Showing papers on "Pulse duration published in 1983"
TL;DR: In this paper, the problem of nonlinear pulse propagation in optical fibers, as governed by the nonlinear Schrodinger equation, is reformulated as a variational problem and approximate solutions are obtained for the evolution during propagation of pulse width, pulse amplitude, and nonlinear frequency chirp.
Abstract: The problem of nonlinear pulse propagation in optical fibers, as governed by the nonlinear Schr\"odinger equation, is reformulated as a variational problem. By means of Gaussian trial functions and a Ritz optimization procedure, approximate solutions are obtained for the evolution during propagation of pulse width, pulse amplitude, and nonlinear frequency chirp. Comparisons with results from inverse-scattering theory and/or numerically obtained solutions show very good agreement.
867 citations
TL;DR: In this paper, the energy requirements for short-pulse writing and erasing are greater than or equal to those obtained for typical CW lasers in all cases investigated, including BaTiO 3, Bi 12 SiO 20, and LiNbO 3.
Abstract: Solutions are obtained for the refractive index grating in a photorefractive material in which the writing or erasing beams are short-pulse (less than tens of nanoseconds), high-irradiance (greater than kW/cm2) lasers. The response of the photorefractive material is modeled using the continuity equation for the charge carriers, a rate equation for the ions, a current equation, and Poisson's equation for the space charge field. Two cases are discussed in detail: 1) the time for recombination of carriers with ions is much less than the pulse length of the laser; and 2) the recombination, drift, and diffusion times are all much longer than the pulse length. The energy requirements for short-pulse writing and erasing are greater than or equal to those obtained for typical CW lasers in all cases investigated. Application to previous observations in BaTiO 3 , Bi 12 SiO 20 , and LiNbO 3 is discussed.
144 citations
TL;DR: In this article, the authors describe use of colliding pulse mode locking to generate pulses of 65 fs duration and pulse compression to reduce those pulse durations to 30 fs, and amplify femtosecond pulses to gigawatt powers.
Abstract: Recent advances in generation, amplification, compression, and frequency broadening of femtosecond optical pulses are reviewed. We describe use of colliding pulse mode locking to generate pulses of 65 fs duration and pulse compression to reduce those pulse durations to 30 fs. Amplification of femtosecond pulses to gigawatt powers and frequency broadening to obtain white light continuum pulses while retaining femtosecond pulse durations are also examined.
102 citations
Patent•
06 Dec 1983
TL;DR: A side printing apparatus for providing latent images of characters, numerals, symbols and the like on a photographic film moving in continuous motion includes a film sensitivity responsive means for generating several kinds of pulse having different pulse lengths which are predetermined in accordance with sensitivity of film.
Abstract: A side printing apparatus for providing latent images of characters, numerals, symbols and the like on a photographic film moving in continuous motion includes a film sensitivity responsive means for generating several kinds of pulse having different pulse lengths which are predetermined in accordance with sensitivity of film. The pulse operates to cause a light image forming device to be energized for a time defined corresponding to the pulse length thereof so as to provide a latent image of character, numeral, symbol or the like on a photographic film.
97 citations
TL;DR: In this article, an analytical solution in the time and frequency domain for the cylindrical pressure wave generated by a laser pulse traveling in a liquid, which is valid over a wide range of laser beam dimensions and pulse durations, is given.
81 citations
TL;DR: In this article, the concept of pulse shortening velocity is introduced as a simplified measure of pulse width performance in passively mode-locked ring dye lasers and the influence of coherent coupling in colliding pulse systems is found to be essentially equivalent to that of an increased saturable absorber cross section.
Abstract: The concept of "pulse shortening velocity" is introduced as a simplified measure of pulse width performance in passively mode-locked ring dye lasers Pulse shapes have been computed for a variety of operating conditions The influence of coherent coupling in colliding pulse systems is found to be essentially equivalent to that of an increased saturable absorber cross section
74 citations
TL;DR: The methods and techniques for extending time-resolved measurements into the femtosecond (10–15 second) time domain are described, and recent applications and fertile areas for investigation with femTosecond pulses are discussed.
