PROCEEDINGS ARTICLE | December 30, 2008
Proc. SPIE. 7132, Laser-Induced Damage in Optical Materials: 2008
KEYWORDS: Optical components, Gaussian beams, Silica, Laser induced damage, Error analysis, Crystals, Nd:YAG lasers, Beam shaping, Pulsed laser operation, Data analysis
A rasterscan test procedure [L. Lamaignère et al, Rev. Sci. Instrumen. 78, 103105 (2007)] has been implemented
in order to determine low laser damage density of large aperture UV fused silica optics. This procedure was improved in
terms of accuracy and repeatability and is now used for the determination of bulk damage density for KDP crystals. The
large area (volume) scanned during tests permits to measure very low damage density. On small samples, small area are
tested using the normalized 1/1 test procedure consisting on the irradiation of few sites at several fluences. The classical
damage probability plot is converted in terms of damage density. The two testing procedures are complementary: the 1/1
mode is practical to test a wide fluence range while the rasterscan mode allows exploring low damage densities with
higher accuracy.
Tests have been carried out on several facilities using several pulse durations and spatial distributions. We
describe the equipment, test procedure and data analysis to perform this damage test with small beams (Gaussian beams,
about 1mm @ 1/e, and top hat beams). Then, beam overlap and beam shape are the two key parameters which are taken
into account in order to determine damage density. After data analysis and treatment, a repeatable metrology has been
obtained. Moreover, the consideration of error bars on defects distributions permits to compare data between these
installations. This allows us to reach reproducibility, a necessary condition in order to share results and to make reliable
predictions of laser damage resistance.
Other tests are realized with larger beams (centimeter sized) and with a single shot. Due to a large beam contrast,
a large fluence range is then covered. Then after data treatment, we find a good correlation between tests realised with
small and large beams. This allows us to make tests with different laser characteristics (spectral modulations, pulse
duration, laser polarisation) and then to study their influences on laser damage.
