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Advances In Glass Filter Materials For Laser Fusion Systems

The recent move to shorter wavelengths in laser fusion research via harmonic conversion of the Nd: glass fundamental has resulted in the need for special filter glasses of sizes, optical homogeneity, and transmission properties not available in conventional filters. Typically, filter glasses are produced in diameters less than 25 cm and thicknesses less than 1 cm. In contrast, beam filters up to 90 cm diameter are required for Lawrence Livermore National Laboratory's NOVA laser, with homogeneity equivalent to that of the highest quality optical glass. Additionally, laser damage and thermal shock considerations require volume absorption, and thus greater thicknesses than are normally produced. Fabrication of such filters necessitates utilizing new glass types along with dopant combinations chosen specifically for the application. In the present paper we review the design and fabrication of several such filter glasses for large aperture frequency-converted laser systems.