Range Of Pulse Widths Research Articles

Nonlinear pulse distortion in single-mode optical fibers at the zero-dispersion wavelength.

The propagation of optical pulses is considered at the zero-dispersion wavelength of nonlinear dispersive fibers. Even in the absence of group-velocity (first-order) dispersion, higher-order dispersive effects in single-mode silica fibers are found to be strong enough to cause significant broadening and distortion of picosecond optical pulses for fiber lengths of 10--100 km. Using the parameters appropriate for a 1.55-\ensuremath{\mu}m dispersion-shifted single-mode fiber, we have studied the evolution of pulse shapes and pulse spectra along the fiber length for a wide range of initial pulse widths. For peak powers \ensuremath{\sim}10 mW, the dispersive and nonlinear effects are comparable for pulse widths \ensuremath{\sim}1 ps and their mutual interplay leads to new qualitative features in the pulse shape and spectrum that are largely independent of the input profile. The theoretical results are useful for an understanding of the higher-order dispersion and, at the same time, have implications for high-capacity, long-haul, optical communication systems.

Ocular effects of pulsed Nd laser radiation: variation of threshold with pulsewidth.

This study of retinal damage thresholds in the rhesus monkey eye investigated the effects of Nd:YAG laser radiation at four pulsewidths; 4, 30, and 200 ns, and 10 microseconds. The thresholds for induction of minimal ophthalmoscopically visible lesions for the four pulsewidths were 158, 326, 170, and 425 microJ, respectively, incident at the eye in single-pulse exposures. The data are interpreted to imply a flat trend of threshold with pulsewidth over the range of pulsewidths examined, in agreement with maximum permissible exposures quoted in existing laser safety standards. This finding is in contrast with the hypothesis of an anomalous trend of increasing threshold with decreasing pulsewidth which was suggested for the nanosec-microsec pulsewidth range based on the sparse data base previously available.

Detection sensitivity and spatial resolution of reverse-bias pulsed deep-level transient spectroscopy for studying electric field-enhanced carrier emission

Reverse-bias pulsed deep-level transient spectroscopy (RDLTS) has recently been used for studies of electric field-enhanced emission from a deep-level defect. The sensitivity, spatial, and temperature resolutions of this technique are investigated and compared with those of DLTS. The electric field strength in a narrow region, where the transient capacitance signal comes from, can be accurately controlled by using RDLTS. The calculated results indicate that there is an optimal operating condition given by a range of emission pulse widths and heights. This operating condition is given for the best compromise of the temperature and spatial resolutions.

Grid controlled x-ray tube switching time: implications for rapid exposure control.

The transient response properties of a conventional grid controlled x-ray source and the implications for rapid exposure control are studied. The use of a cathode cable with a length of only 1 m to connect the x-ray tube and the grid control electronics results in a switching time of 19 microseconds. The phototiming artifacts from the delayed radiation delivered during this transition time can be severe for short pulses. An analog correction technique that anticipates the magnitude of the delayed radiation is used to overcome this limitation and allows accurate phototiming over a wide range of pulse widths ranging down to 20 microseconds.

Generation of a train of soliton pulses by induced modulational instability in optical fibers

The modulational instability of a cw optical signal in a glass fiber combined with an externally applied amplitude modulation can be utilized to produce a train of optical solitons with a wide range of pulse width (50-1 psec) and repetition period ( less, similar250 psec).

A sensitive single-pulse beam charge monitor for use with charged particle accelerators

An inductive, non-intercepting beam charge monitor which measures the charge in single bunches of accelerated electrons over the range 5 pC-2 micro C is described. The range of electron pulse widths covered by the monitor is 1.5 ns–5 micros. The charge response is essentially linear and independent of pulse width. The device is used for beam alignment and for recording pulse-to-pulse variations of dose in a target cell during pulse radiolysis experiments.

