Showing papers on "Pulse duration published in 1969"

Backward Stimulated Raman Scattering

Abstract: This paper describes in detail the initiation and growth of backward-traveling stimulated Raman-Stokes pulses. The radiation-transfer equations for the pulse development are derived, and a general analytic solution is given in the rate-equation approximation. Special solutions are given for a variety of pulse-initiation conditions. It is shown that in the presence of residual linear absorption, a steady-state Stokes pulse is expected, and its characteristics are described. Extensive experimental observations in C${\mathrm{S}}_{2}$ of the properties of the backward pulse and the forward emission are reported, including measurements of the pulse energy as a function of position in the cell, the pulse duration as measured by the intensity-autocorrelation technique, and the time sequence of the emission of the forward and backward pulses. Various experimental results indicate the dominant role played by self-focusing in the initiation of the backward pulse and the role of competing processes. The growth of the pulse energy is found to be consistent with the theory; a minimum pulse duration of 30 psec and a peak pulse power 20 times the instantaneous laser pump power are reported, indicating substantial depletion of the incident laser pump light.

A study of the parameters of electrical stimulation of unmyelinated fibres in the pituitary stalk.

Abstract: 1. The milk-ejection response in lactating rabbits has been used to study the effect of electrical stimuli of different types applied to the supraopticohypophysial tract in the pituitary stalk. 2. Sine-wave alternating-current pulses were compared with balanced biphasic square-wave pulses of the same frequency and peak-to-peak current strength. At a pulse duration of 2-4 msec the square-wave stimulation was less effective than the sine wave, but at a pulse duration of 8 msec and over, more effective. 3. Above threshold levels of 0·12 mA for the current strength, and of 0·5 msec for the pulse duration, the response increased with increasing current strengths to 2·4 mA and increasing pulse durations to 10 msec. 4. With constant and effective strength and duration of the pulse a slight diminution of the response was seen as the frequency was diminished from 100/sec to 50/sec. Further diminution in the frequency revealed that at some point between 50 and 10 c/s a sudden abrupt diminution in the magnitude of the responses occurred over a small range of frequency. This was a reversible phenomenon and it is suggested that it may be related to neurosecretory events occurring in the nerve terminals. 5. Stimuli with parameters within the ranges mentioned above are effective in eliciting an oxytocic response on the uterus in the rabbit and ovulation responses (when applied to the hypothalamus) in rats and rabbits. It appears likely that stimuli with such parameters are suitable for experiments concerned with stimulation of the hypothalamus.

Efficient Second‐Harmonic Generation with Diffraction‐Limited and High‐Spectral‐Radiance Nd‐Glass Lasers

Abstract: Efficient second‐harmonic generation (SHG) at 5300 A has been achieved with KDP and LiNbO3 crystals when Nd‐glass lasers of high radiance and narrow bandwidth were used. With KDP and a diffraction‐limited laser system having a 19 A bandwidth, 15 J of radiant energy at 5300 A were obtained with a 51% energy‐conversion efficiency. Since the harmonic light pulse was narrower than the fundamental pulse, the peak‐power‐conversion efficiency was 70%. The peak power in the green was 1.0 GW. The ratio of harmonic‐fundamental pulse duration increased as SHG increased into the saturation region as expected. For LiNbO3, the relatively large dependence of phase‐matching angle on wavelength limits the maximum SHG efficiency to several percent when broad‐band lasers are used. With LiNbO3, therefore, a laser system was used having mode selectors which limited the bandwidth to less than 0.5 A while the beam divergence was 1.5 mrad. In this case 21% energy conversion and 33% peak‐power conversion were obtained with a fundamental flux density of only 2 MW/cm2 inside the crystal. The values found for the elements of the nonlinear dielectric tensor, corrected for the random multimode nature of the laser, are d36(KDP) = (1.1±0.1)×10−9 esu and d31(LiNbO3) = (17±6)×10−9 esu. At low conversions a laser beam with fluctuations due to random multimoding is expected to give as much as twice the harmonic produced by a single‐mode laser. At high conversions in the saturation region this ``doubling'' does not occur as verified by our measurements.

Pulse risetimes in proportional counters.

