Showing papers on "Rise time published in 1974"

Short CO2 laser pulse generation by optical free induction decay

Abstract: Short CO2 laser pulses, adjustable in the range between 0.1 and 0.5 nsec, have been produced by a new pulse‐shaping technique. A laser breakdown spark is the active switching element, but the pulse is actually generated by optical free induction decay in a passive linear medium. This approach features simplicity, fast rise time, high contrast ratio, unity switching efficiency, and is suitable as the input to high‐power amplifier stages.

Time Domain Oscillographic Microwave Network Analysis Using Frequency-Domain Data

Abstract: Oscillographic plots of various time-domain responses of microwave networks are generated by computer simulation, based upon measurements taken in the frequency domain. Frequency-response data are obtained with a computer-controlled automatic network analyzer, this information is processed in an associated computer, and selected time-domain responses are plotted immediately on an x-y recorder. Voltage versus time responses have been simulated for various excitations includlng impulse, step, and pulse-modulated RF waves. When impedance data are used, the plots are interpretable as from a time-domain reflectometer with high precision, high sensitivity, and high resolving power. As an oscillograph the rise time may be as short as 0.04 ns. In transmission 70 dB or more loss can be tolerated. In reflection measurements, the results are interpretable for discrete discontinuities with 40 dB or more return loss, and with separations on the order of 1 cm in space. In certain types of circuits, time-domain data can be used to reconstruct the frequency-domain response data in an approximate manner for separate parts of a network without separate measurements. In this manner, the interference of generator, load, and transducer mismatches can be substantially reduced.

Picosecond semiconductor electronic switch controlled by optical means

Abstract: A microstrip transmission line on the surface of a photoconductive semiconductor medium has a small gap, thereby producing an open circuit between a microwave (or other electrical signal) source and a detector connected at opposite ends of the line. This gap is suddenly filled (and the microwave circuit thereby completed) by copious electrical charges which are generated in a semiconductor surface region across the gap, in response to a first pulse of optical radiation characterized by a picosecond rise time and by a wavelength which is substantially completely absorbed at the surface of the semiconductor medium. Accordingly, this first pulse produces a correspondingly sharp rise in the microwave energy (switch''''ON'''') reaching the detector. Within a few picoseconds thereafter (while the electrical charges due to the first pulse still persist), a second optical pulse, which is also characterized by a picosecond rise time but of a wavelength which is absorbed into the bulk of the semiconductor medium, is directed at the gap sufficient to increase significantly the conductance across the gap, thereby short-circuiting the microwave line to a ground plane on the opposed major surface of the semiconductor. Accordingly, the second pulse produces a correspondingly sharp decline (switch-'''' OFF'''') in the microwave energy reaching the detector from the microwave source.

Subnanosecond rise time pulses from injection lasers

Abstract: The hybrid integration of an injection laser with a simple avalanche transistor modulator is shown to produce optical peak powers of several tens of watts magnitude and pulse rise times appreciably shorter than 1 ns. In certain circumstances the pulse leading edge assumes the form of a spike having a displayed rise time of 120 ps.

Wide bandwidth solid state input buffer

Abstract: An input buffer circuit provides a series of output electronic pulses, substantially identical to each other and having relatively fast rise and fall times, even though the input pulses to the buffer may be unlike each other and have relatively slow rise and fall times. A first inverter receives and inverts the input pulses while a second inverter provides the uniform output pulses. A first latching circuit, comprised of a third and fourth inverter first opposes and then changes state to aid the inversion of a pulse by the first inverter resulting in a net speed-up of inversion. A second latching circuit first opposes and then changes state to aid the inversion, in the opposite direction, of a pulse by the first inverter resulting in a net speed-up of inversion in the opposite direction. The two latching circuits thereby provide an inverted pulse to the second inverter that has fast fall and rise time. This inverted pulse is nearly independent of the input pulse, except as to the triggering function of the first inverter, therefore, the pulses out of the second inverter are substantially identical.

Single-crystal electrooptic thin-film waveguide modulators for infrared laser systems.

