| Abstract [eng] |
The main components of laser systems are optical elements. Thus, in order to prolong the life of systems, it is important to know the laser induced damage threshold (LIDT) of those optical elements. Different LIDT values are obtained in different laboratories, as LIDT is determined using different exposure algorithms, lasers of different stability and other parameters. Thus, the aim of this work was to investigate the influence of test protocol, laser pulse shape and wavelength on LIDT values of standard dielectric mirrors, commercial fused silica substrates and anti-reflective coatings. To this end, LIDT was measured using different testing protocols such as 1-on-1, S-on-1, where S = 1000, R-on-1 and Raster Scan. The tests were repeated using single-mode and multi-mode laser regime. The research found that in all cases, the LIDT value is inversely proportional to the scanned area: the LIDT is highest (R-on-1), where the exposed area is the smallest, and the smallest LIDT is obtained during the Raster Scan protocol, where the exposed area is the largest, therefore Raster Scan method is recommended for the safe characterization of LIDT of optical elements. It has also been observed that the damage mechanisms in the case of I and III harmonics are possibly different, as the damage morphologies, specific to these cases, are also different. These differences are most likely due to the fact that UV radiation is well absorbed by the defects and their degradation begins at lower pulse energies than in the case of IR. Additional studies are needed to unambiguously investigate the differences between damage morphologies. Summarizing the experiments using single and multiple longitudinal mode pulses, a difference in LIDT values is observed in the results: in many cases, a lower LIDT value is obtained with multimode pulses, which have higher intensity fluctuations due to longitudinal mode beating. The differences between the LIDT values obtained by the different test protocols are different for different sample types and wavelengths, so it is likely that these differences are due to sample inhomogeneity in terms of optical resistance: each sample has different LIDT limiting defect ensembles. |
