Zdenek Kucerovsky

Excitation processes and relaxation rates in the pulsed water vapor laser.

This paper presents an experimental study of time-resolved gain in H(2)O, H(2)O-He, and H(2)O-H(2) mixtures as a function of gas composition and excitation current. Utilizing the fast rising (~70 nsec) pulse from H(2)O-He laser as a probe, the amplifier gain was measured with a time resolution of about 100 nsec. The gain was observed to follow the excitation current pulse rather closely indicating that population inversion was established in times less than 100 nsec. This suggested that excitation was most likely by means of rapid cascading from higher levels and/or by direct electron impact. The gain was found to be describable by a two-level rate equation model containing one dominant relaxation rate and assuming immediate excitation of the levels involved by inelastic collisions with electrons. With pure H(2)O, the relaxation rate was proportional to pressure to within 10%, indicating that the upper level was de-excited primarily by c llisions with other H(2)O molecules. At a pressure of 1 Torr the relaxation rate in pure H(2)O was 0.35 +/- 0.05 for the 28-microm transition. The addition of small amounts of foreign gases was observed to increase this relaxation rate, consistent with the measured decrease in the amplifier gain. By subsequently increasing the water vapor pressure it was found possible to optimize the gain at an enhanced level over the pure H(2)O case. The peak gain obtained in water vapor at 1000 A was 0.34 m(-1). Under foreign gas addition this increased to 0.68 m(-l) for the same peak current. In this case the relaxation rate, as a function of the foreign gas (He or H(2)) pressure, remained constant to within 10%, suggesting that these gases at higher concentrations may enhance the system gain by altering the discharge conditions without appreciably collisionally de-exciting the upper laser level.

Triboelectric charging between polytetrafluoroethylene and metals

Measurements were obtained on charge exchange processes occurring between small metal ballistic pellets and a polytetrafluoroethylene (PTFE) tube. Lead pellets of 5.5-mm diameter were propelled at a range of speeds through PTFE tubes of different lengths by compressed carbon dioxide. The charge incurred by the pellets and the tube was compared with the charge observed on copper and lead spheres rolled through the tube, driven by gravity. In all experiments, the charge on the moving pellet was measured with a Faraday cup. The experiments determined the effect of pellet speed on the magnitude of the charge accumulated on the pellet and on the PTFE tube. Sectioned shielding on the PTFE tube allowed the determination of surface charge distribution along its length by means of an electrometer. It was observed that the charge also depended on the work functions of the materials involved (lead, copper, PTFE). The charge on the pellets was found to range from +0.5/spl times/10/sup -8/ to +3.0/spl times/10/sup -8/ C, for pellet speeds from 10 to 80 m/spl middot/s/sup -1/. The reproducibility of results is discussed and comment provided on the degree of charge imbalance observed.

Experimental determination of ESD latent phenomena in CMOS integrated circuits

A series of measurements were performed on two types of commercially available and custom-made CMOS integrated circuits to investigate the latent mode of failure due to ESD. The current injection test method was used for both polarities of discharge. Test parameters studied included threshold failure, constant amplitude multiple stress, step stress, and the stress hardening effect. Statistical analysis of the results demonstrate the presence of latent failure in CMOS integrated circuits due to ESD. The work is used to further expand a charge injection model for latent failures. >

Spectroscopic Analysis of a Corona Space Charge in a Cylindrical System with Air-Carbon Dioxide Medium

Positive corona glow discharge was studied in a system with cylindrical geometry in air and air-carbon dioxide mixtures at normal temperature and pressure (NTP). A spatially resolved spectroscopy technique was used in an attempt to explain the previously observed anomalous charging of particles traveling through the glow region. The results corroborate the existence of the previously reported anomaly. The apparatus developed for taking the spatially resolved spectra and the methods employed may be of interest in fundamental studies of corona discharge behavior in a practical electrostatic precipitator system.

Absorption Line Parameter Measurements Using Laser Spectroscopy

An analytical method is described for obtaining the precise location of an absorption line and the pressure broadening coefficients due to self-broadening or foreign gas broadening from experimental measurements using a laser operating on a single line near the absorption line. These absorption line characteristics are obtained from the pressure dependence of the transmittance of the laser radiation for the gas of interest, the analysis involving a least squares fit to a family of Lorentz curves. The method includes a computer search for the region of best fit to the Lorentz profile and provides both the values of and errors in the above coefficients. The pressure broadening coefficient obtained is the same as for the more general Voigt curve. The method is applied to the absorption line of vinyl chloride near 27.972 microm and of methane near 3.392 microm and the results compared with a graphical fit to a Voigt profile. The self-broadening coefficients obtained were alpha = 0.15 x 10(-3) +/- 0.97 x 10(-4) cm(-1) Torr(-1) for vinyl chloride and alpha = 0.14 x 10(-3) +/- 0.46 x 10(-4) cm(-1) Torr(-1) for methane. The separation between the helium-neon laser line at 2947.903 cm(-1) and the methane absorption line at 2947.888 +/- 0.015 cm(-1) was found to be 0.21 x 10(-2) +/- 0.15 x 10(-2) cm(-1).

