Different conditioning and absorption behavior of fluoride material combinations for dielectric multilayers at 193 nm

Pulsed surface thermal lens (TL) technique is used to investigate the laser conditioning and to measure the nonlinear absorption of LaF3/MgF2 dielectric multilayers deposited on CaF2 substrate at 193 nm. The conditioning effect is monitored starting from the first shot of irradiation and in a shot-by-shot basis. The LaF3/MgF2 multilayers show a very strong conditioning. The ratio of the absorptions before and after the laser irradiation is approximately 4 - 8 for a highly reflective (LH)20 LaF3/MgF2 multilayer, and approximately 4 for (1L3H)7 and (3L1H)7 multilayers. For comparison, a (LH)20 LaF3/AlF3 multilayer shows only weak laser conditioning effect, with an absorption ratio of approximately 1.4. Our experimental results suggest that the strong conditioning effect of the LaF3/MgF2 multilayer is due to the possible interaction between the LaF3 and MgF2 layers, which results in considerable increase and conditionability effect of the LaF3 absorption. The fluoride multilayers present non-negligible nonlinear absorption, and the two-photon absorption coefficient of the multilayers is estimated to be 5(DOT)10-7cm/W.

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