Pulse Shape Measurements Research Articles

Observation of Hidden Asymmetry in Polarization Space for Dissipative Soliton Fiber Lasers

Dissipative solitons appear widely in physical systems with dissipative energy exchange, which have been regarded as an excellent platform for exploring nonlinear dynamics. The complex interactions among dispersion management and nonlinearity result in abundant asymmetric behaviors in diverse parameter spaces. Nevertheless, conventional detection methods impede direct and single-shot measurements of the transient polarization dynamics of dissipative solitons. Here, by using the division-of-amplitude method combined with dispersive Fourier transform techniques, we have experimentally observed the internal evolution of dissipative solitons in polarization space. By disturbing the cavity birefringence, we obtain asymmetrical spectra due to nonlinear phase evolution within numerous temporal roundtrips. The different phases across the lasing wavelengths result in wavelength-resolved symmetric breakage in polarization space, which is difficult to find in spectrum or pulse-shape measurements. The direct observation of hidden asymmetry in polarization space for dissipative soliton fiber lasers will facilitate theoretical modeling of mode-locked laser systems with complicated configurations, and it may also promote applications for polarization spectroscopy.

TIGER: TIme‐Gated Electric field Reconstruction

Herein, a novel self-referenced method for the complete temporal characterization (phase and amplitude) of ultrashort optical laser pulses is presented. The technique, called TIme-Gated Electric field Reconstruction (TIGER), measures a second-order nonlinear signal (namely, second-harmonic generation or two-photon absorption) produced by four time-delayed replicas of the input pulse. The delays are spatially encoded in the beam profile using a four-faced pyramid-like optical element. The presented technique enables single shot measurement and does not require any spectral measurements, in contrast with well-known self-referenced characterization methods. Depending on the chosen geometry, the recorded TIGER signal can be either interferometric (i.e., carrier frequency resolved) or intensimetric. This article describes the principle operation of the device together with a detailed theoretical analysis. TIGER measurements of various laser pulse shapes with their reconstructions are then presented, demonstrating the relevance of this original approach.

Measurement of Multi-Stokes Ultrashort Pulse Shapes of Synchronously Pumped Stimulated Raman Scattering on Combined Vibrational Modes in a BaWO4 Crystal

Multi-Stokes ultrashort pulse shapes and their relative positions of synchronously pumped stimulated Raman scattering (SRS) on combined primary and secondary vibrational modes in a BaWO4 crystal are investigated. An original method of its simultaneous measurement with the help of a streak camera has been developed. The structure of SRS pulses at the pulse shortening effect down to the pulse duration, close to the dephasing time of the secondary Raman mode of the BaWO4 crystal, is registered and analyzed for the detuning of the Raman laser cavity length.

On-Orbit Pile-Up Detection and Digital Pulse Shape Measurement Results in the Radiation Telescope

We have developed a radiation environment monitor called the Technical Data Acquisition Equipment (TEDA) installed in the RAPid Innovative payload demonstration Satellite 1 (RAPIS-1) which was launched on January 18, 2019. The TEDA measured the energy spectra of electrons, protons, and He ions. In addition to the functions of a conventional sensor, we added a fast digital sampling function to the TEDA. The operational verification in orbit was successful, and the pile-up waveform signal was acquired for the first time at The Japan Aerospace Exploration Agency (JAXA). The TEDA also obtained data showing that pile-up detection also worked properly.

Improving laser standards for three-photon microscopy.