Abstract: Wideband, low power electrooptic modulators of optical waveguide structure have been developed for infrared laser applications. They allow a reduction in driver power of two orders of magnitude below that of conventional devices. The modulators are composed of very thin layers of single-crystal GaAs, bounded on both sides by evaporated films of lower refractive index material: CdTe or As2S3. Minimum propagation loss, measured at 10.6 μm, was less than 1 dB/cm for TE modes and less than 5 dB/cm for TM modes. A 20-pF modulator exhibited a pulse response rise time of 3 nsec and showed useful frequency response to beyond 200 MHz. The basic capability for advanced design modulators of this type to operate at 10 μm with driver powers of less than 25 mW/MHz for 50% modulation depth is shown.

Electronic musical instrument capable of generating tone signals having pitch frequency, tone color and volume envelope varied with time

Abstract: An electronic musical instrument comprising a voltage controlled oscillator, a voltage controlled filter, a voltage controlled amplifier and envelope generators. An output envelope of the envelope generator has various parameters such as rise time and decay time or times. The envelope generator is of the voltage controlled type so that the parameters of the output envelope of the envelope generator are controllable in response to parameter controlling voltages from a parameter controlling voltage generator. In an attempt to enhance performance effects a switch circuit is provided, in accordance with the invention, to interchange between a rise time controlling voltage and a decay time controlling voltage which are both coupled from the parameter controlling voltage generator to the envelope generator.

Dependence of human brainstem evoked potentials on signal duration and rise‐fall time

Abstract: This report extends observations presented by Hecox and Galambos at the 1973 Los Angeles Meeting of this Society on the acoustical dependencies of the human brainstem evoked potential. We report here on the latency and amplitude dependency of wave V, the most reliably elicited response component, as a function of signal duration and rise‐fall time. Increasing the rise time of a 30‐msec noise burst produces a striking increase in response latency and no change in response amplitude. With rise time held constant, changing stimulus fall time alters neither response latency nor amplitude. Longer latencies and smaller amplitudes occur whenever stimulus duration (the ontime, 0.5–30 msec) increases with a silent period (off‐time) under 60 msec, and whenever off‐time shortens with on‐time held constant. The sensitivity of these responses to signal rise time, and their relative insensitivity to fall time and duration, demonstrate that the human brainstem evoked potential is an onset response.

Optimization of the Clipping Time Constant for BF3 Neutron Detectors Operated in a High Level Gamma Environment

Abstract: Radiation-hardened BF3 neutron detectors (proportional counters) have been selected for use as delayed neutron detectors in the failed fuel monitoring system of the Fast Flux Test Facility (FFTF) being constructed by the Westinghouse Hanford Company at Richland, Washington. These detectors must exhibit fpproximately 6 to 7 counts/sec (cps) per neutron/cm2-sec (nv) for neutrons while operating in a gamma environment of a about 1000 R/hr; thus, electronic counting systems capable of providing the best possible sensitivity must be used. In addition to exhibiting appropriate charge gain and sufficiently low noise, the preamplifier (or amplifier) must include at least one stage of differentiation to reduce gamma interference (pulse pileup) effects. The selection of the time constant depends on the rise time of the neutron-caused pulse from the BF3 tube and on the maximum gamma level in which the tube must operate. The conflicting requirements of large time constant to maintain pulse amplitude and small time constant to reduce gamma effects lead to an optimum value to achieve the best possible neutron detection sensitivity.

High current, fast turn-on pulse generation using thyristors

Abstract: The dynamic turn-on characteristics of inverter type SCR's can be employed to achieve high current densities with short rise times (106a/cm2µs). Little carrier modulation occurs during these turn-on times which results in large forward voltage drops. Resultant dissipations necessitate short pulse width operation but repetition rates up to 50KHz are reported. By comparing turn-on voltage waveforms of specially developed 35A (rms) devices when gate and dv/dt triggered, it was concluded that about 50% of the gate triggered emitter area is effective during the rise time interval. These devices were life tested and should prove usefull as modulators for radar or GaAs injection laser applications. It was determined that the properly designed SCR could out-perform all of the functions served by: 1) Avalanche transistors in laser pulsers, 2) Hydrogen thyratrons, ignitrons and spark gaps in radar modulators and, 3) High speed (turn-on) switching transistors where turn-off is not critical.