Abstract: We present a method of calculating proportional counter pulse shapes for both point and extended ionization tracks. The method is applicable to any counter gas for which the electron drift velocity as a function of the electric field is known. The mobility of the positive ions that are responsible for pulse formation is a parameter of the theory. If we assume there is only one species of positive charge carrier, we can identify it by measuring counter pulse shapes for point ionization tracks and comparing them to calculated pulse shapes. The theory is consistent with measurements of actual pulses in four counter gases: 90% Ar‐10% CH4, 90% Ar‐10% N2, 90% Kr‐10% CO2, and 90% Xe‐10% CO2.

Electrical Pulse Breakdown of Silicon Oxide Films

Abstract: Pulse breakdown tests on individual specimens with self‐healing breakdowns resulted in information on both the thermal and the electric breakdown properties. Thermal breakdown due to Joule heat was found to occur nearly uniformly over the whole specimen at voltages generally lower than the electric breakdown. voltages. Calculations with relations derived for the thermal breakdown field agreed well with observations showing increase of breakdown field with decreasing pulse duration. Electric breakdown was found to be a chance event producing breakdown holes tens of microns in diameter. The process was interpreted to consist of three consecutive stages: (1) the field produces a very small charge pulse causing a temperature rise of a few hundred degrees centigrade in a breakdown channel; (2) this induces thermal runaway in the channel; and (3) the energy stored in the specimen discharges through the channel causing destruction. The magnitude of the charge pulse, duration of the process, and the size of the b...

Relativistic Beaming of Radiation from Pulsars

Abstract: THE observation that the pulsar CP 0328 radiates single pulses which seem to be basic elements of the total radio radiation, and which are highly polarized1, led at first to the suggestion that the mechanism of radiation was that of synchrotron radiation, forming a beam of radiation which swept across the observer as the source rotated. The shape of the elementary pulse, and the pattern of polarization across the pulse, were seen to be very similar to the angular distribution of radiation from a highly collimated beam of electrons, and it was suggested that the ratio of the pulse duration of the period of the pulsar provided a measure of the beam width of the radiation, and hence a measure of the energy of the electrons. On this hypothesis the width and polarization of the pulse would be expected to change with radio frequency. We have now looked for any such change in the elementary pulses from CP 0328, and we find none.

FREQUENCY PULLING AND PULSE POSITION MODULATION OF PULSING cw GaAs INJECTION LASERS

Abstract: The frequency pulling and locking of intensity pulsations from continuously operating GaAs injection lasers have been studied by varying the frequency of the externally applied locking signal in the vicinity of the self‐induced pulse rate or one of its harmonics. The ability of the laser pulse rate to follow a rapidly varying locking signal has led to the first realization of optical pulse position modulation with microwave repetition rates. Modulation rates attainable with this effect are expected to be as high as one‐half the self‐induced pulse rate.

Pulsed gas ion laser

Abstract: AN ARRANGEMENT FOR PULSING A GAS ION LASER AT RELATIVELY HIGH PRESSURE BY SUPERIMPOSING UPON A STEADY CURRENT SUFFICIENT TO ESTABLISH ION DISCHARGE IN THE POSITIVE RESISTANCE RE- GION BUT BELOW THE LASER THRESHOLD, A HIGH CURRENT PULSE OF VARIABLE PULSE LENGTH.

Velocity Modulation System for Enhancement of 50 Picosecond Radiation Pulse

Abstract: Radiation pulses 50 ps in duration have been attained at the EG&G/AEC electron linear accelerator by isolation of individual microstructure groups of electrons which normally occur at the fundamental accelerating frequency. Pulse compression by means of velocity modulation techniques has been used to increase the intensity of these pulses from 0.02 nC to 1.5 nC per pulse, or 30 A for the 50-ps pulse length. The injector pulse is synchronized to the RF acceleration frequency with a precision of 30 ps, which results in pulse-to-pulse reproducibility to within a few percent, permitting recurring pulse measurements to be made with sampling oscilloscopes. These intense short bursts of radiation allow the study of radiation detectors, scintillators, and chemical systems in the subnanosecond time domain. Neutron time-of-flight measurements with a total resolution of 400-500 ps have also been demonstrated. The calculated charge enhancement resulting from velocity-modulation bunching is compared to measured performance, and the system is described in detail.

