Leeds 2Silica glass specimens were heated in water vapour and the resulting infra-red absorption at 2.7 p was measured. Betwecn 600" and 1200"C, the diffusion coefficient for entry of absorbing centres wasand for removalAt 1OOO"C the saturation concentration of absorbing centres varied as the square root of the pressure of the surrounding water vapour, suggesting that the water molecule dissociates on entry, with the production of two hydroxyl groups in the atomic network of the glass. Using a value of extinction coefficient determined for the hydroxyl group in the molecule of triphenylsilanol, the solubility under 700 mm Hg water vapour pressure, expressed as the number of hydroxyl groups per Si02 "molecule", was estimated to range from 6 x 10-3 at 600°C to 3 x 10-3 at 1200°C.

No abstract

No abstract

Two-photon-absorption coefficients are measured for fused silica, LiF, and the alkali earth halides BaF(2), SrF(2), CaF(2), and MgF(2), using 0.7-psec, 248-nm pulses with intensities in the range (0.5-30) x 10(10) W/cm (2) . The conse-quences of these measurements in the design of high-brightness excimer lasers are discussed.

A terawatt-class laser, based on the amplification of subpicosecond pulses in XeCl discharge amplifiers, is described. The system generates 250-mJ, 335-fsec pulses at a sustained 1-Hz repetition rate. Using f/3.7 optics, focal-spot dimensions of 3.4 microm x 4.1 microm are measured for the fully amplified output beam, thus demonstrating a mean focalvolume intensity of 4.6 x 10(18) W/cm(2). With f/l optics, this system is therefore capable of producing a focused intensity of 6.4 x 10(19) W/cm(2).