Durability of experimental fused silicas to 193-nm induced compaction

Using birefringence monitoring, several experimental fused silicas are tested for 193-nm compaction durability. f N ( I J2 't 10.1 All samples exhibit densification that can be described by the equation: (Lip/p )u = 1C · l--7 · - · _.!!_J where 10 10 't 'tis the pulse length ('t0 = lns), Np is the pulse count, K is a constant, and I is the 193-nm energy density (I., = 1 mJ/cm2). The extracted value of K varies from 84ppB to 660ppB for experimental (1995-1996) fused silicas, as much as a factor of two improvement compared to (1990-1994) grades. The role of irradiation geometry in compaction is also investigated using finite element simulations. The net optical path difference formed for a given level of damage is found to increase by approximately 25% when the damage radii is increased from 30% to 70% of the total sample diameter in a relatively thin optical element. Keywords: damage, fused silica, two-photon, densification, compaction, lithography, 193-nm, stress-birefringence