  11. M. Born, E. Wolf, Principles of Optics (Pergamon, Oxford, 1980).

2000 (1)

W. K. Bajdecki, L. Calero, R. Meucci, “Nonlinear infrared optical measurements of elastic constants in nematic liquid crystal,” Opt. Commun. 176, 473–477 (2000).
[CrossRef]

1998 (1)

P. Jagemalm, D. S. Hermann, L. Komitov, “Opto-thermal reorientation in nematics with two-fold degenerate alignment,” Liq. Cryst. 24, 335–340 (1998).
[CrossRef]

1988 (1)

S. T. Wu, R. J. Cox, “Optical and electro-optic properties of cyanotolanes and cyanostilbenes: potential infrared liquid crystals,” J. Appl. Phys. 64, 821–826 (1988).
[CrossRef]

1987 (1)

1984 (1)

1981 (1)

1980 (1)

A. S. Zolot’ko, V. F. Kitaeva, N. Kroo, N. N. Sobolev, L. Chillag, “The effect of an optical field on the nematic phase of the liquid crystal OCBP,” JETP Lett. 32, 158–162 (1980).

Arakelian, S. M.

Bajdecki, W. K.

W. K. Bajdecki, L. Calero, R. Meucci, “Nonlinear infrared optical measurements of elastic constants in nematic liquid crystal,” Opt. Commun. 176, 473–477 (2000).
[CrossRef]

Born, M.

M. Born, E. Wolf, Principles of Optics (Pergamon, Oxford, 1980).

Calero, L.

W. K. Bajdecki, L. Calero, R. Meucci, “Nonlinear infrared optical measurements of elastic constants in nematic liquid crystal,” Opt. Commun. 176, 473–477 (2000).
[CrossRef]

Chillag, L.

A. S. Zolot’ko, V. F. Kitaeva, N. Kroo, N. N. Sobolev, L. Chillag, “The effect of an optical field on the nematic phase of the liquid crystal OCBP,” JETP Lett. 32, 158–162 (1980).

Cox, R. J.

S. T. Wu, R. J. Cox, “Optical and electro-optic properties of cyanotolanes and cyanostilbenes: potential infrared liquid crystals,” J. Appl. Phys. 64, 821–826 (1988).
[CrossRef]

Durbin, S. D.

Finn, G. M.

Hermann, D. S.

P. Jagemalm, D. S. Hermann, L. Komitov, “Opto-thermal reorientation in nematics with two-fold degenerate alignment,” Liq. Cryst. 24, 335–340 (1998).
[CrossRef]

Hou, J. Y.

Jagemalm, P.

P. Jagemalm, D. S. Hermann, L. Komitov, “Opto-thermal reorientation in nematics with two-fold degenerate alignment,” Liq. Cryst. 24, 335–340 (1998).
[CrossRef]

Khoo, I. C.

Kitaeva, V. F.

A. S. Zolot’ko, V. F. Kitaeva, N. Kroo, N. N. Sobolev, L. Chillag, “The effect of an optical field on the nematic phase of the liquid crystal OCBP,” JETP Lett. 32, 158–162 (1980).

Komitov, L.

P. Jagemalm, D. S. Hermann, L. Komitov, “Opto-thermal reorientation in nematics with two-fold degenerate alignment,” Liq. Cryst. 24, 335–340 (1998).
[CrossRef]

Kroo, N.

A. S. Zolot’ko, V. F. Kitaeva, N. Kroo, N. N. Sobolev, L. Chillag, “The effect of an optical field on the nematic phase of the liquid crystal OCBP,” JETP Lett. 32, 158–162 (1980).

Liu, T. H.

Meucci, R.

W. K. Bajdecki, L. Calero, R. Meucci, “Nonlinear infrared optical measurements of elastic constants in nematic liquid crystal,” Opt. Commun. 176, 473–477 (2000).
[CrossRef]

Michael, R. R.

Santamato, E.

Shen, Y. R.

Siegman, A. E.

A. E. Siegman, Lasers (University Science, Mill Valley, Calif., 1986).

Simoni, F.

F. Simoni, Nonlinear Optical Properties of Liquid Crystals and Polymer Dispersed Liquid Crystals (World Scientific, Singapore, 1997).

Sobolev, N. N.

A. S. Zolot’ko, V. F. Kitaeva, N. Kroo, N. N. Sobolev, L. Chillag, “The effect of an optical field on the nematic phase of the liquid crystal OCBP,” JETP Lett. 32, 158–162 (1980).

Wolf, E.

