ABSTRACTWe have measured transition-metal ion (Ti, V, Cr, Mn, Fe, Co, Ni, Cu) spectra and their effects on Nd fluorescence quenching in Nd-doped phosphate and silicate glasses. Our purpose was to determine the maximum allowable impurity content given particular limits on the absorption loss at 1053 nm and the Nd fluorescence quenching rate. To keep the absorption loss <0.1 m−1 the transition-metal impurity content should be kept below 0.5 ppmw. To keep the increase in the Nd fluorescence decay rate below 1%, the impurity content should be <3 ppmw. We have also found that the Nd quenching rates do not scale as predicted by the Forster- Dexter dipole-dipole energy transfer theory if we assume that the dominant variation with transition metal is the overlap integral of the Nd fluorescence spectrum and the transition-metal absorption. We suggest that phonon-assisted energy transfer to transition metals is effective in quenching Nd. We find that quenching rates increase 1.5 to 4 times as the Nd concentration increases from 0.5 to 10 × 1020 cm−2.

A laser scanning system designed for inspection of patterned wafers is described. This system addresses the inspection needs for 64 Mb (0.35 micrometers ) and 256 Mb (0.25 micrometers ) DRAM process technologies. The system is capable of detecting contaminant particles and planar pattern defects on memory and logic devices. The throughput of the system is designed for 30 wafers (200 mm in diameter) per hour. The beam at 488 nm is brought to a focal spot and is scanned on the wafer surface using an acousto-optic deflector (AOD). The entire wafer is scanned under oblique illumination in narrow strips in a serpentine fashion. The specular beam is collected and processed in, what we have named, the autoposition sensor (APS) to servo- lock the height position of the wafer during the scan. The system utilizes multiple independent collection channels positioned around the scan line and it is possible to select the polarization of the collected light for enhanced signal-to-background ratio. The engineering tradeoffs for realizing a system with high throughput and sensitivity are formulated and discussed. Calculations ilustrating scattering from submicron size particles under various polarization conditions are shown. These results lead to optimum design for collection optics. The APS channel is described and illustrated by results indicating that it is possible to keep the surface height of the wafer constant to within 0.4 micrometers in the presence of large changes in topography and wafer reflectivity. Results obtained from a range of production wafers demonstrating detection of 0.1 micrometers anomalies on bare wafer, 0.3 micrometers on memory devices, and 0.4 micrometers on random logic structures are presented.

We have constructed a model that will be useful in designing Nd: phosphate glass lasers that are heated when run repetitively, continuously, or in the burst mode. The model predicts the temperature dependence of the gain coefficient and the extractable stored energy density. Changes in the populations of the upper and lower laser levels are described by Boltzmann distributions. The generalized Einstein relations are used to relate the stimulated-emission and absorption cross sections. Variations of the cross sections with temperature have been inferred from measurements of the threshold energies of a flash-lamp-pumped rod oscillator, over the range 288 to 365 K. With only a single input of the gain coefficient at one temperature, our model predicts the gain coefficient and the extractable stored energy density at other temperatures.

Visible and ultraviolet light reflectometry provides a fast, convenient, and nondestructive method of characterizing multilayer film structures that include polycrystalline silicon. Reflectance measurements of silicon wafers containing such films have provided information as to the roughness of the poly surface, the thickness of the films, and the optical properties of the poly.

Refractive index variations of film materials are measured using a spectral micro-reflectometer, the Tencor® TF-1. The principles of thickness and refractive index determination are discussed. An effective medium model of film materials is applied to calculating refractive indices and their wavelength dependence. Refractive indices for typical poly-crystalline silicon are given. Compositional and structural inhomogeneities cause refractive index variations. Neglecting these index variations leads to misinterpretation of film thickness measurements.

We report on methods for eliminating of optical absorption in neodymium, chromium doped gadolinium scandium gallium garnet (Nd;Cr:GSGG) due to tetravalent chromium at the laser wavelength. These methods include doping of the crystal melt with specific additive as well as post growth heat treatments.

Nd,Cr:GSGG crystal boules up to 13 cm in diameter and 20.5 cm long have been grown by the Czochralski method. Several problems with Nd,Cr:GSGG growth were identified, and solved separately but not all at once; these problems included spiral boule growth, 1- mu m absorption loss, iridium on the melt surface, iridium inclusions, boule cracking, dislocation, and fine scattering (smoke). In the grown ...

