Showing papers on "Pulse duration published in 1974"

The choice of pulse duration for chronic electrical stimulation via surface, nerve, and intramuscular electrodes.

Abstract: The peak current, peak voltage, charge transfer and energy dissipation necessary for equivalent stimulation were measured for several pulse durations in the range from 0.01 to 1.0 msec. The unidirectional, regulated current, rectangular waveform was studied for subcutaneous nerve and intramuscular stimulation in animals and for surface stimulation in humans. In addition, the unidirectional, regulated current, exponential waveform was studied in humans and was compared with the rectangular waveform. The question of the relationship between charge transfer and energy dissipation and possible tissue damage due to the electrochemical formation of toxic compounds or a temperature rise in the surrounding tissue was examined. The optimal pulse duration for reducing the possibility of tissue damage was concluded to be less than or equal to 0.01 msec for intramuscular stimulation in the test situation. No conclusion was made as to the optimal duration for nerve or surface stimulation. Excitation of muscle fibers was found to take place indirectly by was of muscle nerves during intramuscular stimulation. The exponential waveform required less charge transfer and energy dissipation than the rectangular waveform, but higher peak currents.

Self-phase modulation and short-pulse generation from laser-breakdown plasmas

Abstract: This paper is a complete report on both the experimental and theoretical aspects of the recently discovered self-phase modulation in laser-breakdown plasmas. Mainly responsible for these effects is the sudden index change which accompanies the ionization of the gaseous medium. Two theoretical models are introduced for the phase and amplitude modulation induced by the plasma. These effects are applied to the problem of short-optical-pulse generation, with emphasis on the prospects for producing a pulse consisting of only a few optical cycles. The techniques described here have the unique advantage that the generation mechanism is linear, resulting in particularly clean, reproducible and predictable optical transients. Methods are suggested for raising the plasma nucleation intensity by further cleaning up the gas. It is shown that index dispersion of the optical components may place a lower limit on pulse duration.

Some numerical solutions for Lamb's problem

Abstract: We consider a version of Lamb9s Problem in which a vertical time-dependent point force acts on the surface of a uniform half-space. The resulting surface disturbance is computed as vertical and horizontal components of displacement, particle velocity, acceleration, and strain. The goal is to provide numerical solutions appropriate to a comparison with observed wave forms produced by impacts onto granite and onto soil. Solutions for step- and delta-function sources are not physically realistic but represent limiting cases. They show a clear P arrival (larger on horizontal than vertical components) and an obscure S arrival. The Rayleigh pulse includes a singularity at the theoretical arrival time. All of the energy buildup appears on the vertical components and all of the energy decay , on the horizontal components. The effects of Poisson9s ratio upon vertical displacements for a step-function source are shown. For fixed shear velocity, an increase of Poisson9s ratio produces a P pulse which is larger, faster, and more gradually emergent, an S pulse with more clear-cut beginning, and a much narrower Rayleigh pulse. For a source-time function given by cos 2 ( πt / T ), − T /2 ≦ T /2, a × 10 reduction in pulse width at fixed pulse height yields an increase in P and Rayleigh-wave amplitudes by factors of 1, 10, and 100 for displacement, velocity and strain, and acceleration, respectively. The observed wave forms appear somewhat oscillatory, with widths proportional to the source pulse width. The Rayleigh pulse appears as emergent positive on vertical components and as sharp negative on horizontal components. We show a theoretical seismic profile for granite, with source pulse width of 10 µsec and detectors at 10, 20, 30, 40, and 50 cm. Pulse amplitude decays as r −1 for P wave and r − 1 2 for Rayleigh wave. Pulse width broadens slightly with distance but the wave form character remains essentially unchanged.

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.

