Showing papers on "Pulse duration published in 1971"

Micromachining and image recording on thin films by laser beams

Abstract: A theoretical and experimental description of laser machining of thin metallic films is given. Calculations are carried out for the temperature rise of a thin film in response to a pulse of incident light energy and for the dependence of the temperature rise on the different thermal constants of the substrate and film and on the illumination conditions. Experiments have been conducted on the pulsed machining of thin bismuth films with glass and mylar as substrates using a lowest-order transverse mode argon laser with an average power output capability of 20 milliwatts. A fast intracavity acoustooptical modulation system produced optical pulses with durations controllable from 25 ns to several ms. The pulse repetition rate could be varied from a single pulse up to several MHz. The peak power depended on the duty cycle but was limited to 2 watts for low duty cycles. Experiments were done with both front and back illumination. (In back illumination the laser beam is incident on the film through the substrate.) For optimal machining conditions in which the optical beam diameter is adjusted to produce the maximum diameter of transparent area for a given pulse energy, less than 50 percent of the removed material left the surface of the substrate. The remainder was displaced so as to leave some areas free of bismuth while the thickness of bismuth in other areas was increased. With a pulse duration of 25 ns and a 600-A-thick bismuth film on mylar, the peak power required to machine a 6-µm-diameter spot was about 0.7 watt. Variable amplitude light pulses produced by the intracavity modulation system with a 1-MHz repetition rate and duration of 25 ns were used to write images on a 600-A-thick bismuth film, deposited on a mylar substrate, by deflecting the laser beam in raster fashion over the surface of the bismuth film. The average laser power output was 20 mW. The film area was 8 × 10 mm2. Both positive and negative continuous-tone images were recorded. The images consisted of an array of 1200 by 2000 completely independent spots of varying diameter and a spot density of 4 × 106/cm2. Images of documents which were originally of size 8½ × 11 inches showed a limiting resolution of over 175 lines per inch when magnified to the original size.

Electrical cardiac defibrillator

Abstract: 1. APPARATUS FOR ELECTRICALLY STIMULATING THE HEART COMPRISING: ELECTRODE MEANS, SENSING MEANS HAVING AN INPUT CONNECTED TO SAID ELECTRODE MEANS FOR SENSING CARDIAC ELECTRICAL SIGNALS, PULSE RATE DETECTOR MEANS FOR DETECTING THE AVERAGE RATE OF OCCURRENCE OF THE ORS COMPLEXES OF SAID CARDIAC ELECTRICAL SIGNALS OVER A PREDETERMINED TIME PERIOD, PULSE DURATION DETECTOR MEANS FOR DETECTING THE Q TO S PERIOD OF EACH SAID QRS COMPLEX IN SAID CARDIAC ELECTRICAL SIGNAL, SAID PULSE DURATION DETECTOR MEANS BEING CONNECTED TO SAID PULSE RATE DETECTOR MEANS TO PERMIT RATE DETECTION FOR PULSES WHOSE DURATION IS GREATER THAN A PREDETERMINED VALUE, THRESHOLD LOGIC MEANS CONNECTED TO SAID PULSE RATE DETECTOR MEANS AND SAID PULSE DURATION DETECTOR MEANS FOR PROVIDING AN OUTPUT PULSE WHEN THE AVERAGE RATE OF OCCURRENCE OF SAID QRS COMPLEXES EXCEEDS A PREDETERMINED VALUE AND A PREDETERMINED NUMBER OF SAID Q TO S PERIODS EXCEED A PREDETERMINED TIME PERIOD, AND DEFIBRILLATOR MEANS CONNECTED TO THE OUTPUT OF SAID LOGIC MEANS FOR GENERATING A DEFIBRILLATING PULSE ON SAID ELCTRODE MEANS IN RESPONSE TO RECEIVING A PULSE FROM SAID THRESHOLD LOGIC MEANS.

Gas‐Breakdown Dependence on Beam Size and Pulse Duration with 10.6‐μ Wavelength Radiation

Abstract: Gas‐breakdown threshold measurements with 10.6‐μ wavelength radiation have been made in air, argon, and helium. The threshold was determined with 50‐ and 200‐nsec‐duration pulses and was found to depend on the peak intensity of the pulse, showing that the breakdown process is a balance between the rate of energy absorption and some rate of energy loss. The threshold also decreased as the focal spot size was increased from 10−2 to 10−1 cm, showing that the loss process is reduced for larger beam sizes. The threshold varied inversely with gas pressure from 0.1 to 4 atm, which is evidence that the loss mechanism is not electron diffusion but must be some other process which exhibits a beam‐size dependence and is apparently weakly dependent on gas pressure.

