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Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 19, Iss. 13 — Jun. 20, 2011
  • pp: 12496–12502

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Nanoscale interlayer that raises response rate in photorefractive liquid crystal polymer composites

Hua Zhao, Chao Lian, Xiudong Sun, and Jingwen W. Zhang  »View Author Affiliations


Optics Express, Vol. 19, Issue 13, pp. 12496-12502 (2011)
http://dx.doi.org/10.1364/OE.19.012496


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Abstract

By depositing a nanoscale photoconductive layer on a stable photorefractive (PR) polymeric film, consisting of the polymer poly[N-vinylcarbazole] (PVK) doped with 4,4’-n-pentylcyanobiphenyl (5CB) and C60, both the response rate and beam coupling properties were improved greatly. Systematic measurements and observations unveiled the role played by the additive layer in preventing ion injection from the ITO layer into the PR film and hence in mitigating the charge compensation. A strong fanning effect and high diffraction orders at small angles have demonstrated the excellent PR property in the modified samples used. To demonstrate great potential of the PR composite in the updatable applications, real time double exposure interferometry was performed accordingly with good results.

© 2011 OSA

1. Introduction

Real time holographic display is promising for a very broad spectrum of applications, ranging from the low end in gaming and automobile industry, to the high end of space exploration, military training and deployment. Photorefractive (PR) polymers, well known for their high figures of merit, easy processing, and flexibility, are seen as one of potential material candidates which can satisfy the challenging requirements imposed on the material platform [1

O. Ostroverkhova and W. E. Moerner, “Organic photorefractives: mechanisms, materials, and applications,” Chem. Rev. 104(7), 3267–3314 (2004). [CrossRef] [PubMed]

–3

W. E. Moerner and S. M. Silence, “Polymeric photorefractive materials,” Chem. Rev. 94(1), 127–155 (1994). [CrossRef]

]. Following the first observation of the PR effect in polymers [4

S. Ducharme, J. C. Scott, R. J. Twieg, and W. E. Moerner, “Observation of the photorefractive effect in a polymer,” Phys. Rev. Lett. 66(14), 1846–1849 (1991). [CrossRef] [PubMed]

], interest has grown quickly and been focused on the exploration of new materials and investigation of the mechanism of photorefraction [5

K. Meerholz, B. L. Volodin, B. Sandalphon, Kippelen, and N. Peyghambarian, “A photorefractive polymer with high optical gain and diffraction efficiency near 100%,” Nature 371(6497), 497–500 (1994). [CrossRef]

]. High performance polymers have been reported to possess large gain coefficients, high diffraction efficiencies, and short response times [1

O. Ostroverkhova and W. E. Moerner, “Organic photorefractives: mechanisms, materials, and applications,” Chem. Rev. 104(7), 3267–3314 (2004). [CrossRef] [PubMed]

]. To address real-time updatable requirement, PR polymeric composites with fast response were reported in past years [6

S. Tay, P.-A. Blanche, R. Voorakaranam, A. V. Tunç, W. Lin, S. Rokutanda, T. Gu, D. Flores, P. Wang, G. Li, P. St Hilaire, J. Thomas, R. A. Norwood, M. Yamamoto, and N. Peyghambarian, “An updatable holographic three-dimensional display,” Nature 451(7179), 694–698 (2008). [CrossRef] [PubMed]

–9

M. Eralp, J. Thomas, G. Li, S. Tay, A. Schülzgen, R. A. Norwood, N. Peyghambarian, and M. Yamamoto, “Photorefractive polymer device with video-rate response time operating at low voltages,” Opt. Lett. 31(10), 1408–1410 (2006). [CrossRef] [PubMed]

], ushering in the development of holographic display systems [6

S. Tay, P.-A. Blanche, R. Voorakaranam, A. V. Tunç, W. Lin, S. Rokutanda, T. Gu, D. Flores, P. Wang, G. Li, P. St Hilaire, J. Thomas, R. A. Norwood, M. Yamamoto, and N. Peyghambarian, “An updatable holographic three-dimensional display,” Nature 451(7179), 694–698 (2008). [CrossRef] [PubMed]

,7

P.-A. Blanche, A. Bablumian, R. Voorakaranam, C. Christenson, W. Lin, T. Gu, D. Flores, P. Wang, W.-Y. Hsieh, M. Kathaperumal, B. Rachwal, O. Siddiqui, J. Thomas, R. A. Norwood, M. Yamamoto, and N. Peyghambarian, “Holographic three-dimensional telepresence using large-area photorefractive polymer,” Nature 468(7320), 80–83 (2010). [CrossRef] [PubMed]

].

