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Optical Materials Express

Optical Materials Express

  • Editor: David J. Hagan
  • Vol. 1, Iss. 5 — Sep. 1, 2011
  • pp: 943–952
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Nonlinear optical properties of fast, photoswitchable cholesteric liquid crystal bandgaps

Uladzimir A. Hrozhyk, Svetlana V. Serak, Nelson V. Tabiryan, Timothy J. White, and Timothy J. Bunning  »View Author Affiliations


Optical Materials Express, Vol. 1, Issue 5, pp. 943-952 (2011)
http://dx.doi.org/10.1364/OME.1.000943


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Abstract

The reflection and transmission properties of photosensitized cholesteric liquid crystals (CLCs) are examined. Introduction of mesogenic push-pull azobenzene dyes into blue and green reflective CLCs enables fast (sub-second), photoswitchable optical properties due to the overlap of the trans and cis absorption states. Upon irradiation with CW blue-green laser radiation, the bandgap reflection is erased in a fraction of a second and reversibly restored approximately one second after the blue-green laser radiation is removed. Given the strong overlap of the trans and cis absorption maxima, we believe that repeated trans-cis and cis-trans isomerization cycles induced with irradiation lead to a destruction of the ordered LC phase. The sensitivity to the irradiating wavelength scales with the wavelength-dependent absorption of the mesogenic push-pull dye. A detailed examination of the transmitted and reflected laser beams are presented as a function of power and wavelength of CW sources.

© 2011 OSA

1. Introduction

Cholesteric liquid crystals (CLCs) are fascinating materials due to their unique optical properties. In planarly aligned cells, macroscopic orientation of their helical superstructures perpendicular to the substrates leads to films which will selectively reflect the same handedness radiation as itself [1

1. P. G. de Gennes, The Physics of Liquid Crystals (Clarendon, Cambridge, 1977)

]. When the pitch length is on the same order as visible light, vibrant, highly colored films are formed which have been examined for numerous display [2

2. D. M. Makow and C. L. Sanders, “Additive colour properties and colour gamut of cholesteric liquid crystals,” Nature 276(5683), 48–50 (1978). [CrossRef]

], sensing [3

3. S.-T. Wu and D.-K. Yang, Reflective Liquid Crystal Displays (Wiley, 2001).

], and photonic applications [4

4. A. Chanishvili, G. Chilaya, G. Petriashvili, R. Barberi, R. Bartolino, and M. P. De Santo, “Cholesteric liquid crystal mixtures sensitive to different ranges of solar UV irradiation,” Mol. Cryst. Liq. Cryst. (Phila. Pa.) 434(1), 25/[353]–38/[366] (2005). [CrossRef]

8

8. S. Furumi, S. Yokoyama, A. Otomo, and S. Mashiko, “Phototunable photonic bandgap in a chiral liquid crystal laser device,” Appl. Phys. Lett. 84(14), 2491–2493 (2004). [CrossRef]

]. A large amount of work has been performed on making this coloration dynamic [9

9. T. J. White, M. E. McConney, and T. J. Bunning, “Dynamic color in stimuli-responsive cholesteric liquid crystals,” J. Mater. Chem. 20(44), 9832–9847 (2010). [CrossRef]

], through the use of heat [10

10. F. Ania and H. Stegemeyer, “Cholesteric pitch behavior at the phase transition cholesteric to smectic B,” Mol. Cryst. Liq. Cryst. Lett. 2(3–4), 67–76 (1985).

13

13. M. E. McConney, V. P. Tondiglia, J. M. Hurtubise, L. V. Natarajan, T. J. White, and T. J. Bunning, “Thermally induced, multicolored hyper-reflective cholesteric liquid crystals,” Adv. Mater. (Deerfield Beach Fla.) 23(12), 1453–1457 (2011). [CrossRef] [PubMed]

], light [14

14. E. Sackmann, “Photochemically induced reversible color changes in cholesteric liquid crystals,” J. Am. Chem. Soc. 93(25), 7088–7090 (1971). [CrossRef]

21

21. S. Kurihara, S. Nomiyama, and T. Nonaka, “Photochemical switching between a compensated nematic phase and a twisted nematic phase by photoisomerization of chiral azobenzene molecules,” Chem. Mater. 12(1), 9–12 (2000). [CrossRef]

