Benjamin Lax

Ferrite Phase Shifters in Rectangular Wave Guide

The problem of the propagation of electromagnetic energy down an infinitely long rectangular wave guide partially filled by a ferrite slab is solved. The solution is expressed in the form of a transcendental equation involving the propagation constant. Calculations are carried out for a lossless ferrite, and the phase constant is evaluated as a function of the appropriate parameters, namely, the ferrite slab thickness, the lateral position of the slab in the guide, and the applied transverse static magnetic field intensity. The results are plotted in graphic form for values of the static magnetic field in the region of ferrite saturation both above and below ferromagnetic resonance. The electromagnetic field configurations within the wave guide are plotted in detail for values of the parameters of practical interest. Two versions of the nonreciprocal phase shifter are discussed. The first consists of a single slab placed asymmetrically in the wave guide, while the second consists of two symmetrically plac...

Microwave studies of a tunable free electron laser in combined axial and wiggler magnetic fields

Measurements of narrow‐band (Δω/ω≤0.02) microwave emission from a tunable (7≤ω/2π≤21 GHz) Raman, free‐electron laser operating in a single TE11 waveguide mode are reported. Approximately 100 kW of rf power has been observed at an electronic efficiency of 12%, and ∼1 MW of rf power has been generated at a reduced efficiency of 8%. Frequency, gain, and rf power measurements have been carried out for various values of the guide magnetic field, below, above, and near to the resonance between the cyclotron frequency of the guide magnetic field and the frequency associated with the periodic wiggler magnetic field. The results are in very good agreement with the predictions of three‐dimensional free‐electron laser theory.

The effect of magnetic field on the breakdown of gases at microwave frequencies

The effect of magnetic field on the high frequency breakdown of gases has been studied. The presence of energy resonance and the modification of diffusion are shown experimentally and explained theoretically. An application is made of both the average electron theory and the Boltzmann theory, and the correspondence between these two theories is discussed.

Reflectance line shapes from GaAs/Ga1−xAlxAs quantum well structures

Reflectance experiments on GaAs/Ga1−xAlxAs single quantum well structures were performed at 4.2 K, with different thicknesses of the front GaAlAs barrier layer (100–1000 A). The observed exciton reflectance line shapes depend strongly on the thickness of the front barrier layer due to the interferences between the reflected waves from the front surface and the quantum well interfaces. Calculations of the reflectance line shapes show good agreement with the observations. The absorption coefficient for the electron heavy‐hole exciton transition in a single quantum well sample is determined. Our study also provides a new understanding of the line shapes measured in photoreflectance experiments.

Frequency and Loss Characteristics of Microwave Ferrite Devices

The four major microwave ferrite devices, ie., the Faraday rotator, the resonance isolator, the nonreciprocal phase shifter, and the field displacement devices are discussed in terms of their loss properties over a range of frequencies. By means of perturbation theory the figure of merit of these devices is derived in the idealized limits for various ferrite geometries. These limiting values are analyzed in terms of the experimental results of the resonance loss for polycrystalline and single crystal measurements and compared with existing data on practical devices. The analysis indicates a possible low-frequency limit of Faraday and nonreciprocal phase shift circulators at about 1000 mc. The low-frequency limit of the resonance isolator is estimated at about 200 mc with a reverse-to-forward ratio of about 10. The problem of broad banding is also discussed in terms of the perturbation results.

High frequency gyrotrons and their application to tokamak plasma heating

Abstract High frequency (⩾ 200 GHz) gyrotrons are potentially useful for several important applications, including plasma heating and radar. For electron cyclotron resonance heating of a moderate-size, high power density tokamak power reactor to ignition temperatures, a gyrotron frequency around 200 GHz appears to be necessary. The design of high frequency gyrotrons is discussed. Analysis of overall gyrotron efficiency indicates that high efficiency may be obtained in fundamental electron cyclotron frequency (ω c ) emission at high frequencies. The linear theory of a gyrotron operating at the fundamental frequency is derived for the TE mpq modes of a right circular cylinder cavity. An analytic expression is given for the oscillator threshold or starting current versus magnetic field.

Oscillatory magneto-absorption in gallium antimonide JA-1149∗☆

Abstract High-resolution magneto-absorption measurements made at photon energies just above the intrinsic absorption edge in GaSb have revealed an oscillatory spectrum having a strong resemblance to the corresponding spectrum for direct transitions in germanium. Eight successive transmission minima were observed in magnetic fields up to 38.9 kG at both 1.5 and 4.2°K, using polarized incident radiation. The value of the energy gap found is g = 0.813±0.001 eV and is shown to be attributable to direct transitions of electrons between the valence and conduction bands. The electron effective mass, m∗ = (0.047 ± 0.003)m0, was determined by considering transitions from the heavy holes to the conduction band and employing the data of the E||B spectrum. The existence of fine structure, although not resolved, is indicated by the unsymmetrical character of some of the transmission minima. The first absorption line is believed to contain exciton absorption. The inability to resolve the fine structure and exciton absorption is attributed to line broadening and overlapping due chiefly to scattering by the high impurity density in the sample.

Laser pumped molecular lasers - Part I: Theory

The density matrix formalism describing the interaction between a three level molecular system and two nearly resonant laser fields of arbitrary intensity is extended to include the molecularM-level degeneracy. Expressions for gain on the two possible relative polarizations of a laser pumped molecular laser are derived and its saturation behavior discussed. Numerical results for the 385 μm transition in D2O and 496 μm transition in CH3F are presented.

Laser-pumped molecular lasers - Part II: Submillimeter laser experiments

We report the first experimental determination of the gain spectrum of a laser-pumped submillimeter laser amplifier. Single-mode pump and submillimeter oscillators were used to determine the gain as a function of submillimeter laser frequency, pump intensity, relative polarization, and molecular gas pressure. The 385 μm transition in D2O and the 496 μm transition in CH3F, both pumped by a CO2laser, were investigated. The use of single-mode lasers allows a direct comparison with theory. Good agreement is obtained with our recent theory which takes into account two photon contributions to the gain as well as space orientation (M-level) molecular degeneracy.

cw generation of tunable narrow‐band far‐infrared radiation

Tunable narrow‐band cw generation of far‐infrared radiation has been achieved for the first time in the 70‐μm to 1‐mm wavelength region by noncollinear difference‐frequency mixing of two single‐mode CO2 lasers in GaAs at 80 K. Using a Schottky diode as a heterodyne harmonic mixer with a carcinotron local oscillator, the far‐infrared signal is shown to have a linewidth of less than 100 kHz and a fine tuning capability in excess of 50 MHz.