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We have studied both theoretically and experimentally a new scheme of active pulse compression in a free electron laser (FEL) amplifier. The pulse compression scheme presented here is the following. A frequency-chirped pulse is injected into the FEL interaction region. Because of the high gain and narrow bandwidth of the FEL interaction, only the resonant frequency band of the pulse is actively amplified, resulting in a short pulse of high power coherent radiation at the output of the laser. For our experimental parameters (beam voltage ∼ 150 kV, current ∼ 5.0 A, wiggler period ⋍ 3.5 cm and gain ∼ 10 dB), pulses of a few nanoseconds were generated at ⋍ 10 GHz after an interaction length of 2.30 m, in good agreement with theoretical expectations. For the same input pulses (width > 100 ns, frequency chirp α2π∼ 5 MHz/ns), the obtention of such compression ratios would require hundreds of meters of dispersive medium (waveguide, for example), with prohibitively high attenuations. These experimental result represent what we believe to be the first measurements of FM effects in an FEL amplifier.

A cyclotron-resonance maser (CRM) experiment with a transverse electromagnetic (TEM) wave is presented in this paper. A nonrelativistic electron beam is spiraling in this device in a non-dispersive parallel-line waveguide. The CRM oscillator output frequency is tuned by the axial magnetic field in the range of 3.2–4.8 GHz.

This article explores the feasibility of particle beam weapons, identifies the physical principles that would govern their operation, assesses the technical difficulties, and evaluates their potential uses.

Experimental investigations of the intensity distribution in the region of the focus of microwave lenses are described. The circularly symmetric lenses, made from polystyrene plastic, were illuminated by a linearly polarized beam of radiation of 1.25-cm wavelength. Most of the measurements are presented in the form of intensity contours in planes both containing the principal ray and lying perpendicular to it. Images formed by nearly perfect optical systems and by systems suffering from various third-order monochromatic aberrations were examined. In most cases the results are compared with calculations made from the scalar-diffraction theory of optical systems. In general, good agreement between theory and experiment is found.Some preliminary measurements of the phase variations of the electromagnetic field in the vicinity of the focus are given and the results discussed.

The average electron concentration of a gas-discharge plasma can be inferred from the phase change suffered by an electromagnetic wave in its passage through the medium. With available microwave generators, the maximum electron density that can be measured is approximately 3×10^14 cm^−3. On the other hand, interferometers that operate at optical wavelengths become insensitive at electron densities less than approximately 10^16 cm^−3. An infrared interferometer is described here which operates at 0.03 cm wavelength and is able to detect densities above 5×10^13 cm^−3 in a plasma column 1 cm thick. In the design, incoherent radiation from a mercury arc lamp is split by a diffraction grating and the plasma placed in one of the diffracted beams. The beams are then recombined and fringe shifts measured by a Golay detector.

The electric field intensity distribution was measured in the image space of solid dielectric microwave lenses at a wavelength of 1.25 cm for various displacements of the source from the principal axis of the system. The experimental results are presented in the form of contours of constant intensity in several receiving planes and also as plots of field intensity versus radial positions of the point of observation. It was found that the deviations of the intensity patterns from the ideal, Airy aberration-free distribution could be interpreted quantitatively in terms of the third order aberrations of optics. The very good agreement obtained with the scalar diffraction theory of aberrations suggests the usefulness of the optical concepts in their application to the centimetric wavelength range.

The average electron concentration of a gas-discharge plasma can be inferred from the phase change suffered by an electromagnetic wave in its passage through the medium. With available microwave generators, the maximum electron density that can be measured is approximately 3×10^14 cm^-3. On the other hand, interferometers that operate at optical wavelengths become insensitive at electron densities less than approximately 10^16 cm^-3 . An infrared interferometer is described here which operates at 0.03 cm wavelength and is able to detect densities above 5 × 10^13 cm^-3 in a plasma column 1 cm thick. In the design, incoherent radiation from a mercury arc lamp is split by a diffraction grating and the plasma placed in one of the diffracted beams. The beams are then recombined and fringe shifts measured by a Golay detector.

The imaging properties of two types of solid dielectric, circularly symmetric lenses were studied at a wavelength of 1.25 cm. One of these was a wide-angle aplanat proposed some time ago by Martin; the other was a modification of the two-point corrected lens recently discussed by Sternberg. The work was carried out for the purpose of finding their scanning characteristics and to compare their ability to produce good pencil beams of radiation. Measurements disclosed that in these lenses (having focal number of 1.5), a beam, of half-power width1.25\deg, could be scanned up to about20\degof arc from the optical axis by displacement of the source. The presence of astigmatism prevented either lens from being employed for wider scanning angles. In view of this fact, there appears to be little advantage in this case in using the two-point corrected lens over the simple aplanat which can be more easily designed.

Experimental investigations of the intensity distribution in the region of the focus of microwave lenses are described. The circularly symmetric lenses, made from polystyrene plastic, were illuminated by a linearly polarized beam of radiation of 1.25-cm wavelength. Most of the measurements are presented in the form of intensity contours in planes both containing the principal ray and lying perpendicular to it. Images formed by nearly perfect optical systems and by systems suffering from various third-order monochromatic aberrations were examined. In most cases the results are compared with calculations made from the scalar-diffraction theory of optical systems. In general, good agreement between theory and experiment is found.Some preliminary measurements of the phase variations of the electromagnetic field in the vicinity of the focus are given and the results discussed.