Frequency doubling of diode laser radiation was achieved by operating an AR-coated diode laser in an extended laser cavity which contained a monolithic potassium niobate frequency doubling resonator as an intracavity element. Extended cavity operation ensured that the diode laser would oscillate only at frequencies that were resonant with the intracavity resonator. A diffraction grating was used to ensure single mode oscillation at the wavelength needed for noncritically phase-matched second harmonic generation. At 100 mA of injection current to the GaAlAs diode laser, 14 mW of 429 nm light were produced.

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GaAs metal-semiconductor field-effect transistors (MESFETs) and other integrated-circuit elements were characterized by including extensive process test sites on wafers with digital logic and memory circuits. A self-aligned, refractory-gate enhancement/depletion (E/D) process was employed which included 47SiF+ channel and source/drain implants, capless arsenic overpressure furnace annealing, WSi0.11 gate metal with in situ sputter cleaning, Ni-Au-Ge ohmic contacts, Si3N4 or SiO2 insulation, and Ni-Au wiring. On-water threshold voltage standard deviations as low as 31 mV for 1-μm E-FETs and 49 mV for 1-μm D-FETs were measured using 51-mm standard semi-insulating liquid-encapsulated Czochralski GaAs substrates. Threshold voltage control from wafer to wafer was of order 100 mV. Schottky diode barrier height was about 0.73 eV with an ideality of 1.2, although small self-aligned Schottky gates often showed excess conduction believed to occur at the gate edges. FET square-law coefficient, subthreshold leakage, gate capacitance, backgating, contact resistance, and wiring and insulation characteristics were also measured and found satisfactory. Fully functional 1-μm gate E/D MESFET circuits including a 4×4 bit multiplier, a 4×4 crosspoint switch, a 448-bit static RAM, and an integrated photodiode amplifier were demonstrated.

Optical fibre Bragg grating sensors inscribed in polymer optical fibre have been shown to be sensitive to the water content of the medium surrounding the fibre and this property has been applied, for example, to the monitoring of humidity and the water content of aviation fuel. In this work we assess the feasibility of using such sensors for monitoring the saturation of soils, which is important for civil engineering applications. We find a very non-linear response, with a rapid increase in Bragg wavelength as the water content increases from 0 to 0.5%, with a much more gradual, but still monotonic, increase thereafter. We speculate on the causes of this response.

Several electron-beam resists suitable for lift-off processing have been investigated with particular attention to the requirements for fabricating Pb-alloy Josephson integrated circuits. The desired resist must perform well with a baking temperature near 70°C, provide a reproducible undercut edge profile with good linewidth control, and adhere to the necessary substrates. Diazo resists as well as the commonly used FMMA and copolymer materials were studied. Initial results suggest that *AZ-1350J soaked in chlorobenzene to enhance the undercut profile can satisfy many of these requirements. At present, the amount of undercut obtained is larger than desired, limiting the minimum separation between exposed features to about 1.5 pm.