Experimental investigation of thermal lens effect in a flashlamp pumped CTH:YAG laser rod

Abstract

In this article, the thermal lens effect in a CTH:YAG laser crystal was studied experimentally using the probe beam technique. The thermally induced changes of the refractive index were made using flashlamp pumping in the CTH:YAG laser rod along with the transmission of a low power probe beam (532nm) through the crystal. The time-resolved dynamics of the lens-like behavior of the rod were inspected within a range of pumping energies, several repetition rates, and cooling temperatures. For 1ms pumping pulse length, it can be concluded from the results that in the early stage of the pumping pulse (500−600µs after the initiation of the pump pulse), the rod focal length is negative. It takes around 1 s for the rod to return to its equilibrium after the lamp was turned on which is around half of the thermal time constant for a 6 mm CTH:YAG rod. It has been shown that the dioptric power of the three mode lenses increases when pumping energy increases. The effect of increasing the flashlamp repetition rate (1, 5, and 10Hz) as well as the coolant temperature (8−20°C) for constant lamp energy and constant pulse length is also discussed.