A Fast Response Surface Thermocouple

Abstract: A fabrication technique is described for a cheap, robust surface thermocouple having a rise time of the order of 5 μs. Experimental results using the thermocouple are also presented.

Pulsed Optical and Electron Beam Excitation of Silicon Position Sensitive Detectors

Abstract: Silicon two dimensional position sensitive detectors were fabricated by ion implantation and their response to pulsed electron beam and optical excitation was determined. The results of measurements of rise time, position resolution, linearity and current gain as a function of electron accelerating voltage are presented. It is shown that the gain-voltage curves are consistent with a model incorporating a thin (?0.5 ?m) dead layer at the surface of the detector.

A simple method for the generation of a step magnetic field with short rise time

Abstract: Presents a simple method of generating a step magnetic field with very fast rise times for the test of square loop magnetic cores The main components used are a conventional constant direct current supply, an inductor coil and mercury relays The device generates a step field, the rise time of which is of the order of 10 ns The performance of the device shows good results in the experiment on flux reversal of magnetic cores

Constant rise time controller for current pulse

Abstract: A circuit that ensures that the rise time of the leading edge of a temperature-compensated word drive current pulse is constant irrespective of drive current pulse amplitude variation with temperature is disclosed. The circuit samples a variable amplitude reference voltage that is generated by a temperature sensor located in a magnetic memory, such as a core, film or plated-wire memory stack, and generates a correspondingly variable amplitude drive current pulse. The circuit includes a current-mirror comprising two directly-coupled-base transistors to ensure proportional current amplification as required by an associated RC charging circuit that controls the drive current pulse generating output transistor. The proportional current amplification provides the necessary variation in the charging current to fully charge the charging capacitor over the same duration irrespective of drive current pulse amplitude. A pre-charging transistor also ensures rapid turn-off of the output transistor to maintain an abrupt trailing edge of the drive current pulse.

Electro-erosion machine wiyh controlled current discharge - using sequential transistors for current pulses with inclined wavefront

Abstract: In an electro-erosion machining process controlled discharge current pulses are applied intermittently to the working gap between electrode and workpiece by an assembly of semiconductor devices. The current pulses differ from the conventional square pulses by having an inclined wavefront. The inclined wavefront is produced by successive switching of the semiconductor devices in a programmed sequence and in certain intervals. The rise time of the discharge current pulse is adjusted to 0.5-1.0 mu per A depending on the peak value of the current pulse. This reduces the electrode consumption to a min. and ensures a stable operation without making excessive demands on the skill and experience of the operator.

Berechnung der Aufbauzeit eines doppeltresonanten optischen parametrischen Oszillators

Abstract: The rise time for the output power of a doubly resonant optical parametric oscillator with ring resonator configuration is calculated for the special case of subharmonic generation. It is shown that the rise time decreases by increasing the pumping level (for a constant threshold power) and, for a constant pumping level, by increasing the resonator loss.

Means and method for transmitting a high count rate pulse signal over a common well logging cable

Abstract: A conventional type radiation detector in cooperation with a photomultiplier tube provides data pulses of one polarity, corresponding in peak amplitude and number to detected radiation in a borehole traversing an earth formation. Each data pulse is effectively converted to two pulses of different polarities, with one pulse starting when the other is completed and transmitted over a common well logging cable. The creation of a second pulse of an opposite polarity cancels out the low frequency component of the pulse so that they arrive at the surface as a pulse of a single polarity having a very short tail and a fast rise time. This permits more pulses to be transmitted within a given time period than heretofore existed. Surface electronics process the transmitted pulses to provide a record of the sensed condition in the borehole.

Once More the Two-Stage Cathode Follower

Abstract: The article describes a new method of calculating the amplification coefficient of cathode followers and states expressions for calculating the rise time of cathode followers. Experimental results are given.