In view of practical applications, phase separation problem [10

C. Poga, D. M. Burland, T. Hanemann, Y. Jia, C. R. Moylan, J. J. Stankus, R. J. Twieg, and W. E. Moerner, “Photorefractivity in new organic polymeric materials,” Proc. SPIE 2526, 82–93 (1995). [CrossRef]

] in materials has to be dealt with for a long, stable lifetime. To maximize the orientational enhancement effect [11

W. E. Moerner, S. M. Silence, F. Hache, and G. C. Bjorklund, “Orientationally enhanced photorefractive effect in polymers,” J. Opt. Soc. Am. B 11(2), 320–330 (1994). [CrossRef]

] and eliminate the need of plasticizer, liquid crystal (LC) forming compounds were chosen in a unique superb stable PR composite, believed to be uniform in molecular scale [12

J. Zhang and K. D. Singer, “Homogeneous photorefractive polymer/nematogen composite,” Appl. Phys. Lett. 72(23), 2948–2950 (1998). [CrossRef]

]. However, according to the theoretical analysis, both the orientational enhancement effect and the response rate should be improved two orders in magnitude for a freely rotating chromophores. In fact, the early report on photorefraction in neat LCs [13

I. C. Khoo, H. Li, and Y. Liang, “Observation of orientational photorefractive effects in nematic liquid crystals,” Opt. Lett. 19(21), 1723–1725 (1994). [CrossRef] [PubMed]

,14

G. P. Wiederrecht, B. A. Yoon, and M. R. Wasielewski, “High photorefractive gain in nematic liquid crystals doped with electron donor and acceptor molecules,” Science 270(5243), 1794–1797 (1995). [CrossRef]

] and the following intensive research activities globally [15

I. C. Khoo, “Nonlinear optics of liquid crystalline materials,” Phys. Rep. 471(5-6), 221–267 (2009). [CrossRef]

–17

L. Sznitko, A. Anczykowska, J. Mysliwiec, and S. Bartjiewicz, “Influence of grating period on kinetic of self-diffraction in nematic liquid crystal panel with photoconducting polymeric layer,” Appl. Phys. Lett. 96(11), 111106 (2010). [CrossRef]

], have demonstrated excellence of the LC materials in photorefaction [18

J. Zhang, V. Ostroverkhov, K. D. Singer, V. Reshetnyak, and Yu. Reznikov, “Electrically controlled surface diffraction gratings in nematic liquid crystals,” Opt. Lett. 25(6), 414–416 (2000). [CrossRef]

–20

X. Sun, F. Yao, Y. Pei, and J. Zhang, “Light controlled diffraction gratings in C60-doped nematic liquid crystals,” J. Appl. Phys. 102(1), 013104 (2007). [CrossRef]

], and affirmed us LCs as ideal chromophores in polymeric systems. Moreover, several intriguing findings of ours have turned our attention towards the interfaces of PR and ITO layers. In this regard, the interesting work of Ref [17

L. Sznitko, A. Anczykowska, J. Mysliwiec, and S. Bartjiewicz, “Influence of grating period on kinetic of self-diffraction in nematic liquid crystal panel with photoconducting polymeric layer,” Appl. Phys. Lett. 96(11), 111106 (2010). [CrossRef]

]. concerning the addition of nanoscale interlayer in between ITO and LC layers and its great impact have inspired this research effort. Consequently, several approaches had been proposed and used, proving to be effective in raising both the response rate and orientational enhancement effect. The experimental observations and related analyses offer insight on how to optimize the orientational effect in LC + polymer PR material systems, and open a novel way in producing multiple functional layer, large-size PR film in low cost and operation voltage. Finally, to demonstrate the improvement in PR properties, double exposure interferometry experiments were performed and reported in the last section of the paper.

