NP:PH glass laser and registration system for LIDAR Thomson scattering

A one-channel prototype of a Neodymium laser based LIDAR Thomson scattering system is being experimentally tested at the time of this brief report. The design incorporated the necessity (i) to increase the beam cross section for the compensation of self-focusing, (ii) to apply laser radiation filtering for the elimination of the most dangerous spatial modes, (iii) to provide a proper laser pulse shape (> 100 ps) through the use of electro-optical shutters, (iv) to achieve a beam divergence below about one half of one milli-rad (with a wavelength variation below one Angstrom and a depolarization level less then 0.5 percent) and a high intensity distribution uniformly across the KDP crystal in order to efficient frequency conversion output, and (v) to achieve compact and high reliability of the system as a whole. The laser design parameters are suitable for the effective conversion of the laser radiation into the second harmonic with at least 60 percent efficiency. For the development of a laser system with output parameters on the level of 3 to 5 Joule for energy and 30-50 ps for the pulse time, because self-focusing constrains the intensity of laser media to 1-3 GWt per square cm, the output active elements aperture must be of the order of 100 square cm. Because the energy flux would be of the order of 0.1 Joule per square cm, implying poor extraction efficiency, multi-pulse plasma probing is subsequently discussed here. Signal-to-noise analysis of the plasma-scattered laser radiation shows that the multi-pulse probing enables to diminish the exit aperture by order of magnitude, thereby making the method feasible for plasma diagnostic applications. 2 refs, 5 figs