Abstract: A high power gas discharge laser for and method of producing laser output light pulses of high energy density is disclosed which may comprise a laser output light pulse beam optical track having a plurality of modular components arranged in order from a laser light source to a laser system output port and defining a laser output light pulse beam path having a single centerline axis; a first optical module and a second optical module in series in the optical track; a flexible interface element intermediate the first and the second optical module and rigidly attached to each of the first and second optical modules; and an optical element having a fixed position in the output laser pulse beam path comprising a rigid attachment to the first optical module, and extending within the flexible interface element. The optical element may comprise a beam expander, which may comprise a lensed beam expander.

Abstract: An apparatus and method are disclosed for an optical element which may comprise a main optical body comprising a crystal containing halogen atoms; a reflectivity coating for changing the reflectivity of a surface of the main body; and, an intermediate protective layer comprising a material containing free halogen atoms. The crystal may comprise an alkaline earth metal and may comprise fluorine atoms, e.g., calcium fluoride or magnesium fluoride. The intermediate protective layer may comprises a material containing free fluorine atoms, e.g., a material doped with fluorine atoms, e.g., doped fused silica. The intermediate layer comprises an amorphous portion and a polycrystalline portion.

Abstract: A method for stabilizing a multi-layered dielectric reflectivity coating subject to compaction/densification upon exposure to DUV or shorter wavelength light, is disclosed which may comprise: applying the reflectivity coating to a reflective surface forming a coating bulk on the surface; exposing the coating bulk to a pretreatment of a sufficient amount of DUV radiation to induce sufficient densification in enough of the coating bulk to inhibit subsequent densification during continued exposure to DUV or shorter wavelength radiation. The method may also comprise the pretreatment radiation exposure amounting to energy of at least the equivalent of about 2 Bp at 9 mJ per pulse. The method may also comprise the pretreatment radiation exposure amounting the energy being delivered in at about 3 KHz pulse repetition rate. The method may also comprise the pretreatment radiation exposure amounts to energy of at least the equivalent of 15-18 mJ per pulse delivered over about 700 M-1 B pulses, i.e.