Showing papers on "Pulse duration published in 1970"

FM and AM mode locking of the homogeneous laser - Part I: Theory

Abstract: A new general analysis for mode-locked operation of a homogeneously broadened laser with either internal phase (FM) or amplitude (AM) modulation is presented in this paper. In this analysis, a complex Gaussian pulse is followed through one pass around the laser cavity. Approximations are made to the line shape and modulation characteristics to keep the pulse Gaussian. After one round trip, a self-consistent solution is required. This yields simple analytic expressions for the pulse length, frequency chirp, and bandwidth of the mode-locked pulses. The analysis is further extended to include effects of detuning of the modulator, in which case analytical expressions are obtained for the phase shift of the pulse within the modulation cycle, the shift of the pulse spectrum off line center, the change in pulse length, and the change in power output. Numerical results for a typical Nd:YAG laser are given. In the case of the FM mode-locked laser it is found that there is a frequency chirp on the pulse and that this causes pulse compression and stretching when the modulator is detuned. Etalon effects and dispersion effects are also considered.

Pulse Power Failure Modes in Semiconductors

Abstract: Semiconductor devices operating under both biased and unbiased conditions are vulnerable to permanent damage from relatively moderate levels of pulsed electrical energy, particularly of submicrosecond pulse duration. An experimental study was performed to determine the permanent damage levels associated with a number of different devices and to identify the failure mechanisms associated with each. The device types investigated included general purpose and high speed computer diodes, a medium power diode, medium frequency and UHF transistor amplifiers, and a dielectrically isolated diode gate expander. The permanent damage levels associated with these devices were determined both for positive and negative polarity pulses at different conditions of quiescent bias and pulse width. The pulse duration times included the range of 30 to 300 nanoseconds, and in some instances, up to 1 microsecond. Failure models for both thermal second breakdown induced damage to the semiconductor junction and thermal damage to the device interconnecting leads and metallization patterns were also developed.

Efficient internal optical parametric oscillation

Abstract: Efficient internal optical parametric oscillation has been obtained using a LiNbO3 crystal inside the resonator of a continuously pumped repetitively Q‐switched 1.06μ Nd:YAG laser. Dielectric mirrors are coated directly on the plane‐parallel end faces of the crystal, and no focusing optics are used inside the laser. The oscillator operates near degenerate with outputs near 2μ. Average output powers as high as 350 mW and 75 % depletion of the available pump power are observed. This represents an order of magnitude larger output power than previously reported for a parametric oscillator. Internal oscillation causes stretching of the laser pulses to as much as five times the normal length, with corresponding increases in oscillator pulse length. Operation of this internal oscillator is compared to that of a similar external oscillator pumped by the same laser.

Some ionosonde observations of ionosphere modification by very high power, high frequency ground‐based transmission

Abstract: Some early observations of significant ionospheric modification resulting from F-region heating by a very high power, high frequency transmitter located near Boulder, Colorado, are presented in this paper. A description of the Platteville heating transmitter facility, the locations of ionosonde and photometric diagnostic equipments, and the geometry of the experiment are given in a companion paper by Utlaut [1970]. A single-plane inverted log periodic antenna, which has a half-power beam-width of the order of 90°, was used for transmitting. The ionosonde transmitter, which has a peak power of about 25 kw, was operated by using a 200-Hz pulse repetition rate with a pulse duration of 64 μsec.

Visible Laser Action in Fluorine I

Abstract: Pulsed laser oscillation in atomic fluorine at 7039, 7129, and 7024 A (vacuum) has been observed and identified as belonging to the 3p 2P – 2s2P transitions in fluorine I. Emission originates from an electrically pulsed CF4, C2F6, or SF6 and helium mixture with pressure of 0.1 and 5 Torr, respectively. Optical pulse duration is 1–2μsec with a peak power in all three lines of 150 W. Laser action takes place in a 4‐m cavity with active discharge lengths from 1 to 3 m.

Long-pulse laser emission from rhodamine 6G

Abstract: The properties of the rhodamine 6G flashlamp-pumped circulating dye laser with cyclooctatetraene and cycloheptatriene as triplet-state quenchers are described. Particular attention is given to such observables as pulse duration, frequency sweep, and early termination of the laser pulse. From the experimental results and the theory of dye lasers, it is concluded that the thermal effects may not play a dominant role in such lasers.