], or electrical fields [22

22. S. S. Choi, S. M. Morris, W. T. S. Huck, and H. J. Coles, “Simultaneous red-green-blue reflection and wavelength tuning from an achiral liquid crystal and a polymer template,” Adv. Mater. (Deerfield Beach Fla.) 22(1), 53–56 (2010). [CrossRef] [PubMed]

24

24. C. A. Bailey, V. P. Tondiglia, L. V. Natarajan, M. M. Duning, R. L. Bricker, R. L. Sutherland, T. J. White, M. F. Durstock, and T. J. Bunning, “Electromechanical tuning of cholesteric liquid crystals,” J. Appl. Phys. 107(1), 013105 (2010). [CrossRef]

]. Both tunable and switchable constructs are continuing to be explored and methodologies to increase both the response and relaxation speeds are at the forefront of this research.

The ability to use light itself as a means to control the optical properties of CLCs has recently been reviewed [9

9. T. J. White, M. E. McConney, and T. J. Bunning, “Dynamic color in stimuli-responsive cholesteric liquid crystals,” J. Mater. Chem. 20(44), 9832–9847 (2010). [CrossRef]

,25

25. N. Tamaoki and T. Kamei, “Reversible photo-regulation of the properties of liquid crystals doped with photochromic compounds,” J. Photochem. Photobiol. Chem. 11(2–3), 47–61 (2010).

]. Photoresponsive CLCs have employed a variety of photochromic moieties including azobenzenes, methones, fulgides, and overcrowded alkenes. Azo-based compounds have been extensively explored due to the comparative ruggedness of the photochemistry and the ease of inducing liquid crystallinity into this class of dyes [26

26. K. G. Yager and C. J. Barrett, “Novel photo-switching using azobenzene functional materials,” J. Photochem. Photobiol. A 182(3), 250–261 (2006). [CrossRef]

]. Most prior examinations of azobenzene-based CLCs have employed the conventional photochromic structure known for its metastable cis isomer species and large difference in absorbance profile between the trans and cis isomers. Functionalizing the azobenzene chromophore with electron donating and withdrawing moieties on opposite ends is known to red shift the absorption spectra, reduce the wavelength separation between the trans-cis and cis-trans peak absorption, and greatly speed up the relaxation behavior of the cis-trans dark relaxation [27

27. O. Tsutsumi, A. Kanazawa, T. Shiono, T. Ikeda, and L.-S. Park, “Photoinduced phase transition of nematic liquid crystals with donor-acceptor azobenzenes: mechanism of the thermal recovery of the nematic phase,” Phys. Chem. Chem. Phys. 1(18), 4219–4224 (1999). [CrossRef]

,28

28. U. A. Hrozhyk, S. V. Serak, N. V. Tabiryan, L. Hoke, D. M. Steeves, B. Kimball, and G. Kedziora,”Systematic study of absorption spectra of donor–acceptor azobenzene mesogenic structures,” Mol. Cryst. Liq. Cryst. 489, 257[583]–272[598] (2008).

]. These materials enable the reduction of the relaxation times of the photoexcited state of the cis-isomer molecules to less than a second from tens of hours [29

29. U. A. Hrozhyk, S. V. Serak, N. V. Tabiryan, L. Hoke, D. M. Steeves, and B. R. Kimball, “Azobenzene liquid crystalline materials for efficient optical switching with pulsed and/or continuous wave laser beams,” Opt. Express 18(8), 8697–8704 (2010). [CrossRef] [PubMed]

,30

30. U. Hrozhyk, S. Serak, N. Tabiryan, D. Steeves, L. Hoke, and B. Kimball, “Azobenzene liquid crystals for fast reversible optical switching and enhanced sensitivity for visible wavelengths,” Proc. SPIE 7414, 74140L, (2009). [CrossRef]

]. Due to their mesogenic nature, these azo dyes can be introduced into liquid crystal solutions at much higher concentrations than classic non-mesogenic azobenzene chromophores. As a result, the energy density required for observing substantial nonlinear response was reduced to ~10 mJ/cm2 for ns pulsed excitation and to several mW/cm2 for a CW laser beam operating at a green wavelength [29

29. U. A. Hrozhyk, S. V. Serak, N. V. Tabiryan, L. Hoke, D. M. Steeves, and B. R. Kimball, “Azobenzene liquid crystalline materials for efficient optical switching with pulsed and/or continuous wave laser beams,” Opt. Express 18(8), 8697–8704 (2010). [CrossRef] [PubMed]

31

31. L. De Sio, S. Serak, N. Tabiryan, and C. Umeton, “Mesogenic versus non-mesogenic azo dye confined in a soft-matter template for realization of optically switchable diffraction gratings,” J. Mater. Chem. 21(19), 6811–6814 (2011). [CrossRef]

].

