Showing papers on "Rise time published in 1973"

High‐gain imaging electron multiplier

Abstract: The chevron‐shaped channel electron multiplier is a device which combines the high‐gain pulse‐counting operation of single channel electron multipliers with the imaging capabilities of microchannel arrays. It produces charge pulses averaging more than 107 electrons and these gain magnitudes fall into a quasi‐Gaussian distribution with a full width at half‐maximum FWHM of approximately 130%. Suppression of ion feedback makes possible both imaging and low noise counting applications over large areas. Dark count rates are typically 1 count/sec cm2, and the dynamic range of operation covers 5–6 decades. Active areas over 45 mm diam have been fabricated, with uniform characteristics. Limiting resolution has been measured at 5 line pairs per millimeter. Because of the short length of each channel electron multiplier, the rise time and width of the output charge pulses are extremely short; large signal pulses have been detected with rise times as short as 400 psec.

Capacitive transistorized signaling device

Abstract: An electronic device incorporating a circuit for providing a signal with respect to an on or off mode dependent upon the degree of capacitance. The invention comprises a first and basic embodiment utilizing a signal source having a slope of a step function or specifically one having a fast rise time initiated for example by a clock element. The operative signal criteria demands that the length and slope thereof respectively have an effective amplitude and an effective frequency compatible with the circuit components. The signal source is fed to a transistor or suitable amplifier having its base connected to a capacitance sensing means. Resistors are provided for appropriate biasing, current limiting and drain functions as well as capacitors for capacitance balancing purposes. The capacitance sensing means can comprise a touch switch which when touched has its capacitance increased causing the device to function. The transistor or amplifier is connected to a load so that when a change of capacitance is sensed, the change will be registered. Other embodiments can incorporate differential amplification means and means to drive the active components with the voltage of the signal source or the clock voltage. Alternative embodiments of this invention incorporate capacitance sensing means in the form of transducers which can operate in a linear or a sequential mode. The transducers functionally incorporate a change of capacitance by means of moving mechanical elements so that when such change in capacitance is detected by the circuit it will provide an on or off sensing for the circuit or an analog of the change in capacitance. Thus, a reading of the extent of mechanical movement of a mechanically moving object can be transduced into an electrical function or output having substantial linearity. In summation, the circuit of this invention can be used for a transducer, or a solid state switch.

Method and apparatus for producing isolated laser pulses having a fast rise time

Abstract: Disclosed herein is a laser oscillator system which provides laser pulses having a characteristically short rise time and high energy content. A laser oscillator is Q-switched to produce short duration pulses of radiation and a small amount of each pulse is tapped off to trigger a spark gap discharge in an electro-optic modulator. A pair of polarizing elements and the modulator are located along the axis of the optical cavity in the oscillator. With selective activation of the modulator, the polarizer elements interrupt the resonant reflections of the optical flux between the mirrors defining the oscillator and the Q-switched pulse energy is rapidly dumped from the cavity as fast rise time pulses.

Fast spectrophotometric detection system for coupled physical and chemical electric field effects in solution.

Abstract: A fast spectrophotometric detection system is described which extends the electric field jump relaxation techniques to complex systems of biochemical and molecular biological interest. In these systems chemical relaxation, which yields a concentration change, is accompanied by physical relaxation which is mainly due to orientation processes. The simple versatile set-up allows the measurement of the different effects using only one piece of apparatus with a transmission path and two emission channels, which can all be equipped with polarizing elements. The high intensity optical system and the low noise optoelectronic circuits result in an attainable signal-to-noise ratio of 1000∶1 for transmission measurements with a rise time of the order of 10 nsec and 100∶1 for fluorescence measurements with a rise time of 50 nsec.