2. Preparation of films

All materials we have chosen for the PR composite were commercially available, including the polymer poly[N-vinylcarbazole] (PVK) (Aldrich) as the photoconductive agent and matrix, 4,4’-n-pentylcyanobiphenyl (5CB) (Merck) as the nonlinear chromophore, and C60 (Aldrich) as the sensitizer. To raise the response rate and PR property of the PR film, trinitrofuorene (TNF) (Ultra Scientific) + PVK interlayers were inserted in between the ITO and PR layers. This PR composite indeed exhibited good stability without need for a plasticizing agent. The ratio of nonlinear chromophore could be varied from 30% to 60% by weight. To choose right methodology in preparation of samples and to know more about the physical surrounding of the LC molecules at ambient temperature, the glass transition temperature (Tg) of the composite with different concentrations of 5CB was measured. Six samples with different ratios of 5CB were prepared for measurement by differential scanning calorimetry. The Tg value varied from 229 °C for the pure PVK to 28 °C for the 60% 5CB sample.

In preparing a sample, measured amounts of PVK, 5CB and C60 were dissolved in a toluene and cyclohexanone (weight ratio was 2.5:1) solvent mixture. The mixture was then cast onto an ITO glass plate and put into a leveled container for the sake of slowly drying to achieve a smooth film surface. Following the air drying, the sample was placed in a vacuum oven for 48 hours at 60°C to remove all remaining solvent. A second piece of ITO glass plate spin-coated with PVK + TNF nanoscale thin layer was placed on top of the film. The sample was then pressed in a vacuum oven at 120°C to fuse the structure for the samples with 40% 5CB or more. In making a sample with 30% 5CB or less another approach was used, by directly depositing an ITO transparent conducting layer on top of the thin film which was cast on an ITO glass plate.

3. Theoretical consideration

Judging from Tgs of the samples with 30% 5CB or higher, the role of the orientational enhancement effect in these materials should contribute greatly to the effective electro-optic response reff [10

C. Poga, D. M. Burland, T. Hanemann, Y. Jia, C. R. Moylan, J. J. Stankus, R. J. Twieg, and W. E. Moerner, “Photorefractivity in new organic polymeric materials,” Proc. SPIE 2526, 82–93 (1995). [CrossRef]

]. By using the treatment of Ref 11

W. E. Moerner, S. M. Silence, F. Hache, and G. C. Bjorklund, “Orientationally enhanced photorefractive effect in polymers,” J. Opt. Soc. Am. B 11(2), 320–330 (1994). [CrossRef]

, the effective electro-optic coefficient for s- and p-polarization is given by:
r eff (s)=2× A E0 n4sin Ψ tilt,  r eff (p)= A E0 n4sin Ψ tiltcos θ int [ ( CA−1)+ ( CA+1)cos θ int],
(1)
where n is the refractive index of the sample, and Ψtilt the tilt angle (inside the sample) of the bisector of the beams with respect of the normal of the sample, θint the internal interbeam angle, the material constant A=CEO/3- CBR/2, and C=CEO + CBR, CEO and CBR are the coefficients from contributions of electro-optic (EO) and the induced birefringence (BR) effects. These are given by,
C EO= 15N β 333 ( μ kBT),  C BR= 2 45N( α ‖ ω− α⊥ω) β 333 ( μ kBT)2,
(2)
where N is the density of chromophores, μ the ground-state dipole moment, α⊥ and α// the linear optical polarizabilities of the chromophore molecule parallel and perpendicular to the molecular axis, and β333 the hyperpolarizability of the chromophore.

Using above formulae, the direct comparison between the experimental results and the theoretical model stated above was done in [11

W. E. Moerner, S. M. Silence, F. Hache, and G. C. Bjorklund, “Orientationally enhanced photorefractive effect in polymers,” J. Opt. Soc. Am. B 11(2), 320–330 (1994). [CrossRef]

] and suggested the orientational enhancement effect, though large, is considerably smaller than would be expected for freely rotating chromophores. For 30% and 40% 5CB specimens, the ambient working temperature is below Tg, orientational motion is apparently restricted. Along this line, it seems that by further increasing weight percentage of 5CB, Tg would decrease, the orientional effect will be enhanced. As a result, the gain coefficient, which is proportional to reff, should increase accordingly. However, when we measured the samples with 50% and 60% 5CB, very surprisingly, no gain coefficient increase was evidenced. Even worse, the response rates were getting slower and more unstable energy transferring occurred with increasing of 5CB. No doubt, these surprising outcomes deserve further study to peek into the mechanism in the PR samples to optimize this superb stable polymeric PR material system.

