Showing papers on "Pulse duration published in 1982"

Independently variably controlled pulsed R.F. plasma chemical vapor processing

Abstract: Semiconductive wafers are processed, i.e., etched or layers deposited thereon, by means of a plasma enhanced chemical vapor processing system wherein the plasma is generated by a train of R.F. power pulses. The pulse repetition rate, pulse length and peak power level of the individual pulses are independently variably controlled to variably control the uniformity of the processing of the semiconductive wafers within the processing gaps.

Electric pulse-induced fusion of 3T3 cells in monolayer culture

Abstract: Swiss mouse 3T3-C2 fibroblasts, grown to confluence in monolayer culture, are shown to fuse when exposed to electric fields. Exposure to five repetitive electric pulses of about 1 kilovolt per centimeter with a duration of 50 microseconds caused approximately 20 percent of the cells to become fused (multinucleate) when 1 millimolar magnesium was present in the medium. The effects of minimum thresholds of field strength, pulse duration, and number of pulses were determined. Cell disruption was observed when the electric field exceeded 2.0 kilovolts per centimeter or the pulse was of longer duration than 120 microseconds.

Analysis and modelling of edm parameters

Abstract: Metal removal in electro-discharge machining (edm) is basically a thermal erosion process where the heat transfer is predominantly through conduction. In this paper, a two-dimensional heat transfer model, assuming the plasma channel to be a disc heat source, has been employed to study the effects of edm input parameters, such as pulse duration, pulse energy and material properties, on metal removal and crater shape. Reasons for somewhat poor correlation between theoretical and experimental data are discussed.

Laser drilling system utilizing photoacoustic feedback

Abstract: A laser drilling control system utilizing photoacoustic feedback is described. The control system provides an accurate monitoring of the laser drilling of a multilayered printed circuit board thereby allowing uniform drilling through layers of different optical and photoacoustic properties by both analyzing the photoacoustic feedback signals received, and adjusting optimally the laser parameters such as pulse duration, wavelength, energy, pulse repetition rate, and the number of pulses, for each successive layer. The system also provides an end point detection which prevents underdrilling overheating, and overdrilling of underlying layers and associated damages. According to another aspect of this invention, the control system can be used as a sensitive misregistration detector for aligning the laser beam to a selected drill site for subsequent drilling at the selected drill site.

Clinical studies on high and low power laser radiation upon some structures of the anterior and posterior segments of the eye Experiences in the treatment of some pathological conditions of the anterior and posterior segments of the human eye by means of a Nd:YAG laser, driven at various power levels

Abstract: A Q-switched Nd:YAG laser apparatus Manufactured by LASAG AG, CH-3600 Thun has been used in the treatment of a number of pathological conditions of the anterior and posterior segments of the human eye. This laser system may be driven in a free running mode, thereby allowing variation of pulse duration over a range of 12 ns to 10 ms. With increasing pulse duration, non-linear, mechanical damage patterns characteristic of the biological effects at the lower exposure duration range become unimportant when compared to the so-called thermal effects met at the upper pulse duration range. The thermal damage mechanisms may be useful when applied together with the mechanical damage mechanism, for instance when iris perforations are intended. Because the Wise-Witter irradiation method for the treatment of open angle glaucoma depends on low power, thermal mechanisms, this instrument may also be useful for the treatment of this disease entity. This same irradiation mode may also be applied to at least some irradiation tasks of the retina and choroid.

Measurements of mode partition noise of laser diodes

Abstract: Mode partition noise may become the dominant performance limitation for single-mode fiber systems. We define the mode partition coefficient k for laser diodes which can be used as a universal index, like threshold current and spectral width, to characterize laser diodes. The k value varies between 1 and 0, and for larger k , the mode partition noise will be higher. We also demonstrate two simple techniques for measuring k : the low-pass filter method and the sampling method. We discuss the k values measured under different operating conditions (pulse width, dc bias) for several types of laser diodes, k values are around 0.4-0.6 with short pulse width (1.5-5ns), and decreases to 0.14 pulse width of 50 ns. The largest k values were obtained for a laser exhibiting strong relaxation oscillation. For that laser, k did not depend on the pulse width. The k value is an important factor for system and fiber design as well as laser diode design.