2. Experimental Details

Material compositions examined here were based on CPND series mesogenic azo dyes, 1-(2-chloro-4-N-n-alkylpiperazinylphenyl)-2-(4-nitrophenyl)diazenes, containing two benzene rings with push-pull π-π conjugation. The synthesis and fundamental properties of such dyes are described in [27

27. O. Tsutsumi, A. Kanazawa, T. Shiono, T. Ikeda, and L.-S. Park, “Photoinduced phase transition of nematic liquid crystals with donor-acceptor azobenzenes: mechanism of the thermal recovery of the nematic phase,” Phys. Chem. Chem. Phys. 1(18), 4219–4224 (1999). [CrossRef]

] and references therein. While the response time of those materials depend essentially on the power/energy density of the radiation, they are characterized by cis-trans relaxation times on the order of seconds which is considerably shorter than for azobenzene materials based on symmetric conjugation [33

33. U. Hrozhyk, S. Serak, N. Tabiryan, and T. J. Bunning, “Wide temperature range azobenzene nematic and smectic LC materials,” Mol. Cryst. Liq. Cryst. (Phila. Pa.) 454(1), 235/[637]–245/[647] (2006). [CrossRef]

]. Nematic LCs 5CB (Tcl = 35°C) and E7 (Tcl ~60°C) from Merck Ltd, and mixtures thereof were utilized. Thermodynamically stable fast CLC compositions with bandgaps at green-blue wavelengths were obtained by combining chiral dopants R1011 (HTP ≈25 μm−1) and CB15 (HTP ≈7 μm−1), both from Merck Ltd. Green/blue CLC mixtures fabricated with just CB15 proved unstable, crystallizing within a day after fabrication, and thus R1011 was utilized to obtain the appropriate pitch with a minimum of CB15. Table 1

Table 1. Material Compositions used in the Study and Their Optical Properties

table-icon
View This Table
summarizes the three material compositions used in the study and their Bragg reflection wavelengths (λB) and absorption coefficients measured in the isotropic phase at the peak absorption wavelength. All cells were 5 μm thick, had planar orienting boundary conditions key to this study, and possessed a small fraction of the mesogenic push-pull azobenzene dye.

The experimental setup, schematically shown in Fig. 1
Fig. 1 Schematic of the experimental setup: NDF, set of neutral density filters; QW, quarter waveplate; BS1 and BS2, beam splitters; PM1 – PM3, power meters.
, comprises a pump laser, a set of neutral density filters for controlling the power/energy of the pump beam, a quarter waveplate for circularly polarizing the pump beam, and a beam splitter allowing the power of the beam transmitted and reflected from the CLC cell to be simultaneously measured. An argon-ion (Ar+) laser was used for obtaining CW beams at 458 nm and 488 nm wavelengths while a diode-pumped solid state laser was used when performing measurements at 532 nm.

3. Results

The peak absorption of π-π* band for CPND-n azo dyes in 5CB is observed at λmax = 471 nm wavelength. Figure 2
Fig. 2 Absorption spectra of 3.1-μm thick planar NLC cell CPND-8(10%)/5CB measured (1) before and (2) during an exposure to a blue laser beam of 473 nm wavelength and 35 mW/cm2 power density. The inset shows the chemical structure of CPND series azo dyes: R = C7H15 for CPND-7 and R = C8H17 for CPND-8.
shows the absorption spectra of trans and cis isomers of the azo dye CPND-8 in 5CB; the inset shows the core chemical structure of the CPND dye used in the study. The absorption spectrum of the cis isomers was obtained by exposing the NLC cell to a blue CW laser beam (λ = 473 nm, I = 35 mW/cm2) expanded to a size larger than the spectrometer beam. The dip in the absorption spectrum of cis-isomers seen in Fig. 2 is caused by the presence of the pump beam. Very small changes in the material absorption spectrum as a result of exposure to a blue light are evident including a slight red-shift and a slight increase in the peak absorption. These differences are relatively small compared to changes that take place in azo LCs with symmetrical π−π conjugation as a result of trans-cis photoisomerization [34