Abstract: Considerable progress has taken place in the generation and application of ultrashort optical pulses. The methods and techniques for extending time-resolved measurements into the femtosecond (10(-15) second) time domain are described, and recent applications and fertile areas for investigation with femtosecond pulses are discussed.
72 citations
TL;DR: In this paper, it was shown experimentally and by calculations, using average Hamiltonian theory, that the decoupling efficiency of the composite decoupled schemes MLEV-4 and MLEv-16, introduced by Levitt, Freeman, and Frenkiel, can be improved by inserting delays and changing one pulse length of a composite pulse.
70 citations
TL;DR: In this article, the authors investigated the stimulated emission of new infrared dyes, which have shortS1-lifetimes between 5 and 12 ps with corresponding low fluorescence quantum efficiencies of 10−3 to 10−4.
Abstract: The stimulated emission of new infrared dyes was investigated. The dyes have shortS
1-lifetimes between 5 and 12 ps with corresponding low fluorescence quantum efficiencies of 10−3 to 10−4. In spite of this, 2% of the pumping energy were converted to an intense infrared pulse with frequencies between 5550 cm−1 (1.8 μm) and 7150 cm−1 (1.4 μm). The dye solutions were excited by single picosecond pulses of a Nd:glass laser in a travelling wave system consisting of a diffraction grating and a tranversely pumped dye cell. The pulse duration at 6250 cm−1 was measured to be 6 ps.
64 citations
TL;DR: In opener muscles of the first walking leg of 3 species of crayfish, quantal synaptic currents were recorded focally at synaptic spots by means of a macro-patch-clamp electrode, finding the point of block of conduction in the terminal branch seems to lie father from the terminal in distal than in proximal synapses.
Abstract: In opener muscles of the first walking leg of 3 species of crayfish, quantal synaptic currents were recorded focally at synaptic spots by means of a macro-patch-clamp electrode. Proximal stimulation of the motor axons elicited excitatory postsynaptic currents (nEPSCs). In addition, current pulses through the recording electrode depolarizing the nerve terminal elicited similar synaptic release (pEPSCs). Artefact waveforms generated in the recording electrode after a pulse were compensated by a special circuit, allowing the pEPSC to be recorded from 0.3 to 1.5 ms after the pulse. In all terminals identified by recording nEPSCs, pEPSCs were also elicited, with a threshold pulse amplitude between −0.1 and −2μA at 2 ms pulse duration. Most of the investigated terminals showed graded pEPSCs to rising amplitudes and durations of depolarizing pulses, and no effect of tetrodotoxin (TTX) on the pEPSCs. In these inexcitable terminals pEPSCs and nEPSCs showed mutual facilitation, with no signs of refractoriness for intervals as short at 3 ms. Some excitable terminals were found also: in these the amplitude of the pEPSC rose very steeply in an approximately all-or-nothing response on passing a threshold, while application of TTX reduced this response to one similar to that of inexcitable terminals. However, stimulation of such excitable terminals did not lead to antidromic conduction of action potentials into the main axon. In both mexcitable and excitable terminals, approximately the product of suprathreshold pulse amplitude and pulse duration determined the rate of release. The dependence of this response on pulse amplitude showed characteristic differences in proximal and distal synapses. The maximal double-logarithmic slope of this relation (s
D) was 3.3 on the average in proximal synapses, while for distal synapses the averages
D was 6.3. Further, in proximal synapses the nEPSC reached on average 86% of the maximum pEPSC, while the nEPSC in distal synapses amounted to only 5% of the maximum pEPSC. Therefore, the point of block of conduction in the terminal branch seems to lie father from the terminal in distal than in proximal synapses.
