Waveguiding was used to measure the extinction coefficient of a thin film while it was being deposited in a vacuum
chamber. Experimental results are presented and compared to calculations and measurements by other techniques.
Experimental results are presented on using one or more additional windows to reduce the distortion from existing windows transmitting high average power laser beams. A concept is presented for a compound window that will neither distort nor depolarize a high power beam.
A number of concepts using the principle of the refraction of light have been developed to steer light beams. Refractive beam steering concepts involve the use of optical wedges in order to deviate a light beam. This principle is ideally suited for steering laser light since dispersion is minimal due to the monochromatic nature of the laser. The methods used to form the optical wedge and the means developed to adjust it are what distinguish the various concepts and have resulted in many patents over the years for their innovators. A new concept called a Lubricated Adjustable Optical Wedge (LAOW) has been recently developed that does not require complicated mechanical systems to form the wedge and provide the adjustment necessary to deviate the light beam. An optical wedge is formed using plano-convex and plano-concave lenses that are contacted together using a thin film of transparent index matching lubricant between the spherical surfaces. The forces of capillary action and surface tension provide the sole means of keeping the lens elements together. This technique has demonstrated a repeatability ≤±0.12 arc seconds in beam deviation angle.
The development of separate confinement, heterostructure, semiconductor lasers diodes continues to be facilitated by the use of models. These models allow one to examine how the performance of a laser diode depends on epistructure growth and device processing parameters. In this way one can determine the optical and thermal constraints on a semiconductor laser's performance. For pulsed operation at low duty factor this is generally sufficient to design a laser diode system. Although the models are a good predictor of the initial performance of laser diode bars operated either in cw or a high duty factor mode, the performance degrades during the first 100 hours of operation. In our investigation of the design of cw operating, AlGaAs laser diode bars we have found that degradation mechanisms along with thermal properties provide design constraints. The problem which we have encountered is that a laser diode bar generally contains many independently emitting laser diodes. Each laser diode bar therefore has an unscreened population of laser diodes. In an unscreened population of laser diodes there are generally some which exhibit `infant mortality,' i.e., they cease lasing in the first 50 to 100 hours of on time. We have found that the `infant mortalities' among the laser diodes can significantly lower the yield of bars by reducing the number of emitting laser diodes on the bars below acceptable limits. The sources of this initial, rapid degradation of laser diode bars are discussed.
In 1991, strained InAlGaAs quantum well lasers were first proposed as alternatives to AlGaAs lasers for various applications, including solid-state pumping. Enhanced reliability was the rationale for their development, having been inspired by earlier observations of lattice hardening in strained InGaAs lasers. The hoped-for dark-line defect (DLD) suppression as well as a threshold current advantage for this system have already been documented. In this update, we will present further aspects of this work, including long-term reliability, maximum (catastrophic) power limits, epitaxial structure design bounds and parametric crystal growth investigations. Our work has enabled the demonstration of 15 W cw linear arrays and pulsed V-Groove Phased Arrays. Their performance and potential applications will also be discussed.