Monolithic Edge-Cladding Process for the Elliptical Disk of N31-type Nd-doped High Power Laser Glass

This paper investigates the monolithic edge-cladding process for the elliptical disk of N31-type Nd-doped phosphate laser glass, which will be utilized under liquid cooling conditions for high-power laser systems. The thermal stress, interface bubbles and residual reflectivity, which are due to high-temperature casting and bonding during the monolithic edge-cladding process, are simulated and determined. The applied mould is optimized to a rectangular cavity mould, and the casting temperature is optimized to 1000 degrees C. The resulting lower bubble density makes the mean residual reflectivity as low as 6.75 x 10(-5), which is enough to suppress the amplified spontaneous emission generated in the Nd-glass disk, and the resulting maximum optical retardation is converged to 10.2-13.3 nm/cm, which is a favourable base for fine annealing to achieve the stress specification of less than or equal to 5 nm/cm. After fine annealing at the optimized 520 degrees C, the maximum optical retardation is as low as 4.8 nm/cm, and the minimum transmitted wavefront peak-to-valley value is 0.222 wavelength (632.8 nm). An N31 elliptical disk with the size of 194 mm x 102 mm x 40 mm can be successfully cladded by the optimized monolithic edge-cladding process, whose edge-cladded disk with the size of 200 mm x 108 mm x 40 mm can achieve laser gain one-third higher than that of an N21-type disk of the same size.