61 citations
Patent•
27 Sep 1983
TL;DR: In this article, the null transitions of an audio frequency signal are converted by Schmitt trigger circuits, one having a small hysteresis range centered on the null value and the other having a much larger hystereis range likewise centered on null value, into two binary pulse sequences of variable pulse lengths.
Abstract: The null transitions of an audio frequency signal are converted by Schmitt trigger circuits, one of which has a small hysteresis range centered on the null value and the other of which has a much larger hysteresis range likewise centered on the null value, into two binary pulse sequences of variable pulse lengths. The Schmitt trigger circuits are so constituted that a positive pulse length is produced by a negative null transition of the audio signal and vice versa and, moreover, the Schmitt trigger circuits return to their quiescent state 2 milliseconds after a positive null transition of the signal, also producing a positive pulse length, in this case beginning the indication of the pause. The pauses in the two binary pulse sequences thus produced, which exceed predetermined length (60 milliseconds in both cases and, additionally, 30 milliseconds in the case of the pulses formed by the Schmitt trigger with the narrower hysteresis range) and from the three different pause detection operations logic circuits derive either a speech recognition signal, a music recognition signal or an indication of an unidentifiable signal. The logic circuit uses as criteria the number of pauses and the time span of simultaneous or alternating appearance of signal pauses derived from the two different pulse sequences.
TL;DR: The main effects and interaction of pulse duration and pulse charge on sensory, motor and painful stimulation were examined on six male subjects and selective excitation of these different physiological responses was easier and required less charge as pulse duration became shorter.
Abstract: The main effects and interaction of pulse duration and pulse charge on sensory, motor and painful stimulation were examined on six male subjects. Surface electrodes were placed over the triceps brachii muscle. Pulse duration was varied between 5 and 1000 µ s. Peak current, muscle torque and four excitatory responses were determined. Sequential order of sensory, motor and painful stimulation was evidenced. Selective excitation of these different physiological responses was easier and required less charge as pulse duration became shorter. The greatest non-painful torque was reached at 100 µ s pulse duration. The most suitable range for motor stimulation was 20 to 200 µ s. For painful stimulation, a 5 to 10 µ s duration was favoured. A range of 20 to 100 µ s was recommended for sensory stimulation.
TL;DR: In this paper, a transversal pumping scheme for amplified spontaneous emission (ASE) was proposed, which achieved a duration of 6 ps, corresponding to one half of the pump pulse duration.
Abstract: A new scheme for travelling-wave excitation of amplified spontaneous emission (ASE) employing transversal pumping is presented. ASE pulses emitted in the forward direction had a duration of 6 ps, corresponding to one half of the pump pulse duration. The spectrum was strongly structured, with individual components having a width of 0.1–1.0 A. Essential characteristics of longitudinal and transversal excitation of travelling wave ASE are compared.
TL;DR: In this paper, a short-pulse amplifier was constructed in which the level of amplified spontaneous emission could be kept below 10−3 by properly taking into account the polarization anisotropy of the gain and by precise timing of the pump pulses.
Abstract: We have shown that distributed feedback dye lasers are capable of generating single transform-limited pulses of 1.6–3.5 ps duration when pumped by a mode-locked Nd: YAG laser. A short-pulse amplifier has been constructed in which the level of amplified spontaneous emission could be kept below 10−3 by properly taking into account the polarization anisotropy of the gain and by precise timing of the pump pulses. A sensitive autocorrelator is described which allows to measure pulse duration in a single shot.
TL;DR: In this article, the output of a mode-locked ring laser was measured for various concentrations of saturable absorbers and the down-frequency modulation was demonstrated by experiments of pulse compression in glass.
Abstract: Measurements performed on the output of a mode-locked ring laser show the pulses to be chirped. The down-frequency modulation is evidenced by experiments of pulse compression in glass, for various concentrations of saturable absorbers.