Dielectric Breakdown in Perspex

Abstract: Experiments have been carried out to investigate the breakdown mechanism in Perspex over a temperature range from 20 to 160°C, using impulse voltages of widely differing rise times. The electric strength was found to be sensitive to voltage rise time, reaching a maximum as the rise time is increased, but falling again at longer rise times towards the dc value. The results are discussed in terms of a model in which space charges accumulate at the electrodes, positive charges at the anode, and negative charges at the cathode.

Temperature dependence of the pyroelectric voltage response to step infrared signals in triglycine sulphate

Abstract: An expression is derived for the pyroelectric (PE) voltage response to step radiation signals which can be applied up to temperatures close to the Curie point Tc under a ``small‐signal'' condition. Based on the Curie‐Weiss law and the thermodynamic theory of a second‐order ferroelectric transition, a discussion is given of the temperature dependence of the parameters of the PE voltage response: initial slope, peak value, rise time, and fall time as functions of sample parameters and load resistance. It is found that the PE voltage may reach a maximum close to Tc, and expressions are derived for this value as well as for the temperature at which it occurs. These results were checked in detail on 12 samples of single‐crystalline triglycine sulphate for temperatures from 20 °C to the Curie point, and good agreement between theory and experiment was observed. The application of the results to PE detection of ir is considered.

Optimum design of electron beam-semiconductor linear low-pass amplifiers—Part II: Output capabilities

Abstract: This paper presents a simplest case analysis of the peak quasi-static output capability of a linear lumped-target beam-semiconductor amplifier. The basic assumptions in the response analysis of Part I [1] are used, together with the premise that the semiconductor velocity-field characteristic exhibits strong saturation at fields well below avalanche breakdown. The analysis applies to the ultimate pulsed output at low duty cycle since thermal effects are not considered. The fundamental current and voltage limitations on target output are discussed separately in limiting cases, and it is shown that the linear output capability is determined jointly by the drift-region width, bias field profile, and avalanche multiplication constraint. The dynamic electric field behavior is calculated for the general case where voltage and current effects appear simultaneously, and it is shown how the output capability can be maximized for a given target area and load impedance by proper choice of drift-region width and doping level. The ultimate pulsed dc output current, voltage, and power levels are evaluated for semiconductor targets in terms of the target area, load impedance, carrier drift velocity, semiconductor band gap, and avalanche multiplication constraint. Detailed numerical predictions are given for silicon targets. The usefulness of the quasi, static analysis is discussed, and it is shown that the results obtained apply with minor modification to the case of step-function excitation. In conjunction with the results of Part I, the combined gain, rise time, and pulsed output power performance boundaries are established for the basic lumped-target beam-semiconductor amplifier. The feasibility of a subnanosecond-rise-time linear amplifier with 50-dB gain and a multikilowatt pulsed output level is shown. Various semiconductor materials are evaluated for application in a beam-semiconductor amplifier by examination of an overall figure of merit comprising gain, rise time, and peak output capability, and it is demonstrated that Si, Ge, and GaAs are nearly equal in overall merit. In conclusion, several novel devices are described that illustrate the adaptability of the electron beam-semiconductor concept to multiple-signal amplifiers, fast waveform sampling, and traveling-wave amplification.

Transient current overshoot to electrostatic probes in continuum, slightly ionized plasmas

Abstract: A spherical probe is subjected to a potential ramp with rise time of the order of the electron diffusion time, after which, the final potential is maintained constant. The electron current overshoots its final value by an amount proportional to the electron conductivity.

Optimum design of electron beam-semiconductor linear low-pass amplifiers—Part I: Bandwidth and rise time

Abstract: This paper begins with a brief description of the basic electrical characteristics and principles of operation of the lumped-element electron-beam-excited-semiconductor amplifier. It is shown that stable current gains of several thousand may be obtained through the interaction of a 10-keV electron beam with a shallow reverse-biased p-n junction device (semiconductor target). Simplest case analyses of the transient-response rise time and RF gain and bandwidth are presented for an idealized nondistributed target structure, using the assumptions of shallow beam penetration across the drift region, carrier transport with a constant velocity, and a resistive load impedance. The dynamic response is shown to be determined jointly by the carrier transit time and the target capacitance in such a way that it is possible to optimize the target rise time or bandwidth by appropriate choices of drift-region width. The optimum drift-region width and the ultimate rise times and bandwidths are evaluated in terms of the target area, load impedance, carrier drift velocity, and semiconductor dielectric constant. It is shown that lumped-element semiconductor targets can readily be designed for subnanosecond rise times and broad bandwidths without compromise of the high current gain possible in these devices.