Design of an Electroocular Computing Interface

The human retina consists of an electrically-charged nerve membrane. This potential is a constant value for a given adaptation without stimulation; it is the retinal resting potential. The retinal resting potential causes an electric field around the eyeball, centered on the optical axis, which can be measured by placing electrodes near to the eye. As a result, the motion of the eye causes a measurable change of DC voltage between the surface electrodes. The same vector coordinate system employed in the modern computer mouse may be adapted for use with our electro-ocular interface. Such a device would provide a relative position of gaze and have application in both hands-busy and assistive research. The theory behind our device, hardware design, the experimental results, and efficacy of the system are presented

Data acquisition system for the measurements of corona currents

The measurements of voltage-current relationships in gas discharge systems often require special equipment not readily available on the market. In the presented study, a data requisition system is described, which was used for the measurements of corona currents in a pin-plane corona generator of the array type, with pins negative. The pins were made of tungsten and were arranged in two rows. The ground plane was planar, made of aluminum, and equipped with circular current-sensing electrodes made of brass and insulated from the planar anode with teflon rings. Each of the sensing electrodes was connected to 50 k/spl Omega/ resistor. The voltage across each of the resistors was measured with an operational amplifier circuit. The output of the operational amplifier was connected to an electronic scanner, the output of which was used as the input for a microcontroller (HC11, Motorola). The microcontroller was connected via the RS 232 link to an interfacing board inserted into the PCI bus of a personal computer. The computer provided a graphical user interface was used to store and process the collected data, and supported the popular data processing programs. The system allowed the measurements of the current magnitudes on up to sixteen corona pin, simultaneously. The computer interfacing board can parse the data into up to eight separate data streams. The data acquisition unit can be configured to operate with four, eight, or sixteen input channels, trading their number for the sampling rate and frequency response in three steps: 4 channels, 16,000 samples.s/sup -1/; 8 kHz; 8 channels, 8,000 samples.s/sup -1/, 4 kHz; 16 channels, 4,000 samples.s/sup -1/, 2 kHz. In the described experiment, the system was set to sample four simultaneous data streams and provided adequate response. The system operated at the same ground level as the high voltage ground. The cost of the parts used in the unit is approximately fifty dollars. With an appropriate set of sensors, the unit can be used in other high voltage applications.

Investigation of the optical and electrical characteristics of a spark gap

A spark gap apparatus and a high speed optoelectronic measurement system were used to examine the optical and electrical characteristics of spark discharges. Parameters studied included the magnitude and polarity of the discharge voltage, gap length and the impedance of the discharge circuit. Analyses were performed to compare the measured optical signatures as a function of the discharge current. Results of the experimentally measured parameters compare well with theoretically computed values. The work has application in the study of electrostatic discharge (ESD) events.

A method for determining electric parameters of multibody configurations

A method for solving the two-body, ground-plane problem is described. The method yields the capacitances in the system, which are calculated by iteration using the method of electrostatic images. Although the result is rendered in the form of an infinite series, a low number of terms is sufficient to produce reasonably accurate results for the systems capacitance. The minimum surface-to-surface separation of the bodies controls the number of terms required and, hence, the computation time needed for achieving a desired accuracy. The size of the spheres is not especially important; the decisive factor is the separation between bodies. The calculated results agree within 10% with measurements of systems consisting of two bodies and a ground plane and are qualitatively comparable to those obtained for a somewhat similar three-body system. The method can be used in calculations of susceptibility to ESD of electrical and electronic systems. >

Carbon dioxide absorption of He–Ne laser radiation at 4.2 μm: characteristics of self and nitrogen broadened cases

A laser resonance absorption spectrometer is used to investigate the characteristics of both self and nitrogen collision broadened carbon dioxide in resonance with He-Ne laser radiation at 4.2 microm. The absorption coefficient in these broadening conditions has contributions from the R(28) to R(34) absorption lines of the nu(3) CO(2) spectrum. The Fletcher-Powell optimization method is used to reduce the raw absorption data and to find the best value average collision broadening coefficient and laser emission frequency for a Lorentzian line shape model of the contributing lines. Pure carbon dioxide absorption in a pressure range of from 0.0016 atm (1.25 Torr) to 0.33 atm (250 Torr) is described well by the model with an average self broadening coefficient of 0.084 +/- 0.008 cm(-1) atm(-1) for laser frequencies located at either 2370.591 +/- 0.020 cm(-1) or 2371.135 +/- 0.019 cm(-1). Nitrogen broadened carbon dioxide in the total pressure range of from 0.13 atm (100 Torr) to 1.18 atm (900 Torr) is characterized by the same model with the laser frequency at 2371.102 +/- 0.007 cm(-1) atm(-1). The average absorption coefficient for low concentrations of carbon dioxide in a 1-atm total pressure nitrogen environment has been determined experimentally as 9.90 +/- 1.49 cm(-1) atm(-1). All the listed results are at 296 K.