Investigating the ArF laser stability of CaF_2 at elevated fluences

摘要

Combined measurements of transmission T, absorption A and total scattering TS revealed the high accuracy of all applied measurement techniques by obtaining a sum T+A+TS+R = (100±0.3)% (R denotes the Fresnel reflection). In order to investigate CaF_2 at high fluences, a variety of samples from high purity excimer grade to research grade was irradiated (80 ... 150 mJ/cm~2, 2*10~6...7*10~6 pulses) and characterized before and after irradiation by total scattering, laser induced fluorescence (LIF) and transmission measurements. Total scattering mappings showed negligible and measurable scattering in excimer grade and some research samples of minor purity, respectively. For the first time to our knowledge, laser induced fluorescence measurements revealed increasing (580nm, 740 nm) as well as decreasing (313 nm, 333 nm) emissions. The small increases of the linear absorption, obtained in all samples by transmission measurements, were used to distinguish high from minor quality material. For high quality samples the linear absorption change scales with NH~3 (N: number of pulses), whereas for minor quality research samples a NH~2-scaling was found.