Ps Duration Research Articles

Formation of 1.4 MeV runaway electron flows in air using a solid-state generator with 10 MV/ns voltage rise rate

Fulfillment of the condition that the voltage rise time across an air gap is comparable with the time of electron acceleration from a cathode to an anode allows a flow of runaway electrons (REs) to be formed with relativistic energies approaching that determined by the amplitude of the voltage pulse. In the experiment described here, an RE energy of 1.4 MeV was observed by applying a negative travelling voltage pulse of 860-kV with a maximum rise rate of 10 MV/ns and a rise time of 100-ps. The voltage pulse amplitude was doubled at the cathode of the 2-cm-long air gap due to the delay of conventional pulsed breakdown. The above-mentioned record-breaking voltage pulse of ∼120 ps duration with a peak power of 15 GW was produced by an all-solid-state pulsed power source utilising pulse compression/sharpening in a multistage gyromagnetic nonlinear transmission line.

All-fiber all-normal-dispersion femtosecond laser with a nonlinear multimodal interference-based saturable absorber.

In this Letter, we demonstrate, to the best of our knowledge, the first all-fiber all-normal-dispersion ytterbium-doped oscillator with a nonlinear multimodal interference-based saturable absorber capable of generating ultrashort dissipative soliton pulses. Additional to functioning as a saturable absorber, the use of multimode fiber segments between single-mode fibers also ensures the bandpass filtering via multimode interference reimaging necessary to obtain dissipative soliton mode locking. The oscillator generates dissipative soliton pulses at 1030nm with 5.8mW average power, 5ps duration, and 44.25MHz repetition rate. Pulses are dechirped to 276fs via an external grating compressor. All-fiber cavity design ensures high stability, and ∼70 dB sideband suppression is measured in the radio frequency spectrum. Numerical simulations are performed to investigate cavity dynamics, and obtained results are well matched with experimental observations. The proposed cavity presents an alternative approach to achieve all-fiber dissipative soliton mode locking with a simple and low-cost design.

X-ray absorption spectroscopy study of energy transport in foil targets heated by petawatt laser pulses

X-ray absorption spectroscopy is proposed as a method for studying the heating of solid-density matter excited by secondary X-ray radiation from a relativistic laser-produced plasma. The method was developed and applied to experiments involving thin silicon foils irradiated by 0.5–1.5 ps duration ultrahigh contrast laser pulses at intensities between 0.5×1020 and 2.5×1020 W/cm2. The electron temperature of the material at the rear side of the target is estimated to be in the range of 140–300 eV. The diagnostic approach enables the study of warm dense matter states with low self-emissivity.

A 5 pJ/pulse at 1-Gpps Pulsed Transmitter Based on Asynchronous Logic Master–Slave PLL Synthesis

This paper presents an ultralow power asynchronous logic transmitter operating at 1 Gpps that achieves pulse synthesis using a double phase-locked loop (PLL) architecture for applications exploiting large-scale neuronal interfacing with CMOS probes. The 4 GHz center frequency OOK transmitter synthesizes 500 ps duration pulses from a 31.25 MHz crystal oscillator using a cascade of a master and a slave PLL with the latter locked to the former. Both PLLs are implemented with CMOS digital cells and ring oscillator-based VCO. A prototype fabricated in a 130 nm RFCMOS process operates at a measured 5 pJ/pulse energy budget for an active area of 0.04 mm2. To generate timing references and packets for high data rate recording devices, the synthesizer core feeds also a logic interface operating at 250 MHz with four 1.2–3.3 V external parallel channels. From reset time, the master–slave PLL combination achieves locking in a measured time of 450 ns, settling is resolved in $\sim 4~\mu \text{s}$ , and the output pulses across the antenna load are generated with a 3.42 ps RMS jitter standard deviation. The obtained phase noise of a continuous OOK stream at 1 and 4 GHz, 1 MHz offset, is −103 and −93 dBc/Hz, respectively.

