Observation of hysteresis effects in POLICRYPS holographic gratings.

We report on the observation of hysteresis effects that take place in the electro-optical response of a polymer-liquid-crystal-polymer slice grating named POLICRYPS. Investigation of transmittance as a function of an applied external voltage reveals an hysteresis area that is strongly correlated to the delay between consecutive applications of square wave voltages of different amplitude. A suitable software has been implemented to control this delay: when it is long, results show a large hysteresis area, which can be reduced by diminishing the delay. In addition, correlation between this area and the frequency of the applied voltage is analyzed, taking into account that the effect of impurity ions migration is not negligible in the case of low frequencies.