34. N. V. Tabiryan, S. V. Serak, and V. A. Grozhik, “Photoinduced critical opalescence and reversible all-optical switching in photosensitive liquid crystals,” J. Opt. Soc. Am. B 20(3), 538–544 (2003). [CrossRef]

37

37. U. Hrozhyk, S. Serak, N. Tabiryan, L. Hoke, D. M. Steeves, G. Kedziora, and B. Kimball, “High optical nonlinearity of azobenzene liquid crystals for short laser pulses,” Proc. SPIE 7050, 705007 (2008).

].

The reflection spectra of the three CLC mixtures are shown in Fig. 3
Fig. 3 Reflection spectra for 5-μm thick CLC cells in the blue-green portion of the pectrum: 1 – CLC-1, 2 – CLC-2; 3 – CLC-3. Dotted curve corresponds to absorption spectrum of the CPND azo dye.
. An overlay of the absorption spectra of the pure mesogenic dye and the lines for the three laser wavelengths utilized are superimposed. The three CLC mixtures were formulated to be accessible to the three distinct laser lines. Two of the three mixtures are composed of CPND-7 and one is composed of CPND-8. The photochemical response of these two compounds is indistinguishable at the concentrations employed here. The distortions apparent in the reflection spectra are due to the convolution of the dye absorption and the reflection bandgap.

Figure 4
Fig. 4 Intensity of reflected light as a function of time for response (■) and relaxation (○) of CLC bandgaps with laser beams of different wavelengths: (a) 458 nm (CLC-1) (Media 1), (b) 488 nm (CLC-2) (Media 2), and (c) 532 nm (CLC-3) (Media 3). The intensity of the beam is 28 mW/cm2 in (a) and (b), and 65 mW/cm2 in (c).
shows the rapid destruction of the reflective phase due to the light induced formation of an isotropic phase for all three mixtures at low power densities. The dynamics of transmission and reflection was measured with an oscilloscope and power meters for irradiation with violet, blue and green wavelengths. A movie (Media 1, Media 2, and Media 3) of the CLC cell undergoing photoinduced modulation of its spectral properties is included in the Supplemental Information. In the movie (Media 1, Media 2, and Media 3), the laser wavelength can be seen as a spike superimposed on the reflection notch when turned on and the reflectivity is quickly driven to zero. The reflectance of the CLC cell during and after laser exposure was monitored with a fiber optic spectrometer (Ocean Optics) and is shown in Fig. 4 for each wavelength. More impressively, once the specific laser wavelength is turned off (dotted line), a fast return (a few seconds) to the aligned reflective phase occurs. The exposure time for all samples to respective laser beams is 10 seconds. Within this time scale, all CLC order is destroyed for all three cells.More detailed steady state examinations shown in Fig. 5
Fig. 5 Transmission (T) and reflection (R) coefficients as a function of the input beam power: (a) corresponds to the CLC-1 subject to circularly polarized 458 nm laser irradiation; (b) CLC-2 with 488 nm irradiation; and (c) CLC-3 with 532 laser irradiation.
clearly show that the reflection intensity goes to zero while the transmission through the cell increases. The higher the input power, the more energy is transferred between the transmitted and reflected beams. These measurements examine only the polarized state that is the same handedness of the CLC material system. The fact that transmission and reflection are inversely proportional is an indirect confirmation that the loss of reflectivity is not due to the formation of transient scattering entities. The power (power density) thresholds of nonlinear transmission at the different wavelengths were 0.38 mW (110 mW/cm2) at 458 nm, 0.4 mW (117 mW/cm2) at 488 nm and 2.9 mW (370 mW/cm2) at 532 nm. The data in Fig. 5 relate to steady-state values whose kinetics are shown in Fig. 4.

Careful comparison of these two plots reveals that the reflectivity response times are shorter compared to that of transmission as indicated in Fig. 7
Fig. 7 The ratio of the response times for transmission and reflection obtained for CLC-2 exposed to the blue laser beam (488 nm).
. We speculate that the change in reflection is registered as soon as the input layer of the CLC is affected. Due to averaging through the thickness of the cell, the transmission measurements are a convoluted average of each individual layer’s response. Even though thin cells were utilized, this difference is observed at low power densities but diminishes as the power density is increased.