Transmission and reception system for generating and receiving base-band pulse duration pulse signals without distortion for short base-band communication system

Abstract: An electromagnetic signal communication system utilizing short base-band pulse signals of sub-nanosecond duration employs dispersionless, broad band antenna transmission line elements for generating and preserving the character of the short base-band pulses in respective transmitter and receiver sub-systems.

Temporal Summation and Its Limit for Wavelength Changes: An Analog of Bloch's Law for Color Vision

Abstract: Temporal summation and its limits were studied at subjective threshold by varying the pulse duration t of (a) constant-luminance pulse changes of wavelength Δλ, and (b) constant-wavelength pulse changes of luminance ΔL. Threshold depends on Δλ and ΔL for pulse durations longer than about 150–300 and 60 ms, respectively. Psychophysical sensitivity to a pulse of wavelength change improved as pulse duration was increased for short pulses, but was unaffected by pulse duration for long pulses. Although there are departures from full temporal summation for pulse durations longer than roughly 20 ms, a formal analog of Bloch’s law tΔλ = constant gives a fair description of the wavelength-pulse data for short pulses. The critical duration for wavelength pulses (tcw) is much longer than the critical duration for luminance pulses (tcL) at any given mean wavelength. Although tcL does not depend on mean wavelength, tcw is roughly twice as long in the blue-green as in the red. These data bear on the question of what part is played in color vision by the neural encoding of information in the time domain. They can provide fresh empirical tests of current theories of color vision. The findings are tentatively interpreted (a) in terms of different critical events in Walraven’s luminosity and chromaticity channels; these critical events are supposed to limit temporal summation for luminance pulses and wavelength pulses, respectively, and (b) from the viewpoint that central neural processing plays an important part in (task dependent) summation.

Ultrashort Pulse Formation in a Short‐Pulse‐Stimulated Raman Oscillator

Abstract: A train of picosecond pulses was used to pump a stimulated Raman oscillator designed such that the generated Stokes pulse was amplified by successive pump pulses. In this way partial group velocity matching could be achieved and significant time narrowing of the Stokes pulse realized. With benzene as the Raman active material, a minimum Stokes‐pulse duration of ≃ 0.3 psec was recorded.

Transformer Type Accelerators for Intense Electron Beams

Abstract: The principles and designs of transformer accelerators (TA) generating intense beams of charged particles over energy ranges 0.5-5 Mev are described. Pulse electron accelerators with pulse length of 10-8 to 10-5sec are investigated (some of them have a repetition rate of several hundreds pps) as well as one-phase d three-phase 50-cps transformers. The most models' power conversion efficiency is in the range of 60-95%, the averaged beam power comes up to or exceeds 10 kW and is in excess of 150 kW for one of the last models. The design of a 5 Mev single-pulse TA with peak current of 30 kA at pulse length of 40 nsec and of 1.2 Mev proton TA with average beam power of 10 kW are described. The features of main components of high voltage transformers and of intense current acceleration tubes are discussed.

Filamentary Tracks Formed in Transparent Optical Glass by Laser Beam Self-Focusing. II. Theoretical Analysis