Picosecond, tunable ArF* excimer laser source

Abstract: A 40‐mJ ArF* laser with pulse duration ∼10 ps and spatial and spectral properties close to the transform limits is described. Substantial extraction of the available energy from the final amplifier is demonstrated, a fact providing direct evidence against the presence of significant nonlinear losses in the amplifying medium up to an intensity of ∼1 GW/cm.2

Digital circuit for control of gradual turn on of electrical tissue stimulators

Abstract: A circuit for causing the gradual turn-on of electrical tissue stimulation in a digitally controlled stimulator is disclosed. A stimulation pulse counter and a pulses per step memory circuit are connected to a decoder to provide an amplitude incrementing signal after a presettable count of stimulation pulses. An amplitude counter receives the incrementing signal to increment the amplitude of the stimulation output pulse through a digital to analog converter circuit and to reset the pulse counter. A maximum amplitude memory circuit and decoder operate in conjunction with the amplitude counter to latch the counter when a preset pulse amplitude is obtained. At the end of a stimulation interval, the amplitude counter is reset and stimulation pulses begin at the minimum amplitude at the start of the next stimulation interval.

Pulse signal amplitude storage-holding apparatus

Abstract: A pulse signal amplitude storage-holding apparatus utilizes a plurality of series connected storage-holding circuits which store and hold the pulse magnitude of an electrical pulse signal whose amplitude is to be stored. At least one electrical pulse signal amplitude compensating circuit may be added to compensate for a storage error with respect to the pulse magnitude of the electrical pulse signal caused by the charge and discharged characteristics of each of the storage-holding circuits. In the alternative, at least one of the storage-holding circuits may be arranged so as to output an output signal accompanied by an overshoot of a fixed amount with respect to the input pulse signal, the overshoot thereby compensating for the abovenoted storage error.

Laser ignition apparatus for an internal combustion engine

Abstract: A laser ignition apparatus includes a laser oscillator which generates at least two successive pulse-shaped laser beams during each compression stroke of the engine. A first pulse-shaped laser beam is generated by a Q switching action of the laser oscillator and thus has a high peak output and a second pulse-shaped laser beam is generated without the Q switching action and has a low peak output but a larger pulse duration than the first laser beam. The first and second pulse-shaped laser beams are guided and directed into the combustion chamber of the engine and the first laser beam of a high energy density causes the breakdown of the air-fuel mixture in the combustion chamber to develop a plasma and the second laser beam further increases the energy of the plasma thereby to ensure the setting fire of the air-fuel mixture.

Brushless ultra-efficient regenerative servomechanism

Abstract: A servomechanism regeneratively controls motion by a brushless coreless axial-field motor, exerting torque thru its permanent-magnet disk rotor, resulting from synchronized polyphase sinusoidal stator currents, controlled by a switching controller responsive to input commands and to Hall-effect transducer signals that vary sinusoidally with rotor angle and respectively correspond to stator phases. The controller operates with a dc power source and sink. Its signal processors derive from the transducer signals instantaneous magnitudes and polarities thereof and continuous lagless speed feedback. The instantaneous magnitudes are multiplied by a torque amplitude signal to provide respective synchronized amplitude control signals. Current transformers having primary windings in series with power switching transistors provide current feedback pulses with amplitude proportional to instaneous current in associated stator windings. Pulse control means initiate bi-phase pulses having restricted duty-cycle, and dictate pulse duration by comparing each current feedback pulse with the associated synchronized amplitude control signal. Switching logic responsive to the bi-phase pulses, to forward and reverse drive and brake commands, and to said polarities, accordingly controls selection and duty-cycle of said power switching transistors which, cooperative with free-wheeling diodes and inductors, effect controlled alternating stator currents. Various signal interface means process the input commands with feedback derived from the transducer signals, such as speed, direction of rotation, and interpolated digital position, to provide said torque amplitude signal, and variously, said drive and brake commands; so the motor and controller constitute a complete servomechanism, that provides precise speed and position control with regenerative reversing and braking, ultra-high efficiency, and fast dynamic response.

Wide aperture self‐sustained discharge KrF and XeCl lasers

Abstract: A UV‐preionized rare‐gas halide laser with a large aperture to 7×7 cm2 and active volume of 4 l has been operated at a high pressure regime of 5 atm. Beam profile measurements at the midplane between electrodes have shown the beam widths of 7 cm at a half‐energy density both in KrF and XeCl. The improvement in discharge homogeneity and extension of the optical pulse duration have been obtained by the peaking of the discharge current with a small stray capacitance between the rail gap and the laser head as well as by the use of Ne rather than He as a buffer gas, resulting in the output energy of 13.8 J in XeCl and 5.0 J in KrF.

