Pulse Shape Variations Research Articles

Signal processing for cryogenic micro-calorimetry

We describe electronics and signal processing techniques used to acquire data with our micro-calorimeters. The system includes front end electronics with cold FETs, an amplitude-independent trigger, pulse digitization and storage, and digital signal processing in software. We discuss some ideas for processing signals from devices which exhibit a variation in pulse shape.

Shaping of femtosecond pulses using phase-only filters designed by simulated annealing

We describe generation of shaped femtosecond waveforms by using frequency-domain phase-only filters designed by numerical optimization techniques. The task of filter design for pulse shaping in the time domain is directly analogous to the design of phase-only filters for beam shaping and array generation in the spatial domain. We experimentally tested phase filters that were designed to produce ultrafast square and triangle pulses and femtosecond pulse sequences. Our results demonstrate the ability to generate high-quality terahertz-repetition-rate sequences of femtosecond pulses by means of low-loss phase-only filtering. On the other hand, experiments that tested generation of individual shaped pulses, such as square pulses, were less successful than previous experiments that used simultaneous phase and amplitude filtering. Our results indicate the importance of building increased robustness against variations in the input pulse shape into the phase-only filter design.

The Effect of a C02Laser Pulse Shape on the Accuracy of DIAL Measurements

Abstract The temporal pulse shape varies at different wavelengths, within the same wavelength, and between identical lasers. In differential absorption lidar (DIAL) measurements the variance introduced into the deduced average pathlength concentration from variation of laser pulse shape through the approximation of the normalized energy of the lidar return by sampling peak power values is small but can be significant for detecting low-level concentrations. The magnitude of this uncertainty is on the order of that caused by measurement errors on the order of a few percent.

Pulse-shape effects and laser-induced avoided crossings in photodissociation

In a dressed state representation, laser-induced avoided crossings occur between field—molecule electronic surfaces giving rise to stable laser-induced resonances. It is shown that such states can be used to interpret short-pulse (subpicosecond and picosecond) induced molecular photodissociation. Time-dependent numerical calculations of photodissociation probabilities in H + 2 are used to illustrate pulse-shape effects on photodissociation. It is found that stable (long-lived) laser-induced resonances produce many kinetic energy peaks in photofragmentation, and are sensitive to pulse shapes. Short-lived resonances are insensitive to pulse details. At high intensities, nonadiabatic effects due to pulse-shape variation dominate.

Asymmetric crosscorrelation from actively mode-locked semiconductor laser

It is observed that under certain conditions the second harmonic crosscorrelation of pulses from a mode-locked semiconductor laser is asymmetrical. Theoretical and experimental studies show that these asymmetries result from cyclic pulse-shape variations.

A study of the variation of glottal pulse shape with fundamental frequency by inverse filtering of the speech wave

The acoustics of speech production is based on the concept of a source and a filter function. In current models the source of voiced sounds is represented by a quasiperiodic succession of pulses of air emitted through the glottis, as the vocal cords open and close, and the filter function is assumed to be linear and short‐time invariant. The source term or the acoustic excitation produced by the larynx is subject to variation in speech produced by a natural speaker. The analysis described here forms part of an investigation into variation of the shape of the glottal volume velocity waveform as a function of fundamental frequency. The deconvolution of the speech wave, i.e., separation of the glottal pulse signal from the vocal tract impulse response, is done by inverse filtering the speech signal using a filter derived in the closed phase of the glottal cycle. Linear predictive covariance analysis is used in estimating the inverse filter coefficients. A linear relationship between the glottal parameters, open phase, opening duration, and closing duration with time period is shown. A model is then proposed for the variation of these glottal parameters with fundamental frequency.

15–100 keV variability in her X-1 observed by HEAO-1

During the 18 month mission lifetime of HEAO-1, Her X-1 was observed for 183 days of scanning by the UCSD/MIT Hard X-Ray and Low Energy Gamma-Ray Experiment, producing 14 hours of on-source livetime over five 35 day cycles. Included in this time are 13 pointed observations made at various 35 day phases, accounting for 29 hours of livetime on-source. Four complete main-ons were observed to have varying durations. Two complete short-ons and two partial short-ons were also observed. We present here results on pulse shape variations with 35 day phase as well as with energy, spectral variations with pulse phase, and pulse fractions with energy and phase. These results may indicate that the the 35d intensity profile is not due to a simple blocking mechanism at the distance of the accretion disk, and that repeatable changes in the accretion geometry near the pulse formation region may be occurring with 35d phase.

