Temperature Effects On The Properties Of Material Under Intense Laser Irradiation

As we all know, laser induced damage of optical elements has been a crucial factor restricting the power of high-power laser systems further improve, due to lower temperature can effectively suppress the laser-induced thermal damage, also can significantly limit the avalanche process. Therefore, this method is expected to be a new ideas and technologies to improve the optical element load capacity significantly; and the mechanism of laser-induced damage to fused silica and other materials had a more profound understanding for the laser pulse width less than 100 femtoseconds.This thesis mainly studied laser irradiation damage on fused silica and other materials under different temperatures(from several tens of degrees Kelvin to room temperature) from experimental, and some physical trend were obtained. The main contents and conclusions are summarized as follows:1. The visible light reflection determination method and N-on-1 measurement method are used to obtain damage threshold of fused silica and other glasses samples after nanosecond laser irradiation under different ambient temperature. And the trends of initial laser-induced damage threshold-temperature of these materials under nanosecond laser irradiation are obtained. The results show that under nanosecond laser irradiation the damage threshold of fused silica, K9 and others first increased and then dropped with the temperature decreased, apparently, there is a maximum value. That is to say, lower temperature is an effective way to improve the damage threshold of fused silica and other materials.2. The effects of temperature on the front surface damage threshold of fused silica and other materials under 37 femtoseconds laser irradiation are investigated by using damage area-energy value method. And the damage thresholds of these materials under different temperature are obtained. Experimental results show that the initial damage thresholds of these materials under different temperatures are almost unchanged.Namely, the mechanism of avalanche ionization is not the main factor in the mechanism of laser-induced damage to fused silica and other materials under the condition of the laser pulse width less than 100 femtoseconds.3. The effects of temperature on the front surface damage threshold of fused silica and other materials under the 37 femtoseconds laser pluses irradiation are investigatedby using damage area-energy value method. And the trends of the number of pulses-threshold of front surface damage of these materials at different temperatures are obtained. The results show that at the same ambient temperature, the threshold first dropped quickly and then became stable with the number of laser pulse increased. And the damage morphology of fused silica and K9 glass are different, that can be described as spot center melt zone with cracks around the spot and only spot center melt zone,respectively, because that fused silica is more brittle than K9 glass.