Michael J. Sansone

Large Kerr effects in transparent encapsulated liquid crystals

The encapsulation of liquid crystals in a polymer matrix produces a material with interesting and potentially useful optical properties. The earliest efforts generated a dispersed phase whose dimensions were comparable to optical wavelengths and therefore afforded materials which were highly scattering. These materials have already been found useful for display applications. We have found that when these materials are fabricated so that the dimensions of the dispersed phase are substantially smaller than the incident radiation wavelengths, the material is far less scattering. dc Kerr measurements on these liquid‐crystal composites yield quite large values, ranging as high as 30 000 times CS2 This activity is shown to be a strong function of the liquid‐crystal loading and the temperature.

Observation of the photorefractive effect in a dialkylaminonitrostilbene copolymer

We report observations of the photorefractive effect in a 1:1 side-chain copolymer of N-methacryloxyethyl-N-methylaminonitrostilbene with methyl methacrylate. Without the addition of a photoconducting component, gratings were written in this polymer at 633 nm in 8-μm-thick films at low powers and were detected by use of a four-wave mixing measurement. Diffraction efficiencies of the order of 10−5 −10−4 were measured by four-wave mixing.

Large Kerr effects in transparent encapsulated liquid crystals. II. Frequency response

The encapsulation of liquid crystals in polymer matrices produces materials with interesting electro‐optical and scattering properties. When the dispersed phase dimensions are substantially smaller than the incident radiation wavelengths, the material is optically clear with a large Kerr effect. These materials had been shown to behave as orientational Kerr media with Kerr constants as high as 30 000 times CS2 [J. Appl. Phys. 67, 4253 (1990)]. In this paper, the frequency response is studied with sinusoidal and pulsed electric fields. The electroactivity rolls off at higher frequencies with the 3 dB point in the range of 2000–12 000 Hz depending on liquid crystal loading and temperature. This indicates response times are in the microsecond range which is consistent with the pulsed field data.

Photorefractive effect in an aminonitrostilbene side-chain copolymer

The photorefractive effect has been observed in a 1/1 side chain copolymer of N- methacryloxyethyl-N-methylaminonitrostilbene and methylmethacrylate. Holographic gratings were written in this polymer at 633 nm in 4 - 8 micrometers thick films at low laser powers and detected using four wave mixing and two beam coupling. The polymer which has a high linear electro-optic coefficient was intrinsically photorefractive and did not require the addition of photoconducting or charge generative components. Diffraction efficiencies on the order of 10-5 - 10-4 were measured by four wave mixing. Two beam coupling provided conclusive evidence that the observed effect was photorefractive in nature.

Electro-optic and nonlinear optical polymers and devices

Early work at Hoechst Celanese1 demonstrated that methacrylate polymers with mesogenic side chains could be made with reasonably large electro-optic activity. The mesogenic side chains are polar so that a non-centrosymmetric structure can be obtained by heating a film near its Tg in a strong d.c. electric field and thus orienting the side chains. In Figure 1, the general structure of methacrylate based electro-optic polymers using polar nitro-stilbene chromophores is shown.