SYMPOSIA PAPER Published: 01 January 1988

Reverse Thermal Wave Approximation for Temperature Transients in Optical Thin Films and Substrates — Reflective Optics for High Power Repetitive Pulsed Lasers


This is the companion paper to the Reverse Thermal Wave Approximations for High Power Continuous Wave Lasers. The purpose of this paper is to provide equations that will allow the optical designer to evaluate the temperature gradient in optical thin films and substrates under transient conditions. The semi-infinite plate models have been described rather extensively in other publications. However, the problem that is treated in this paper is that set of boundary conditions that do not satisfy the semi-infinite plate condition.

It is not uncommon to have coated reflective optics that have very thin substrates. For those conditions it is necessary to evaluate the temperature transient much differently than one would if the substrates were of sufficient thickness to satisfy the semi-infinite plate boundary. One finds that the temperature rise and gradients are substantially different for very thin substrate conditions. The Reverse Thermal Wave Modelwill provide the ability to evaluate the temperature gradients during the transient with closed form approximations.

The repetitive pulsed case has a substantially different characteristic temperature profile from that of the continuous wave and in this paper the equations and figures are provided to reflect the unique character of the temperature gradients in the optical thin films and substrates as a function of the hertz rate and pulse width. It becomes clear that the duel cycle of heating and cooling coupled with the thermal shock play important roles in the damage thresholds of many optical components in high power laser systems.

Author Information

Palmer, JR
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Developed by Committee: F01
Pages: 546–578
DOI: 10.1520/STP24466S
ISBN-EB: 978-0-8031-5033-1
ISBN-13: 978-0-8031-4481-1