When sufficient intense laser pulse interacts with semi-conductors, permanent damage results due to formation of scattering centers in the semi-conductor surface. Reflectance of the damaged surface is reduced as compared to the smooth surface. Generally, damage threshold is defined as a value for which the reflectance is decreased by more than 10%. It is interesting that reflectance change can be seen below the damage threshold value. In the present work it has been shown that these changes occur at the rate of 0.5% per pulse. These changes are not due to any type of irreversible process in the material and slow but continuous decrease can be seen in the reflectance if the number of pulses is increased. Although when the fluence is increased, remarkable change can be seen in the reflectance decrease for the first pulse (in some cases, for 2-3 pulses), but if the number of incident pulses are further increased, the slow and continuous decrease is shown in reflectance value.
The present experiments were performed in the CdZnTe <111> single crystal surface exposed to Nd:YAG laser (pulse duration: 20ns, prs:1pps, wavelength: 1.064µm) in the ambient air.