A. P. Kushelevsky

Photoionization of excited atoms in dc gas discharges by low‐intensity light and its analogy to gas‐breakdown with high‐intensity lasers

Spectral effects and nonlinearities that characterize illumination of dc discharges by low‐intensity light and illumination of gas cells by high‐intensity lasers are described. The similarities suggest an analogy between both cases. This analogy can be used to deepen the understanding of the low‐intensity EM radiation interaction with gas discharges and as a possible tool for further study of gas breakdown by high‐intensity lasers, including further investigation of the ’’effective photon’’ concept.

Improved detection of ultraviolet radiation with gas-filled phototubes through photoionization of excited atoms.

Using dc biases higher than those recommended by manufacturers, it is possible to exploit photoionization of excited atoms to obtain high sensitivities to uv radiation using gas-filled phototubes. Spectral response, nonlinearity of response, and dc bias effects are discussed. Comparisons are made with uv semiconductor detectors, and suggestions for future research are made. If a photocathode is used in a gas tube such devices are quite sensitive to both visible and uv radiation.

The role of excited atoms in UV photopreionization TEA lasers

A simple model of photoionization of excited atoms by UV photons from capacitor spark discharges is suggested to explain the improvement in both plasma density production and laser efficiency noticed by several investigators when the proportion of helium in high-pressure CO 2 laser mixtures is increased. Such improvements with increased He proportion take place both with and without seeding with low ionization potential dopants. The model is also applicable to explaining the arc suppression qualities of helium as well as the ability to ignite discharges at higher total pressures when the proportion of helium is increased. Several implications regarding future TEA laser work are suggested.

Spectral tuning and linewidth narrowing of shallow-junction surface emitting GaAs LED́s through γ-ray irradiation

Alterations of device characteristics as a result of γ-ray irradiation of shallow-junction surface emitting devices are different from those of deep-junction devices with respect to LED emission intensity reduction, I-V curve, line shape, and spectral shift. In particular, much larger spectral shifts in the opposite direction-toward longer wavelengths-are reported here than those found in the literature for deep-junction devices. A qualitative model based upon photochemical doping and changes in surface band bending is proposed to explain these phenomena. Changes in surface emitting shallow-junction optical radiation source device characteristics brought about by γ-ray irradiation are desirable ones for utilization in most optical fiber communication systems. These changes include linewidth narrowing, decreased time response, and decreased material dispersion because of the emission wavelength change.

Photoionization of excited atoms by low intensity light: experimental test of the effective cross section

The effective cross-section concept, analogous mathematically to Panarellas effective photon concept, is confirmed experimentally. Uniform spatial profiles of excited atom cross sections yield linear response to incident light, unlike previous results with Gaussian spatial profiles. Implications include potentially improved wavelength tuning sensitivity with the optogalvanic effect, obtaining response linearity in gas discharge detectors of uv and visible light and, because of the analog, modeling the geometrical aspects of Panarellas effective photon concept.

Effects of ionizing radiation on glow discharge detectors

Glow discharge detectors in the abnormal glow mode can be used as sensitive detectors of microwave and millimeter wave radiation even in the presence of very intense γ ionizing radiation fields where semiconductor devices cannot operate. In the subnormal glow mode, glow discharge detectors give promise of being able to monitor ionizing radiation fields so intense that the usual electronic detectors saturate.

A simple qualitative model of surface versus bulk effects in gamma‐ray irradiated p‐n diodes

Various Si and Ge rectifier diodes are tested at frequent intervals of γ‐radiation doses for changes in ideality factor η and minority carrier lifetime τ. Although both parameters are well known to decrease with dosage, here they are probably for the first time measured to also subsequently increase, decrease, increase, etc., at higher dosages. Examination of diodes in vacuum prior to and following even modest irradiation levels indicates experimentally that noticeable changes in surface properties have been induced by the irradiation. Such experimental techniques permit greater insight into the basic structure of surface phenomena long suspected to play a significant role in diode changes brought about by nuclear irradiation. Utilization of such surface changes leads to a broad general concept to explain the reversals and changes in the dosage dependences of η and τ in terms of bulk versus surface effects.

Spectral Tuning Of Shallow-Junction Surface-Emitting Light-Emitting Diodes (LEDs) Through γ-Ray Irradiation

Effects of nuclear radiation on GaAs emitting diodes have been studied in various investigations. These studies included both devices in which the IR radiation was emitted from the N-side and devices in which the IR radiation was emitted from the P-side. In the references cited the devices were heavily doped with various dopants and the junctions were located approximately 20 μm below the semiconductor surfaces. Measurements following γ-ray irradiation indicated in all cases small shifts (1-4 nm) in peak wavelength of emission towards shorter wavelengths, with the amount of shift depending on the specific impuritiesl. This led to a hypothesis that interaction of nuclear radiation-induced-defects with impurities plays a role in the spectral shift. Other effects of the irradiation were to decrease slightly minority carrier lifetime, to attenuate heavily the emission intensity of the diode emitters, and to increase slightly the forward I-V slope.