Results 1 - 10 of 2261
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[en] We study nonlinear Landau-Zener tunnelling in discrete Gross-Pitaevskii systems accounting for finite energy-level shifts generated by broadened pulse shapes in the non-adiabatic regime. Under these conditions, the tunnelling dynamics is generally sensitive to the pulse arrival time, however, we show that through variation of the pulse shape one can recover a case of rapid high fidelity population transfer independent of the pulse arrival time. We demonstrate how population transfer is possible in two-mode and three-mode systems. In large systems, we expect that population transfer between a pair of modes can be achieved through the application of a sequence of pulses that select pairs of neighbouring modes at each step.
[en] The conventional split Hopkinson pressure bar (C-SHPB) technique with a special experimental apparatus is used to obtain a dynamic deformation material behavior under a high strain rate loading condition. An experimental modification is introduced to reduce the non-equilibrium on the dynamic material response during a short test period for two polymeric materials. The proposed method uses aluminum pressure bars to achieve a closer impedance match between the pressure bars and the specimen materials such as hot temperature degraded POM (Poly Oxy Methylene) and PP (Poly Propylene) to obtain more distinguishable experimental signals. In addition, a pulse shaper technique is used for increasing the rise time of the incident pulse to ensure the dynamic stress equilibrium and the homogeneous deformation in the specimen under dynamic compression loading condition. The details on the dynamic stress equilibrium and the duration of uniform strain rate during the dynamic deformation of the specimen are experimentally investigated. The effects of degradation at a few different hot temperatures on the maximum compressive stresses are also experimentally studied under varying impulsive loading conditions
[en] LAMPS is a Data Acquisition software (DAQ) supporting varied controller type on CAMAC and VME platform. The thrust of recent software development has been centered on VME platform. This paper talks about recent improvements made in VME-LAMPS, as a result
[en] A configurable electronic system has been developed for button BPMs readout in the storage ring of Iranian Light Source Facility (ILSF). This system calculates the beam position through the output voltage of BPMs. Output signals of BPMs pass through a 500 MHz and 50ohm front-end for noise filtering and also gain control purposes. Then the signal is digitized based on under sampling method by a 130MHz ADC for further analysis in FPGA. Safe dynamic range of 0dBm to -90 dBm can be covered by this electronic system with white noise measured to be around -110dBm. Trigger for this electronic is 2-10Hz as Slow data acquisition for Slow orbit feedback system and 4-10 KHz as Fast data acquisition for fast orbit feedback system. This paper describes the design, analysis, and measurements of the developed electronic system. (author)
[en] The present work deals with the compensation of third-order dispersion (TOD) in view of parabolic pulse (PP) generation in standard normal dispersion-decreasing fiber (NDDF) links by using phase modulator (PM) at certain position within the link. Since the inherent TOD in the fiber leads to an asymmetric pulse shape and thus degrades the PP formation, there is a strong requirement to minimize the TOD within the fiber link. It is seen that insertion of PM at the estimated critical length reduces misfit parameter satisfactorily at the output end and an equivalent PP is regenerated. A three-stage cascaded system comprising the first section of NDDF, dispersion-shifted fiber (DSF) and a normal dispersion fiber (NDF) may also be useful to mitigate TOD by showing the equivalent performance as that obtained by employing PM in the previous case.
[en] This review is concerned with pulse stretchers and compressors as key components of ultra-high power laser facilities that take advantage of chirped-pulse amplification. The potentialities, characteristics, configurations and methods for the matching and alignment of these devices are examined, with particular attention to the history of the optics of ultra-short, ultra-intense pulses before and after 1985, when the chirped-pulse amplification method was proposed, which drastically changed the view of the feasibility of creating ultra-high power laser sources. The review is intended primarily for young scientists and experts who begin to address the amplification and compression of chirped pulses, experts in laser optics and all who are interested in scientific achievements in the field of ultra-high power laser systems. (review)
[en] The conditions under which optical materials are susceptible to laser-induced damage is a topic which has been the subject of considerable study. Laser parameters such as wavelength and temporal pulse duration have been studied extensively. Until this work the effect of temporal pulse shape has not been considered. The authors present here data from a simple single-parameter model and a supporting experiment which predicts that a flat-in-time pulse will produce damage at approximately 80% of the fluence of a Gaussian pulse of the same duration
[en] We have analyzed the accuracy of distance determination by range–intensity correlation methods in the case of an arbitrary pulse shape. We show that the absolute error is proportional to the pulse duration τL. For a trapezoidal pulse shape, which is a reasonable approximation of the real pulse shape, we obtain an analytical estimate of the extremal error and the distance at which is it realized. The maximum error in the distance obtained in calculations with trapezoidal pulses corresponds to an extremely asymmetric pulse and is a little over 10% of the spatial pulse length τLc, where c is the speed of light. Symmetric pulses give an error due to nonrectangularity of the pulse that is smaller by a factor of ~2. Since a trapezoidal shape can qualitatively reproduce the shape of practically any real pulse, probably the trapezoidal pulse model gives an estimate of the highest possible error.
[en] For gated viewing systems with triangular and trapezoidal illuminating pulses, we have obtained the range-intensity profiles (RIPs) of the signal as the time delay was varied between the leading edges of the gate pulse and the illuminating pulse. We have established that if the duration of the illuminating pulse Δtlas is less than or equal to the duration of the gate pulse ΔtIC, then the expressions for the characteristic distances are the same as for rectangular pulses and they can be used to determine the distance to objects. When Δtlas > ΔtIC, in the case of triangular illuminating pulses the RIP is bell-shaped. For trapezoidal pulses, the RIP is bell-shaped with or without a plateau section. We propose an empirical method for determining the characteristic distances to the RIP maximum and the boundary points for the plateau section, which we then use to calculate the distance to the object. Using calibration constants, we propose a method for determining the distance to an object and we have experimentally confirmed the feasibility of this method.
[en] We present all the information necessary for construction and characterization of acousto optic pulse shapers, with a focus on ultraviolet wavelengths, Various radio-frequency drive configurations are presented to allow optimization via knowledgeable trade-off of design features. Detailed performance characteristics of a 267 nm acousto-optic modulator (AOM) based pulse shaper are presented, Practical considerations for AOM based pulse shaping of ultra-broad bandwidth (sub-10 fs) amplified femtosecond pulse shaping are described, with particular attention paid to the effects of the RF frequency bandwidth and optical frequency bandwidth on the spatial dispersion of the output laser pulses