Abstract

This work investigates the optical Kerr property of azo-dye doped nematic liquid crystal films using the biphotonic Z-scan technique. The results indicate that the nonlinear effect measured using the Z-scan technique with a red light can be modulated or switched with the simultaneous application of a green light, because of photoisomerization and thermal effects, as determined by dynamic measurements. The former dominates in the early stage when the green light is applied, while the latter dominates in the later stage.

© 2005 Optical Society of America

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References

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    [CrossRef]
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    [CrossRef] [PubMed]
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    [CrossRef]

Appl. Phys. Lett.

M.-R. Lee, J.-R. Wang, C.-R. Lee, and A. Y.-G. Fuh, "Optically switchable biphotonic photorefractive effect in dye-doped liquid crystal films," Appl. Phys. Lett. 85, 5822 (2004).
[CrossRef]

C.-R. Lee, T.-S. Mo, K.-T. Cheng, T.-L. Fu and A. Y.-G Fuh, "Electrically switchable and thermally erasable biphotonic holographic gratings in dye-doped liquid crystal films," Appl. Phys. Lett. 83, 4285 (2003).
[CrossRef]

S.Slussarenko, O. Francescangeli and F. Simoni, "High resolution polarization gratings in liquid crystals," Appl. Phys. Lett. 71, 3613 (1997).
[CrossRef]

Andy Y.-G. Fuh, M.-S. Tsai, L.-J. Huang, and T.-C. Liu, "Optically switchable gratings based on polymer-dispersed liquid crystal films doped with a guest-host dye," Appl. Phys. Lett. 74, 2572 (1999).
[CrossRef]

IEEE J. Quantum Electron.

I. C. Khoo, "Orientational photorefractive effects in nematic liquid crystal films," IEEE J. Quantum Electron. 32, 525 (1996).
[CrossRef]

M. Sheik-Bahae, A. A. Said, T. H. Wei, D. J. Hagan, and E. W. Van Stryland, "Sensitive measurement of optical nonlinearities using a signal beam," IEEE J. Quantum Electron. 26, 760 (1990).
[CrossRef]

J. Appl. Phys.

I. V. Tomov, T. E. Dutton, B.VanWonterghem and P. M. Rentzepis, "Temperature dependence of degenerate four wave mixing in azo dye doped polymer films," J. Appl. Phys. 70, 36 (1991).
[CrossRef]

J. Opt. Soc. Am. B

Mol. Cryst. Liq. Cryst.

P. Palffy-Muhoray, H. J. Yuan. L. Li, and Michael A. Lee, "Measurements of third order optical nonlinearities of nematic liquid crystals," Mol. Cryst. Liq. Cryst. 207, 291 (1991).
[CrossRef]

Opt. Lett.

Opt.Lett.

A. Y.-G Fuh, C.-C. Liao, K.-C. Hsu and C.-L. Lu, "Laser-induced reorientation effect and ripple structure in dye-doped liquid-crystal films," Opt.Lett. 28, 1179 (2003).
[CrossRef] [PubMed]

A. Y.-G Fuh, C.-C. Liao, K.-C. Hsu, C.-L. Lu and C.-T. Tsai, "Dynamic studies of holographic gratings in dye-doped liquid-crystal films," Opt.Lett. 26, 1767 (2001).
[CrossRef]

Phys. Rev. E

Andy Y.-G. Fuh, M.-S. Tsai, C.-R. Lee, and Y.-H. Fan, "Dynamical studies of gratings formed in polymer-dispersed liquid crystal films doped with a guest-host dye," Phys. Rev. E 62, 003702 (2000).
[CrossRef]

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Figures (8)

Fig. 1.
Fig. 1.

Experimental set-up: P – polarizer; L – lens, I – iris; NDF – neutral density filter; CF – color filter; PBS – polarized beam splitter and PD – photodetector.

Fig. 2.
Fig. 2.

Variations of the Z-scan transmittance in a nematic liquid crystal film doped with 1% azo-dye (DR1) with various intensities of green light. The curves are normalized with the transmittance measured at a point far behind the focus point.

Fig. 3.
Fig. 3.

The absorption spectra of the sample with the irradiation of a DPSS laser having an intensity of ~124 mW/cm2 for various times.

Fig. 4.
Fig. 4.

Typical temperature-dependent refractive index of a nematic LC. (a) Diamonds plot temperatures of the sample without green light. (b) Squares and circles plot temperatures of the sample irradiated with green light with low and high intensities, respectively. Open and solid dots plot temperatures of the outer and central regions of the illuminated spot. TC is the clear temperature of the LC.

Fig. 5.
Fig. 5.

Temperature variation of the sample with respect to the green light intensity.

Fig. 6.
Fig. 6.

Comparisons of Z-scan measurements made using the setup presented in Fig. 1 when the polarizations (P) of the He-Ne and DPSS lasers are perpendicular to the LC director (n)with those obtained with P//n under IG=0. Intensity of green light is 153mW/cm2.

Fig. 7.
Fig. 7.

Effects of dynamic Z-scan when green light is applied (98mW/cm2). Curves (a) and (b) are the transmittances at the two positions, at which the transmittances are maximal and minimal when no green light is applied.

Fig. 8.
Fig. 8.

Transient responses of the transmittances at the valley position (curve (b) in Fig. 7) when a pulse of green light is applied (IG ~ 98 mW/cm2).

Equations (3)

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Δ T abs β 2 2 I 0 ( 1 R ) L eff ,
Δ T p v 0.406 ( 1 S ) 0.25 Δ Φ 0 ,
Δ n 0 = n 2 I 0 ,

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