.Significance: Three-photon excitation microscopy has double-to-triple the penetration depth in biological tissue over two-photon imaging and thus has the potential to revolutionize the visualization of biological processes in vivo. However, unlike the plug-and-play operation and performance of lasers used in two-photon imaging, three-photon microscopy presents new technological challenges that require a closer look at the fidelity of laser pulses.Aim: We implemented state-of-the-art pulse measurements and developed innovative techniques for examining the performance of lasers used in three-photon microscopy. We then demonstrated how these techniques can be used to provide precise measurements of pulse shape, pulse energy, and pulse-to-pulse intensity variability, all of which ultimately impact imaging.Approach: We built inexpensive tools, e.g., a second harmonic generation frequency-resolved optical gating (SHG-FROG) device and a deep-memory diode imaging (DMDI) apparatus to examine laser pulse fidelity.Results: First, SHG-FROG revealed very large third-order dispersion (TOD). This extent of phase distortion prevents the efficient temporal compression of laser pulses to their theoretical limit. Furthermore, TOD cannot be quantified when using a conventional method of obtaining the laser pulse duration, e.g., when using an autocorrelator. Finally, DMDI showed the effectiveness of detecting pulse-to-pulse intensity fluctuations on timescales relevant to three-photon imaging, which were otherwise not captured using conventional instruments and statistics.Conclusions: The distortion of individual laser pulses caused by TOD poses significant challenges to three-photon imaging by preventing effective compression of laser pulses and decreasing the efficiency of nonlinear excitation. Moreover, an acceptably low pulse-to-pulse amplitude variability should not be assumed. Particularly for low repetition rate laser sources used in three-photon microscopy, pulse-to-pulse variability also degrades image quality. If three-photon imaging is to become mainstream, our diagnostics may be used by laser manufacturers to improve system design and by end-users to validate the performance of their current and future imaging systems.

Pulse shape measurement and experimental validation of noise theory developed under consideration of finite pulse width in D-T neutron generator driven subcritical system

Degweker and Rana (2007) had postulated a noise theory assuming the external neutron source as exponentially correlated Gaussian character for finite pulse width comparable to prompt neutron decay constant of subcritical system. They considered various conditions of source correlation time (i.e. the decay time of correlated neutrons), accelerator pulse width and pulse period. This noise theory has been validated experimentally for the first time in D-T neutron generator coupled BRAHMMA subcritical system. The present work has been carried out under the consideration that the source correlation time is small compared to the pulse width and rectangular pulse shape. The pulse shape of the neutron generator was characterised through an AC Current Transformer (ACCT) placed in the D+ beam path of the neutron generator. Variations of source correlation time with pulse widths were studied; it has been observed that source correlation time decreases with smaller pulse width. In validation experiments, data have been analysed using Auto Covariance, Variance to Mean ratio, and Auto Power Spectral Density method. The measured prompt neutron decay constant was found to be in good agreement with the theoretical estimate of the system. Furthermore, the present research also discusses the modulation of the correlated and uncorrelated part in variance to mean ratio method for a wide range of accelerator frequency at fixed source strength. The present research findings also lay the criteria for choosing the proper accelerator frequency for reactivity measurement in ADS.

Codoped Lithium Sodium Iodide With Tl+ and Eu2+ Activators for Neutron Detector

Investigations of high-efficiency neutron-sensitive scintillators are very important for a wide variety of applications including special nuclear material detection, fundamental research, radiation safety, and industrial monitoring, among others. Responding to this need, we have been studying the Li x Na(1– x )I (conventionally called LNI) crystal system, using enriched 6Li because of its high neutron cross section. We have successfully grown single crystals of LNI with $x$ values in the range of 4%–20%, by the vertical Bridgman technique. Sodium iodide (NaI) and lithium iodide (LiI) have the same rock salt crystal structure capable of forming a monolithic solid solution over the entire concentration range. These LNI crystals are codoped with a few mol percent of Tl+ and Eu2+ activator to achieve the desired scintillation properties. X-ray excited luminescence spectra of LNI crystals show nearly identical main emission peaks around 440 nm independent of Li concentration. Neutron detection measurements using an americium/beryllium (AmBe) source show that increasing Li concentration from 4 to 20 mol% causes the neutron light yield (LY) to drop from 150 000 to 50 000 photons/neutron, while the gamma equivalent energy (GEE) for neutrons rises from 3.65 to 4.8 MeV. When measured at 662 keV (137Cs), the gamma ray LY behaves similarly, decreasing with the increase of Li content. This can be attributed to the lower fraction of Na, which affects both stopping power and scintillation efficiency. Pulse-shape discrimination measurements show well-defined differences between the gamma and neutron scintillator response.

A Cherenkov EAS Light Detector with High Temporal Resolution

A fast-acting Cherenkov light detector with a high temporal resolution is described. The interest in such extensive air shower detectors is due to the need for more precise measurements of the Cherenkov pulse shape. The efficiency of the integral Cherenkov detector is demonstrated.