Performance of electron beam-semiconductor amplifiers

Abstract: Experimental results obtained with developmental electron beam-semiconductor devices used as video-pulse and RF pulsed amplifiers are discussed. These devices employ a grid-modulated electron beam to control the current in a semiconductor target. Power gains of 26 dB and peak pulse powers of 40 W were obtained at up to 600 MHz with an untuned output impedance of 20 Ω. Peak powers in excess of 30 W were obtained at 600 MHz with a 50-Ω load. Power gains of 20 dB were obtained at up to 860 MHz for both output impedances. Also described is the performance of a video-pulse amplifier with a peak power of 2 kW and a rise time of 2 ns. The experimental results are compared to the theoretically predicted values. A problem of diode deterioration encountered with these developmental devices is discussed and solutions to the problem are presented. The reverse breakdown characteristic of both nonpassivated mesa diodes and silicon dioxide passivated planar diodes using "p on n" material decreased by over 50 percent during the first few hours of operation. "p on n" diodes with phosphorous glass over the silicon dioxide have been operated up to 59 h with little deterioration, and a planar diode with "n on p" construction has been operated satisfactorily for 1000 h.

The design and coherence properties of a simple N2 laser

Abstract: A compact electrical pulse circuit suitable for exciting pulsed gas lasers has been developed. The advantages are the low input voltage (10-20 kV) and the possibility of an output voltage of more than 100 kV. The rise time was found to be less than 10 ns. The design is described and has been used to excite a nitrogen laser. A maximum output power of 500 kW (pulselength 5 ns) with a repetition rate of 1 Hz was achieved from a 36 cm long tube, 6 mm diameter. When the repetition rate was 100 Hz the output power was about 50 kW. The spatial and temporal coherence was also studied. It was found that the spatial coherence existed over the whole cross section of the beam. By operating the laser below the saturation level and introducing mirrors the pulse length could be changed in the range 4-10 ns. The time coherence was approximately equal to the halfwidth of pulse. The beam divergence was improved by a factor of 1o by using a complete cavity instead of a single rear mirror.

A Magnetic Beam Position Monitor

Abstract: We give the theory and describe the execution of the magnetic beam position monitors in use in the AGS injection line. These are strictly linear devices of very low impedance with a rise time of the order of 1 ?sec. They do not require electronics close to the device and have been constructed to withstand considerable radiation. Their construction is simple and not critical.

The Effect of A.C. Bias Fields on the Impulse Strength of Point-Plane and Sphere-Plane Gaps

Abstract: Present laboratory impulse tests do not simulate the large power-frequency voltages which may be present in practice. Experiments up to 850 kV (impulse) show that such bias fields have no significant effect on impulse breakdown. The 50% breakdown strength for both fast "lightning" impulses (1.7 As rise time) and for slower "switching" impulses (80O?s rise time) was measured on 1.75 m point-plane and sphere-plane gaps with bias voltages from zero up to 200 kV r.m.s. and at various points-on-wave. A laser triggered gap was used to protect the impulse generator from the power frequency voltage.