TL;DR: In this article, a picosecond infrared laser pulse can excite a molecule from the ground state to a certain vibrational level, all the other levels being nonpopulated.
TL;DR: High-efficiency pulse compression has been obtained by using an intracavity Raman oscillator using hydrogen gas as the Raman medium, which permits shortening of the pulse duration of a ruby laser by a factor of 6.7 with 87% effective quantum efficiency.
Abstract: High-efficiency pulse compression has been obtained by using an intracavity Raman oscillator. The energy of a primary laser stored in its high-Q cavity is extracted at the Stokes frequency by means of a Stokes laser having a high Raman gain and a low-Q cavity. This technique, using hydrogen gas as the Raman medium, permits shortening of the pulse duration of a ruby laser by a factor of 6.7 with 87% effective quantum efficiency. It would be especially useful with low-gain (alexandrite) and with short-storage-lifetime lasers.
TL;DR: The linear and nonlinear transient behaviour of a platinum electrode in physiological saline (0·9% NaCl) was investigated and it is concluded that the interface can be analysed and modelled in either domain in the linear range and at the onset of nonlinearity.
Abstract: The linear and nonlinear transient behaviour of a platinum electrode in physiological saline (0·9% NaCl) was investigated. The interface overpotential (current) in response to a step current (voltage) was monitored over six decades of pulse duration starting at 10 μs, both in the linear range, i.e. where the polarising current and the polarisation voltage are proportional, and in the nonlinear range, where this proportionality is lost. The time invariance of the Pt electrode/physiological saline interface parameters in the linear range and at the onset of nonlinearity over the studied band of frequencies and pulse durations is deduced from the equivalence of experimental results obtained in the frequency and time domains using the appropriate transformation when mapping the two domains. We conclude that the interface can be analysed and modelled in either domain in the linear range and at the onset of nonlinearity.
TL;DR: In this paper, the conditions of crack length, pulse amplitude, and pulse duration predicted by each criterion for crack instability under stress wave loads are presented and compared, and a data base was generated by performing plate impact experiments on epoxy specimens embedded with thin circular disks that acted as internal penny-shaped cracks.
Abstract: Previously proposed dynamic crack instability criteria are reviewed. The conditions of crack length, pulse amplitude, and pulse duration predicted by each criterion for crack instability under stress wave loads are presented and compared. To discriminate among these criteria, a data base was generated by performing plate impact experiments on epoxy specimens embedded with thin circular disks that acted as internal penny-shaped cracks. The observed instability behavior of these cracks under 2-µs stress pulses of various amplitudes was best described by a criterion that requires the dynamic stress intensity to exceed the dynamic fracture toughness for a certain minimum time.
TL;DR: In this paper, a model for estimating the minimum pulse duration (valve open time) required for a pulsed nozzle to produce a supersonic beam comparably cold to that obtained from a continuous source is presented.
Abstract: A new and simple model is presented for estimating the minimum pulse duration (‘‘valve open time’’) required for a pulsed nozzle to produce a supersonic beam comparably ‘‘cold’’ to that obtained from a continuous source. The model is based on the notion that cooling will be complete if the leading edge of the beamlet reaches the terminal temperature prescribed by the steady state flow equations before the sound wave created at the back of the pulse by the nozzle’s closing catches up with the leading edge. The times predicted from this model for reasonable stagnation conditions are all ≲10 μs.
TL;DR: In this article, it was shown that the pulse width dependence is more complex than either (Δr) or (δr)2 for conditions of Fresnel scattering, and that the scattered power should be proportional to the pulse length.
Abstract: In a recent series of papers a model was developed to explain the strengths of VHF radio echoes backscattered from the atmosphere. The model assumed that a process called ‘Fresnel scattering’ was operating. One feature of the model was the proposal that the scattered signal power should be proportional to the square of the radar pulse length (Δr) used. This paper reexamines that proportionality and concludes that for conditions of Fresnel scattering, the scattered power should rather be proportional to the pulse length. It is then shown that under conditions more general than those proposed in these earlier works, the pulse width dependence is more complex than either (Δr) or (Δr)2. These revised assumptions are more appropriate to the real atmosphere and may help explain some experimental results. Experimental data and computer simulations are also discussed.