New method of out-of-time energy subtraction for the CMS hadronic calorimeter

The CMS hadronic calorimeter employs plastic scintillator active material in the barrel and endcap (HBHE). In Run 2, the LHC operates at 13 TeV center-of-mass energy with up to 50 simultaneous collisions per bunch crossing (pileup) and a 25 ns bunch spacing. The HBHE scintillator light pulse is only 60% contained in a 25 ns window, resulting in significant pulse overlap for consecutive events (out-of-time pileup). This talk presents a novel algorithm that will be used in 2018 for subtracting out-of-time pileup in HBHE both online in the software trigger and offline. The algorithm includes methods for both the barrel with hybrid photodiode photosensors and QIE8 digitizers, and the endcap with silicon photomultipliers and QIE11 digitizers, including the challenging charge-dependent pulse shaping effects of the QIEs. The on-detector pulse shape measurement method and results are also shown. The new algorithm is five-to-ten times faster than the previous one, and for the first time CMS will use the offline method at the trigger level.

Modelling of picosecond timing signals from fast vacuum photodiodes

Very high bandwidth vacuum photodiodes with 10 s of picoseconds rise time are utilised in Cherenkov detectors for inertial confinement fusion diagnostics. Experimental measurements of the pulse shape and time resolution of a fast Photek PD010 photodiode tube, undertaken using very fast pulsed laser illumination at the ORION facility, Atomic Weapons Establishment, Aldermaston UK, were compared with a computer model to understand detector performance with the aim of improving the time resolution. The physical processes defining the performance of the photodiode detector were modelled using CST Studio Suite software. This package combines very high frequency electromagnetic field modelling, particle tracking, space charge effects and secondary electron emission simulation, and has enabled a realistic simulation of detector behaviour and performance predictions to be made. We present a comparison between experimental measurements of time resolution and pulse shape over a range of device operating voltages, with simulations obtained with CST particle tracking software using the device CAD design file to accurately model the PD010 device. These results demonstrate the remarkable correlation that can be achieved between experiment and simulation, even at picosecond time-scales. • Time resolution of fast vacuum photodiodes is limited by detector geometry. • Impedance matching between anode and signal cable is critical. • Physics of the detector were modelled using CST Studio Suite software. • Remarkable correlation between experiment and simulation is demonstrated.

Precision measurements of the scintillation pulse shape for low-energy recoils in liquid xenon

We present measurements of the scintillation pulse shape in liquid xenon for nuclear recoils (NR) and electronic recoils (ER) at electric fields of 0 to 0.5 kV/cm for energies <15 keV and <70 keV electron-equivalent, respectively. The average pulse shapes are well-described by an effective model with two exponential decay components, where both decay times are fit parameters. We find significant broadening of the pulse for ER due to delayed luminescence from the recombination process. In addition to the effective model, we fit a model describing the recombination luminescence for ER at zero field and obtain good agreement. We estimate the best performance of a combined S2/S1 and pulse shape ER/NR discrimination and show that even with 2 ns time resolution, the improvement over S2/S1 discrimination alone is marginal, so that pulse shape discrimination will likely not be useful for future dual-phase liquid xenon experiments looking for elastic dark matter recoil interactions.

