A short programme has been carried out to examine the preparation of strengthened polycrystalline alkali halide optics by hot-forging of single crystals. Potassium chloride and caesium iodide were chosen as subjects for this study which began with the optimisation of forging conditions for preparation of 25 mm diameter plano and plano-convex specimens. The following parameters were varied; temperature, load, deformation ratio, strain rate, lubricant, and crystal orientation. The use of optically polished die platens resulted in a surface quality suitable for direct use in lower grade optics; further improvement could be made by standard optical polishing methods. Variation in grain size was investigated by etching the surfaces of forged pieces and examining the grain structure by optical microscopy. Following initial results on 25 mm forgings the work has been extended to 75 mm diameter forgings of potassium chloride. Some experiments have also been carried out with a hot isostatic pressing system using pressurised helium as an improved lubricating medium. Initial results of strength and optical quality measurements are presented.
B. E. Kinsman,
R. W. Sparrow,
"Hot Forging Of Alkali Halides", Proc. SPIE 0508, Production Aspects of Single Point Machined Optics, (11 December 1984); doi: 10.1117/12.944970; https://doi.org/10.1117/12.944970