A large area diamond-based beam tagging hodoscope for ion therapy monitoring

The MoniDiam project is part of the French national collaboration CLaRyS (Contrôle en Ligne de l’hAdronthérapie par RaYonnements Secondaires) for on-line monitoring of hadron therapy. It relies on the imaging of nuclear reaction products that is related to the ion range. The goal here is to provide large area beam detectors with a high detection efficiency for carbon or proton beams giving time and position measurement at 100 MHz count rates (beam tagging hodoscope). High radiation hardness and intrinsic electronic properties make diamonds reliable and very fast detectors with a good signal to noise ratio. Commercial Chemical Vapor Deposited (CVD) poly-crystalline, heteroepitaxial and monocrystalline diamonds were studied. Their applicability as a particle detector was investigated using α and β radioactive sources, 95 MeV/u carbon ion beams at GANIL and 8.5 keV X-ray photon bunches from ESRF. This facility offers the unique capability of providing a focused (~1 μm) beam in bunches of 100 ps duration, with an almost uniform energy deposition in the irradiated detector volume, therefore mimicking the interaction of single ions. A signal rise time resolution ranging from 20 to 90 ps rms and an energy resolution of 7 to 9% were measured using diamonds with aluminum disk shaped surface metallization. This enabled us to conclude that polycrystalline CVD diamond detectors are good candidates for our beam tagging hodoscope development. Recently, double-side stripped metallized diamonds were tested using the XBIC (X Rays Beam Induced Current) set-up of the ID21 beamline at ESRF which permits us to evaluate the capability of diamond to be used as position sensitive detector. The final detector will consist in a mosaic arrangement of double-side stripped diamond sensors read out by a dedicated fast-integrated electronics of several hundreds of channels.

Demonstration of Two-Atom Entanglement with Ultrafast Optical Pulses.

We demonstrate quantum entanglement of two trapped atomic ion qubits using a sequence of ultrafast laser pulses. Unlike previous demonstrations of entanglement mediated by the Coulomb interaction, this scheme does not require confinement to the Lamb-Dicke regime and can be less sensitive to ambient noise due to its speed. To elucidate the physics of an ultrafast phase gate, we generate a high entanglement rate using just ten pulses, each of ∼20 ps duration, and demonstrate an entangled Bell state with (76±1)% fidelity. These results pave the way for entanglement operations within a large collection of qubits by exciting only local modes of motion.

Sub-nanosecond resolution electric field measurements during ns pulse breakdown in ambient air

Electric field during ns pulse discharge breakdown in ambient air has been measured by ps four-wave mixing, with temporal resolution of 0.2 ns. The measurements have been performed in a diffuse plasma generated in a dielectric barrier discharge, in plane-to-plane geometry. Absolute calibration of the electric field in the plasma is provided by the Laplacian field measured before breakdown. Sub-nanosecond time resolution is obtained by using a 150 ps duration laser pulse, as well as by monitoring the timing of individual laser shots relative to the voltage pulse, and post-processing four-wave mixing signal waveforms saved for each laser shot, placing them in the appropriate ‘time bins’. The experimental data are compared with the analytic solution for time-resolved electric field in the plasma during pulse breakdown, showing good agreement on ns time scale. Qualitative interpretation of the data illustrates the effects of charge separation, charge accumulation/neutralization on the dielectric surfaces, electron attachment, and secondary breakdown. Comparison of the present data with more advanced kinetic modeling is expected to provide additional quantitative insight into air plasma kinetics on ~ 0.1–100 ns scales.

