We examine the film-temperature and the exposure-time dependence of optically induced birefringence in semicrystalline azopolyester films. Around the glasstransition temperature Tg, the birefringence increases markedly after interception of the pump beam. Consequently, the birefringence at Tg reaches a value of three times as large as that induced at room temperature. In addition, the value of the thermally enhanced birefringence depends on exposure time; it is almost proportional to that induced during the pump beam irradiation. Thus, since the semicrystalline azopolyester suitably restricts the thermal enhancement, the value can easily be controlled. This property allows us to make the thermal enhancement compatible with the controllability of the value.

© 2001 Optical Society of America

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