MP24-10 WAVELENGTH AND PULSE SHAPE EFFECTS ON STONE FRAGMENTATION OF LASER LITHOTRIPTERS

You have accessJournal of UrologyStone Disease: Basic Research & Pathophysiology II1 Apr 2018MP24-10 WAVELENGTH AND PULSE SHAPE EFFECTS ON STONE FRAGMENTATION OF LASER LITHOTRIPTERS Andreas Gross, Benedikt Becker, Mark Taratkin, Dmitry Enikeev, Leonid Rapoport, and Christopher Netsch Andreas GrossAndreas Gross More articles by this author , Benedikt BeckerBenedikt Becker More articles by this author , Mark TaratkinMark Taratkin More articles by this author , Dmitry EnikeevDmitry Enikeev More articles by this author , Leonid RapoportLeonid Rapoport More articles by this author , and Christopher NetschChristopher Netsch More articles by this author View All Author Informationhttps://doi.org/10.1016/j.juro.2018.02.763AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookTwitterLinked InEmail INTRODUCTION AND OBJECTIVES Pulsed Holmium:YAG lasers are the energy source of choice in the endoscopic management of urolithiasis. Until recently, pulse frequency and pulse energy were the most investigated parameters to improve efficiency of such lasers. Newer research focusses on the influence of pulse width and pulse shape. Aim of our study was to compare the efficiency of stone dusting of pulsed 2.1µm Holmium:YAG lasers and a pulsed 1.94µm Thulium-fiber laser (TFL) using identical pulse energy, pulse frequency, and average power settings. METHODS The lasers systems tested were the Lumenis Versa Pulse Power Suite P 100 (Ho short pulse), the Lumenis Pulse 120H (Ho long pulse) and a commercially not available prototype of a pulsed TFL (Fig.1, A) to C)). The lasers were tested at 0.2 J and 40 Hz (average power of 8-W). Pulse energies and pulse shapes were measured. Subsequently, efficiency of stone ablation (ablation speed) was compared in vitro on human COM, COM-phosphate, and Uric Acid stones for the three lasers. The in vitro experimental setup included a specially designed cuvette with several levels of metallic meshes allowing for precise quantification of size distribution of stone fragments. RESULTS The pulsewidths (range in ms) of all three lasers are shown in Fig. 1 below. The following values of the peak power were derived from the pulse shape and pulse energy measurements: P100: 1650-W, P120: 1040-W, TFL: 660-W. The measured values of stone ablation speed (in dusting mode, i.e. fragments < 1mm) are summarized in Fig.2. CONCLUSIONS The new pulsed TFL shows a clearly defined pulsewidth with a large area under the curve. This in combination with the wavelength superior in terms of water absorption leads to better efficiency of stone fragmentation in dusting mode. © 2018FiguresReferencesRelatedDetails Volume 199Issue 4SApril 2018Page: e293-e294 Advertisement Copyright & Permissions© 2018MetricsAuthor Information Andreas Gross More articles by this author Benedikt Becker More articles by this author Mark Taratkin More articles by this author Dmitry Enikeev More articles by this author Leonid Rapoport More articles by this author Christopher Netsch More articles by this author Expand All Advertisement Advertisement PDF downloadLoading ...

Pulse Height, Pulse Shape, and Time Interval Analyzer for Delayed $\alpha /\beta$ Coincidence Counting

In this paper, we present a newly constructed analyzer dedicated to measuring the activity of a variety of radioisotopes with an emphasis on the delayed coincidence method. The analyzer acquires arriving pulses whose amplitudes exceed the preset voltage threshold by selectively storing the sampled incoming voltage pulses. This creates data sets that are marked with additional time stamps. These data are given as a sequence, allowing the detection of decay pairs and different types of afterpulses or reduction of the detector’s background. Here, the pulse analyzer was verified with a thick $\alpha $ and $\beta $ sources from 232Th and 238U decay chains and a $\beta $ source from 40K. The simultaneous pulse height, pulse shape, and time interval measurement allowed the differentiation of $\beta /\alpha $ pulse pairs arising from 212Bi/212Po, 214Bi/214Po decay pairs with 300 ns and 160 $\mu \text{s}$ polonium half-life, respectively.

Development of high sensitivity 4H-SiC detectors for fission neutron pulse shape measurements.

4H-silicon carbide (4H-SiC) detectors are well suited for measurements of fission neutron pulse shape for their compact size, excellent radiation resistance, and hydrogen free composition. The aim of this study is to improve the 4H-SiC detector's sensitivity to fission neutron pulses. 4H-SiC detectors with varied epilayer thicknesses are fabricated and then tested in the pulsed neutron field of the Chinese Fast Burst Reactor II (CFBR II). The sensitivity of the 4H-SiC detector to the CFBR II neutron pulse is increased by 139.8%, with the enlargement of epilayer thickness from 20 μm to 120 μm. By employing the proton-recoil method, the sensitivity of the 4H-SiC detector to the CFBR II neutron pulse is further increased by 11.6%. With enhanced sensitivity to fission neutron pulses, 4H-SiC detectors are promising devices for high intensity neutron pulse measurements.