TL;DR: In this article, the influence of a transient absorber grating on the pulse parameters of a dye laser in the "colliding pulse mode-locking" (CPM) regime is given.
Abstract: A calculation of the influence of a transient absorber grating on the pulse parameters of a dye laser in the "colliding pulse mode-locking" (CPM) regime is given. It is shown that, compared to other passive methods, considerably shorter pulses with a more favorable stability region can be obtained. Within the stability range of single pulse operation the shortest pulses in the CPM are obtained by operating far above threshold where the saturation energy of the amplifier is much greater than that of the absorber. Deviation from an amplifier position that is symmetric with respect to the amplification of the counter-running pulses leads to different energies of the pulses and to a strong decrease of the stability range. Taking the dispersive properties of absorber and amplifier into consideration, equations for the time dependent phase of the laser pulse are established and solved by an analytical ansatz. The resulting pulse chirp is shown to be mainly dependent on the detuning of the pulse frequency from the center frequency of the saturable absorber. The estimated values for the pulse duration and the down-chirp for typical experimental conditions of a rhodamine 6G-DODCI CPM laser agree well with the measured ones.
Patent•
22 Nov 1983TL;DR: In this article, an improved amplitude sensing system for detecting the signal amplitude from the read head in a magnetic storage device was proposed, where the amplitude is compared to a threshold voltage.
Abstract: An improved amplitude sensing system for detecting the signal amplitude from the read head in a magnetic storage device wherein the signal amplitude is compared to a threshold voltage. When the signal amplitude is greater than the threshold voltage, the amplitude sensor output is high, indicating sufficient amplitude, and when the signal amplitude is less than the threshold voltage, the amplitude sensor output is low, indicating insufficient amplitude. The threshold voltage is selected to be the higher of a fixed minimum voltage, the minimum long term acceptable read head signal level, or an adaptive voltage derived from the peak voltages of the read head signal amplitude, which is a fixed percentage of the long term read head signal level. When the read head signal is not present for a long time, or while tape motion is starting, the fixed minimum voltage prevents invalid amplitude sensor output. When the read head signal is present, the adaptive voltage allows the threshold to vary with the characteristic signal output of the read head signal and the signal amplitude produced by different magnetic media.
Patent•
26 Sep 1983TL;DR: In this article, a method of detecting an object that may be coated with material for preventing or attenuating reflections of incident electromagnetic waves is disclosed in which pulses of electromagnetic wave energy are generated with a large relative bandwidth in the band from about 0.1 GHz to about 12.0 GHz.
Abstract: A method of detecting an object that may be coated with material for preventing or attenuating reflections of incident electromagnetic waves is disclosed in which pulses of electromagnetic wave energy are generated with a large relative bandwidth in the band from about 0.1 GHz to about 12.0 GHz. Preferably, the generated pulses have a pulse duration in the range from 0.1 nanosecond to 1 nanosecond. Those pulses of electromagnetic wave energy are directed toward the object and reflections of those pulses of electromagnetic wave energy which are incident on the object are detected by receiving apparatus. The method enables coated objects to be differentiated from uncoated objects.
Patent•
26 Apr 1983
TL;DR: In this article, a method and an apparatus for determining the difference between the transit times of measuring pulse signals from a transmitter to a receiver along a measuring signal path establishing an unknown time of travel which is representative for a physical quantity of interest is presented.