4. Experiments and discussions

4.1 Four-wave mixing

Choosing the conventional oblique geometry [1

O. Ostroverkhova and W. E. Moerner, “Organic photorefractives: mechanisms, materials, and applications,” Chem. Rev. 104(7), 3267–3314 (2004). [CrossRef] [PubMed]

,2

W. E. Moerner, A. Grunnet-Jepsen, and C. L. Thompson, “Photorefractive polymers,” Annu. Rev. Mater. Sci. 27(1), 585–623 (1997). [CrossRef]

], we have studied properties of PR polymers with degenerate four-wave mixing (DFWM). We concentrated on three samples (40, 50, and 60 wt. % 5CB, 0.2 wt. % C60, with thicknesses all around 100 μm) in this work. The absorption coefficients of the three samples were 17.5 cm−1, 18.0 cm−1 and 18.3 cm−1 at 632.8 nm, and the glass transition were about 40, 33, and 28 °C, in the samples with 40, 50, and 60 wt. % 5CB, respectively. The external diffraction efficiency was measured with DFWM and the response time on the grating spatial period can be obtained accordingly. Selected dynamic curves of diffraction signals in DFWM obtained in the sample with 50 wt% 5CB were shown in Fig. 1(a) . The two writing beams with equal intensities, 30 mW·cm−2, formed gratings with spatial period 1.0 to 4.5 μm. The intensity of the probe beam, which was counterpropagating to one of the two writing beams, was 3.0 mW·cm−2. The applied field corresponding to Fig. 1(a) was 135 V/μm and the maximum external diffraction efficiency was 61%. To see the erasure time of the gratings written in the PR film with grating spacing period (crossing angle), the erasure time versus grating spacing was shown in Fig. 1(b). It is seen that the recording and erasure times depend on the spacing almost exponentially. With increasing of the grating spacing, the erasing time decreases quickly and approaches constant time of 15.8 s, much longer than the theoretical values of sub-ms to tens of ms.

Fig. 1 (a) A dynamic curve of diffraction intensity in different crossing angles and (b) erasure time versus grating spacing in the degenerate FWM configuration.

Compared with the experimental results obtained in 5CB liquid crystal slightly doped with fullerene C60 [18

J. Zhang, V. Ostroverkhov, K. D. Singer, V. Reshetnyak, and Yu. Reznikov, “Electrically controlled surface diffraction gratings in nematic liquid crystals,” Opt. Lett. 25(6), 414–416 (2000). [CrossRef]

–20

X. Sun, F. Yao, Y. Pei, and J. Zhang, “Light controlled diffraction gratings in C60-doped nematic liquid crystals,” J. Appl. Phys. 102(1), 013104 (2007). [CrossRef]

], it inspired us to turn our attention towards the ITO –polymer interface. In LC cells, the observed behavior of the PR grating dynamics was consistent with a predominantly surface mediated PR effect, the typical response time was tens of seconds, the compensation of the space charge could even hide the grating completely [18

J. Zhang, V. Ostroverkhov, K. D. Singer, V. Reshetnyak, and Yu. Reznikov, “Electrically controlled surface diffraction gratings in nematic liquid crystals,” Opt. Lett. 25(6), 414–416 (2000). [CrossRef]

]. To pinpoint the real reason behind this slow response rate, several experiments were designed as follows.

4.2 Elevating temperature technique

To confirm the key role of the ITO –polymer interface, a PR film was heated up purposely to elevated temperature which was much higher than its Tg point. Very interestingly, when the sample was heated up to 60°C, the diffraction signal began to drop quickly and approached zero while applied field was on (shown in Fig. 2(a) ). However, while the applied electric field was turned off, the diffraction signal jumped back sharply. After reaching the value which was comparable to the original diffraction efficiency, it went off very quickly.

Fig. 2 (a) Measured external diffraction efficiency versus applied electric field at elevated temperature; (b) Diffracted intensity in a 5CB +C60 liquid crystal cell for a continuously incident He–Ne probe beam during a program of applying an electric field.