HV discharge acceleration by sequences of UV laser filaments with visible and near-infrared pulses

We investigate the triggering and guiding of DC high-voltage discharges over a distance of 37 cm by filaments produced by ultraviolet (266 nm) laser pulses of 200 ps duration. The latter reduce the breakdown electric field by half and allow up to 80% discharge probability in an electric field of 920 kV m–1. This high efficiency is not further increased by adding nanosecond pulses in the Joule range at 532 and at 1064 nm. However, the latter statistically increases the guiding length, thereby accelerating the discharge by a factor of 2. This effect is due both to photodetachment and to the heating of the plasma channel, that increases the efficiency of avalanche ionization and reduces electron attachment and recombination.

Modifying the Morphology of Silicon Surfaces by Laser Induced Liquid Assisted Colloidal Lithography.

Single, or isolated small arrays of, spherical silica colloidal particles (with refractive index ncolloid = 1.47 and radius R = 350 nm or 1.5 μm) were placed on a silicon substrate and immersed in carbon tetrachloride (nliquid = 1.48) or toluene (nliquid = 1.52). Areas of the sample were then exposed to a single laser pulse (8 ps duration, wavelength λ = 355 nm), and the spatial intensity modulation of the near field in the vicinity of the particles revealed via the resulting patterning of the substrate surface. In this regime, ncolloid < nliquid and the near-field optical intensification is concentrated at and beyond the edge of the particle. Detailed experimental characterization of the irradiated Si surface using atomic force microscopy reveals contrasting topographies. The same optical behavior is observed with both liquids, i.e., the incident laser light diverges on interaction with the colloidal particle, but the resulting interaction with the substrate is liquid dependent. Topographic analysis indicates localized ablation and patterning of the Si substrate when using toluene, whereas the patterning induced under carbon tetrachloride is on a larger scale and extends well below the original substrate surface—hinting at a laser induced photochemical contribution to the surface patterning.

Mode suppression of 53 dB and pulse repetition rates of 2.87 and 36.4 GHz in a compact, mode-locked fiber laser comprising coupled Fabry-Perot cavities of low finesse (F = 2).

Multiplication of the pulse repetition frequency (PRF) of a compact, mode-locked fiber laser by a factor as large as 25 has been achieved with two coupled Fabry-Perot (FP) resonators of low finesse (F = 2). Reducing the FP finesse by at least two orders of magnitude, relative to previous pulse frequency multiplication architectures, has the effect of stabilizing the oscillator with respect to pulse-to-pulse amplitude, dropped pulses, and other effects of cavity detuning. Coupling two Fabry-Perot cavities, each encompassing a 3.3-3.6 cm length of fiber, in a hybrid geometry resembling that of the coupled-cavity laser interferometer has yielded side mode suppressions ≥ 50 dB while simultaneously doubling the laser PRF to 2.87 GHz. Pulses approximately 3.9 ps in duration (FWHM) are emitted at intervals of 27.5 ps, and in groups (bursts) of pulses separated by 350 ps. Thus, the PRF within the pulse bursts is 36 GHz, a factor of 25 greater than the free spectral range for a conventional mode-locked cavity having a length of 6.9 cm. Experimental data are in accord with simulations of the phase coherence and temporal behavior of the mode-locked pulses.

Compact fiber CPA system based on a CFBG stretcher and CVBG compressor with matched dispersion profile

In this work, a compact fiber chirped pulse amplification system exploiting a tandem of a chirped fiber Bragg grating stretcher and a chirped volume Bragg grating compressor with matched chromatic dispersion is presented. Chirped pulses of 230 ps duration were amplified in a Yb-doped fiber amplifier and re-compressed to 208 fs duration with good fidelity. The compressed pulse duration was fine-tuned by temperature gradient along the fiber Bragg grating stretcher.

