H. R. Fetterman

Far‐ir heterodyne radiometric measurements with quasioptical Schottky diode mixers

We have made heterodyne radiometric measurements with GaAs Schottky diode mixers, mounted in a corner‐reflector configuration, over the spectral range 170 μm to 1 mm. At 400 μm, system noise temperatures of 9700 K DSB (NEP=1.4×10−19 W/Hz) and mixer noise temperatures of 5900 K have been achieved. This same quasioptical mixer has also been used to generate 10−7 W of tunable radiation suitable for spectroscopic applications.

Submillimeter detection and mixing using Schottky diodes

Schottky diodes have been used for the first time as harmonic mixers in the 0.1–1.0‐mm wavelength region. Beat notes between the 33rd harmonic of a 74‐GHz V‐band klystron and 118.8‐μ laser radiation are observed directly without the need of narrow‐band synchronous detection. The demonstrated performance of these room‐temperature diodes as wide‐band or heterodyne detectors of submillimeter radiation and their rugged construction make them superior to current point contact devices.

cw submillimeter laser generation in optically pumped Stark‐tuned NH3

Submillimeter laser action has been achieved in ammonia by Stark shifting vibrational absorption lines into resonance with a CO2 laser pump. In two of the three observed cases the absorption line was between states of the same parity, i.e., forbidden in the absence of the applied Stark field. Stark tuning of a vibrational absorption into resonance with a pump laser line is a general technique which should greatly increase the number of stable cw submillimeter lines available at milliwatt power levels.

Real‐time spectral analysis of far‐infrared laser pulses using an SAW dispersive delay line

Spectral analysis of high‐power pulsed D2O lasers has been accomplished using SAW dispersive delay lines. Both the contributions of longitudinal modes and the tuning of the stimulated Raman line at 385 μm have been observed.

Optically pumped vibrational transition laser in OCS

Laser oscillation between vibrational states has been demonstrated at 19 μm in OCS by optical pumping on the ν2 overtone with a CO2 TEA laser. Analysis of the molecular kinetics indicates this technique to be general and capable of yielding many high−power (≳1000 W) laser lines below 50 μm.

Thin‐film VO2 submillimeter‐wave modulators and polarizers

Submillimeter‐wave modulators and switchable polarizers have been fabricated from VO2 thin films deposited on sapphire substrates. By passing electric current pulses through elements made from these films, the films can be thermally cycled through the insulator‐to‐metal transition that occurs in VO2 at about 65 °C. In the insulating state, the films are found to have negligible effect on the transmission at submillimeter wavelengths, while above the phase transition the transmission is strongly reduced by the free‐electron effects characteristic of a metal. Other possible applications of such switchable VO2 elements include variable bandpass filters and diffraction grating beam‐steering devices.

Tunable submillimeter sources applied to the excited state rotational spectroscopy and kinetics of CH3F

Tunable submillimeter radiation, generated and detected using optically pumped lasers and Schottky diode mixers, has been used in an infrared‐submillimeter double resonance investigation of CH3F. This technique permits the direct observation of the molecular rotational spectra and kinetics of excited vibrational states and is particularly important for those molecules which are candidates for optically pumped submillimeter lasers.

Identification of donor species in high‐purity GaAs using optically pumped submillimeter lasers

An optically pumped NH3 laser has been used in conjunction with careful doping experiments in high‐purity GaAs to determine the ionization energy of isolated tin donors. The energy obtained is 5.820 meV, which corresponds to a central‐cell correction of 0.081 meV. This technique for impurity analysis is estimated to be sensitive to donor concentrations of less than 1011 cm−3.

InAs spin‐flip laser operation at 3 μm

Stimulated spin‐flip Raman scattering in InAs has been achieved using an HF laser pump near the band‐gap resonance. Thresholds were determined to be less than 20 W and conversion efficiency is estimated to be in excess of 20%.

Compositional dependence of effective masses in n-type GaxIn1−xAs alloys using submillimeter cyclotron resonance

Abstract Conduction band effective masses have been measured for the first time by cyclotron resonance in GaxIn1−xAs alloys as a function of alloy composition. These measurements were made on high-purity epitaxially grown crystals, ranging in alloy concentration from 100 to 84.6% GaAs, using submillimeter laser sources at 119 and 337microm. The values obtained for the band edge effective masses are consistently heavier than predicted from k ⋯ p perturbation theory.