This result resembles the PR diffraction dynamics in LC cells [18

J. Zhang, V. Ostroverkhov, K. D. Singer, V. Reshetnyak, and Yu. Reznikov, “Electrically controlled surface diffraction gratings in nematic liquid crystals,” Opt. Lett. 25(6), 414–416 (2000). [CrossRef]

]. For direct comparison, the diffraction dynamics in 5CB + C60 cells was taken and plotted in Fig. 2(b). The applied electric voltage was 2.2 V on the sample of 12.5 µm in thickness at ambient temperature 24 °C, the grating spacing was 74 µm. It is seen when the applied electric field was turned off, a big jump (even over 2 times higher than the stable diffraction efficiency) was observed and then went off rapidly. These two experimental results suggest that the surface charge accumulation can compensate the space charge distribution, and thus cut short of the gain coefficient in two beam coupling as well as the diffraction efficiency in DFWM.

This also gives an alternative explanation to the remarkable improvement of gain coefficient in moving grating technique reported previously [21

J. Zhang and K. D. Singer, “Novel photorefractive liquid crystal polymer composites,” SPIE 3471, 14 (1998).

]. When the interference fringe was moving at appropriate speed, the charge compensation was efficiently mitigated. As the result, the energy transferring was enhanced, so was the gain coefficient.

4.3 Introduction of nanoscale mediated layer and direct sputtering technique

A straightforward approach in raising the response rate is to introduce a nanoscale TNF + PVK interlayer (around 100 nm in thickness) in between ITO and PR layers. Encouragingly, remarkable response rate and gain coefficient increases were obtained by this simple modification. (1) Gain coefficients obtained from the samples with interlayers were 2 to 3 times higher than that gotten from similar samples without interlayer,; (2) After introducing interlayers, the gain coefficients in 50% 5CB samples were 1.4 time higher than that in the one with 40% 5CB, while the optimal applied electric voltage was 1.0 kV lower; (3) for a small crossing angle situation, over 4 to 6 high diffraction orders were observed in degenerate two wave mixing experiments. This demonstrated the excellent PR properties in the material system proposed from a different perspective; (4) a strong fanning effect, long regarded as the solid proof for an excellent PR material, had been also observed in the PR samples used. All these results are consistent with the orientational enhancement expectation (refer to Eqs. (1) to (2)).

According to the analysis in Section 4.2, it seems that some sort of ion injection results in charge accumulation near the interface of ITO and polymeric films. Based on the hole dominant mechanism in polymeric PR effect, it is believed ion injection is mainly from one side of the two electrodes. To mitigate the charge compensation effect, some samples were prepared by directly depositing ITO layers on top of the cast and dried polymeric mixture film with 30% or lower 5CB. It was quite encouraging to see that dramatic response time reduction was achieved by this simple modification (shown in Fig. 3(a) ). One can see the response time was reduced over two orders of magnitude.

Fig. 3 (a) A dynamic curve of diffraction intensity in the degenerate FWM configuration with a typical sample prepared by directly depositing ITO layer on top of the sample; (b) A typical mobility measurement results obtained in PVK + TNF thin film.

According to the measured mobility in PVK + TNF thin film by time-of-flight technique (Fig. 3(b)), the response time can be reduced even to ms or shorter. The PVK + TNF sample was 12µm in thickness and the experimental setup was similar to the conventional one used by Shiyanovskaya et al [22

I. Shiyanovskaya, K. D. Singer, V. Percec, T. K. Bera, Y. Miura, and M. Glodde, “Charge transport in hexagonal columnar liquid crystals self-organized from supramolecular cylinders based on acene-functionalized dendrons,” Phys. Rev. B 67(3), 035204 (2003). [CrossRef]

]. This directly depositing methodology provides a way in making samples in large size (area) with multiple layers to optimize PR effect. Apparently, this is highly desirable in real world applications. To demonstrate the great improvement, double exposure interferometry was performed with modified PR films as following.

4.4 Double exposure Interferometry

When a PR plate is located at a certain distance before a focal lens, a perfect imaging replica of the incident image can be obtained at the output plane (see Fig. 4(a) ). This geometry can be used to monitor tiny phase changes of the incident wave front, i.e., real-time double-exposure holographic interferometry could be demonstrated. Let O(x,y,t) be the original object wave and O’ (x,y,t) the object wave when the object is disturbed by an external stimulus. If only a change of phase ΔΦ results from the external disturbance, then it can be expressed as O'(x,y,t)=O(x,y,t)exp[iΔΦ(x,y,t). Suppose that the self diffraction and transmitted ratio are R(t) and R’(t), which depend on the development of the writing time, for the two input signals O(x,y,t) and O’(x,y,t), respectively; then the observed intensity in the output plane is proportional to

Fig. 4 Double-exposure interferometry: (a) schematic diagram; (b) original imaging spot; (c) photograph of the observed interference fringe pattern of a reflective test plate under a thermo-induced strain.
IR(t)= | O(x,y,t)|2[ (R(t))2+ (R'(t))2+2 RR'cosΔΦ].
(3)

The system of double-exposure interferometry can perform measurements of great precision. Our experiment on double-exposure interferometry with two wave mixing is suitable for wavefront-change detection of weak object waves from a weak incident beam.

