Abstract

Transient thermal focal length calculations of side-pumped Nd:YAG and Ti:sap- phire laser rods indicate an appreciable deviation from standard steady-state average-power calculations using Koechner's well-known formulation.¹ When started from an inactive condition, the thermal focal length of a Nd:YAG rod (length, 7.6 cm; radius, 0.25 cm) stabilized at about 3 s. However, the steady-state calculations indicated a higher focusing power of about 15%30% at frequencies of 610 Hz. The pump pulse duration was 100 s with a 10 J input. The thermal focal length varied from 28 m at 100 ms to 4.4 m at steady state. Other examples of thermal-focal-length calculations for end-pumped configurations are provided. The present model for temperature distribution in laser rods² can be applied to both side-pumped and end-pumped situations. The model was used to estimate the effect of surface cooling on the thermal focal length. Koechner's formulation, by comparison, is for a fixed surface temperature.

© 1990 Optical Society of America