M.B. Sai Prasad

Study of laser assisted decontamination of commonly used clad surfaces

The decontamination factor, defined as the ratio of initial to residual activity, is studied as a function of laser fluence for three kinds of clad surfaces viz., plain zircaloy, autoclaved zircaloy, and stainless steel with cesium as the simulated contamination. It has been found that the decontamination factor exhibits a maximal behavior with the laser fluence and its maximum value occurs at different laser fluences in the three cases. The maximal behavior is attributed to reduced coupling of energy from the laser beam to the substrate due to the initiation of surface-assisted optical breakdown. The results obtained in the experiment carried out in helium environment qualitatively support this explanation.

Switch-less operation of a TEA CO2 laser.

We report here the operation of a UV pre-ionised mini-TEA CO2 laser where the use of an external switch has been dispensed with. This was rendered possible by making the preioniser spark array play a dual role- that of a switch as well as of a source of UV photons that pre-conditioned the inter-electrode volume.

Second harmonic conversion of 10 µm emissions of pulsed and CW CO2 lasers in ZnGeP2

The paper reports on the satisfactory performance of a ZnGeP2 crystal towards second harmonic conversion of a pump beam at 10 μm wavelength and thus establishes its utility in the generation of coherent radiation not only around 4.5 μm but also in the neighbourhood of the 5 μm region of mid-infrared. Experimental results comparing performance of a thin crystal when pumped alternately with the emissions of continuous wave (CW) and TEA CO2 lasers are presented. The performance was also studied as a function of the duration of the pump TEA CO2 laser pulse and the observed anomaly is qualitatively explained. The significant increase in conversion efficiency in the case of pulsed operation is attributed to the much higher irradiating intensity to which the crystal is subjected to in comparison with the CW case. Of particular interest is the finding that the pump intensity below which the second harmonic generation process ceases is lower by almost 3 orders of magnitude in case of the CW operation.

Exploitation of thermophoresis effect to prevent re-deposition of expelled particulates in laser assisted surface cleaning

Evidence in the improvement of the cleaning efficiency in the case of laser assisted surface decontamination wherein the phenomenon of thermophoresis has been exploited to prevent re-deposition of minute particulates is reported. The thermophoresis effect was made to set in by providing an appropriate temperature gradient in the vicinity of the laser exposed surface. The effectiveness of thermophoresis towards improving the laser assisted cleaning efficiency of polished stainless steel (SS) surface contaminated with copper telluride metal chalcogenide nanoparticles has been studied and compared with that obtained under ambient and dynamic vacuum conditions.