Near field transient radiation patterns for circular pistons

Abstract: The exact impulse response of field parameters for any field point on or off axis for the case where a circular disc radiator face is subjected to a displacement step corresponding to a velocity impulse is reviewed. By convolution, the transient field pattern for any arbitrary motion of the disc can be obtained. The exact response for a half-sine monopulse is computed. An approximate representation of the transient pressure response to the velocity impulse input at the disc is derived, and it is shown to correspond to the replica pulses described previously. The regions of validity of the approximation are quite limited and the replica pulses are displaced in time from the positions formerly attributed to them. The displaced replica approximation is applied to an examination of the structure of the near field for continuous sinusoidal excitation and a plot of positions of extrema is produced. It is shown that this approximation gives good agreement with the exact values and is superior to the previous published approach in this regard. For short sinusoidal pulses the effect of pulse length on the field pattern, and of field point on the time history of a transient wave are shown. When the excitation is a short sinusoidal pulse the effect of the pulse length and field point position on the field pattern and wave shape are demonstrated.

Generation of Picosecond and Subpicosecond Light Pulses with Saturable Absorbers

Abstract: Single light pulses, generated by a mode-locked Nd-glass laser, were shortened with saturable absorbers of low initial transmissionT0. The pulse duration was reduced from 8 to 2.6 ps after a single pass through a dye cell ofT0=10−7. Light pulses as short as 0.5 ps were observed after five transits through an absorberamplifier system. Detailed calculations of the stationary and the transient situation (with respect to the dye relaxation timeτ) are presented to demonstrate optimum conditions for the pulse shortening.

Laser technology for high precision satellite tracking

Abstract: Fixed and mobile laser ranging stations have been developed to track satellites equipped with retro-reflector arrays. These have operated consistently at data rates of once per second with range precision better than 50 cm, using Q-switched ruby lasers with pulse durations of 20 to 40 nanoseconds. Improvements are being incorporated to improve the precision to 10 cm, and to permit ranging to more distant satellites. These include improved reflector array designs, processing and analysis of the received reflection pulses, and use of sub-nanosecond pulse duration lasers.

Transient currents and electron mobility in polythene

Abstract: Transient currents in polythene were measured by a charge storage method. The relationship between the logarithms of quantity of charge stored and pulse time is linear, if the pulse duration is shorter than a certain critical time; if it is longer, a linear relationship also exists, but the graph has a steeper slope. It is suggested that this critical time is the transit time across the specimen of electrons injected from the virtual cathode. The electron mobility calculated from the critical time is 2·6 × 10−4 cm2 V−1 S−1 at room temperature (24 °C) and is associated with an activation energy of about 0·24 eV. The corresponding figures given by similar experiments on polyethylene-terephthalate are 1·0 × 10−4 cm2 V−1 S−1 and 0·23 eV. The results are related to a theoretical model for conduction in noncrystalline materials proposed by Mott, and shown to be consistent with it. The model postulates valence and conduction bands exhibiting a tail with strongly localized states which can give rise to electron hopping.

Generation and measurement of frequency-tunable picosecond pulses from dye lasers

Abstract: Experimental techniques for the generation of frequency-tunable picosecond pulses from passively mode-locked dye lasers are reviewed. Direct photoelectric measurements of pulse durations with a streak-camera of time resolution <3 ps are described. Recent studies of the build-up of pulse shortening and of saturable absorber photochemistry are discussed and related to the mode-locking processes in dye lasers.

Spectra of digital phase modulation by matrix methods

Abstract: We derive the spectral density of a sinusoidal carrier phase modulated by a random baseband pulse train in which the signaling pulse duration is finite and the signaling pulses may have different shapes. The spectral density is expressed as a compact Hermitian form in which the Hermitian matrix is a function of only the symbol probability distribution, and the associated column vector is a function of only the signal pulse shapes. If the baseband pulse duration is longer than one signaling interval, we assume that the symbols transmitted during different time slots are statistically independent. The applicability of the method to compute the spectral density is illustrated by examples for binary, quaternary, octonary, and 16-ary PSK systems with different pulse overlap. Similar methods yield the spectral density of the output of a nonlinear device whose input is a random baseband pulse train with overlapping pulses.