Pulse stretching utilizing two-photon-induced light absorption

Abstract: The effect of inserting an element exhibiting induced absorption into a Q -switched laser cavity is investigated theoretically and experimentally. The rate equations are solved assuming two types of nonlinear loss, one being proportional to the square of the laser intensity and the other being proportional to the product of laser intensity and density of excited electrons in the nonlinear absorber. Experiments are performed with a rotating-prism ruby laser with a CdS crystal in its cavity. It is established that two-photon absorption takes place, and as predicted by the theory that the output intensity and output energy both decrease and pulse length increases as compared with the normal Q -switched case. In addition, the output pulse has an oscillatory behavior, and it is suggested that this is caused by loss due to the excited electrons, which are found to have a lifetime of approximately 24 ns.

Digital-to-analog converter utilizing pulse duration modulation

Abstract: Described is a novel digital-to-analog converter employing pulse duration modulation techniques, and wherein the desired analog signal is derived by integrating pulses of short duration and relatively high repetition rate rather than longer pulses of lower repetition rate. This materially reduces the ripple content of the filtered pulses and reduces the requirements of the lowpass filter connected to the output of the converter.

Electronically controlled fuel injection arrangement for internal combustion engines

Abstract: A fuel injection arrangement for internal combustion engine in which one monostable multivibrator provides a pulse the duration of which is determined by a temperature-sensing device thermally coupled to the engine. The pulse duration of this monostable multivibrator is also a function of a pressure within the intake manifold of the engine. A second monostable multivibrator with the pulse being controlled by the first multivibrator has a pulse duration determined by a second and separate temperature-sensing device at a different location from the first temperature-sensing device. The quantity of fuel injected is determined by the combination of the pulse durations of the two multivibrator circuits.

Time limited impulse response antenna

Abstract: An antenna for producing an output pulse of desired duration in response to an impulsive wave front includes a resistive plate mounted above a ground plane. A coaxial transmission line projects through the ground plane so that its center conductor contacts the resistive plate and its outer conductor terminates flush with the ground plane. The resistive plate consists of a submicron film of resistive material deposited on a dielectric backing and is spaced from the ground plane at a distance approximating the distance travelled by an electromagnetic wave in a time equal to the desired pulse duration.

Bias circuit oscillations in Gunn devices

Abstract: A theoretical and experimental study of low-frequency oscillations in the bias circuit of short (nominally 12 µ) Gunn devices is presented. Sinusoidal oscillations and relaxation oscillations including damped sinusoids and exponentially decaying pulses have been observed. The frequency, pulse width, and repetition rate are adjustable with bias voltage, bias circuit impedance, and the impedance of the microwave circuit. This behavior, as well as the conditions for stable bias, is explained in terms of an average terminal i-v characteristic for those devices which exhibit a terminal current drop. The oscillation amplitude is determined by the shape of this i-v curve. Pulses have been observed with subnanosecond rise times, peak voltages of 35 volts and adjustable pulse widths ranging from 3 to 200 ns for typical driver pulse widths of 100 to 500 ns. The sinusoidal frequencies were adjustable in the range of 300 to 550 MHz. The microwave output was in X-band and was self modulated by the bias circuit oscillations. The measured waveforms agree well with theory.

Design and performance of photo-cell systems for pulsed laser power and energy measurements

Abstract: The optical and electrical problems in the design of a beam-sampling detector for laser power, energy and pulse duration measurements are discussed with a view to achieving an accuracy of 2% relative to a fundamental detector for pulses down to 3 nsec duration. Experiments show that a beam sampler using an ITT F4000 biplanar vacuum cell mounted in a coaxial taper is capable of this accuracy, but that the silicon diodes (EG + G SD100, Mullard BPY13A) trap some of the photoelectric charge and then release it with a time constant of up to a few microseconds giving a pulse length-dependent sensitivity: they can be used for energy measurements, however. The Mullard 90CV vacuum photo-cell holds back about 6% of the photo-electric charge for about 1μsec and can also give erratic currents up to ten times the computed saturation current: effects probably due to residual gas in the cell. The limits set on performance by the rise time and maximum linear current of the various detectors are discussed. The design of a holder for the ITT F4000 photo-cell giving a rise time constant of 0.25 nsec is given.