Photocurrents Due to Pulse Illumination in the Presence of Trapping

Abstract: The expression for transient photocurrent due to light pulse of arbitrary intensity has been derived in the presence of trapping and detrapping. The pulse duration is assumed to be short compared to the transit time and the analytic solutions are obtained for ``weak'' trapping case alone. Transcendental equations involving transit time and injected charge density have been solved numerically and the solutions are displayed graphically. In various limiting cases our expressions reduce to previously reported results. Analysis presented in this article may be useful in obtaining trapping parameters from experimental data.

Method and means for stabilizing the amplitude and repetition frequency of a repetitively q-switched laser

Abstract: A technique for stabilizing the amplitude and repetition frequency of a repetitively Q-switched laser includes a first step or operation in which all light from each output pulse above a given amplitude level is removed to provide a series of output pulses having uniform amplitudes. A second step or operation then involves selecting a narrow time channel within the pulse width of each pulse at precise points in time to provide final output light pulses of uniform amplitude, pulse width, and repetition frequency.

Parametric Behavior of the Atmospheric Pressure Pulsed CO2 Laser

Abstract: Megawatt peak powers have recently been reported from a pulsed electrical discharge CO2 laser operating at atmospheric pressure [A. J. Beaulieu, Laser Focus 6, 14 (1970)]. The electrical discharge was struck across the transverse dimension of the laser producing the large electric field strengths required for laser excitation at high gas pressures. This paper describes the small signal gain, pulse energy, and duration as a function of gas pressure and discharge voltage of a 1.5‐m laser tube utilizing 60 separate capacitor discharges along the axis of the tube. The gain coefficient is of the order of 1% per cm or less, typical of dc excited CO2 lasers. The peak power increases approximately as the square of the total gas pressure as a result of an increase in pulse energy and decrease in pulse duration with gas pressure.

Optical timing of the pulsar np 0532 in the crab nebula.

Abstract: Crab Nebula pulsar NP 0532 optical timing, measuring frequency, arrival times and pulse interval

Thermoelastic Response of Polycrystalline Metals to Relativistic Electron Beam Absorption

Abstract: A model is presented for the one‐dimensional thermoelastic response of homogeneous isotropic metals to pulsed relativistic electron beam absorption. The effect of the time dependence of the electron power pulse was examined for two cases: a delta function and a rectangular pulse of duration τ0. Equations were obtained in both cases which explicitly relate properties of the electron beam (energy absorption profile, total energy, and pulse duration) to properties of the material (density, dilatational wave velocity, and Gruneisen parameter). Experiments were performed to test the developed model for polycrystalline aluminum, copper, and tantalum. Electron beam dosimetry was accomplished by means of calorimetry and a passive film technique. Material response data was obtained by measuring the back surface motion by means of a laser interferometer. The experimental results indicated that an assumption of instantaneous energy deposition was incorrect except possibly for the case of the lowest Z metal, i.e., al...

Fuel injection system for internal combustion engine

Abstract: To extend the time of opening of fuel injection valves during starting, a timing circuit, having a time constant preferably between 5 and 30 seconds, and desirably about 25 seconds, is connected to the electronic control circuit controlling the opening times of the fuel injection valves. The timing circuit provides a decreasing signal to extend the time during which the injection valves are open from the time the starter switch is operated. Preferably, the fuel injection system includes a pulse duration multiplier circuit, having a multiplication factor varying between 1 and 5, and the timing circuit affects the multiplication factor.

Counting system for measuring a difference between frequencies of two signals

Abstract: A counting system for measuring a difference between respective frequencies of the first input signal and the second input signal, where the first and second input signals are converted to a first pulse train whose pulses are each timed with each of the cycles of the first input signal and to a second pulse train whose pulses are each timed with each of the cycles of the second input signal; the first pulse train and the second pulse train are applied to a sequential logical circuit having three possible states to generate an output pulse in response to every received pulse of at least one of the first and second pulse trains so as to obtain output pulses the number of which corresponds to the difference between the numbers of received pulses of the first and second pulse trains; and the number of output pulses of the sequential logical circuit is counted by a counter to obtain the difference desired.