Abstract: An electrostriction mechanism for laser-beam self-focusing and track formation in transparent optical glass is analyzed theoretically. Electrostrictive self-focusing occurs when a laser pulse of sufficiently high power and rapid rise time passes through a transparent medium. For a pulse duration of 50 nsec, trapping thresholds vary from 20 kW to 2 MW. During self-focusing, the beam collapses to a small radius. In solid dielectrics, self-focusing causes permanent damage in the form of isolated regions of gross fracture, termed "damage stars" and long straight tracks of very fine fractures. Typical tracks have a diameter of a few wave-lengths of light and extend up to several centimeters. Self-focusing occurs because of an interaction between light and sound. The laser beam electrostrictively excites an ultrasonic cylindrical disturbance or sound wave. The sound wave initially increases the refractive index along the beam axis. This focuses the beam into a waveguide channel called a filament. In the filament, the intensity is so high that many nonlinear mechanisms may occur, leading to damage and track formation. This paper analyzes only the self-focusing mechanism, not the various damage mechanisms. We assume the beam always remains Gaussian. The propagation of the beam is described by the quasioptics beam-tracing equation, which includes the effects of diffraction. The sound wave and beam-tracing equations are solved in several approximate models. A trapping threshold is derived for three pulse shapes, covering the steady-state, transitional, and transient regimes of pulse duration and beam size. There is a trapping-power coefficient $K$ for each material, calculable from the density, speed of sound for a compression wave or elastic moduli, and refractive index at the laser wavelength. A formula for computing the power to achieve a given constant maximum intensity $I$ as a function of beam size, and pulse duration, and trapping-power coefficient is derived. Values of this given constant intensity have been selected so the constant-intensity curve closely matches experimental track-formation thresholds for three optical glasses. The results are $K=221$ kW and $I=2.5$ ${\mathrm{G}\mathrm{W}/\mathrm{c}\mathrm{m}}^{2}$ for dense flint glass, $K=937$ kW and $I=60$ ${\mathrm{G}\mathrm{W}/\mathrm{c}\mathrm{m}}^{2}$ for borosilicate crown glass, and $K=1119$ kW and $I=180$ ${\mathrm{G}\mathrm{W}/\mathrm{c}\mathrm{m}}^{2}$ for fused silica, at a fixed pulse duration of 55 nsec and a laser wavelength of 694.3 nm. A computer movie of beam trapping shows the collapse of the beam to a relatively constant small radius, which causes track formation. It also shows the extremely rapid upstream motion of the focal points at speeds greater than 100 times the speed of sound. The long period of time they dwell at the upstream end of their motion explains the appearance of damage stars at the upstream ends of the tracks.

Pulse duration dependence of laser damage mechanisms

Abstract: A number of mechanisms for internal laser damage in transparent dielectrics are examined for pulse duration dependence and the results are compared with experimental measurements when possible. The differences in dependence on pulse duration and other variables from one mechanism to another suggest that different mechanisms may initiate damage in different parameter ranges. Experimental identification of these mechanisms will be aided by measuring the pulse duration dependence of the damage threshold.

Pulsed CO2 Gas‐Dynamic Laser

Abstract: We report a pulsed combustion‐operated CO2 gas‐dynamic laser. A gas mixture is ignited in a combustion chamber to form heated CO2 and N2. The mixture expands through a supersonic nozzle, thereby causing population inversion in the CO2. Laser energy was about 20 J and pulse duration 0.3 sec. Variations of gain and pulse energy with gas composition and stagnation pressure are described.

Axial trajectory sensor having gating means controlled by pulse duration measuring for electronic particle study apparatus and method

Abstract: A sensor for use with apparatus operating in accordance with the principles of the Coulter electronic particle studying device, for discriminating between signals from particles passing on axial or near axial paths through an aperture and particles passing off center on the basis of their differing durations. The pulse duration of a portion of the pulse is measured and only those which meet the criteria of duration established by the electronic circuitry are permitted to pass for use in pulse height analysis apparatus following the sensor. The other pulses are discarded on the basis of their greater durations. The apparatus provides structure for deriving a duration-measuring pulse whose duration extends in one case from the peak of a particle pulse to a fractional amplitude thereof, and in another case from the time of maximum slope of the leading edge to the time of maximum slope of the trailing edge. In each case the duration-measuring pulse is converted into a signal which has an amplitude proportional to duration and the latter signal is compared with a certain maximum signal level to operate gating means for rejecting the longer duration pulses and passing the shorter duration ones. Multiple peak pulses are also discarded by means of suitable circuitry.

Efficient high‐gain parametric generation in adp continuously tunable across the visible spectrum

Abstract: Coherent visible light, continuously tunable over the range from 4200 to 7300 A, has been obtained by pumping an ammonium dihydrogen phosphate (ADP) crystal with the ultraviolet fourth harmonic of a Nd: YAG laser. Parametric gains sufficient to produce up to 25% average power conversion of the pump to the tunable visible output were obtained without the use of an external resonator. The output radiation typically had a 5‐A bandwidth, 2‐nsec pulse duration, 100‐kW peak power, and 5‐mW average power at 30 pps. Wavelength tuning was accomplished either by varying the crystal temperature, or by varying its orientation with respect to the pump beam. Angle tuning allows the output to be rapidly tuned across the visible spectrum.

Equipment for continuous measurements of pulse wave velocities.

