Observation of temporary degeneration of material transmittance under strong laser irradiation

Abstract

Laser induced temporary degeneration of transmissivity in optical materials has been observed under strong laser irradiation. In the experiment, a green light laser beam was focused onto a transparent sample, an ultra fast photo-tube was used to detect the laser signals behind the sample, an oscilloscope was used to record the amplitude change of the signals. When the laser power density on the sample increases to some levels, the detected signal starts to decrease relatively, which means the transmissivity of the sample commences to degenerate. In this case, if the laser power density is reduced back a little bit, the transmittance of the sample can restore. This means that the degeneration of the transmittance is temporary. When the laser power density increase further more after the degeneration has commenced, damage to the material will happen. Therefore, there is a transition course in material before it is damaged. The transition course is from the beginning of transmittance degeneration to damage rising. The influence of laser repetition rate on the damage formation has been also investigated.