Intracellular [Ca2+] transients in voltage clamped cardiac Purkinje fibers.

Abstract: The Ca2+-activated bioluminescent protein aequorin was used to observe intracellular [Ca2+] transients in voltage clamped canine Purkinje fibers The pattern of luminescence during a voltage clamp pulse was characterized by two components: L1, which is a rapid initial increase in luminescence and L2, which is a slower, secondary rise of variable configuration 1 L1, L2, inward current, and contraction were abolished by D 600 (2 μM) 2 Paired clamp pulses L1 reprimes more rapidly than L2; L1 reprimes within 100 ms, L2 does not 3 Clamp pulse duration Peak inward current was the same for 50 ms or 500 ms clamp pulses; L1 was either the same or slightly reduced in 50 ms clamp pulses compared to 500 ms clamp pulses L2, however, was abolished in repetitively given 50 ms pulses compared to repetitively given 500 ms pulses When 500 ms pulses were alternated with 50 ms pulses, L2 was greater in the 50 ms pulse than in the 500 ms pulse 4 Clamp pulse potential In the range −35 to 0 mV, peak L1 and peak inward current occurred at nearly the same time, had the same threshold potential, and had a similar dependence on membrane potential

Laser-Generated Electron Emission from Surfaces: Effect of the Pulse Shape on Temperature and Transient Phenomena.

Abstract: Surface temperatures generated by gaussian, rectangular, and triangular laser pulses are determined by solving a heat diffusion equation. The dependence of the temperature on the pulse shape and, in turn, the dependence of the thermal diffusivity and absorptance on the temperature are investigated. The lifetime of an adspecies on a laser‐heated solid (e.g., Cs on W) is estimated in terms of the temperature, the desorption energy, and the coverage. The mechanism of laser‐generated electron emission from the adspecies is analyzed by means of the Richardson equation. A condition for generating an intense electron beam is that the laser pulse duration and the rise time of the temperature must be less than the lifetime of the adspecies.

Generation of short optical pulses in semiconductor lasers by combined DC and microwave current injection

Abstract: We report picosecond pulse generation in low threshold buried optical guide lasers using combined direct and microwave current excitation. The pulse widths were obtained as a function of direct current for several levels of RF excitation using lasers 125 and 380 μm long. The pulses have a Gaussian shape with full widths at half maximum intensity ranging from 19 to 57 ps. The pulse widths were obtained from the second harmonic autocorrelation. The experimental results are in reasonable agreement with the theory of short pulse formation in sinusoidally modulated lasers. The pulse width decreases with increasing dc and microwave current, and decreasing laser length. The shortest pulses were obtained with a 125μm long laser using 0.25 W RF at 1 GHz and 35 mA de bias. Multiple pulses are emitted at high dc excitation levels. Using the above laser at the indicated current levels the emission consists of a burst of ∼10 pulses which are separated by 30 ps, and has an approximately exponentially decaying amplitude. Saturable absorption was introduced in the lasers by degradation and results in shortening the pulses. A comparison is made of the pulse widths obtained for sinusoidal microwave current modulation and for pulsed excitation where the excitation is obtained from a step recovery diode. Reduced pulse widths are obtained for short current pulse excitation.

Observations and interpretations of the pulsed emission from the Crab pulsar

Abstract: HEAO 1 observations of the 18-200 keV pulsed emission from the Crab pulsar show that the systematic variation of spectral slope as a function of pulse shape rises continuously from 4-60 keV to at least 150 keV. This strengthens the claims for the existence of both the emission from the two main pulse peaks, and a separate, interpulse emission connecting the two peaks which contributes 22% of the total pulsed flux in the 15-200 keV range and has a harder spectrum than that of the two pulse peaks. These observations are combined with others from IR to gamma-ray energies. It is concluded that the phase-averaged pulsed spectrum, dominated by the emission from the two pulse peaks, calls for at least three power law components, and that the interpulse emission has a spectrum which is better fitted by either a thin, thermal bremsstrahlung model or a Comptonization model.

Frequency-modulation spectroscopy with a pulsed dye laser.

Abstract: We report the use of frequency-modulation spectroscopy with a Nd:YAG-pumped dye laser of 5-nsec pulse duration. In spite of the fact that the dye laser is not transform limited and has 30% peak-to-peak intensity fluctuations, we are easily able to measure absorptions as small as 2%.