Abstract: Equipment that measures continously ‘foot to foot’ time intervals between two peripheral arterial pulse waves is described. To calculate the pulse wave velocity one has to know, besides this time interval, the distance between the sites of the proximal and distal pulse wave transducers. The foot of the proximal and the distal pulse waves is detected by differantiation and by marking signals generated by a zero crossig marker. These signals start and stop a time interval counter connected to a digital printer and a D/A converter. Gating circuits prevent the operation of the time interval counter by extrema of the pulse wave other than its foot. The accuracy of the differentiator, the accuracy in detecting the zero crossing of the differentiated pulse wave, and the influence of a sloping baseline on the position of the pulse foot, are discussed. In a similar fashion, it is possible to measure the time interval between theR-wave and the foot of a peripheral pulse wave. The equipment is being tested clinically. Examples of recordings are given. Cases where the equipment fails to measure, due to peculiarities in the shape of the pule wave, are pointed out.

The general uncertainty relation for real signals in communication theory

Abstract: The general uncertainty relation for real time functions in communication theory is derived. The product of pulse duration and spectral width referred to the positive frequency spectrum only, is not less than 1.1802…, as compared with 2 in the Heisenberg and Gabor cases. This minimum is reached with a pulse whose time and spectral functions are numerically evaluated.

Digitally operated signal regenerator and timing circuit

Abstract: A digitally operated signal timing circuit employs a single synchronous up-down counter with overriding set and reset in combination with a group of flip-flops and logic gates. In effecting the regeneration of input pulses, such as the pulses produced by a telephone dial, a plurality of signal timing functions are provided by the combination indicated, which functions include the establishment of an operate threshold delay, a release delay, a minimum output pulse duration, a minimum duration interval between pulses and an idle condition holdover period.

Pulse width coded signal detector

Abstract: Two one-shot circuits are triggered by an input data pulse to be interrogated. At the leading edge of the input pulse, one of the two one-shot circuits generates a pulse of the specified width minus the specified tolerance. The other one-shot circuit generates a pulse width equal to the specified tolerance at the trailing edge of the interrogated pulse. The output of the first one-shot circuit triggers a third one-shot circuit which in turn generates a pulse of a width equal to twice the specified tolerance. The outputs of the second and third one-shot circuits are combined in a NAND gate which generates the detection pulse to indicate that the interrogated pulse is within the specified tolerance. The detection pulse is generated as soon as the trailing edge of the interrogated pulse is received. Thus, two input data pulses can be placed as close together as possible as long as the individual pulse identity is maintained, making it possible to maximize the date rate. A multiplicty of detector circuits may be connected in a parallel manner, each generating a detection pulse upon the reception of a pulse specified length, thus permitting the decoding of an entire pulse-width-coded message.

Apparatus and method for radio-frequency pulse generation in tuned radio-frequency loads

Abstract: This disclosure describes a radio frequency (RF) pulse generation system employing magnetic pulse compression circuits coupled through individual matching transformers into a tuned RF load. The pulse compression circuits are operated sequentially, and each circuit is matched to the tuned load the impedance of which (volt-ampere relation) is a function of the current amplitude during the generation of fast rising pulses. Variations in amplitude, pulse width and position of each half-cycle current pulse are obtained by control of the corresponding magnetic pulse compression circuit.

A laser temperature-jump apparatus for the study of fast reactions in solution

Abstract: An apparatus for the determination of the rates of fast chemical reactions in solution is described. The temperature of a solution is raised by a pulse of radiation from a laser, and the resulting shift of chemical equilibrium is followed spectrophoto metrically. If the laser is used in the non-Q-switched mode, and the optical energy is converted to thermal energy by a dye, temperature rises of 5K in 300 mu s are readily obtained, giving signal-to-noise ratios of over 100. If the laser is used in the Q-switched mode, so that the light pulse duration is of the order of 1 mu s, dye conversion is inefficient, due to the finite lifetime of the excited states of the dye, and temperature rises of less than 1 K are obtained. Direct conversion of optical energy to thermal energy by solvent absorption is also inefficient, since the absorbance of the usual solvents does not have a suitable value at any of the wavelengths of the light generated by the widely used lasers (694 nm and 1060 nm). Shock-wave transients, caused by high rates of energy input to the solvent, also limit the temperature-jump which can be usefully produced.

Ionospheric dispersion of an FM electromagnetic pulse

Abstract: Mathematical relationships are derived for evaluating the effects of a dispersive medium, such as the ionosphere, on an FM Gaussian shape pulse The distortion of the amplitude, pulse length, and modulation caused by the ionosphere is examined in terms of the integrated electron density along the transmission path and the system parameters of the transmitted signal

Control arrangement with a pulse-length modulator for a piston

Abstract: A servo loop for correcting the position of a piston operating against a load has a control unit comprising a three point regulator for operating two on-off valves and a pulse length modulator for operating a switch over valve, the on-off and switch over valves being connected to the piston cylinder, a pressure tank, and a collection tank, so as to move the piston in either of two directions. The three point regulator and the pulse length modulator are driven by the difference between the desired signal and the actual signal, the latter being obtained from an inductive displacement pickup coupled to the piston rod.