Means and method for controlling the occurrence and the duration of time intervals during which sparks are provided in a multicylinder internal combustion engine

Abstract: A control system controls the occurrence and duration of time intervals during which sparks may be provided in the cylinders of an internal combustion engine driving a crankshaft as a function of loading parameters on the engine. In an automotive engine control system, parameters such as the vacuum in the carburetor, the throttle setting and the torque of the crankshaft are sensed and corresponding signals are provided by the sensors. A first pulse signal is provided. The pulses in the first pulse signal correspond to the rotational speed of the crankshaft. The distributor provides a second pulse signal. Each pulse in the second pulse signal has a width corresponding to a predetermined rotational displacement of the crankshaft and has a relationship to the position of a piston in a corresponding cylinder. A circuit shapes the pulses of the second pulse signal and provides them to a network which provides a start pulse in accordance with the shaped pulses and the first pulse signal. A preload circuit preloads a counter in the start pulse network in accordance with the sensed parameter signals and the first pulse signal to control the occurrence of the start pulses. A second network provides a stop signal in accordance with the first pulse signal and a spark time interval pulse signal. A pulse circuit receiving the spark pulses and the stop signal provides the spark time interval pulse signal to the ignition system and to the stop signal network so that the stop signal network controls the duration of each pulse in the spark time interval pulse signal. The ignition system provides sparks in the engine in a predetermined manner during the occurence of a pulse in the spark time interval pulse signal.

Pulse compression for more efficient operation of solid‐state laser amplifier chains

Abstract: We propose a pulse compression scheme which reduces the peak intensity while increasing the energy density achievable in a Nd:glass amplifier chain. Self‐focusing is the dominant effect responsible for limiting the power of a short‐pulse Nd:glass amplifier chain, and the reduction of the intensity (through this compression scheme) greatly reduces these problems. We recommend injecting a lower‐intensity and longer‐duration pulse into the chain. Under some circumstances, the glass nonlinearity will impress upon the pulse a chirp suitable for efficient subsequent temporal compression, and this may result in higher effective peak power operation. If a 1‐nsec (full 1/e duration) temporally Gaussian pulse with a chain‐averaged peak intensity of 2 GW/cm2 propagates 2 m in a Nd:glass laser chain, we calculate that the pulse could be subsequently compressed (by a series of Gires‐Tournois interferometers) to 125 psec with good stability against input pulse amplitude noise. Such short pulses are of major interest for laser fusion.

Gas breakdown by single, similar 40 ps-50 ns, 1·06 μm laser pulses

Abstract: The pressure and pulse length dependence of the threshold intensity for optical frequency breakdown of N2 and Ar has been studied using 1·06 μm pulses from an Nd3+ laser. The pressure range covered was from similar 1-105 Torr and the pulse duration (which is approximately twice the FWHM value) from similar 40 ps-50 ns. At low intensities less, similar 1012 W cm−2 the results are shown to satisfy a simple scaling law of the type found in the analysis of DC breakdown data.

A TEA CO 2 laser with output pulse length adjustable from 50 ns to over 50 &#181;s

Abstract: By adjusting the proportions of CO 2 and N 2 in a TEA laser gas mixture and by also adjusting the coupling losses of the optical resonator, it is shown that the same laser system can produce laser outputs of relatively uniform energy but with pulse lengths adjustable from 0.05 to 50 \mu s.

Impulse produced by the interaction of CO2 TEA laser pulses

Abstract: This paper describes measurements of the impulse transmitted to metallic targets by CO2 TEA laser pulses with duration around 100 ns. This represents the first such measurements for submicrosecond duration pulses. The impulse was measured as a function of target material and diameter, laser power, laser beam focusing, and ambient air pressure.

Method and apparatus for providing primary coincidence correction during particle analysis utilizing time generation techniques

Abstract: A method and apparatus for correcting a particle pulse count subject to coincidence error is disclosed wherein particle pulses, developed in response to passage of particles in a particulate system through a sensing zone, are counted for a predetermined period of time. The predetermined period of time is increased or extended in response to each pulse counted by a time increment that is related to a characteristic of the counted pulse, such as the pulse width, duration, or amplitude. The total additional time period allows the counting of additional particle pulses such that the total count at the end of the extended time period is an error corrected count for the number of particles detected in the predetermined time period.

