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2000
Conference Paper
Titel
Pulsed top-hat beam thermal lens: a simple and sensitive tool for in situ measurement on ultraviolet dielectric components
Abstract
A mode-mismatched surface thermal lens technique with pulsed top-hat beam excitation and near field detection scheme is developed to measure in situ the thermoelastic response of ultraviolet dielectric coatings and bulk materials under excimer laser (193 nm or 248 nm) irradiation. The thermal lens technique is demonstrated to be not only convenient for an accurate determination of the laser-induced damage threshold (LIDT), but also sensitive to measure the thermoelastic response of dielectric coatings irradiated with fluences much below the LIDT, and hence, to carry out time resolved predamage investigation. The minimum detectable surface displacement of approximately 0.002 nm is achieved with a simple experimental configuration. Nonlinear absorption of ultraviolet dielectric materials and coatings are demonstrated. The surface thermal lens technique is also a convenient technique to distinguish different damage mechanisms: thermal stress induced damage or melting induced damage, depending on the thermoelastic properties of the substrate. Hence, this technique allows to indicate qualitatively the relative contribution of linear and nonlinear absorption as possible causes for laser damage. Moreover, the nonlinear effect in laser conditioning of a LaF(3)MgF(2) highly reflective dielectric coating has been observed experimentally.
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Language
English