Abstract

With the development of 193-nm and even 157nm photolithography as well as laser micro machining, coherent light sources in the deep-UV (ultraviolet) spectral region have become more and more important. The simplest way to produce deep UV coherent light is to use the fourth harmonic generation of a Ti:sapphire laser (from 800 nm to 700 nm). So far, only KBBF crystals can be used to achieve this.¹ However, a major problem of the crystal is its platelike nature that makes it very difficult to grow it thicker than a millimeter. Recently, we succeeded in growing platelike KBBF crystals of 10 × 10 × 1.2 mm³ in size and of high optical quality. The platelike crystals can be polished but is still too thin to be cut along the phase-matching direction for fourth harmonic generation. To solve this problem, we adopted a special prism coupling technique (PCT) to avoid the difficulty in cutting the crystal² (Fig. 1(b)). We measured the optical transmission spectrum in the UV region with a spectrophotometer. The cut-off wavelength is located at 155 nm.

© 2002 Optical Society of America