Characterization of laser-produced plasma x-ray sources for use in x-ray radiography

We report the absolute conversion efficiency ξx from the incident laser light energy to x-ray photons for laser-produced plasmas. Potential x-ray backlighting (radiography) line sources having photon energies from 1.4 to 8.6 keV are studied as a function of laser wavelength, pulsewidth, and intensity. The laser intensity and pulsewidth range from 1014 to 1016 W/cm2, 100 ps to 2 ns and include incident wavelengths of 1.06, 0.53, and 0.35 μm. We found that K-shell x-ray line emission ξx : (1) decreases with increasing x-ray energy, (2) decreases with increasing laser intensity, (3) decreases rapidly with pulselength, and (4) moderately increases with decreasing laser wavelength. On the contrary, for Au M band emission, at a fixed laser intensity and pulsewidth, ξx significantly increases (∼25×) upon decreasing the laser wavelength from 1.06 to 0.35 μm.

Ultrasonic switching of a bistable liquid crystal cell

The response of a twisted nematic cell to a tone burst of ultrasound has been investigated. The cell is more sensitive than an ordinary nematic cell and, because it has two stable configurations, can store the acoustic signal. Over a wide range of acoustic pulse widths, the threshold for switching from one stable state to the other depends on the total acoustic energy of the pulse.

A High-Power W-Band (90--99 GHz) Solid-State Transmitter for High Duty Cycles and Wide Bandwidth

A high average power W-band solid-state transmitter using a 2-diode and a 4-diode IMPATT power combiner has achieved over 1.89 W and exceedingly versatile performance over a broad range of pulsewidths and duty cycles with a tunable bandwidth from 90 GHz to 99 GHz.

Laser-induced damage measurements in CdTe and other II–VI materials

Results of laser-induced damage measurements in CdTe and other selected II-VI materials are reported. These studies were conducted using pulsed 1.06-microm radiation from a Nd:YAG laser. The laser pulse width was varied from approximately 40 to 9000 psec (9 nsec). The laser-induced surface breakdown irradiance measured for CdTe over this pulse width range scaled as t(p)(-1/2)[t(p) is the laser pulse width (FWHM)]. This indicates that laser-induced damage in this material is due to linear absorption by a thin surface contamination layer.

Investigation of laser temporal pulse duration on Rayleigh scattering

Relative Rayleigh-scattering cross sections from nitrogen have been measured for various pulse durations and wavelengths of incident laser radiation. No pulse-duration dependence has been observed for laser pulses as short as 5 ns, and classical theory is found to be still valid over the pulse-width range (5< or =..delta..t< or =110 ns) of our observations.

On the pumping of plasma lasers by a high-frequency-modulated electron beam

The possibility of effective pumping of plasma lasers by a high-frequency-modulated electron beam, i.e. an electron beam in the form of a periodic train of electron bunches, is discussed. It is shown that if such parameters of the medium as the relaxation times of the electron temperature ρ T e and the electron density ρ N e are in agreement with the pulse width ρ p and the interval between pulses, 1/ƒ m, this will facilitate effective laser pumping and amplitude modulation of the laser radiation. Existing microwave tubes, such as a traveling-wave tube and a klystron, provide the required parameters of a periodic train of current pulses (electron bunches) over a wide range of pulse widths ρ p and pumping current amplitudes.

Pulse evolution in injection mode locked TECO2 lasers

The pulse train evolution in an injection mode locked TECO2 laser has been investigated for a wide range of input pulse widths e.g., ranging from the cavity round-trip time to near the bandwidth-limited value for the system. Regimes in which pulse narrowing and pulse broadening occur have been identified and are discussed. The combined use of injection and saturable-absorber mode-locking techniques has produced reliable subnanosecond pulse trains from a large aperture TEACO2 laser.

ND : YAG regenerative amplifier

The Nd : YAG regenerative amplifier produces short-duration, optical pulses with the stability and pulse width range characteristic of actively mode-locked lasers and the pulse energy characteristic of passively mode-locked lasers. Other important properties, including large amplification and optical pulse storage, have also been achieved.

