Photoinduced Anisotropy and Reorientation of Anisotropic Axis in Amorphous $As_2S_3$ Thin Film

비정질 $As_2S_3$ 박막의 광유도 비등방성과 비등방축의 가역성

Photoinduced anisotropy (PIA) in amorphous As2S3 (a-As2S3 ) thin film, deposited by vacuum evaporation, is investigated. PIA is induced by linearly polarized Ar+ laser beam (λ=514.5nm) and probed by weak Ar+ laser (λ=514.5nm) and He-Ne laser (λ=632.8nm) beam through the crossed analyzer. Keeping pump beam intensity constantly, rotation of pump beam polarization direction induces reorientation phenomina of anisotropic axis. Introducing directional factor into simplified 3-level system, which is used to analyze photodarkening phenomina, an analytical expression of PIA is derived. Temporal behavior of PIAand its reorientation phenomina are investigated andcompared with theory. In the experiment pump beam intensity is 100mW/$\textrm{cm}^2$ and thickness of a-As2S3 thin film is 3${\mu}{\textrm}{m}$. In those condition, time constant of photoinduced anisotropy obtained by method of least square curve fitting is 4.0$\times$10-2sec-1. The time constant of PIA we obtained is larger than that of photodarkening, 2.8$\times$10-2sec-1.