M. Born, E. Wolf, Principles of Optics (Pergamon, Oxford, 1980).

Wu, S. T.

S. T. Wu, R. J. Cox, “Optical and electro-optic properties of cyanotolanes and cyanostilbenes: potential infrared liquid crystals,” J. Appl. Phys. 64, 821–826 (1988).
[CrossRef]

I. C. Khoo, S. T. Wu, Optics and Nonlinear Optics of Liquid Crystals (World Scientific, Singapore, 1993).

Yan, P. Y.

Zolot’ko, A. S.

A. S. Zolot’ko, V. F. Kitaeva, N. Kroo, N. N. Sobolev, L. Chillag, “The effect of an optical field on the nematic phase of the liquid crystal OCBP,” JETP Lett. 32, 158–162 (1980).

J. Appl. Phys. (1)

S. T. Wu, R. J. Cox, “Optical and electro-optic properties of cyanotolanes and cyanostilbenes: potential infrared liquid crystals,” J. Appl. Phys. 64, 821–826 (1988).
[CrossRef]

J. Opt. Soc. Am. B (1)

JETP Lett. (1)

A. S. Zolot’ko, V. F. Kitaeva, N. Kroo, N. N. Sobolev, L. Chillag, “The effect of an optical field on the nematic phase of the liquid crystal OCBP,” JETP Lett. 32, 158–162 (1980).

Liq. Cryst. (1)

P. Jagemalm, D. S. Hermann, L. Komitov, “Opto-thermal reorientation in nematics with two-fold degenerate alignment,” Liq. Cryst. 24, 335–340 (1998).
[CrossRef]

Opt. Commun. (1)

W. K. Bajdecki, L. Calero, R. Meucci, “Nonlinear infrared optical measurements of elastic constants in nematic liquid crystal,” Opt. Commun. 176, 473–477 (2000).
[CrossRef]

Opt. Lett. (2)

Other (4)

F. Simoni, Nonlinear Optical Properties of Liquid Crystals and Polymer Dispersed Liquid Crystals (World Scientific, Singapore, 1997).

M. Born, E. Wolf, Principles of Optics (Pergamon, Oxford, 1980).

A. E. Siegman, Lasers (University Science, Mill Valley, Calif., 1986).

I. C. Khoo, S. T. Wu, Optics and Nonlinear Optics of Liquid Crystals (World Scientific, Singapore, 1993).

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Figures (6)

Fig. 1
Fig. 1

Experimental apparatus. 1, total reflecting mirror; 2, gas tube; 3, Brewster window; 4, outcoupling mirror; 5, ZnSe lens; 6, liquid crystal cell and thermostat; 7, Spiricon infrared telecamera; 8, infrared radiometer; 9, personal computer; 10, temperature controller.

Fig. 2
Fig. 2

Experimental temperature profile on the LC sample, (circles) as recorded by the infrared radiometer, for an incident laser power of 380 mW and a relative fit by Eq. (2).

Fig. 3
Fig. 3

Experimental peak temperature versus the peak laser intensity I 0 (solid squares) and relative linear regression (solid line).

Fig. 4
Fig. 4

Laser beam radius on the detection plane of the telecamera versus the incident laser power (solid circles). The solid line is a fit of the experimental curve obtained by integrating Kirchhoff’s diffraction integral for n T = 7 × 10-4 °C-1. A self-defocusing effect can clearly be seen.

Fig. 5
Fig. 5

Schematization of the self-defocusing phenomenon. The LC film behaves as a nonlinear diverging lens that defocuses the incident laser beam. As the LC film is between the ZnSe lens and its focus, the result is a reduction of the beam radius on the observation plane with an increasing of the laser intensity.

Fig. 6
Fig. 6

(a) Image of self-phase modulation phenomenon as it has been recorded by the Spiricon telecamera. An outer ring clearly can be distinguished. (b) Comparison between theoretical and experimental profiles of the laser beam on the detection plane for an incident laser power of 600 mW.

Equations (11)

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dTdr+1rDTr=A,
Tr=ArD+B exp-rrD.
Ir=I0 exp-2r2w2,
I0=2Pπw02.
T0=Tb+kI0,
Tr=Tb+kI0 exp-rrD,
n=n0-nTT,
nr=n0-nTTb+kI0 exp-rrD.
Ir1, Z=2πλZ2I00rdrJ02πrr1/λZ×exp-2r2w2exp-iϕD+ϕNL2,
ϕD=k0r22Z+r22R,
ϕNL=-k0nTkdI0 exp-rrD.

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