Pcm system including a pulse pattern analyzer

Abstract: A delta pulse code modulation system includes a feedback loop comprising a pulse pattern analyzer for detecting a large instantaneous modulation index within a fixed time interval. The system exhibits a wide range of modulation and suppresses whistling and interference tones at low pulse rates.

The two-flash threshold: An evaluation of critical-duration and visual-persistence hypotheses

Abstract: The two-flash threshold is reduced by increasing the duration of both pulses of light or light adapting the eye. Increasing the duration of the first pulse also decreases the two-flash threshold, contrary to what a critical-duration explanation of the threshold would predict. Decreasing the duration of the second pulse increases the threshold when the second pulse is very brief. Light adapting the eye under such conditions serves to increase the two-flash threshold, unlike the effect adaptation has when a long second pulse is used.

Pulse jitter measurement especially for heart beat measurement

Abstract: Apparatus for measuring the difference in intervals between pulses of a pulse train and providing a continuous output indicative of the interval variation or the pulse jitter. Circuitry having the pulse train as an input and including a pair of interval timers, for producing a series of constant width pulses related to the input pulses in amplitude and repetition rate. An averager and a difference amplifier for providing an output which is a function of the difference between each pulse interval and the average pulse interval.

Q‐switched laser with controllable pulse length

Abstract: Experimental results of a recently proposed technique for obtaining Q‐switched laser pulses of controllable length are presented. A lithium iodate doubling crystal inside the cavity of a Nd: YAG laser running at 0.946 μ is used to provide both output coupling and an easily adjustable, nonlinear loss mechanism. Controllable pulse lengths in the range of 200 nsec to 1 μ at 0.473 μ have been achieved at nominally constant energy.

Time-dependent fracture criteria for 6061-T6 aluminum under stress-wave loading in uniaxial strain

Abstract: New spallation threshold data for 6061-T6 aluminum were obtained under stress-wave loading conditions in uniaxial strain, covering the range of tensile pulse durations of 60 to 200 nsec. This range of pulse duration was achieved by using exploding-foil techniques to accelerate thin Mylar plates against thin aluninum specimens. A comparison was made between exploding-foil spallation tests on 6061-T6 aluminum in air and vacuum. The data indicate that the spallation threshold of 6061-T6 aluminum is sensitive to the tensile pulse duration, amplitude, and impulse at the spall location. The exploding-foil impact conditions were reduced to stress-pulse loading parameters by using a one-dimensional elastic-plastic hydrodynamic computer code. The time-dependent aspects of the spallation threshold of 6061-T6 aluminum were found to obey failure theories which were rate process oriented, and which combine the effects of tensile-pulse duration, peak tensile stress, tensile impulse, and tensile-pulse shape. The present data have been used to quantitatively establish failure relationships for 6061:T6 aluminum. Where applicable, supplemental information in the literature concerning dynamic fracture of 6061-T6 aluminum was utilized.

Digital-to-analog conversion apparatus and method

Abstract: An indirect digital-to-analog conversion apparatus and method which combines the advantages of pulse rate modulation with pulse width or pulse duration modulation. Pulse duration modulation is used on the least significant bits; while pulse rate modulation is used on the more significant bits up to the most significant bit. In this manner, the advantages of both systems are combined resulting in a system in which conversion time is minimized while the ripple content in the analog output is also minimized.

Audio system with means for reducing noise effects

Abstract: A system for eliminating noise pulses in the waveform of an audio signal is disclosed. The audio signal is used to produce an envelope signal whose amplitude is a function of the amplitude of a waveform section received during a time period T. The amplitude of the center segment of the waveform section is compared with the envelope signal amplitude. If the former is greater than the envelope signal amplitude it represents a noise pulse, and it is substituted by a pulse whose amplitude is either the envelope signal amplitude or the amplitude of a waveform segment adjacent to the noise representing segment.

Pulse shaping network

Abstract: An electrical network for reducing the effective duration of a pulse by increasing the peak amplitude of the pulse within a predetermined portion of its defining bit period relative to the maximum amplitude of such pulse within a predetermined portion of an adjacent bit period, wherein a signal representation of such pulse, an inverter advanced signal representing such pulse, and an inverted retarded signal representing such pulse are combined to generate a combination pulses of reduced effective duration.