System for flow sorting chromosomes on the basis of pulse shape

Sorting on the basis of the complex features resolved by chromosome slit-scan analysis requires rapid and flexible pulse shape acquisition and processing for determining sort decisions before droplet breakoff. Fluorescence scans of chromosome morphology contain centromeric index and banding information suitable for chromosome classification, but these scans are often characterized by variability in length and height and require sophisticated data processing procedures for identification. Setting sort criteria on such complex morphological data requires digitization and subsequent computation by an algorithm tolerant of variations in overall pulse shape. We demonstrate here the capability to sort individual chromosomes based on their morphological features measured by slit-scan flow cytometry. To do this we have constructed a sort controller capable of acquiring an 128 byte chromosome waveform and executing a series of numerical computations resulting in an area-based centromeric index sort decision in less than 2 ms. The system is configured in a NOVIX microprocessor, programmed in FORTH, and interfaced to a slit-scan flow cytometer data acquisition system. An advantage of this configuration is direct control over the machine state during program execution for minimal processing time. Examples of flow sorted chromosomes are shown with their corresponding fluorescence pulse shapes.

Pulse shapes in single photon, single particle calorimeters

Single photon or single particle calorimeters with energy resolutions of order 1 eV fwhm have recently been proposed as detectors for X-ray astronomy and many other applications. Such devices consist, essentially, of an absorber (linked to a heat bath at ∼ 0.1 K) and one or more thermistors The temperature rise induced in the former element by the absorption of a single photon or particle produces voltage waveforms at the ouput of the latter from which energy information may be abstracted. In this paper, we consider the practical limits to the energy resolution which arise from the “thermal nonuniformity” of the absorber mass. The variation in thermistor pulse shape with position of photon absorption is estimated from solutions of the heat conduction equation, for a number of linear calorimeter designs. An assessment is made of the position-sensing properties of a calorimeter with two line-end thermistors.

Application of reactor pulsing to neutron activation analysis

The TRIGA research reactor operated by the Nuclear Science Center (NSCR) for Texas A&M University has the capability of producing fast transient power pulses by pneumatic ejection of the transient control rod upward out of the core to a preset distance corresponding to the desired input reactivity. The NSCR has been recently relicensed to operate in this mode. An evaluation of linearity of radioactivation to reactivity insertion and integrated pulse energy is presented. Pulse/irradiation timing considerations have proven to be of paramount importance. Pulse shape variations have been shown to significantly effect specific activation, especially at low reactivity insertions. The design and construction of a rapid transfer system for pulsed irradiation activation analysis is discussed.

Electromagnetic Excitation of a Generic Cavity with a Variable e-Beam Pulse

Relativistic electron-beam nose-erosion techniques have been employed to produce an electron beam with variable pulse shape and bremsstrahlung capability (dial a pulse). This capability has been employed to excite a large number of electromagnetic fields inside a canonical cavity. Electron-beam and bremsstrahlung pulse-shape parameters have been varied to produce changes in the electromagntic cavity response. For example, generic cavity test parameters such as displacement currents or conduction currents can be emphasized or de-emphasized. A theoretical interpretation of these electromagnetic excitations is presented.

Electron drift mobility in amorphous Si: H

Abstract The ‘time of flight’ technique has been employed to study the transient photoconductivity due to excess electron carriers in amorphous Si:H, over a wide range of temperature and electric field. The data are analysed in terms of the temperature/field dependence of the carrier transit time, and also in terms of the variation in pulse shape with temperature. In both cases, the behaviour suggests interactions with a tail of states extending about 0·15 eV from the band edge and showing an almost linear variation of trap density with energy over at least the range 0·085 to 0·145 eV. The capture cross-section of the centres is estimated to be of order 10−17–10−l6cm2. Interaction with states beyond the tail is comparatively weak, and is dominated by deep trapping into centres believed to be dangling bonds.

Measurement and fitting of spectrum and pulse shapes of a liquid methane moderator at IPNS

The absolute intensity, energy spectrum and energy variation of the neutron pulse shape have been measured for the IPNS liquid methane “F” moderator, at 108 K. The spectrum has been corrected for attenuation by aluminum in the beam and has been fitted using a simple parametric description. The pulse shapes have been fitted to a function which is the sum of two decaying exponentials convoluted with a Gaussian. These shapes have been corrected for instrumental resolution, parameterised as a function of neutron wavelength, and compared to the results of Monte Carlo simulations for equivalent moderator geometry. Only four parameters are required to describe the normalised spectrum and, in addition to wavelength dependent time delays, only five wavelength independent parameters are needed to describe the variation of the pulse shape over the entire spectrum.