The optical switching presented here is reproducible over many cycles as shown in Fig. 8
Fig. 8 Periodic switching between reflective and transmittive states of CLC-2 (5-μm thick) with the blue laser beam (488 nm).
. Many cycles were tested with no observation of photofatigue. Figure 8 corresponds to 6.3 mW input power of the blue laser beam (488 nm).

4. Discussion

The superposition of the trans and cis absorption peaks (Fig. 2) indicates that upon exposure, repeated trans-cis and cis-trans isomerization cycles are occuring. The equilibrium ratio of cis to trans depends on the lifetime of the cis-isomer and quantum efficiencies of direct and reverse photoisomerization. Since the lifetime of the cis-isomer is quite short and the rate of trans-cis photoisomerization can be assumed to be close to the rate of cis-trans photoisomerization (same absorption peak wavelength), the trans concentration should be similar to that determined previously (Ntrans/Ncis ~3) [38

38. S. Serak and N. Tabiryan, “Microwatt power optically controlled spatial solitons in azobenzene liquid crystals,” Proc. SPIE 6332, 63320Y1–63320Y13 (2006).

]. Taking into account that the concentration of the azo dye in the materials under study is small, ~5 wt.%, we suggest that indeed the repetitive trans-cis-trans isomerization is the driving mechanism (photokinetic) behind the optical changes rather than classic disordering due to accumulation of cis isomers due to trans-cis isomerization. The molecules of the azodye, via repetitive trans-cis-trans processes, transfer the energy of a laser beam onto the LC host decreasing its order parameter. The process is similar to a thermal effect although it is characterized by a different set of microscopic (photoisomerization efficiencies) and phenomenological parameters (the impact factor of the photoisomerization on the order parameter of the LC).

4. Conclusion

Thus, sensitizing cholesteric liquid crystal formulations with blue-green reflection notches with mesogenic push-pull azomolecules has enabled for fast photoinduced switching on sub-millsecond time scales at low powers. The strong overlap of the trans and cis molecules absorption peaks suggests that the repetitive trans-cis-trans isomerizations diminishes the LC order present in the reflective CLC phase. The result is the fast decrease in the reflectivity coupled with the commensurate increase in transmission upon irradiation. The fast inherent relaxation of the azo mesogenic molecules themselves also enables very fast relaxation back from the transparent state to the reflective state when the laser irradiation is turned off. The time scales at a given power density for different laser irradiating wavelengths scale with the wavelength dependence of the absorption. The ability to cycle between reflective and transparent states on sub-second timescales through many cycles was demonstrated.

Acknowledgments

The authors wish to acknowledge AFRL/RX and AFOSR LRIR 09RX04COR.

References and links

1.

P. G. de Gennes, The Physics of Liquid Crystals (Clarendon, Cambridge, 1977)

2.

D. M. Makow and C. L. Sanders, “Additive colour properties and colour gamut of cholesteric liquid crystals,” Nature 276(5683), 48–50 (1978). [CrossRef]

3.

S.-T. Wu and D.-K. Yang, Reflective Liquid Crystal Displays (Wiley, 2001).

4.

A. Chanishvili, G. Chilaya, G. Petriashvili, R. Barberi, R. Bartolino, and M. P. De Santo, “Cholesteric liquid crystal mixtures sensitive to different ranges of solar UV irradiation,” Mol. Cryst. Liq. Cryst. (Phila. Pa.) 434(1), 25/[353]–38/[366] (2005). [CrossRef]

5.

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8.

S. Furumi, S. Yokoyama, A. Otomo, and S. Mashiko, “Phototunable photonic bandgap in a chiral liquid crystal laser device,” Appl. Phys. Lett. 84(14), 2491–2493 (2004). [CrossRef]

9.

T. J. White, M. E. McConney, and T. J. Bunning, “Dynamic color in stimuli-responsive cholesteric liquid crystals,” J. Mater. Chem. 20(44), 9832–9847 (2010). [CrossRef]

10.

F. Ania and H. Stegemeyer, “Cholesteric pitch behavior at the phase transition cholesteric to smectic B,” Mol. Cryst. Liq. Cryst. Lett. 2(3–4), 67–76 (1985).

