Tunable diode-pumped and frequency-doubled Cr:LiSAF lasers.

The performance of a diode-pumped Cr:LiSAF laser and its intracavity frequency-doubled operation is reported. Close to 1 W of quasi-cw power at 870 nm was obtained in multimode operation. Power in excess of 20-mW cw of TEM(00) second-harmonic power at 435 nm has also been obtained by using a lithium triborate crystal with an infrared-to-visible conversion efficiency of 33%. This result is believed to be the highest yet reported for a true cw blue output from a diode-pumped Cr:LiSAF system. However, the maximum attainable output power was limited by thermal fluorescence quenching. The effect of the pump size on the temperature rise and on the small-signal gain is investigated.

Photobleaching of thulium-doped ZBLAN fibers with visible light.

Photobleaching of darkened thulium-doped ZBLAN fibers is observed after short exposure to visible light. The bleaching process is characterized by a stretched-exponential function of time with an exponent beta independent of both the bleaching intensity and the thulium concentration. The bleaching rate 1/ is also shown to scale linearly with the bleaching intensity and to have a 1/3 -power dependence on the thulium concentration. Incomplete and slow recovery of the color centers is observed in previously bleached fibers, suggesting the presence of at least two types of defect.

CO2 laser annular thermokeratoplasty: a preliminary study.

Since most techniques of refractive surgery currently in use or being developed have the potential for significant side effects, there is a need for investigating alternative procedures. We herein report on the use of a pulsed CO2 laser beam delivered through a pair of complementary axicons to produce a ring of stromal collagen contraction resulting in the flattening of the corneal apex of cadaver eyes. Irradiances of 29 W/cm2 and 23 W/cm2 were used for rings of 5.5 mm and 7.0 mm, respectively. The creation of a ring of 7.0 mm in diameter did not affect the corneal curvature significantly but when the diameter was reduced to 5.5 mm, substantial flattening proportional to the dose of radiation took place. In our system, it was possible to achieve up to 11.3 diopters of mean keratometry flattening (90 joules, 5.5 mm of diameter). In addition, a 1 mm posterior displacement of the corneal dome without histological evidence of closure of the iridocorneal angle was observed. Annular thermokeratoplasty (ATK) may minimize side effects encountered with other refractive procedures since it does not require ablation, incisions, or interaction with the central optical zone.

Experimental study of Cu-PbCl(2), Cu-NaF, Ag-PbCl(2), and Ag-NaF cermet thin films.

We present in this paper the experimental spectral transmission curves of four different cermets, Cu-PbCl(2), Cu-NaF, Ag-PbCl(2), and Ag-NaF, as well as the calculated curves obtained from the generalized Maxwell-Garnett theory. The results show that the microstructure of the metal particles in the dielectric matrix is independent of the nature of the dielectric. We also show that this behavior is predicted by the generalized Maxwell-Garnett theory. However, our measurements also indicate that the microstructure is the same for both copper and silver cermets. This last experimental evidence cannot be explained within the context of the Maxwell-Garnett theory.