Simultaneous measurement of bulk absorption and fluorescence in fused silica upon ArF laser irradiation

Abstract

A new setup was established to simultaneously record the bulk absorption of fused silica at 193 nm and its laser induced fluorescence (LIF). Bulk absorption coefficients in the 10^-3/cm range are measured in a compact setup with small samples of 20 x 20 x 10 mm³ using an ArF pump laser and recording the ArF laser induced deflection (LID) of a diode probe laser beam. LIF is measured through an optical fiber coupled to an intensified gated CCD camera. Within the first few pulses of ArF laser irradiation the bulk absorption coefficient and LIF emission around 300 nm and 400 nm (oxygen deficient centers, ODC) decrease considerably, sometimes to a fraction of their initial values. In smoe fused silica samples additional fluorescence in teh green-yellow wavelength region is found. This fluorescence increases in a strongly nonlinear way with the fluence. Assuming fluorescence excitation by single photon absorption the observed behavior can be explained by saturation of the absorption transition which put limitations on the fluence applicable in the experiments. Summarizing the obtained results a measurement instruction for precise absorption measurements of fused silica at 193 nm laser irradiation is suggested and fused silica samples have been investigated concerning their dependence of the absorption coefficient on the fluence. The results, in combination with transmission measurements of 300 mm long fused silica samples, confirm the nonlinear increase of the absorption with increasing fluence.