Abstract
The change in refractive index of liquid-crystalline azobenzenes induced by nanosecond laser pulse was investigated with reference to optical switching. The photoresponsive liquid crystals show nematic phase in the trans form while no liquid-crystalline phase in the cis form. Intensity of reflected light from interface between sample and glass substrate depends on refractive indices of both materials, and hence the change in refractive index of sample results in change in the intensity of the reflected light. We measured the intensity of the reflected light at 633 nm (He-Ne laser) from the interface and found that the reflected light rose up in 100 ms on pulse irradiation at 355 nm (YAG laser, the third harmonic, 10 ns FWHM) and decayed in 1 ms. The decay was 1000 times faster than those observed in the transmittance-mode measurements. The fast decay may be due to different mechanism in the reflection-mode measurements. At first, molecules in the cis form diffuse into molecules in the trans form which did not photoisomerize. Next, the molecules in the trans form reorient on the glass surface. By the use of the reflection-mode light probe, we successfully obtained more rapid change in optical switching than that of the transmittance-mode light probe.