Statistical amplitude and phase variations in mode-locked lasers

Abstract: The influence of statistical amplitude or phase variations in the modes of a mode-locked laser on the time-dependent output intensity and on the relative efficiency of nonlinear optical processes is investigated. The ensemble-averaged intensity, the time-dependent distribution of the resulting complex amplitude, and the second-order moment of the intensity distribution are calculated and discussed for both types of variations. As long as no systematic amplitude or phase changes are introduced, the pulse shape is maintained, but superimposed on a fluctuating background, and the efficiency for nonlinear optical processes is reduced. For random phase fluctuations over 2π the pulse behavior disappears completely and the output becomes Gaussian or chaotic light.

Electron Beam Induced Stress Waves in Solids

Abstract: Large‐amplitude stress waves have been generated in solids by means of a very high current pulsed electron beam. The electron beam has an average energy of 3 MeV, current of 40 000 A, and pulse duration of approximately 70 nsec. The back surface velocity profiles were measured using a laser‐Doppler interferometer. Data obtained for 6061‐T6 aluminum indicated a slow rise of the plastic wave, thus suggesting the importance of strain rate effects. The utility of the technique for materials research at high pressures and temperatures is discussed.

Comparison of photomultipliers and avalanche photodiodes for laser applications

Abstract: Photomultipliers and avalanche photodiodes are compared as detectors of short light pulses such as might be encountered in laser ranging or laser PCM communication systems. Expressions are derived for the optimum spectral response of the amplifier-filter combination which maximizes the signal-to-noise ratio for the two detectors. Assuming that this optimized filter is used, the minimum detectable energy of a laser pulse is then calculated for the two detectors as a function of detector quantum efficiency, laser pulse length, and background light level. As an example, the detectors are compared for laser pulses of lengths 100 ns, 10 ns, and 1 ns at 1.06 µm.

Bidirectional signal seeking remote control system

Abstract: A single frequency remote control system employing long and short pulses to effect bidirectional rotation of a motor driving a signal seeking UHF television tuner. The system includes an ultrasonic tone transmitter, a receiving transducer, and a signal detector for producing a pulse of duration corresponding to that of the transmitted and received tone. A time delay circuit is coupled to the detector output for actuating a direction control relay in response to a pulse of predetermined duration. Termination of the detector output pulse actuates a second relay to energize the motor windings and thereby cause rotation of the tuner drive shaft in the direction selected by pulse duration. This search mode is sustained by a logic circuit until the presence of both a sync signal and picture carrier indicate a new station has been tuned in. A memory circuit charged during the detector output pulse is operative upon pulse termination to assure the original station is vacated at the start of search.

Studies of Stimulated Emission from Discharges in Air and Nitrogen in the Pressure Range 1-760 torr

Abstract: Stimulated emission from gas discharge tubes built up of ceramic disc capacitors (C = 3 000 pF) separated by electrodes and having a central hole (discharge channel) has been studied. Nitrogen has been used as test gas. It is shown that the output power density is appreciably higher from this tube when fed by a high voltage pulse generator than from an ordinary straight tube with end electrodes. 230 kW pulses (superradiant mode without mirrors) have been observed from a tube 7 mm in bore and 102 mm long at at nitrogen pressure of 175 torr. The pulse duration is approximately 2 ns. It is further shown that the stimulated emission occurs during breakdown. In a similar tube with aluminium oxide discs (er = 8) instead of the disc capacitors, laser action has been observed at considerably higher pressure. In air at atmospheric pressure an output of 25 kW has been achieved from a tube 4 mm in bore and 102 mm long. The pulse duration is in this case approximately 1 ns.

Error analysis of optical range measurement systems

Abstract: The ranging error of short pulse optical tracking systems is investigated. The relationships between the tracker characteristics, the characteristics of the received signal and background radiation, and the measurement accuracy are determined. It is found that the effects of characteristics of the tracker, the propagating medium, and/or the target to be tracked will predominate in the derived accuracy expressions. This result is based on the assumption that the transmitted pulse duration is short compared to the delay fluctuations induced by at least one of these three effects.