Abstract: The invention provides a method and an apparatus for determining the difference between the transit times of measuring pulse signals from a transmitter to a receiver along a measuring signal path establishing an unknown time of travel which is representative for a physical quantity of interest, and the transit times of reference pulse signals generated by the same transmitter and forwarded to the same receiver along a reference signal path establishing a known, constant time of travel, whereby for the measurement of each of said transit times the time distance between a trigger signal triggering the generation of the respective measuring pulse or reference pulse signal and a time-significant signal is measured which is generated in a defined time relation to the instant at which the respective pulse signal is received by said receiver. Both average values comprise non-linearity errors to the same extent so that these errors are eliminated when the second one of these average values is subtracted from the first one.
TL;DR: In this article, a new technique for measuring extremely fast excited state relaxation times, on the order of or less than the laser pulse width, in the presence of a longer relaxation time is described.
Abstract: A new technique for measuring extremely fast excited state relaxation times, on the order of or less than the laser pulse width, in the presence of a longer relaxation time is described. The difficulties involved in using the conventional pump‐and‐probe technique and the corresponding advantages of the new technique are illustrated with numerical examples for specific three‐level systems. Qualitative experimental results on semiconductors and organic dye molecules substantiating the results are shown.
TL;DR: In this paper, an experimental study of the shape, delay, and spread of an optical pulse transmitted through a medium containing uniform latex microspheres using a mode-locked Nd:glass laser with a 20-psec pulse width is presented.
Abstract: We present an experimental study of the pulse shape, delay, and spread of an optical pulse transmitted through a medium containing uniform latex microspheres using a mode-locked Nd:glass laser with a 20-psec pulse width. The delay of the arrival time of the peak intensity and the half-power pulse width for three different particle sizes are shown for an optical distance of up to 45.
TL;DR: A bounded band-limited signal may be represented by its sine-wave crossings by a set of points on the time axis at which it crosses a reference sinusoid if, at these points, pulses of a standard shape are generated, and a position modulated pulse train is obtained.
Abstract: A bounded band-limited signal may be represented by its sine-wave crossings, i.e., by a set of points on the time axis at which it crosses a reference sinusoid. If, at these points, pulses of a standard shape are generated, we obtain a position modulated pulse train. This pulse train is analyzed in detail. Two other modulation methods related to sine-wave crossings are also discussed, namely, edge position modulation of a square wave and bipolar pulse duration modulation. In all cases, the modulated waves may be expressed as sums of an infinite number of sinusuidal carriers amplitude modulated by Chebyshev polynomials of modulating signals.
TL;DR: In this article, a high power D2O laser, pumped by a single mode CO2 laser, has been optimized to produce 1 μs pulses at 385 μm, with pump energies up to 100 J using an e−beam preionized CO2 amplifier at 2.5 atm.
Abstract: A high power D2O laser, pumped by a single mode CO2 laser, has been optimized to produce 1 μs pulses at 385 μm. Pump energies up to 100 J were available using an e‐beam preionized CO2 amplifier at 2.5 atm. Far infrared pulse energies of 140 mJ in multimode and 40 mJ in single mode operation have been obtained from a 4‐m unstable resonator. During parametric studies the influence of operating pressure, spatially inhomogeneous pump intensity, resonator feedback as well as saturation effects have been investigated.
TL;DR: In this paper, the effect of the active modulator on the pulse length of an active/passive mode-locked Nd:YAG laser was investigated qualitatively with respect to their dependence on modulation power, dye concentration of the passive modulator, and resonator length mismatch.
Abstract: The influence of the distance of an active modulator to one of the resonator's end mirrors is investigated both theoretically and experimentally and is found not to be critical for high-gain lasers. The effect of the active modulator on the pulse length of an active/passive mode-locked Nd:YAG laser is discussed qualitatively. Threshold, stability, pulse length, and output energy are investigated experimentally with respect to their dependence on modulation power of the active modulator, dye concentration of the passive modulator, and resonator length mismatch. At a repetition rate of 10 Hz the best achievable stability for the pulse-train energy was ± 1 percent with a single pulse length of 25 ps. The resonator length has to be maintained with an accuracy of \pm 100 \mu m.