Colloidal silica coatings for KrF and Nd:glass laser applications

Method for the preparation of porous silica antireflection coatings varying in refractive index from 1.22 to 1.44

Coatings of refractive index that vary between 1.22 and 1.44 were prepared from combinations of a colloidal silica suspension and a polysiloxane solution. The polysiloxane acted both as a binder and a filler for the colloidal silica particles. Increasing ratios gave coatings of lower porosity, hence higher refractive index, and better abrasion resistance. This variation in refractive index allowed highefficiency quarter-wave antireflection coatings to be prepared on substrates whose index varied from 1.45 to 2.1. The laser damage thresholds of all the coatings were >50 J/cm(2) at a wavelength of 1.06 microm with a 10-ns pulse length.

Raman shifting of KrF laser radiation for tropospheric ozone measurements

The differential absorption lidar (DIAL) measurement of tropospheric ozone requires use of high average power ultraviolet lasers operating at two appropriate DIAL wavelengths. Laboratory experiments have demonstrated that a KrF excimer laser can be used to generate several wavelengths with good energy conversion efficiencies by stimulated Raman shifting using hydrogen (H2) and deuterium (D(2)). Computer simulations for an airborne lidar have shown that these laser emissions can be used for the pecise (less than 5% random error) high resolution (200-m vertical, 3-km horizontal) measurement of ozone across the troposphere using the DIAL technique. In the region of strong ozone absorption, laser wavelengths of 277.0 and 291.7 nm were generated using H(2) and D(2), respectively. In addition, a laser wavelength at 302.0 nm was generated using two cells in series, with the first containing D(2) and the second containing H(2). The energy conversion efficiency for each wavelength was between 14 and 27%.

Single layer Al(2)O(3).H(2)O and multilayer Al(2) O(3).H(2) O-SiO(2) optical coatings prepared from colloidal suspensions

Single layer coatings of Al(2)O(3).H(2)O have been prepared on fused silica and BK-7 substrates from aqueous colloidal suspensions of hydrated alumina at room temperature. These coatings were porous and had a refractive index of ~1.44. Multilayer, high reflectivity, dielectric coatings were also prepared by laying down quarterwave-thick, alternating coats of this alumina with silica, also prepared from colloidal suspension, and having a refractive index of 1.22. To achieve 99% reflectivity, 30-35 layers were required. Single shot, laser damage threshold measurements at 1064 nm wavelength with a pulse length of 10 ns were carried out on both the single layer and multilayer system. The thresholds averaged 21 and 12 J/cm(2), respectively.