The alignment of birefringent crystals for use as wave plates and nonlinear frequency converters in high-power, low-repetition-rate laser systems, such as those used for laser fusion, is greatly facilitated through the use of convergent light (conoscopy). In such laser systems, a long shot cycle is necessary to allow laser amplifiers time to thermally equilibrate in order to produce beams of adequate wavefront quality. It is therefore essential that crystal parameters such as phase-matching angle and location of principle axes be determined off-line, and a method developed to easily transfer the alignment to the fusion laser system. Conoscopic methods1–3 have been used for the off-line alignment of two such devices in the 60-beam OMEGA4 laser system because of the simplicity and accuracy of such techniques. Both devices, of which 60 each are required, currently incorporate 30-cm-diam × 1-cm-thick KDP plates with the crystalline optic axis at 59° to the surface normal.
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