Research on Subcutaneous Pulse Shape Measurement by Near-infrared Moiré Technique

A pulse is generated when the heart pumps blood into the arterial system. The heart pumps blood only when it contracts, not when it relaxes; therefore, blood enters the arterial system in a cyclical form. Artery beating is visible in some parts of the body surface, such as the radial artery of the wrist. This paper mainly uses the feature in which near-infrared spectroscopy penetrates skin to construct a non-invasive measurement system that can measure small vibration in the subcutaneous tissue of the human body, and then uses it for the pulse measurement. This measurement system uses the optical moir<TEX>$\acute{e}$</TEX> principle, together with the fringe displacement made by small vibration in the subcutaneous tissue, and an image analysis program to calculate the height variation from small vibrations in the subcutaneous tissue. It completes a measurement system that records height variation with time, and that together with a fast Fourier transform (FFT) program, they can convert the pulse waveform generated by vibration (time-amplitude) to heartbeat frequency (frequency-amplitude). This is a new and non-invasive medical assistance system for measuring the pulse of the human body, with the advantages of being simple, fast, safe and objective.

Second-harmonic frequency-resolved optical gating covering two and a half optical octaves using a single spectrometer

We report the measurement of laser pulse shapes covering the range 580–3250 nm using second-harmonic generation frequency-resolved optical gating equipped with a single inexpensive visible-NIR miniature spectrometer and a single pair of homemade broadband beam splitters. Our experimental scheme exploits frequency up-conversion by BBO crystals and appropriate corrections for dispersion, beam splitter filtering and phase-matching efficiency. The signal and idler waves from a commercial optical parametric amplifier pumped by a Ti:Sapphire laser (26 fs, 1 kHz) have been characterized as well as their second harmonic. The pulse shapes out of a commercial difference frequency generation module mixing signal and idler have also been measured up to 3250 nm. The resulting pulses range from 20 to 120 fs, and their chirp characteristics are also exposed. Our approach is demonstrated over most of the doubling crystal transparency range.

Generation and measurement of complex laser pulse shapes in the SG-III laser facility

The generation and measurement of complex ultraviolet laser pulse shapes is demonstrated in the SG-III laser facility. Relatively high contrast ratio of 300∶1 required by the physics experiment is achieved and successfully measured. Two continuous main shots validate the reproduction and the stability of the pulse shape, which provide solid foundation for precise physics experiment and laser power balance.

Intrinsic scintillation pulse shape measurements by means of picosecond x-ray excitation for fast timing applications

A set-up has been developed for the accurate and temperature-dependent measurement of intrinsic scintillation pulse shapes upon excitation with 100ps x-ray pulses. Intrinsic pulse shapes were measured for LaBr3:(5–30%)Ce, LaBr3:5%Ce, Sr, CeBr3, LaCl3:10%Ce, LYSO:Ce, LYSO:Ce, 20ppm Ca, LSO:Ce, 0.2%Ca, NaI:Tl, GSO:Ce, LuAG:Pr, YAP:Ce, and YAG:Ce in the temperature range between 80K and 400K. The scintillation rise and decay time constants as well as the 10–90% rise time were derived from the measured data.

Supply Voltage Dependent On-Chip Single-Event Transient Pulse Shape Measurements in 90-nm Bulk CMOS Under Alpha Irradiation

Direct on-chip pulse shape measurements of single-event transients (SETs) in a single inverter in 90-nm bulk CMOS have been performed at the microbeam facility at the Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Germany. Alpha particles with an energy of 8 MeV were used as projectiles, and the supply voltage dependence of the arising SETs was investigated. A strong dependence of the resulting pulse heights, widths, and shapes on the supply voltage could be observed.

Pulse-shape instabilities and their measurement

Multi-shot pulse-shape measurements of trains of ultrashort pulses with unstable pulse shapes are studied. Measurement techniques considered include spectral-phase interferometry for direct electric-field reconstruction (SPIDER), second harmonic generation frequency-resolved optical gating (FROG), polarization gate FROG, and cross-correlation FROG. An analytical calculation and simulations show that SPIDER cannot see unstable pulse-shape components and only measures the coherent artifact. Further, the presence of this instability cannot be distinguished from benign misalignment effects in SPIDER. FROG methods yield a better, although necessarily rough, estimate of the pulse shape and also indicate instability by exhibiting disagreement between measured and retrieved traces. Only good agreement between measured and retrieved FROG traces or 100% SPIDER fringe visibility guarantees a stable pulse train.