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Radiation effects on nematic liquid crystal devices

Liquid crystal devices are among the most important elements in today's photonic technology. However, little is known about the effects of ionizing radiation on the electro-optic properties of nematic liquid crystal devices. Therefore, we have performed gamma irradiation experiments on commercially available liquid crystal variable retarders (LCVR). We monitored the voltage tunable birefringence of the LCVRs at 633 nm, using a real-time polarization analyzer, as a function of total dose. The first experiment was conducted at room temperature, using a 60Co source with a dose rate of 3.5 Gy/h, up to a total dose of about 0.5 kGy. A second experiment was conducted at a higher dose rate (85 Gy/h), using a spent fuel irradiator. For voltages exceeding the Frederiksz transition threshold, there was no considerable radiation effect on the birefringence. The sub- threshold birefringence, however, was influenced by radiation and showed post-irradiation recovery. A final experiment at 4.5 kGy/h allowed doses of up to 500 kGy to be reached, for which the LCVR still showed satisfactory operation. Further investigations aim at performing parameter estimations for identifying which liquid crystal material parameters are most affected by radiation.