Red (631 nm), green (532 nm), and blue (448 nm) continuous-wave (CW) lasers have been developed by Evans &
Sutherland (E&S). These multi-watt RGB lasers are used as light sources in E&S' laser projector (ESLP), which delivers
ultrahigh-resolution content (8192 × 4096 pixels) to large-surface-area venues (e.g., planetariums, simulators,
visualization centers, etc.). Efficient visible wavelength generation is obtained by coupling single-frequency nearinfrared
(NIR) beams into free-space enhancement cavities containing critically phase-matched lithium triborate (LBO)
crystals. The NIR energy is produced by a master-oscillator-power-amplifier (MOPA) system which is fiber-based, thus
yielding Gaussian beams which are near-ideal for efficient fundamental-to-harmonic conversion. Both polarizationmaintaining
(PM) fibers and non-PM fibers have been employed with non-PM fiber systems requiring polarization
sensing and control. Green laser light is produced by a second-harmonic generation (SHG) process with a 1064 nm
fundamental. Red laser light is produced by a sum-frequency mixing (SFM) process with 1064 nm and 1550 nm as
fundamentals. Blue laser light is produced by an SFM process with 1064 nm and 775 nm as fundamentals, where 775
nm is first produced by an SHG process with a 1550 nm fundamental. All resulting visible lasers are single-axialfrequency
with FWHM bandwidths less than 400 kHz, and are spatially pure with M² values less than 1.05. At least 18
W of CW optical power has been generated at all three visible wavelengths, with available NIR amplifier power as the
primary limiting factor.
High-efficiency (5%-10% wall-plug efficiency) high-power continuous-wave (CW) visible lasers have been developed
for large-format-display applications (e.g., planetariums, visualization centers, etc.). Using an approach pioneered by
Evans & Sutherland (E&S), a fiber based master-oscillator-power-amplifier (MOPA) architecture is employed to
generate high power near-infrared (NIR) tunable lasers that are then converted to visible wavelengths in external
enhancement nonlinear ring cavities. Depending on the wavelength generated, either second-harmonic generation or
sum-frequency mixing (or both) in lithium triborate (LBO) are utilized to convert 1064 nm and/or 1550 nm to visible
wavelengths, with NIR-to-visible optical-conversion efficiencies of 65%-95% routinely obtained. The resulting visible
lasers are single-axial-frequency (FWHM bandwidth < 200 kHz) spatially pure (m2 < 1.05) Gaussian beams, and are used as light sources in ultrahigh-resolution projectors manufactured by E&S. The current systems reliably produce 6 W of visible laser power at 448 nm, 532 nm, and 631 nm, with short-term CW operation yielding up to 18 W visible-laser output per color. Laser-induced damage (LID) on nonlinear-crystal facets is the primary limitation to long-term operation at visible powers > 6 W, and efforts are underway to increase crystal LID thresholds to allow reliable operation at greater power levels.
Improvements in magnetron sputtering technology have made it possible to deposit compound thin films at total pressures as low as approximately 1 X 10-4 torr. Deposition at these lower pressures increases the mean free path of molecules within the vacuum chamber, thereby allowing for greater adatom energies on the substrate surface. By increasing adatom energy, low-pressure dc-magnetron sputtering can lead to the deposition of dense metal-oxide films that are resistant to the adsorption of atmospheric water (H2O). We report results showing improved environmental stability in single-layer films of silica (SiO2) and alumina (Al2O3) deposited using a 8-in-diameter dc magnetron source. Metal targets were used, with argon (Ar) as the sputtering gas and oxygen (O2) as the reactive gas. The silicon target was doped with 5-percent Al to improve its electrical conductivity. The effects of target voltage, Ar partial pressure, and O2 partial pressure were studied. In addition, several source geometries were tested in order to optimize the coating thickness uniformity. Film moisture content was characterized by spectral transmittance near the H2O optical absorption band at 2.8 micrometers . Deposition at total pressures < 3 X 10-4 torr resulted in SiO2 coatings with minimal H2O content, while all Al2O3 coatings exhibited no H2O content.
Total internal reflection microscopy (TIRM) is an inspection method that yields an image of the defects in a surface and/or a dielectric thin film. By installing a TIRM system in a vacuum-deposition chamber, the formation of thin-film defects (visible as point-scatter sites) is directly observable. By using such a system, we have examined the effects of deposition conditions on thin-film defect generation. In this preliminary investigation, the rate of defect accumulation in ZrO2 thin films produced by electron-beam (e-beam) evaporation displays a dependence on substrate cleanliness, with cleaner surfaces yielding lesser defect-formation rates. In addition, the presence of film crystallites can be observed by in-situ TIRM, and shows a dependence on the oxygen partial pressure during deposition.