Absorption of high power laser pulse makes several phenomena in the optical media. These phenomena contain thermal lens effect, laser damage in the solid, thermooptic property, and optical breakdown in the gas.
For the analysis of thermal lens effect, refractive index and absorption coefficient of slide glass are measured. When the slide glass absorbs Nd-glass laser pulse its changes of thickness and refractive index are measured, and from these measured values linear thermal expansion coefficient and thermooptic coefficient are obtained to $8.3×10^{-6}℃^{-1}$ and $2.8×10^{-5}℃^{-1}$, respectively.
Laser damage pattern is observed in the optical solid material, and the damage thresholds of slide glass and BK-7 glass are measured by the conventional method. For the measurement of microscopic damage thresholds, multi-reflection laser Doppler velocity interferometer, which is able to measure very small displacement, is developed and the usefulness of this system is proved.
Thermooptic property is used to determine small absorption coefficients of benzene and its derivatives at 1.06 ㎛ line. The sample exposed to a high power Nd-glass laser pulse absorbs the light and the change in the refractive index along the path of laser pulse arises in consequence of temperature rising. The absorption coefficient is determined from the interferometric measurement of the refractive index change and the thermooptic coefficient obtained in the same Mach-Zehnder interferometer.
The flash accompanied with the optical breakdown is observed in the air and Ar gas, and it is found that the gas breakdown threshold is inversely proportional to the pressure.
