Active components for the LMJ diode-pumped regenerative amplifier

We developed a number of active devices for use in the regenerative amplifier, which is one of the specific sub- assemblies of the preamplifying section in the french L.M.J. design. The first one is a modular-square-diode pumped laser head, which provides 0.65 Joules pumping energy at 800 nm into a 4 mm side Nd 3+ :phosphate glass, in the form of a close coupling-uniform-configuration. Our original side pumping scheme makes use of symmetric diode stacks and optimized rod holders with a thermal conductivity. Some heat is waste in the volume of glass, as a result of the pumping process, and it is efficiently--since very closely--removed by the latter holders. A (pi) /2 rotation of one pumping section with respect to the next one allows uniform pumping and thermal conduction together with birefringence reduction. No water is required. A complete 3D thermal model is developed, in order to describe temperature and stress distributions, inside the laser head and glass rod. Peak stress values in glass at F equals 10 Hz, with flexible rod holders including Indium parts, equal 5.8 Mpa when the mean thermal power is 22 watts. Preliminary laser tests are experienced at 10 Hz with two similar laser heads around a square Nd 3+ :LHG750 glass rod. With 1.3 Joule pump energy at 400 microsecond(s) pumping duration, the assembly is placed inside a Qswitched stable, multimode plano-concave, resonator. The output energy is 40 mJ, within 80 ns fwhm pulses.