Device for making predictions and corrections from radar data

Abstract: A device for making predictions and corrections in azimuth and a given second coordinate (particularly the range) of a target to be tracked from video signals detected by a pulse radar apparatus. In such a device a varying number of bits is written in a buffer register for each detected video signal. The number of storage elements of that register correspond with the number of increments into which the measuring range is divided. These increments are shorter than the pulse duration. The contents of the register are placed in the store of a computer during each transmitter pulse interval. The real target position is obtained by selection of a group of bits from the total of bit positions as written in the store during consecutive transmitter pulse intervals and by logically processing said group of bits.

Analog signal modifying apparatus

Abstract: In an electrolytic paper recorder of electric signals, an analog signal is converted by a voltage controlled oscillator to a series of pulses with rises spaced in inverse proportion to the analog signal amplitude. The spaced rises trigger a pulse generator whose output is a corresponding series of constant amplitude marking pulses with a spatial density proportional to the original signal amplitude. The marking pulses are applied to the blade and helical electrodes of the recorder through a current starved amplifier which adjusts the pulse amplitude to compensate for random variations in the resistance of the electrolytic recording paper between the marking electrodes. The width of the marking pulses may be varied by a variable current source for the pulse generator so as to compensate for the nonlinear gamma characteristic of the paper.

Pulse rate counter and display and method of operation

Abstract: A pulse rate counter and display applicable for indicating pulse rate of the human body. A counter is advanced at a preset clock rate to measure the time duration between two consecutive pulse beats. Appropriate circuitry determines within which of a group of pulse rate ranges this measured time duration falls. The minimum time per pulse for the determined group is set into the counter and the counter decremented to zero at the preset clock rate. The maximum pulse rate of the group then is preset into the counter and the counter decremented at a selected rate corresponding to the approximate slope of the curve of pulse rate versus time per pulse for the determined group. Decrementing terminates upon occurrence of the third consecutive pulse beat, the contents of the counter then indicating the measured pulse rate.

Electronic data-processing apparatus

Abstract: In a circuit for converting a signal representing by its amplitude an item of data into a signal representing the item of data by its pulse duration, or vice versa, by comparison of an input signal with a ramp signal, a calibrating signal is applied to the amplitude-to-duration converter and the resulting pulse duration is compared with a calibrating pulse having a duration corresponding, at the required conversion scale, to the amplitude of the calibrating signal; any error signal from the comparator is used to adjust the ramp slope or ramp base line in a sense such as to reduce the error

Dispersion of h.f. pulses by ionospheric reflection

Abstract: An approximate expression is presented which gives the duration of an electromagnetic pulse formed by the spectral content in an h.f. bandwidth received after reflection in the ionosphere. The variation of the pulse duration with the bandwidth and a coefficient of the propagation path is shown. Methods of estimating the propagation-path coefficient are discussed. The geomagnetic field is omitted from the computation. Digital computations for a more realistic case than that on which the approximate expression is based are given for comparison.

Electrical discharge machining pulse current control apparatus

Abstract: A circuit for providing electrical discharge machining power pulse on-off time control responsive to gap open circuit condition with controlled timing of pulse narrowing and return to normal pulse duration.

Voice transmission and receiving system employing pulse duration modulations with a suppressed clock

Abstract: A voice transmission system including coded voice information using pulse duration modulation (PDM) with a suppressed clock and wherein this suppressed clock pulse duration modulated voice signal is used to modulate a phase shift keying modulator (PSK). The receiver includes a phase shift keying demodulator which feeds a limiter having a wide bandwidth so as to achieve the highest possible processing gain. The receiver also includes a voltage controlled oscillator which is fed an error signal derived from an integrator so as to produce an output signal from the voltage controlled oscillator to replace the suppressed clock.

A Peak Amplitude Selector for Electrophysiological Data Analysis

Abstract: This paper describes a peak amplitude selector designed to analyze electrophysiological phenomena ranging from slow (0.1 to 1 Hz) EEG to fast (up to 200 kHz) multiple neuronal units. The selector's minimum window height of 10 mV, when used on input signals of 0.5 to 1 volt allows the selection of interesting impulses out of a group of impulses with nearly the same amplitude. To increase the selector's usefulness, four data outputs are provided: for use with a paper recorder, two low speed outputs are available? one giving a pulse out for every impulse in the window, and one giving a pulse out for every 10 pulses in the window (to overcome the problem of losing counts when a fast pulse train is processed by a slow system); a high speed output giving one pulse for every impulse in the window is available; finally, an analog output proportional to rate of arrival of impulses in the window is provided. In addition, reference outputs are supplied to display the upper and lower thresholds relative to the signal, so that the window is clearly defined. The circuit is designed to use low cost components.

