Phase conjugation in amorphous germanium diselenide thin films

We report a phase conjugate mirror (PCM) using germanium diselenide amorphous thin films with a 25 mW He Ne laser. The size of the PCM area can be made very large as opposed to the size limitations of crystal PCMs. The induced hologram may be recorded temporarily or permanently depending on the incident light parameters. The main drawback of this system is the long exposure time, of the order of minutes, required to generate the phase conjugate signal. The modulation of the refractive index is suggested to be due to a photostructural reorientation.