Shown in Fig. 4(b) and (c) are the preliminary experimental results obtained in the double exposure surface measurement setup shown in Fig. 4(a). Figure 4(b) was the transmitted spot for a reflective plate without physical stimulus. Figure 4(c) was the interference pattern for a reflective plate when heating up the border part of the plate. The interference pattern change reflected the thermo-induced distortion of the plate.

3. Conclusion

In conclusion, the specific nanoscale photoconductive interlayer was believed responsible for the dramatic improvement both in response rate and gain coefficient. It seems that the interlayer prevents ion injection from ITO layer into the body of main polymeric layers and the TNF serves as an electron accepter. This might be the reason for the remarkable gain increase as well as the response improvement. For a small crossing angle situation, over 4 to 6 high diffraction orders were observed. Furthermore, a strong fanning effect had been also observed in the PR samples used. The experimental results obtained from the double exposure interferometry demonstrate that the polymeric PR composite is promising in updatable applications.

Acknowledgments

This work has been supported by the grant for 100 talents of Harbin Institute of Technology under AUGA570000710.

References and links

1.

O. Ostroverkhova and W. E. Moerner, “Organic photorefractives: mechanisms, materials, and applications,” Chem. Rev. 104(7), 3267–3314 (2004). [CrossRef] [PubMed]

2.

W. E. Moerner, A. Grunnet-Jepsen, and C. L. Thompson, “Photorefractive polymers,” Annu. Rev. Mater. Sci. 27(1), 585–623 (1997). [CrossRef]

3.

W. E. Moerner and S. M. Silence, “Polymeric photorefractive materials,” Chem. Rev. 94(1), 127–155 (1994). [CrossRef]

4.

S. Ducharme, J. C. Scott, R. J. Twieg, and W. E. Moerner, “Observation of the photorefractive effect in a polymer,” Phys. Rev. Lett. 66(14), 1846–1849 (1991). [CrossRef] [PubMed]

5.

K. Meerholz, B. L. Volodin, B. Sandalphon, Kippelen, and N. Peyghambarian, “A photorefractive polymer with high optical gain and diffraction efficiency near 100%,” Nature 371(6497), 497–500 (1994). [CrossRef]

6.

S. Tay, P.-A. Blanche, R. Voorakaranam, A. V. Tunç, W. Lin, S. Rokutanda, T. Gu, D. Flores, P. Wang, G. Li, P. St Hilaire, J. Thomas, R. A. Norwood, M. Yamamoto, and N. Peyghambarian, “An updatable holographic three-dimensional display,” Nature 451(7179), 694–698 (2008). [CrossRef] [PubMed]

7.

P.-A. Blanche, A. Bablumian, R. Voorakaranam, C. Christenson, W. Lin, T. Gu, D. Flores, P. Wang, W.-Y. Hsieh, M. Kathaperumal, B. Rachwal, O. Siddiqui, J. Thomas, R. A. Norwood, M. Yamamoto, and N. Peyghambarian, “Holographic three-dimensional telepresence using large-area photorefractive polymer,” Nature 468(7320), 80–83 (2010). [CrossRef] [PubMed]

8.

M. Eralp, J. Thomas, S. Tay, G. Li, A. Schülzgen, R. A. Norwood, M. Yamamoto, and N. Peyghambarian, “Submillisecond response of a photorefractive polymer under single nanosecond pulse exposure,” Appl. Phys. Lett. 89(11), 114105 (2006). [CrossRef]

9.

M. Eralp, J. Thomas, G. Li, S. Tay, A. Schülzgen, R. A. Norwood, N. Peyghambarian, and M. Yamamoto, “Photorefractive polymer device with video-rate response time operating at low voltages,” Opt. Lett. 31(10), 1408–1410 (2006). [CrossRef] [PubMed]

10.