11.

R. S. Pindak, C.-C. Huang, and J. T. Ho, “Divergence of cholesteric pitch near a smectic A transition,” Phys. Rev. Lett. 32(2), 43–46 (1974). [CrossRef]

12.

F. Zhang and D. K. Yang, “Temperature dependence of pitch and twist elastic constant in a cholesteric to smectic A phase transition,” Liq. Cryst. 29(12), 1497–1501 (2002). [CrossRef]

13.

M. E. McConney, V. P. Tondiglia, J. M. Hurtubise, L. V. Natarajan, T. J. White, and T. J. Bunning, “Thermally induced, multicolored hyper-reflective cholesteric liquid crystals,” Adv. Mater. (Deerfield Beach Fla.) 23(12), 1453–1457 (2011). [CrossRef] [PubMed]

14.

E. Sackmann, “Photochemically induced reversible color changes in cholesteric liquid crystals,” J. Am. Chem. Soc. 93(25), 7088–7090 (1971). [CrossRef]

15.

W. Haas, J. Adams, and J. Wysocki, “Interaction between uv radiation and cholesteric liquid crystals,” Mol. Cryst. Liq. Cryst. (Phila. Pa.) 7(1), 371–379 (1969). [CrossRef]

16.

J. Adams and W. Haas, “Sensitivity of cholesteric films to ultraviolet exposure,” J. Electrochem. Soc. 118(12), 2026–2028 (1971). [CrossRef]

17.

V. Vinvogradov, A. Khizhnyak, L. Kutulya, Y. Reznikov, and V. Resihetnyak, “Photoinduced change of cholesteric LC-pitch,” Mol. Cryst. Liq. Cryst. (Phila. Pa.) 192(1), 273–278 (1990). [CrossRef]

18.

M. Z. Alam, T. Yoshioka, T. Ogata, T. Nonaka, and S. Kurihara, “Influence of helical twisting power on the photoswitching behavior of chiral azobenzene compounds: applications to high-performance switching devices,” Chemistry 13(9), 2641–2647 (2007). [CrossRef] [PubMed]

19.

R. Eelkema and B. L. Feringa, “Reversible full-range color control of a cholesteric liquid-crystalline film by using a molecular motor,” Chem. Asian J. 1(3), 367–369 (2006). [CrossRef] [PubMed]

20.

A. Chanishvili, G. Chilaya, G. Petriashvili, and D. Sikharulidze, “Light induced effects in cholesteric mixtures with a photosensitive nematic host,” Mol. Cryst. Liq. Cryst. (Phila. Pa.) 409, 209–218 (2004). [CrossRef]

21.

S. Kurihara, S. Nomiyama, and T. Nonaka, “Photochemical switching between a compensated nematic phase and a twisted nematic phase by photoisomerization of chiral azobenzene molecules,” Chem. Mater. 12(1), 9–12 (2000). [CrossRef]

22.

S. S. Choi, S. M. Morris, W. T. S. Huck, and H. J. Coles, “Simultaneous red-green-blue reflection and wavelength tuning from an achiral liquid crystal and a polymer template,” Adv. Mater. (Deerfield Beach Fla.) 22(1), 53–56 (2010). [CrossRef] [PubMed]

23.

M. Xu and D.-K. Yang, “Dual frequency cholesteric light shutters,” Appl. Phys. Lett. 70(6), 720–722 (1997). [CrossRef]

24.

C. A. Bailey, V. P. Tondiglia, L. V. Natarajan, M. M. Duning, R. L. Bricker, R. L. Sutherland, T. J. White, M. F. Durstock, and T. J. Bunning, “Electromechanical tuning of cholesteric liquid crystals,” J. Appl. Phys. 107(1), 013105 (2010). [CrossRef]

25.

N. Tamaoki and T. Kamei, “Reversible photo-regulation of the properties of liquid crystals doped with photochromic compounds,” J. Photochem. Photobiol. Chem. 11(2–3), 47–61 (2010).

26.

K. G. Yager and C. J. Barrett, “Novel photo-switching using azobenzene functional materials,” J. Photochem. Photobiol. A 182(3), 250–261 (2006). [CrossRef]

27.