Variable delay unit for data synchronizer using phase-sensitive counter to vary the delay

Abstract: A signal processing circuit for a signal varying in its properties, e.g., in its degress of distortion, in which the input signal is fed in parallel to two similar processing circuits e.g., equalizers, the characteristic of which can be varied by a control signal, wherein the control signal from the one processing circuit is periodically varied and the output signal is fed to a detector circuit which in optimum signal processing emits a trigger pulse to a holding circuit 52 which stores the corresponding control signal level, which is fed to the second processing circuit. A variable delay unit for the data is controlled by a continuously varying up-down counter, the contents of which continuously vary at the rate of a high frequency clock pulse. The direction of count and the time of the count is controlled by comparing the relative time-positions or phases of a timing pulse received with the data and a timing pulse generated at the receiver.

Method and circuit for controlling an electromagnetic actuator in photographic apparatus

Abstract: An improved control circuit for an electromagnetic actuator of the type having an armature mounted for movement in a magnetic field, and means connected to the armature for urging the armature toward a rest position. The circuit applies an electrical pulse of a first polarity, magnitude and duration to the armature to quickly move the armature to a programmed position determined by the magnitude and duration of said pulse, the programmed position lying within a range of positions between said rest position, and an extreme position achievable by the armature. The control circuit then applies a pulse of opposite polarity and of magnitude and duration effective to stop the armature at the programmed position. The control circuit applies a periodic train of pulses of said first polarity, of fixed magnitude and of duration, effective to hold the actuator in the programmed position, the period of said train of pulses being above the natural cutoff frequency of the actuator. To quickly return the armature to the rest position, the control circuit applies a pulse of opposite polarity and of duration and magnitude effective to the armature to move the armature in cooperation with the urging means, to the rest position. The circuit then applies a braking pulse of said first polarity and of duration and magnitude effective to stop the armature at the rest position. In a preferred embodiment, the actuator controls a shutter/aperture in a camera, the duty cycle (i.e. pulse duration) of the train of pulses determines the aperture size, and the number of pulses in the pulse train determines the shutter time. The control circuit also includes means for boosting the voltage of the moving and braking pulses to achieve extremely short shutter times.

Phase transitions in compound semiconductor films triggered by laser irradiation

Abstract: The preparation of AlSb thin films by pulsed laser annealing of Al‐Sb sandwiches is studied in order to resolve some past uncertainty about the temperature rise induced by the laser pulse Using 1000‐A‐thick 2‐layer films supported by transmission electron microscope grids, we investigate the energy threshold for transformation as a function of pulse duration (from 15 ns to 100 ms) and of ambient temperature up to ∼600 K We thence calculate the temperature effect directly induced by the laser to be ∼930 K, whereas inert gas furnace anneals of identical films show transformation at this temperature occurring only in times ≳100 sec We discuss the isoenergetic nature of the system for short‐laser pulses and the role of the heat of formation, and propose a model which is then shown to work equally well for the systems CdTe, CdSe, and AlAs We conclude that the reaction is thermally triggered by the laser pulse, but is to some extent self‐ sustaining via the heat of formation locally distributed

High-resolution, coherent pulse radar

Abstract: The invention concerns a procedure and a circuit arrangement for a coherent, high-resolution pulse radar applicable to distances from several tens of meters down to less than one meter and which evinces at the same time an accuracy in the cm range; the application is in particular to industrial monitoring operations. Two highly stable pulse sequences are generated in the transmitter and differ only slightly with respect to their pulse repetition frequencies. Both sequences are shaped into microwave pulse bundles and one sequence is processed into transmitter pulses, the other sequence being processed into scanning pulses for a time-expansion procedure. Heterodyning with the scanning pulses takes place in the receiver mixer, the result being a combined formation of intermediate-frequency (IF) and time-expansion. In this manner the signal bandwidth is already decreased by the time-expansion factor in the IF part. This is made possible in that coherent phases are used, i.e., there is an arbitrary but constant time relationship between the rising edge of the controlling pulse and the starting time (initial phase) of the carrier oscillation produced in the microwave oscillator. The oscillators used are microwave resonators driven by extremely short control pulses.

Ultraviolet laser, short pulse‐width measurement by multiphoton ionization autocorrelation

Abstract: An autocorrelation technique for the measurement of ultrashort laser pulse widths in the ultraviolet is demonstrated. Multiphoton ionization is used as the nonlinear process.