A model is introduced that details the complexing between divalent and tetravalent species in garnet melts. This explains the phenomenon of interface instability in Czochralski crystal growth of gallium-containing garnets. Chromium may participate in this process when it is oxidized to its 4+ valence state. This model explains the effects of uncompensated divalent ions and growth atmosphere on absorption in the crystal.

Gadolinium scandium gallium garnet (GSGG) codoped with neodymium (Nd) and chromium (Cr) is a new laser material that can make more efficient lasers. I compare it to Nd-doped yttrium aluminum garnet (YAG) for two types of systems: large zig-zag slab lasers and small rod lasers. Nd:Cr:GSGG has a significant advantage over Nd:YAG in large systems because of its high efficiency and availability in large sizes. In small rod systems, though, the larger thermal lensing and birefringence in Nd:Cr:GSGG make it less desirable than Nd:YAG from an optical standpoint, but its high efficiency means that laser system size and weight can be reduced. I review progress in obtaining large Nd:Cr:GSGG slabs. In this effort, Allied-Signal Corp. has successfully grown 5-inch diameter Nd:Cr:GSGG boules.

A range of glass compositions has been identified in the PbO-Bi2O3-CuO-Al2O3-SiO2 system which will be applied as absorbent claddings to Nd3+ and Cr3+ co-doped gadolinium scandium gallium garnet and Nd3+-doped gadolinium gallium garnet crystal slabs for high-power laser applications. Coefficients of thermal expansion and refractive indices at 1.06 μm of the cladding match those of the crystals. Absorption coefficients are between 30 and 40 cm−1. Estimates of stress birefringence in the crystalline medium indicate that values below 10 nm/cm are achievable with cladding layers of 1 mm thickness and crystal slabs of 50–100 mm width.

In 1958 SCHAWLOW and TOWNES [1] proposed that an optical maser could be made with the right combination of spectroscopic properties of an excited atom, ion, or molecule in a gas or solid, an optical pumping source, and a resonant cavity. The key to their proposal was their choice of a Fabry-Perot cavity as the resonator. This proposal stimulated several efforts to make an optical maser. In 1960 MAIMAN [2] demonstrated coherent emission from a ruby crystal, and the laser era had begun.

We have experimentally determined loss coefficients of OH as 8.1 × 10−7 cm−1 / ppm and of ionic platinum as 8.6 × 10−7-7cm−1/ppm for LHG-5 type phosphate laser glass without Nd2O3 doping. Glass has been produced with absorption loss of about 1 ×c 10−4cm−1 which is one order of magnitude lower than is presently commercially available.

Gadolinium scandium gallium garnet (GSGG) has been grown in boules of 13‐cm diameter by 15 cm long. Three scale‐up issues have been identified and progress made toward their solution. Large slabs of Nd,Cr:GSGG are now being fabricated for efficient, medium power lasers.

Spectroscopic, optical, and thermomechanical properties of gadolinium scandium gallium garnet doped with trivalent neodymium and/or chromium are reported for use in the design of high-power solid-state lasers.

The purpose of the High Average Power Solid State Laser Program at the Lawrence Livermore National Laboratory is to develop new technologies for significantly increasing the average power capability, beam quality, efficiency, and wavelength agility of solid state lasers. The program emphasis is to advanced the state-of-the-art and is not directed toward a specific application. The performance objectives are more quantitatively defined in the following table.

New solid-state laser media will improve the efficiency, average power, and beam quality of laser systems. Recently gadolinium scandium gallium garnet (GSGG) crystals have produced the highest efficiency laser operation reported for a rod laser.1 For high-average-power systems employing the zigzag configuration or the gas-cooled disk configuration, GSGG will be useful for small-aperture systems, in large-aperture systems, new silicophosphate glasses developed by Hoya Optics and by Schott Glass Technologies have advantages over the presently used LHG-5 phosphate glass. Future lasers for fusion research, which will have mega-joule pulse energies, will require an inexpensive phosphate glass with improved thermomechanical characteristics. In the long run laser drivers for inertial confinement fusion reactors will need an efficient low-nonlinear-index crystalline laser medium; fluoride crystals are prime candidates.