O. Tsutsumi, A. Kanazawa, T. Shiono, T. Ikeda, and L.-S. Park, “Photoinduced phase transition of nematic liquid crystals with donor-acceptor azobenzenes: mechanism of the thermal recovery of the nematic phase,” Phys. Chem. Chem. Phys. 1(18), 4219–4224 (1999). [CrossRef]

28.

U. A. Hrozhyk, S. V. Serak, N. V. Tabiryan, L. Hoke, D. M. Steeves, B. Kimball, and G. Kedziora,”Systematic study of absorption spectra of donor–acceptor azobenzene mesogenic structures,” Mol. Cryst. Liq. Cryst. 489, 257[583]–272[598] (2008).

29.

U. A. Hrozhyk, S. V. Serak, N. V. Tabiryan, L. Hoke, D. M. Steeves, and B. R. Kimball, “Azobenzene liquid crystalline materials for efficient optical switching with pulsed and/or continuous wave laser beams,” Opt. Express 18(8), 8697–8704 (2010). [CrossRef] [PubMed]

30.

U. Hrozhyk, S. Serak, N. Tabiryan, D. Steeves, L. Hoke, and B. Kimball, “Azobenzene liquid crystals for fast reversible optical switching and enhanced sensitivity for visible wavelengths,” Proc. SPIE 7414, 74140L, (2009). [CrossRef]

31.

L. De Sio, S. Serak, N. Tabiryan, and C. Umeton, “Mesogenic versus non-mesogenic azo dye confined in a soft-matter template for realization of optically switchable diffraction gratings,” J. Mater. Chem. 21(19), 6811–6814 (2011). [CrossRef]

32.

U. A. Hrozhyk, S. V. Serak, N. V. Tabiryan, T. J. White, and T. J. Bunning, “Optically switchable, rapidly relaxing cholesteric liquid crystal reflectors,” Opt. Express 18(9), 9651–9657 (2010). [CrossRef] [PubMed]

33.

U. Hrozhyk, S. Serak, N. Tabiryan, and T. J. Bunning, “Wide temperature range azobenzene nematic and smectic LC materials,” Mol. Cryst. Liq. Cryst. (Phila. Pa.) 454(1), 235/[637]–245/[647] (2006). [CrossRef]

34.

N. V. Tabiryan, S. V. Serak, and V. A. Grozhik, “Photoinduced critical opalescence and reversible all-optical switching in photosensitive liquid crystals,” J. Opt. Soc. Am. B 20(3), 538–544 (2003). [CrossRef]

35.

U. A. Hrozhyk, S. V. Serak, N. V. Tabiryan, and T. J. Bunning, “Optical Tuning of the Reflection of Cholesterics Doped with Azobenzene Liquid Crystals,” Adv. Funct. Mater. 17(11), 1735–1742 (2007). [CrossRef]

36.

S. Serak, N. Tabiryan, and T. Bunning, “Nonlinear transmission of photosensitive cholesteric liquid crystals due to spectral bandwidth auto-tuning or restoration,” J. Nonlinear Opt. Phys. Mater. 16(04), 471–483 (2007). [CrossRef]

37.

U. Hrozhyk, S. Serak, N. Tabiryan, L. Hoke, D. M. Steeves, G. Kedziora, and B. Kimball, “High optical nonlinearity of azobenzene liquid crystals for short laser pulses,” Proc. SPIE 7050, 705007 (2008).

38.

S. Serak and N. Tabiryan, “Microwatt power optically controlled spatial solitons in azobenzene liquid crystals,” Proc. SPIE 6332, 63320Y1–63320Y13 (2006).

OCIS Codes
(160.3710) Materials : Liquid crystals
(190.4400) Nonlinear optics : Nonlinear optics, materials
(230.3990) Optical devices : Micro-optical devices
(260.5130) Physical optics : Photochemistry

ToC Category:
Liquid Crystals

History
Original Manuscript: July 8, 2011
Revised Manuscript: July 24, 2011
Manuscript Accepted: July 24, 2011
Published: August 16, 2011

Citation
Uladzimir A. Hrozhyk, Svetlana V. Serak, Nelson V. Tabiryan, Timothy J. White, and Timothy J. Bunning, "Nonlinear optical properties of fast, photoswitchable cholesteric liquid crystal bandgaps," Opt. Mater. Express 1, 943-952 (2011)
http://www.opticsinfobase.org/ome/abstract.cfm?URI=ome-1-5-943


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