Thermal effects in a Nd:glass laser rod pumped in a double circular close-coupled cavity

Thermal effects produced in a Hoya LSG-91H Nd:glass laser rod pumped uncooled in a close-coupled double circular chamber, at high input powers, were evaluated in the single shot and repetitively pulsed modes by passing a He-Ne laser probe beam through the rod and observing the changes in the beam intensity. When pumped with a 200 μs, 100 J flashlamp pulse, it was observed that the thermal effects lasted for about 2-2.5 s at the center of the rod and 0.2-0.5 s at the rod edges. The minimum induced focal length of the laser rod was -57.3 cm in the single shot mode and -54.9 cm in the repetitively pulsed mode. In the repetitively pulsed mode, in addition to the lens effect, a prism effect was also observed, which increased in strength with increase in input energy. These lens and prism effects were found to be dependent on the energy deposition profile in the laser rod and on its thermal properties.