Abstract:
An experimental investigation was made of ultrashort pulses generated in yttrium aluminum garnet (YAG) and amplified in YAG and neodymium glass. When the power density was less than 3–5 GW/cm2, the main mechanism which limited the amplified power was large-scale self-focusing of the amplified radiation in the active media, which altered greatly the laser beam divergence. Conditions were found under which this self-focusing was avoided completely. The investigated self-focusing produced, around the main beam, a scattered-radiation halo of divergence much greater than the beam divergence. The proportion of the laser beam energy lost to the halo increased with the amplification, so that beginning from a certain stage further amplification simply resulted in a reduction in the brightness. In this situation the enrgy density in the amplified beam could still be below the damage threshold of the active medium.