SYMPOSIA PAPER Published: 01 October 1981
STP37010S

Dependence of Metal Mirror Damage Thresholds on Wavelength, Material, Pulse Length, and Preparation Method

Source

Multithreshold pulsed laser-damage characteristics of precision diamond-machined Cu, Ag, and Au mirrors have been determined at 10.6, 3.8, 2.7, and 1.06 μm. The effect of pulse length has been examined at 10.6 μm by comparing previously reported results obtained using a 100-nsec TEA laser pulse with new results using a 2-μsec pulse from a hybrid TEA laser. The pulse lengths at 3.8 and 2.7 μm are nominally 100 nsec, while that at 1.06 μm is 9 nsec. Spatial intensity distributions are very nearly Gaussian at all wavelengths with e−2 focal spot diameters ranging approximately from 200 μm at 10.6 μm wavelength to 50 μm at the shorter wavelengths. Melt thresholds were calculated from one-dimensional heat flow considerations with a correction for finite focal spot size. Laser waveforms are accurately modeled, and temperature-dependent absorption based on Drude theory is used. Calculated values for Ag are in excellent agreement with experiment, except at 1.06 μm, while calculated values for Cu and Au are in good agreement at 10.6 μm only. An unusually large discrepancy at 3.8 μm suggests a non-Drude-like absorption mechanism that is enhanced by the multipeaked nature of the waveform at this wavelength. Defect-related damage at submelting fluences has also been studied at the longer 10.6-μm pulse length on Cu mirrors representing a variety of preparation methods. Comparative evaluation of damage characteristics has resulted in identification of two new approaches to improving resistance to defect damage.

Author Information

Porteus, JO
Decker, DL
Seitel, SC
Soileau, MJ
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Details
Developed by Committee: F01
Pages: 201–209
DOI: 10.1520/STP37010S
ISBN-EB: 978-0-8031-4820-8
ISBN-13: 978-0-8031-4500-9