Third-harmonic generation using an ultrahigh-spectral-brightness ArF* source

Abstract: Tunable coherent radiation in the vicinity of 64 nm has been produced by third-harmonic generation of the output of an ultrahigh-spectral-brightness ArF* source in various simple gaseous media. The following performance parameters of the ArF* system are used: pulse energy, ~300 mJ; pulse duration, ~7 nsec; spectral width, <260 MHz; beam divergence, ~5 μrad × 15 μrad; and repetition rate up to 10 Hz. Third-harmonic generation with peak powers up to 30 W has been observed in an apparatus that eliminates photoabsorption of the third harmonic in the differential pumping stages.

Digital player using a pulse width detector

Abstract: In a pulse width detector circuit, a high-level pulse width and a low-level pulse width of a digital signal derived by slicing an analog signal reproduced from a disc at a predetermined level are independently measured and maximum or minimum values thereof in a predetermined time interval are stored, and an average value, sum or difference of the maximum or minimum high-level pulse width and the maximum or minimum low-level pulse width is calculated to detect a correct pulse width of original data recorded on the disc.

Multi-channel micropower communication link

Abstract: A remote controlling apparatus comprising a transmitter including a pulse generating circuit the output of which is a plurality of pulses of radiant energy having an envelope of a selected pulse width and a selected pulse interval and a receiver including an envelope detection circuit, the output of which is a plurality of pulses each having the selected pulse width and having the selected pulse interval of the transmitted radiant energy, concidence pulse generating means for generating coincidence pulses responsive to transitions in the output pulses from the envelope detection circuit, with one such coincidence pulse being generated at a selected time after a transition in each such output pulse and one being generated in coincidence with a transition in each such output pulse, the selected time being selected such that coincidence of the generated coincidence pulses will only occur when the output of the envelope detection circuit has a selected pulse width, and coincidence detection coupled to a triggering circuit for triggering the triggering circuit in response to a pre-selected number of detected coincidences of the coincidence pulses in a pre-selected time period.

The theory of photon echoes for strongly coupled electron–phonon systems

Abstract: We calculate the photon echo decay for a strongly coupled electron–phonon system, without making unrealistic assumptions about excitation pulse durations. We find that asymptotically, the photon echo decay is exponential, and we provide a formal expression for the decay rate 1/T2 which is independent of pulse duration. In contrast to the usual results, our expression for 1/T2 is nonperturbative in the electron–phonon interaction. We calculate the dependences of the echo amplitude on pulse power and duration, finding that the strong electron–phonon coupling modifies the simple two level system result. We also focus on the relationship between the zero phonon line shape in the homogeneous optical absorption spectrum, and the photon echo decay rate. We find that the zero phonon line shape is Lorentzian, with width 1/πT2. We show that the usual optical Bloch equation approach to analyzing time‐domain experiments, which normally is only applicable if the electron–phonon coupling is weak, can be extended to the...

Pulsed-power performance and stability of 880 nm GaAlAs/GaAs oxide-stripe lasers

Abstract: The paper gives the results of an experimental and theoretical investigation of GaAlAs/GaAs oxidestripe lasers under high-pulsed-power conditions. At a pulsewidth of 18 ns the best samples delivered optical powers of more than 2 W per facet. The kink-free light/current characteristics, the well-behaved far-fields and the very-small-amplitude jitter in the optical pulse indicate a stable operation in the fundamental lateral mode up to the maximum power level. The maximum available power is found to vary less than the inverse square root of the pulse width between 20 ns and 1 ?s. Catastrophic failure of these lasers is always accompanied with damage to one or both of the Al2O3-coated mirrors. The experimental power-law dependence and the distinct levels of power limit for lasers with differently prepared mirrors can be explained by a model which assumes a heat source in the mirror plane originating from nonradiative carrier recombination at the surface.

Theory of the synchronously pumped picosecond dye laser

Abstract: The circulation of a synchronously mode locked dye laser pulse in a linear cavity configuration containing a dye cell as an active medium and a bandwidth-limiting element is treated. The condition that the pulse shape reproduces after each cavity round-trip provides a nonlinear integro-differential equation for the steady-state pulse shape. For the solution of this equation an approximate method, not limited to small pulse energies, is given and the pulse duration, intensity, energy, asymmetry of the pulse shape, stable regions and other interesting parameters are discussed.