Topic
Pulse duration
About: Pulse duration is a research topic. Over the lifetime, 19429 publications have been published within this topic receiving 286507 citations.
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TL;DR: In this paper, the authors show that compensation sharpens the probability distribution function of the pulse durations by a factor that decreases with increasing polarization dispersion, and that compensation can be achieved by using principal states of polarization.
Abstract: Polarization mode dispersion in standard telecommunication fibers can be compensated to first order by using the concept of principal states of polarization. At the receiver the pulse is decomposed into the two waveforms polarized along the two principal states for the optical link and their delay is removed. We show by Monte Carlo simulation that compensation sharpens the probability distribution function of the pulse durations by a factor that decreases with increasing polarization dispersion.
109 citations
TL;DR: A systematic study characterizing the achievable performance of 90° and 180° universal rotation pulses as functions of bandwidth, pulse length, and tolerance to B(1)-field inhomogeneity/miscalibration finds that the application of a single optimal refocusing pulse matches or improves the performance of two consecutive inversion pulses in INEPT-like pulse sequence elements of the same total duration.
109 citations
TL;DR: The first measurement of the specific heat of multilayer and monolayer graphene in both supported and suspended geometries is reported, and their thermal conductivity was simultaneously measured using a comprehensive Raman optothermal method without needing to know the laser absorption.
Abstract: The last decade has seen the rapid growth of research on two-dimensional (2D) materials, represented by graphene, but research on their thermophysical properties is still far from sufficient owing to the experimental challenges. Herein, we report the first measurement of the specific heat of multilayer and monolayer graphene in both supported and suspended geometries. Their thermal conductivities were also simultaneously measured using a comprehensive Raman optothermal method without needing to know the laser absorption. Both continuous-wave (CW) and pulsed lasers were used to heat the samples, based on consideration of the variable laser spot radius and pulse duration as well as the heat conduction within the substrate. The error from the laser absorption was eliminated by comparing the Raman-measured temperature rises for different spot radii and pulse durations. The thermal conductivity and specific heat were extracted by analytically fitting the temperature rise ratios as a function of spot size and pulse duration, respectively. The measured specific heat was about 700 J (kg K)-1 at room temperature, which is in accordance with theoretical predictions, and the measured thermal conductivities were in the range of 0.84-1.5 × 103 W (m K)-1. The measurement method demonstrated here can be used to investigate in situ and comprehensively the thermophysical properties of many other emerging 2D materials.
108 citations
TL;DR: A general numerical approach is described that allows obtaining model sets of temporal pulse shapes of free-electron lasers operating in the self-amplified spontaneous emission mode that satisfy statistical criteria of FEL light predicted by established FEL theory.
Abstract: A general numerical approach is described that allows obtaining model sets of temporal pulse shapes of free-electron lasers (FELs) operating in the self-amplified spontaneous emission mode. Based on a random partial-coherence approach, sets of pulse shapes can be calculated that satisfy statistical criteria of FEL light predicted by established FEL theory. Importantly, the numerically retrieved sets of pulses reproduce the experimentally accessible FEL light characteristics as measured at the Free-electron LASer at Hamburg (FLASH), such as the average spectrum, single-shot spectral shape, and pulse duration. The high-precision agreement with the experimental average spectral shape, without further knowledge of FEL machine parameters, makes this approach a convenient tool for the analysis and theoretical modeling of nonlinear optical or pump–probe experiments with FEL light.
108 citations
TL;DR: In this paper, a new method of operating PEM fuel cells with reformed hydrogen with reduced requirements for gas cleaning is presented, which allows the direct feeding of reformate gas into the fuel cell without a significant loss of performance.
Abstract: Proton exchange membrane (PEM) fuel cells are currently being developed as alternative energy conversion systems
for vehicular as well as for stationary power applications. The supply of hydrogen obtained by the reforming
of alcohols or hydrocarbons to PEM fuel cells requires an extensive gas clean-up, as contaminants such as CO are poisonous to the employed catalysts. A new method of operating PEM fuel cells with reformed
hydrogen with reduced requirements for gas cleaning is presented. The pulse technique allows the direct feeding
of reformate gas into the fuel cell without a significant loss of performance. The electrical pulses increase
the anode potential to values at which the CO is oxidised to CO2. In this way the catalyst surface is continuously
cleaned and the loss of cell voltage is minimised. The optimised operating parameters for the pulses
(namely pulse amplitude, duration and frequency) were investigated and determined as a function of CO content
in the feed gas. It was found that the optimised pulse duration is not changed significantly for the different
CO contents investigated (100, 1000 and 10000 ppm). In contrast, the pulse frequency needs to be adjusted
to obtain CO tolerance at different CO concentrations in the hydrogen gas. This operating
method greatly increases the design
options of fuel cell systems for different applications.
108 citations