We report the experimental observation of high efficient multiple stimulated Raman scattering (SRS) of sodium dithionate dihydrate Na 2 S 2 O 6 . 2H 2 O single crystals under picosecond Nd 3+ :Y 3 Al 5 O 12- laser pumping. All the recorded Stokes and anti-Stokes lasing wavelengths in the visible and near-IR are identified and attributed to the SRS-promoting vibration modes ω SRS1 as 1098 cm -1 and ω SRS2 290 cm -1 of this novel X (3) . nonlinear crystalline medium. The comparative measurement of the first Stokes steady-state Raman gain coefficient in the near-IR region allows us to tentatively conclude that its value is not less than 4.8 cm GW -1 . We classify Na 2 S 2 O 6 . 2H 2 O as a promising crystalline material for Raman laser converters.

Laser-induced birefringence patterns which break the symmetry of the experimental setup have been observed in a low molar mass anisotropic glass with nematic orientational order under a polarizing microscope. It is shown that the observed spatial modulations in birefringence can be explained by laser-induced heat flow and stress, leading to molecular reorientation which is then frozen and stored in the glassy state if the optical excitation is switched off. The experimental findings can be regarded as a manifestation of heat-flow alignment caused by a spatially inhomogeneous temperature field.

A study of the temporal response of a biased Fabry–Perot etalon with a nematic liquid crystal exposed to short (∼10 μs) voltage pulses is presented. It is found that the finesse is the crucial factor determining the achievable switching time. For a given maximum transmission the reflectivities of the Fabry–Perot mirrors are optimized to achieve minimum switching times. In particular, switching times of 0.5 μs with an initial transmission of 3% and a maximum value of 70% have been obtained. The experimental results are in good agreement with theory.

Since the discovery of optical phase conjugation in 1972 researchers tried to generate phase conjugated beams with different nonlinear media and various techniques for many applications 1-3 . Self-pumped phase conjugation (SPPC) is obtained by stimulated Brillouin scattering or wave mixing in photorefractive crystals. The SBS-effect is observed with pulsed lasers at a high threshold power in the range of about 10 kW whereas photoreffactives operate with continuous powers in the mW-range. These crystals are expensive and available only for small optical apertures of about 1 cm 2 . In contrast liquid crystal cells may have much larger dimensions and offer also high optical nonlinearities. It was shown 4 that self-pumped phase conjugation in liquid crystals can be realized by wave mixing effects with threshold powers less than 1 W.

Using phaseconjugating mirrors (PCMs) the beam quality of solid state lasers can be improved by compensating the thermal lens of the rods at high average powers. Oscillators with one PCM as a highly reflecting mirror and double-pass amplifiers with PCMs have been investigated. PCMs are realized by stimulated Brillouin scattering (SBS). Nd:YAG and Nd,Cr:GSGG oscillators have been built with pulse repetition rates up to 45 Hz. Stable TEM00-mode operation has been obtained. Average output powers of 10 watts for 15 ns Q-switched pulses of a Nd:YAG laser and 7 watts for Nd,Cr:GSGG have been achieved. In a double pass Nd:YAG amplifier the thermal lens was compensated leading to a nearly diffraction limited beam with a maximum output power of 40 watts.

Laser-diode pumping has been used to excite a single-mode cw stimulated emission from Nd3+ ions via F-4(3/2) --> I-4(11/2) channel in trigonal nonlinear LaBGeO5, La3Ga5.5Nb0.5O14 and La3Ga5.5Ta0.5O14 crystals at room temperature with an efficiency of 30%. The crystals are promising for lasers with self-multiplication of generation frequency.