Random interval timer

Abstract: Apparatus according to the present invention produces an output at random time intervals following a Poisson distribution. A first pulse generator means, comprising first and second time delay circuits, produces a first periodic pulse having a period on the order of minutes. A second pulse generator means provides a second repetitive pulse having a predetermined average period which is much less than the period of the first pulse, with the exact time of occurrence of the second pulse being modulated by a random noise signal. A coincidence detector indicates time coincidence between the first and second pulses and causes an audible output to be produced. The duty factor of the second pulse predetermines the chance for coincidence.

Electrical Stimulation of a Human Ventrolateral‐Subventrolateral Thalamic Target Area

Abstract: A ventrolateral-subventrolateral thalamic target area was electrically stimulated in connection with stereotaxic neurosurgery in 20 alert patients with Parkinson's disease, in 5 patients with hereditary intention tremor and in 1 patient with an atypical congenital tremor. The purpose of the investigation was to study whether an altered pulse duration had any effect on the projected clinical responses evoked by the stimulation. Unidirectional square wave pulses with durations ranging from 0.1 to 25 msec and a repetition frequency of 1 pulse per second were therefore applied. The stimulation threshold for clinical responses was maintained by balancing every pulse duration tested with the peak current. The responses consisted mainly of muscular jerks or twitches projected to various contralateral parts of the body. The localization of the threshold responses depended on the pulse duration used. The motor character of the responses remained unchanged with all pulse durations tested. The peak current-pulse duration relationship for the threshold responses was studied. The results are discussed.

Amplitude compensated pulse duration modulator

Abstract: AN AMPLITUDE COMPENSATED PULSE DURATION MODULATOR INCLUDING A PULSE DURATION MODULATION SYSTEM HAVING MEANS FOR COMPENSATING FOR THE EFFECT OF STRAY CAPACITANCE AT THE AMPLIFICATION STAGES BY MEANS OF AMPLITUDE MODULATING THE PULSE DURATION MODULATED SIGNAL. THE AMPLITUDE MODULATED PULSE MODULATED SIGNAL IS APPLIED TO THE GRID OF AN AMPLIFIER MEANS AND THE OPERATION OF THE AMPLIFIER MEANS IS ESTABLISHED SUCH THAT THE AMPLIFIER IS DRIVEN INTO SATURATION FOR ALL PULSES EXCEPT COMPARATIVELY SMALLER AREA PULSES OF THE PULSE TRAIN. ACCORDINGLY, THE PULSE TRAIN RETAINS A MODULATION EFFECT ONLY FOR THE SMALLER AREA PULSES THEREBY ALLOWING THE AMPLITUDE MODULATION TO COMPENSATE FOR THE REACTANCE EFFECT OF THE AMPLIFIER ON THE SMALLER PULSES ONLY.

Atmospheric distortion of short laser pulses.

Abstract: The possible effects of the atmosphere on the propagation of short optical pulses are estimated, and experiments are described using real time pulse-comparison techniques over a 1.6-km path. With a pulse duration of 1.5 nsec, an optical thickness of 2.8, and a typical angular beamwidth and field of view, pulse distortion was not observed. It is concluded that multiple scattering due to aerosols comprises the only mechanism of possible importance, and should be observable with shorter pulses or large angle optics. The results are pertinent to recently proposed, sophisticated optical communications and radar techniques.

Digital pulse train tracker

Abstract: A pulse train tracking system completely digital in operation is capable of tracking pulse trains in a dense signal environment. An acquisition circuit determines the existence of a unique pulse combination by measurement of the interpulse period between successive pulses within a preselected range of minimum and maximum interpulse periods. Acquired pulse trains are tracked by an available one of several tracking circuits, adapted to individually track different pulse trains of the same or different pulse repetition frequencies. The trackers predict the interpulse period, for a train being tracked and define a gate within which the predicted pulse should occur. The trackers correct the phasing of the gate relative to a received pulse within each period and correct the predicted inter-pulse period at a proportioned rate. Tracking is maintained in the absence of pulses for a preselected number of interpulse periods.