The time dependence of two-phonon ionisation

The authors treat a model for photoionisation in which the atom has many bound atomic levels and the laser may be either monochromatic or possess a finite bandwidth. The treatment is restricted to the case where the laser is not sufficiently intense to cause Stark splitting of the atomic energy levels. They obtain an expression for the two-photon ionisation probability as a function of time which covers both resonant and non-resonant excitation. They identify several time regimes where the probability takes on a particularly simple form. In particular they discuss the short time behaviour and the conditions under which a time-independent transition rate exists. Numerical plots of the ionisation probability against laser frequency for a wide range of pulse durations are given for the two-level model.

Catastrophic degradation of GaAlAs DH laser diodes

The catastrophic degradation of GaAlAs DH laser diodes is examined with the application of pulsed or dc current. The dependence of the pulsewidth on the degradation is measured using samples with or without facet coating. The light output PD at which the catastrophic degradation occurs decreases with an increase in the pulsewidth in the pulsewidth range 100 nsec to 10–50 μsec, and PD is constant over the pulsewidth of 10–50 μsec. The sample with an Al2O3 film coating has the highest PD. Photoluminescence patterns of the active layer in degraded samples both with and without facet coating show the growth of DLD’s in the 〈110〉 direction from the vicinity of a facet in the stripe region.

A 20 kV nanosecond-rise-time pulse generator using Krytrons

A high-voltage pulse generator is described which produces 20 kV rectangular pulses having 10 ns rise and fall times, a duration from 30 ns up to milliseconds and repetition rates up to 50 pulses s-1. The main advantages of the device over customary circuits are low jitter, small triggering power and large range of pulse width.

Pulse propagation in the amplifier of a high-power iodine laser

Pulse propagations in an amplifier in the case of the photodissociation iodine laser are investigated with the use of semiclassical treatments, especially when the input pulse fed into the amplifier has a width comparable to or shorter than the transverse relaxation time of the amplifier medium. In our semiclassical equations for pulse propagation in an iodine amplifier, the populations of all hyperfine levels [ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> P <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</inf> ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F= 3, 2</tex> ), <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> P <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3/2</inf> ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F = 4, 3, 2, 1</tex> )], the polarizations of optically allowed transitions ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\DeltaF = 0, \pm 1</tex> ), and the Doppler detuning effects were taken into consideration. Based on the numerical integrations of the semiclassical equations, the propagated pulse shape and the population distributions of the hyperfine levels are discussed. From our calculations, it has been made clear that bandwidth limitations of pulses in the range of pulsewidths of 0.1 ns and below can be avoided by making use of the nonlinear amplification that results from the coherent interaction between the propagated pulse field and the amplifier medium.

Accuracy of single photoelectron time spread measurement of fast photomultipliers

The accuracy of time spread measurements of fast photomultipliers has been investigated, using single photoelectrons. The effect of the finite light pulse width on the measurement accuracy is determined and discussed. Experimental data have been obtained on a special measuring system for light pulse widths ranging from 200 ps to 10 ns, using fast photomultipliers 8850 and C31024 with optimized operating conditions for minimum transit time spread. A modified exponential function expression and curve-fitting parameters are given, which fit closely the experimentally obtained data over a wide dynamic range of light pulse widths.

Accurate amplitude measurement and time pick-off method for the broad pulse width range of nuclear detectors

Using semiconductor detectors, the optimum shaping time constant varies between 0.1 to 50 μs which leads to a pulse width change of more than two orders of magnitude. In such a wide range, both single- and multichannel analysers can measure amplitudes only at the expense of a loss in the speed of measurement, in energy resolution or accuracy. The device presented here produces square-wave analog pulses by means of sampling technique. Square-wave pulses are ideal both for single- and multichannel amplitude analysers. The choice of the optimum sampling time follows automatically and the time pick-off characteristics are good. There is no additional dead time.