Apparatus and method for digital frequency addition and subtraction

Abstract: The digital frequency system of this invention provides an output signal comprised of pulses which have a frequency equal to the sum or difference of the frequencies of two input signals. Each of the input signals is used to generate a first pulse train for summation or subtraction at the output of the system and a second pulse train for controlling the counting of the pulses of the first pulse train to ensure against error due to pulse overlap. If there is a possibility of error due to pulse overlap, one of the pulses to be counted is inhibited while the other is passed to the output. Each inhibited pulse is replaced by an auxiliary pulse which is then processed in the same manner as the original pulses.

Ng reset and voltage increasing circuits cardiac autopacer with variable refractory non linear feedback latchi

Abstract: A self-contained, implantable cardiac-autopacer providing ultra long battery life and high reliability through parallel battery redundancy and circuit techniques The cardiac-autopacer operates in a demand mode with a variable simulated refractory period which is long during artificial stimulation and short during natural ventricular depolarization In this way the demand functioning of the cardiac-autopacer is maintained from normal to tachycardia rates In the presence of noise or interfering signals with frequencies beyond the tachycardia rate the autopacer will continuously generate artificial heart stimulating pulses of a predetermined interval Both artificial pulse duration and interval are maintained independent of load variation, but pulse interval varies with battery voltage making it possible to externally monitor battery condition by triggering the autopacer into a continuous pulse mode

Sectionalized pulse modulator

Abstract: A solid-state pulse modulator for producing power pulses, the duration of which pulses may be selected by charging one or more of a plurality of series-connected pulse-forming networks (PFN). Desired rectangular pulse shape for each duration of the pulses is retained by dividing the capacitance of the terminating capacitor of each PFN into a basic value that remains connected to the PFN and into a larger terminating value that is charged through a diode when the terminating capacitor is included in the PFN, but which is blocked from receiving a charge by the same diode when there is another PFN following the first one, for the purpose of obtaining pulses of longer duration. Selectively triggerable SCRs that determine pulse duration are connected to each PFN for charging an appropriate number of sections of PFN.

High resolution telemetry for random pulse outputs

Abstract: A system for accommodating random pulses having frequencies above the passband of the pulse transmission channel includes a first accumulating register into which the random pulses are fed. A second accumulator register accumulates the output pulse count of the system, and a comparator produces an output level when the counts stored in first and second registers are at a predetermined relation to one another. A synchronizing clock has an output pulse rate within the passband of the pulse transmission channel and controls the output from the comparator according to the pulse rate, such that pulses applied to the pulse transmission channel are uniformly spaced apart at a frequency within the passband of the transmission channel.

A glass disk calorimeter for pulsed lasers

Abstract: Because existing calorimeters are not adequate to measure Q-switched laser pulses accurately, we have designed a calorimeter in which the beam passes through two glass disks, one of green plate (absorbing from 0?6-1?6 ?m), the other of clear plate. A laser pulse creates a temperature difference which is sensed by thermocouples. 70% of the incident energy passes through the device and is available for experiment. Thermal drift is low enough to obtain 1% accuracy at 10 mJ input energy. For energies up to 0?1 J, any pulse length from 1 s to 0?1 ps can be used. Energies up to 50 J can be used provided the power density at the glass does not exceed 40 MW cm?2. The device is dependent on a conventional calorimeter for calibration (limiting the absolute accuracy to 2%), and the sensitivity is wavelength dependent, thus limiting its use to wavelengths where a free running laser is available; ways of overcoming this disadvantage are discussed.

Pulse analyzing apparatus

Abstract: Apparatus finding the amplitude of a pulse at its center by comparing the pulse with its integral, adjusted to pass through the amplitude of the pulse at its time center, and passing to coincident gating means a signal having the pulse center amplitude at that time and a signal of fixed duration initiated at the finding of the pulse center. Also, a particle analyzing a system intercoupling the amplitude finding apparatus between a pulse generating transducer of liquid suspended particles and pulse classification structure.

Quasi-steady magnetoplasmadynamic arc characteristics

Abstract: Multimegawatt quasi-steady MPD arc accelerator in millisecond pulses, noting applicability to experiments requiring long exposure times