Fractional Talbot effect based measurement of laser-induced-damage thresholds
A method based on fractional Talbot effect is studied for single-shot measurement of laser-induced damage threshold.Using hexagonal phase grating,a laser beam is transformed into an ensemble of Gaussian-like spots with different energy densities at the test sample.Therefore,a statistical determination of the damage threshold of thin-film coatings can be performed by comparison of the intensity distribution with the damage pattern.Basic theories about the spectrum transmission and the fractional Talbot self-imaging are applied to calculating the Fresnel image of the hexagonal phase grating,and the results are testified by experiment.The laser-induced damage thresholds of HfO2/ SiO2 coating sample measured by this method and the traditional 1-on-1 method are 7.9 J/cm2 and 8.0 J/cm2,respectively.The errors of the single-shot measurement are analyzed.