Comparison of different high and low index materials in the manufacture ofhigh laser damage threshold mirrors at the 351 nm wavelength

Sol-gel material based mirrors have been produced by forming alternate laye rs of high refractive index and low refractive index thin films. These mirr ors have proven to have a high laser induced damage threshold [LIDT]. Using nitric acid stabilized zirconia derived from zirconium-n -propoxide and ba se catalyzed silica, a 16 layer mirror with a reflectivity of better than 9 4% at 351 nm and 45 degrees angle of incidence was fabricated. This had an LIDT of 7.7 J/cm(2) at 351 nm with a 0.7 ns pulse width. Crazing prevented further layers being deposited. Both spin and dip coating were attempted wi th dip coating yielding the best results. The coating structure has been analyzed using XPS depth profiling and AES. The bulk materials have been investigated using transmission electron micro scopy (TEM), X-ray diffraction (XRD) and TGA. High refractive index layers using Hafnia with nitric or acetic acid have also been investigated as pros pective high LIDT mirrors. Alternative acidic routes to silica have been studied as a possible low ind ex material and a route to preventing crazing.