Transient space-charge phenomena in semiconductors at high electric fields

Abstract: The transient response of trap-free semiconductors subjected to a voltage step function and unipolar injection of charge is analyzed for the case that the velocity of the carriers is a non-linear function of the electric field The method of characteristics is used to evaluate current, density and field profiles as functions of time Numerical results are presented for the case of n -Si These results show that there is a sharp bunching of charge accompanying the cusp This bunching of charge is shown to be a consequence of the decreased differential mobility at high fields These results are compared with the previously published results for a constant mobility case A simple model is used to derive exactly the results for a saturated-velocity transient It is shown that the numerical results for the actual case of non-linear velocity fit well between the results for these two limiting behaviors for the velocity-field curve Effects of a finite rise-time in the voltage pulse are also studied It is shown that a significant rise time can considerably reduce the sharpness of the current cusp

Rise time of emitter-coupled logic circuits including the effects of collector-to-base capacitances

Abstract: Rise times of emitter-coupled logic circuits are computed, taking into account collector-to-base capacitances as well as gain-bandwidth products, ohmic base resistances, external stray capacitances, and the finite rise time of the input signal. Basic considerations are discussed, and explicit expressions and graphs are given for a wide range of circuit parameters.

Impulse rise and fall times of biplanar vacuum photodiodes.

Abstract: The impulse rise and fall times of biplanar vacuum photodiodes are experimentally investigated by the use of a single ultrashort laser pulse from a train of mode-locked pulses. It was confirmed that the impulse rise time is a function of the photoelectrons' transit time from photocathode to anode, and that the impulse fall time is 2.2 times the capacitance of the photodiode and the resistive component of the load.

Air spark fiducial for ultra‐high‐speed photography

Abstract: A triggered air gap has been developed for inserting timing marks on the film of streaking cameras used in ultra‐high‐speed photography. The gap has a rise time ten times faster than existing xenon flashlamps. The peak output of 7 × 106 cd/cm2 (7Mcd/cm2) achieves the same film density as the lamps. This paper describes both the design used to achieve low inductance in the gap and the driving circuitry.

Effect of laser pulse rise time on heating of a magnetically confined plasma

Abstract: For a magnetically confined plasma the effect of laser pulse rise time on heating is considered theoretically. The hydrodynamic equations are solved analytically in the asymptotic limit. We find that for a certain range the laser pulse energy requirement is quite sensitive to the rise time. By properly choosing the laser pulse rise time, the energy requirement can be decreased as much as 25%. The maximum radiation flux density is however not very sensitive and increases only slightly. It seems that fast‐rising laser pulses are superior as far as flux is concerned but are inferior to slow‐rising laser pulses from the point of view of energy requirement.

Gigahertz-rate 100-V pulse generator

Abstract: A high-density electron-hole plasma generated within a high-efficiency avalanche diode induces a sharp, high-voltage pulse on a transmission line. A novel gigahertz-rate pulse generator has been constructed utilizing the high- efficiency microwave avalanche diode. An impedance discontinuity within the circuit gives rise to a sharp pulse with undistorted waveform, which keeps retriggering the diode for a self-excited pulse generation. The peak- to-peak amplitude of the pulse is 125 V into a 50-/spl Omega/ load. The pulsewidth is 400 ps, the rise time 100 ps, and the fall time 200 ps.

Optimization of delay and rise time in iterative multistage wide-band amplifiers

Abstract: A method is presented for the optimization of the overall delay and overall rise time in iterative multistage wide-band amplifier circuits. The method is applied to an amplifier consisting of emitter-degenerated stages with distributed ohmic base resistances and lumped collector-base capacitances. Explicit expressions are given for the delay and the rise time, and optimization criteria are presented in graphs suitable for use in circuit design.

Lower bounds for the settling time using Bernstein's theorem

Abstract: An easy-to-use formula is derived for measuring the response time of various systems. This formula also gives lower bounds for the settling time of the response for a very large class of input signals. Lower bounds for the rise time of certain responses have also been found.

Fast rise time quenching spark gap

Abstract: Electrically floating wire mesh or perforate plate electrodes are interposed between the two electrodes of a conventional spark gap, with interelectrode spacings from 0.010 to 0.005 inches. Rise times of the order of 2 nanoseconds with repetition rates up to 200 kHz are produced.