Features of three-photon parametric interaction of ultrashort light packets in the nonlinear amplification regime

Abstract: Three-photon parametric interaction of ultrashort light pulses in KDP and α-HIO3 crystals is investigated. The study is carried out without the limitation of the given-pump-field approximation.

End of life increased pulse width and rate change apparatus

Abstract: Pulse generating circuitry which can be used, for example, in an adjustable pulse width pacemaker. The circuitry increases the output pulse width as the power source output is decreased below a predetermined level and indicates that power source depletion by decreasing the output pulse frequency. The pacemaker pulse width can be matched to the patient''s needs and adjusted to pulse widths far below those of the typical pacemaker to conserve battery energy and increase the pacemaker''s useful lifetime. The decreasing pulse rate aids in accurately predicting the end of life of the power source.

Method of and system for the controlling of an apparatus for the electric discharge machining of a workpiece

Abstract: Discrete electric-discharge pulses are applied across a dielectric-swept gap between an electrode and a workpiece by triggering an ON-OFF switch between its conductive and nonconductive states in accordance with parameters of the gap so that per pulse adaptive control of the individual machining discharges is effected. An integrator responsive to the gap current, may be used to operate the switch means which may be turned on upon the detection of a pilot discharge. The number of unsatisfactory discharges is detected and, if this number exceeds a predetermined level, is used to control a gap parameter. The integrator signal may be digitalized for accumulation in a counter controlling pulse duration and other parameters.

Pulse width decoder

Abstract: Herein disclosed is a pulse width decoder comprising an oscillator activated to generate clock pulses of relatively short duration as long as an input signal pulse is applied, a shift register adapted to channelize a multiplicity of pulse widths, means including a divider counter for utilizing locally generated pulses to shift the register, and means including feedback circuitry from the shift register to the divider counter to change the divisor in the counter so that the range of window tolerance provided by the channelizing is effectively increased, in steps, with ascending groups of pulse widths. Additionally, delay means is incorporated to provide for a minimum limit of acceptable input signal pulse width.

Coherent optical pulse reshaping in a resonant molecular absorber

Abstract: Investigation of the coherent reshaping of short-duration (2 to 40 nsec) N2O laser pulses in a resonant NH3 absorber for a variable number of absorption lengths. It is found that, for small-area square pulses, the reshaping can produce subnanosecond pulses at the leading and trailing edges. A rapid phase reversal gives rise to amplification for times comparable to the transverse relaxation time.

Time-domain design of frequency-sampling digital filters for pulse shaping using linear programming techniques

Abstract: The use of time-domain specifications is demonstrated for designing frequency-sampling digital filters that generate data pulses for transmission over an ideal band-limited channel. Desired characteristics of the transmitted pulse are used to formulate the set of constraint equations and objective function used in linear programming to obtain an optimum set of filter coefficients, i.e., frequency samples {| H(k) |} - The constraints are the amplitudes assigned to the set of regularily spaced samples taken from the pulse. The objective function is either to minimize the maximum absolute error between desired and generated pulse samples over the specified pulse duration or to provide zero crossings in the transmitted pulse with near-zero slope in order to protect against intersymbol interference (ISI) due to timing error (jitter).

Linearized force measuring apparatus

Abstract: The force to be measured and a pulsed voltage creating a balanced electrostatic force in opposition thereto are applied to a two- or three-plate capacitor. Displacement of one capacitor plate relative to another is measured and resultant measurement signal converted by an amplitude/pulse converter to pulses having a repetition frequency varying as a function of amplitude of displacement signal. In one embodiment the amplitude/pulse converter furnishes a first and second pulse sequence having, respectively, a number of pulses during a measurement interval increased and decreased in proportion to the amplitude of measurement signal. The force to be measured is applied to central plate, while the first and second pulse sequence are applied to first and second outer plates of a three-plate capacitor in this embodiment. For a two-plate capacitor, an additional amplifier for amplifying the measurement signal and having an amplification factor porportional to the amplitude of the pulses divided by the distance between the capacitor plates furnishes an auxiliary voltage which is applied to a capacitor plate in synchronism with a main pulse sequence to linearize the system.