Rare earth energy levels allow mostly unreported uniwavelength cascade lasing from 0.794 to 1.834 μm. Nd:YAG’s 1.834 μm line is treated in detail. 28 wavelength predictions are presented for Nd, Er, Tm, Ho or Pr.

A search for 4F3/2 to 4I15/2 Nd lasing between 1850 nm and I960 nm is reported. Forty possible materials were identified; seven were tested. The possibility of uni-wavelength cascade lasing was identified for two materials.

A modified prism coupling technique was used inside a vacuum chamber to measure the very low extinction in an optical thin film as it was being deposited. More conventional modifications were also investigated.

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.

This paper reviews the progress and potential of laser removal of particles and other contaminants from semiconductor and dielectric substrates (wafers, masks, blanks, flat panels or windows) by the attenuated total internal reflection of laser light. External laser illumination at near-normal incidence removes metal particles from transparent substrates, even when less than 2% of the laser light is absorbed by the particle. By altering the polarization and angle of incidence, greater absorption and cleaning effectiveness have been reported. We report that still greater absorption can be achieved with internal irradiation at an angle of incidence greater than the critical angle for total internal reflection. With capillary condensation or steam laser cleaning, absorptions of up to 80% are predicted. Internal irradiation offers additional advantages. Multiple internal reflections cause the beam to search for contaminants at the speed of light, rather than at the speed of scanners or translation stages. In the absence of contaminants, the beam is not attenuated so the laser energy is very efficiently used. Particles on the surface cause a small fraction of the total internal reflected light to leak out of the substrate, so internal illumination may also be used to detect particles.

This paper describes recently developed techniques for; (1) measuring very low absorption in certain thin film coatings, (2) reducing both thermal distortion and depolarization from a window and (3) laser cleaning polished window surfaces.

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.

The advantages of backside irradiation and controlling the polarization and angle of incidence of laser beams used to conventionally clean surfaces have been described previously. This paper considers beams internally incident upon the surface of a transparent substrate at angles of incidence beyond the critical angle for total internal reflection. Attenuated total internal reflection provides an efficient means for both finding and removing absorbing contaminants. Beams may enter the substrate through an edge or a coupling prism. Erbium laser pulses were used to remove water from several dielectric and semiconductor materials. In some cases the water was explosively removed, with no sign of damage to the substrate. A 2.94 mum laser should be especially effective whenever water is present, either naturally from adsorption or capillary condensation or when added for steam laser cleaning. Unabsorbed light can be efficiently routed to clean adjacent areas through multiple total internal reflections. Thus some of the scanning is done at the speed of light. Theory indicates that ATR laser cleaning is effective for very small particles that cannot be removed by shock laser cleaning. This paper will describe attenuated total internal reflection laser cleaning and compare it to conventional laser cleaning techniques.

Theoretical studies and preliminary experiments indicate that the efficiency of laser cleaning can be significantly improved by irradiating surface contaminants from within the substrate under conditions of total internal reflection.

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 piano-convex and piano-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 less than or equal to+/-0.12 arc seconds in beam deviation angle.

Lubricated (matched lens) adjustable optical wedges steer laser beams in two dimensions from a single center-of-scan that stays on the original beam axis. These patented refractive beam steerers offer a wide range of apertures, deviations and precision. They do not suffer from the blind spots inherent with conventional Risley Wedge Beam Steerers. Unlike mirrors, they are nearly immune to vibrations and they do not require rerouting or “dog-legging” the beam. We have tested dozens of transparent lubricants and found several that can handle high laser powers. Lubricated adjustable optical wedges may soon replace conventional beam alignment or steering hardware in a variety of applications. This paper will review lubricated adjustable optical wedges and other refractive beam steerers.

We describe a practical device for deviating a transmitted light beam up to several degrees. It keeps the pivot point on the original axis and can offer more sensitive angular control than conventional mirror mounts.

We have characterized a 3.8-cm diam clear-aperture, diode-pumped active-mirror laser amplifier. A direct comparison, based on gain and wavefront measurements, was made between diode and flash-lamp pumping of a Cr:Nd:GSGG mirror.