Quantitative pump-induced wavefront distortions in laser-diode- and flashlamp-pumped Nd:YLF laser rods

Detailed interferometric measurements of the induced thermal distortions due to laser-diode and xenon flashlamp pumping of Nd:LiYF ₄ are presented. The thermal distortions are quantified in terms of the primary aberrations of defocus, astigmatism, coma, and spherical. Defocus and astigmatism are shown to dominate the thermal aberrations. The measured defocus and astigmatism are converted to the conventional thermal-focal lengths in two perpendicular directions with respect to the Nd:YLF crystalline c axis for each of the two polarization states σ and π. A comparison of the thermal-focal lengths measured with our xenon flashlamp and laser-diode-pumped rods is given when the rods are pumped to the same small signal gain. We calculate effective dioptric-power coefficients from our data for comparison to those reported in the literature for krypton-flashlamp pumping. A thermal time constant of 1.5 s is measured for our laser-diode-pumped Nd:YLF laser rod