Transient thermal blooming of a slewed laser beam containing a region of stagnant absorber

Abstract

The transient thermal blooming of a slewed laser beam containing a stagnation point is studied experimentally with pivoted absorption cells and analytically with a 4-D computer code. Natural convection is included in the code to model the experimental situation. Substantial agreement is found between the predictions of the code and the experimental data for a variety of pivot positions and slew rates. The experimental and calculated results show that after an initial transient decay the intensity at the receiver tends toward a steady-state value. The origin of this quasi-steady state is explained in terms of a shrinking stagnation zone in the slewed beam.