The mechanism of long wave electromagnetic signal detection by glow-discharge plasma, based upon gas breakdown theory by high frequency electric fields, is developed to include internal signal amplification of the order of that associated with the photomultiplier, upper and lower limits to response linearity, temporal and spectral response properties, and noise in the abnormal glow discharge. Agreement between signal-to-noise expressions in this analysis and measurements involving simple and inexpensive glow discharge indicator lamps exhibiting excellent sensitivity to microwave radiaion is quite good. An inherent ideal limit to speed of response is derived which indicates picosecond-order risetimes are theoretically possible if parasitic reactance effects which limit risetimes of present day devices to microsecond order can be overcome. Sensitivity can be improved further by increasing the number of free electrons. Enhanced diffusion current losses for a subnormal glow yield spectrally flat response which can be useful in radiometric applications.

Glow Discharge Detection of Long Wavelength Electromagnetic Radiation: Cascade Ionization Process Internal Signal Gain and Temporal and Spectral Response Properties

We report laser‐induced breakdown studies of laboratory air using 0.266, 0.355, 0.532, and 1.06 μm radiation for focal spot varying from 30 to 100 μm. The breakdown intensities were measured for two pulse widths for all four wavelengths. We observe a t−0.5p dependence of pulse width on threshold field at 0.532, 0.355, and 0.266 μm while for 1.06 μm the pulse width dependence of t−0.35p is observed.

Laser‐induced breakdown studies of laboratory air at 0.266, 0.355, 0.532, and 1.06 μm

Diffusion of helium in nickel

The photosensitivity of 50 and 100 μm square microdischarge devices having an inverted pyramidal Si cathode has been demonstrated and characterized in the ultraviolet, visible, and near-infrared (350–1200 nm). When operating with 500 Torr of Ne, (100 μm)2 microdischarge devices exhibit responsivities of 700±150 and 570±120 A W−1 at 850 and 660 nm, respectively, or more than an order of magnitude larger than peak values typical of commercially available Si avalanche photodiodes. Maximum sensitivity occurs in the 800–900 nm region for the larger (100 μm square) devices but is blueshifted to 600–650 nm for (50 μm)2 detectors. The peak response for the 50 μm square device is 950±250 A W−1 (at ∼625 nm), an increase of ∼35% over that for the (100 μm)2 detector. The experimental results indicate that the semiconductor photocathode determines the spectral response of the device whereas the plasma serves as an electron multiplier. The sensitivity and dynamic range of this new hybrid semiconductor/plasma photodetector suggest that arrays of microdischarge photodetectors are potentially valuable for spectroscopic and biochemical applications.

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Photodetection in the visible, ultraviolet, and near-infrared with silicon microdischarge devices

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.

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

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.

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

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.

The role of excited atoms in UV photopreionization TEA lasers

A sensitive ultraviolet radiation detector based on photoionization of excited atoms

The effective cross-section concept, analogous mathematically to Panarella's 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 Panarella's effective photon concept.

A. P. Kushelevsky

Papers

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

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

The role of excited atoms in UV photopreionization TEA lasers

A sensitive ultraviolet radiation detector based on photoionization of excited atoms

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