Wavelength around 940 nm lasing can be obtained by quasi-three-level operation of Nd doped laser crystal. Diode end pumping provides the necessary high pump intensity in the laser crystal. In order to get high efficiency of the end pumped laser system, the overlap coefficient between pump beam and laser beam should be optimized. Thermal lens coefficient is one of the most important parameters to design the laser cavity structure. The time dependent heat conduction equation is solved numerically in order to study the thermal lens effect in pulsed pumping laser crystal. Calculated results showed that the thermal lens coefficients change with different pump frequencies. Experiments are done with Nd:YAG and Nd:GSAG laser rod. The thermal lens coefficient of Nd:YAG at pump frequency 50 Hz with pump beam diameter 1.5 mm is 10.2 Wm, while the thermal lens coefficient of Nd:GSAG at pump frequency 50 Hz with pump beam diameter 1.75 mm is 5.9 Wm.© (2009) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.