X-ray observations of 4U 1626-67 by the monitor counter on the Einstein /HEAO 2/ observatory

The pulsing X-ray source 4U 1626-67 was observed with the Monitor Proportional Counter (MPC) on board the Einstein X-Ray Observatory on three occasions in early 1979. The MPC is a sealed, argon-filled proportional counter with a 1.5 mil beryllium window and is coaligned with the X-ray telescope on board the observatory. The spectral data spanning the energy range from 1.1 to 21 keV are divided into eight logarithmically spaced energy channels which integrate for 2.56 s. The Time Interval Processor (TIP) circuitry of the MPC measures time intervals between events to within 1 microsecond or 1.6%, whichever is larger, for a count rate dependent fraction of all events in all eight energy channels. It is found that in the energy range from 1 to 21 keV, the spectrum and 7.7 s pulse shape of 4U 1626-67 are variable on a time scale of minutes. The pulse shape variations correlate in a complex way with the intensity variations in this source.

Determination of Coordinates for the Orroral Lunar Ranging Station

AbstractUsing models of the Earth-Moon system developed from analysis of 10 years of laser ranging observations from the McDonald Observatory, we have analyzed observations obtained by the Orroral Lunar Ranging Station since April 1978. Normal point residuals from many of the observations performed before April 1980 using a 20 ns, mi tiple-mode laser pulse are discreetly spaced, as multiples of 6 ns, and may have been corrupted by variations in pulse shape. Further evaluation is required before these observations are used in scientific analyses. Observations performed during the MERIT Short Campaign (August - October 1980) using a 6 ns, single-mode pulse are apparently reliable. Using 27 single photoelectron events, obtained on 7 nights during this period, we have estimated the coordinates of Orroral, with respect to McDonald, with uncertainties of 1-2 m in cylindrical radius and longitude and 5-10 m in z-axis distance.

Short time scale integrated pulse shape variations in PSR 0611 + 22

Short time scale integrated pulse shape variations in PSR 0611 + 22

ZDependence of the Laser-Intensity Threshold for Inhibited Electron Thermal Conduction

Temporally resolved sub-kiloelectronvolt x-ray emission pulses have been obtained from disk targets illuminated with 1.06-\ensuremath{\mu}m wavelength laser light at 5\ifmmode\times\else\texttimes\fi{}${10}^{14}$ W/${\mathrm{cm}}^{2}$. Striking variations in the x-ray pulse shape from Be, Ti, Sn, Au, and U targets indicate the onset of strongly inhibited electron thermal conduction during the rise of the laser intensity. The laser intensity threshold for this strong inhibition is found to increase with target atomic number $Z$.

A spectral theory for circular seismic sources; simple estimates of source dimension, dynamic stress drop, and radiated seismic energy

abstract The far-field body wave radiation from a class of circular rupture models is investigated as a function of takeoff angle, rupture velocity, and stopping behavior. In particular, the variation of spectral shape, pulse shape, and energy flux over the focal sphere is quantified. These results provide two new methods for estimating the source dimension, the first through the inversion of a characteristic frequency, and the second using the rise time of the displacement pulse shape. The class of kinematic rupture models which has been constructed also allows a direct estimate of the dynamic stress drop using the velocity pulse shape: as an example, this technique is applied to an SMA1 recording of a high stress drop Aleutian earthquake, Finally, the introduction of a new spectral parameter, the integral of the square of the ground velocity, is shown to considerably simplify calculation of the total radiated energy. Together with a re-evaluation of corner frequency and spectral falloff, these new results constitute a spectral theory for circular seismic sources which includes directivity and is valid for a range of subsonic rupture velocities.

Tunable, narrow bandwidth, 2 MW dye laser pumped by a KrF ∗ discharge laser

Characteristics of p-terphenyl and PBD, the most efficient uv dyes, have been investigated under high intensity pumping by a multi-atmosphere KrF ∗ discharge laser at 248 nm wavelength. Energy conversion efficiencies, spectral features and temporal behaviour of the dyes were studied parametrically. A maximum powerof 2 MW uv emission with a bandwidth of ∼2×10 -2 nm was obtained for PBD. It was found that a mixture of both dyes provided higher (by a factor of 1.3) output in the range 348–366 nm than either of the dyes alone. Significant pump intensity dependent conversion efficiency and pulse shape variations were observed for the most efficient uv dye, p-terphenyl and were related to triplet-triplet adsorption processes in the dye.

Some characteristics of efficient dye laser emission obtained by pumping at 248 nm with a high power KrF ∗ discharge laser

Characteristics of dye laser emission under high intensity uv pumping, at 248 nm wavelength have been investigated with peak pump powers of ∼ 10 MW at a pulse duration of ∼ 30 ns, provided by a multi-atmosphere KrF ∗ discharge laser. Energy conversion efficiencies, spectral features and temporal behaviour of several dyes were parametrically studied. Significant pump intensity dependent conversion efficiency and pulse shape variations were observed for the most efficient uv dye, p-terphenyl.