C. Poga, D. M. Burland, T. Hanemann, Y. Jia, C. R. Moylan, J. J. Stankus, R. J. Twieg, and W. E. Moerner, “Photorefractivity in new organic polymeric materials,” Proc. SPIE 2526, 82–93 (1995). [CrossRef]

11.

W. E. Moerner, S. M. Silence, F. Hache, and G. C. Bjorklund, “Orientationally enhanced photorefractive effect in polymers,” J. Opt. Soc. Am. B 11(2), 320–330 (1994). [CrossRef]

12.

J. Zhang and K. D. Singer, “Homogeneous photorefractive polymer/nematogen composite,” Appl. Phys. Lett. 72(23), 2948–2950 (1998). [CrossRef]

13.

I. C. Khoo, H. Li, and Y. Liang, “Observation of orientational photorefractive effects in nematic liquid crystals,” Opt. Lett. 19(21), 1723–1725 (1994). [CrossRef] [PubMed]

14.

G. P. Wiederrecht, B. A. Yoon, and M. R. Wasielewski, “High photorefractive gain in nematic liquid crystals doped with electron donor and acceptor molecules,” Science 270(5243), 1794–1797 (1995). [CrossRef]

15.

I. C. Khoo, “Nonlinear optics of liquid crystalline materials,” Phys. Rep. 471(5-6), 221–267 (2009). [CrossRef]

16.

S. Bartkiewicz, A. Miniewicz, B. Sahraoui, and F. Kajzar, “Dynamic charge-carrier-mobility-mediated holography in thin layers of photoconducting polymers,” Appl. Phys. Lett. 81(20), 3705–3707 (2002). [CrossRef]

17.

L. Sznitko, A. Anczykowska, J. Mysliwiec, and S. Bartjiewicz, “Influence of grating period on kinetic of self-diffraction in nematic liquid crystal panel with photoconducting polymeric layer,” Appl. Phys. Lett. 96(11), 111106 (2010). [CrossRef]

18.

J. Zhang, V. Ostroverkhov, K. D. Singer, V. Reshetnyak, and Yu. Reznikov, “Electrically controlled surface diffraction gratings in nematic liquid crystals,” Opt. Lett. 25(6), 414–416 (2000). [CrossRef]

19.

X. Sun, Y. Pei, F. Yao, J. Zhang, and C. Hou, “Optical amplification in multilayer photorefractive liquid crystal films,” Appl. Phys. Lett. 90(20), 201115 (2007). [CrossRef]

20.

X. Sun, F. Yao, Y. Pei, and J. Zhang, “Light controlled diffraction gratings in C60-doped nematic liquid crystals,” J. Appl. Phys. 102(1), 013104 (2007). [CrossRef]

21.

J. Zhang and K. D. Singer, “Novel photorefractive liquid crystal polymer composites,” SPIE 3471, 14 (1998).

22.

I. Shiyanovskaya, K. D. Singer, V. Percec, T. K. Bera, Y. Miura, and M. Glodde, “Charge transport in hexagonal columnar liquid crystals self-organized from supramolecular cylinders based on acene-functionalized dendrons,” Phys. Rev. B 67(3), 035204 (2003). [CrossRef]

OCIS Codes
(090.2870) Holography : Holographic display
(190.5330) Nonlinear optics : Photorefractive optics
(090.5694) Holography : Real-time holography

ToC Category:
Holography

History
Original Manuscript: April 29, 2011
Revised Manuscript: May 25, 2011
Manuscript Accepted: June 2, 2011
Published: June 13, 2011

Citation
Hua Zhao, Chao Lian, Xiudong Sun, and Jingwen W. Zhang, "Nanoscale interlayer that raises response rate in photorefractive liquid crystal polymer composites," Opt. Express 19, 12496-12502 (2011)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-19-13-12496


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References

  1. O. Ostroverkhova and W. E. Moerner, “Organic photorefractives: mechanisms, materials, and applications,” Chem. Rev. 104(7), 3267–3314 (2004). [CrossRef] [PubMed]
  2. W. E. Moerner, A. Grunnet-Jepsen, and C. L. Thompson, “Photorefractive polymers,” Annu. Rev. Mater. Sci. 27(1), 585–623 (1997). [CrossRef]
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