Generation of strong cylindrical vector pulses via stimulated Brillouin amplification

Light with transverse polarization structures, such as radial and azimuthal polarization, enables and revives lots of applications based on a light-matter interaction due to its unique focal properties. To date, studies referring to this topic mainly concentrate on a weak-light domain, yet it should have gained more attention in a high-energy domain. Here, we demonstrate the generation of strong single-longitudinal-mode (SLM) cylindrical vector (CV) short pulses via stimulated Brillouin amplification. As a proof-of-principle work, the energy is transferred from a pair of 700 ps pumps to a 300 ps Stokes pulse via parametrically exciting coherent phonons in fluorocarbon liquid. After amplification, a 100 mJ-level SLM CV pulse light with 300 ps duration is obtained. Meanwhile, the phase and polarization structures are high fidelity maintained. This result provides a practicable way to generate strong CV light, and by further extending this mechanism into the beam combination system, even an ultra-high intensity CV light can be expected.

Double-Wall Carbon Nanotube Hybrid Mode-Locker in Tm-doped Fibre Laser: A Novel Mechanism for Robust Bound-State Solitons Generation

The complex nonlinear dynamics of mode-locked fibre lasers, including a broad variety of dissipative structures and self-organization effects, have drawn significant research interest. Around the 2 μm band, conventional saturable absorbers (SAs) possess small modulation depth and slow relaxation time and, therefore, are incapable of ensuring complex inter-pulse dynamics and bound-state soliton generation. We present observation of multi-soliton complex generation in mode-locked thulium (Tm)-doped fibre laser, using double-wall carbon nanotubes (DWNT-SA) and nonlinear polarisation evolution (NPE). The rigid structure of DWNTs ensures high modulation depth (64%), fast relaxation (1.25 ps) and high thermal damage threshold. This enables formation of 560-fs soliton pulses; two-soliton bound-state with 560 fs pulse duration and 1.37 ps separation; and singlet+doublet soliton structures with 1.8 ps duration and 6 ps separation. Numerical simulations based on the vectorial nonlinear Schr¨odinger equation demonstrate a transition from single-pulse to two-soliton bound-states generation. The results imply that DWNTs are an excellent SA for the formation of steady single- and multi-soliton structures around 2 μm region, which could not be supported by single-wall carbon nanotubes (SWNTs). The combination of the potential bandwidth resource around 2 μm with the soliton molecule concept for encoding two bits of data per clock period opens exciting opportunities for data-carrying capacity enhancement.

Temperature stable operation of YCOB crystal for giant-pulse green microlaser.

In this work the performance of two yttrium calcium oxyborate (YCOB) crystals made by Czochralski and Bridgman growth process was measured. By using high peak power, passively Q-switched Nd3+:YAG/Cr4+:YAG microlaser, high conversion second harmonic generation efficiency were obtained. Laser pulses at 532 nm with 1.14 mJ energy and 223 ps duration were obtained with a 15-mm long YCOB crystal that was grown by Bridgman method. The conversion efficiency was 70.2%, comparable with the conversion efficiency of 72.8% that was achieved with 10-mm long lithium triborate (LBO) nonlinear crystal. Also, for the first time, experimental data on temperature tuning in type I YCOB crystal was measured with linear slope in 200°C temperature range equal to -0.057%/°C and -0.064%/°C for the Czochralski and Bridgman grown crystals, respectively. Such YCOB nonlinear crystal can become a serious option for developing laser sources with high-peak power at high repetition rate that can operate in harsh environment.

Limits of coherent supercontinuum generation in normal dispersion fibers

We study the largely unexplored transition between coherent and noise-seeded incoherent continuum generation in all-normal dispersion (ANDi) fibers and show that highly coherent supercontinua with spectral bandwidths of one octave can be generated with long pump pulses of up to 1.5 ps duration, corresponding to soliton orders of up to N=600. In terms of N, this corresponds to an approximately 50 times increase of the coherent regime compared to anomalous dispersion pumping. In the transition region between coherent and incoherent spectral broadening, we observe the manifestation of nonlinear phenomena that we term incoherent cloud formation and incoherent optical wave breaking, which lead to a gradual or instantaneous coherence collapse of supercontimuum (SC) spectral components, respectively. The role played by stimulated Raman scattering and parametric four-wave mixing during SC generation in ANDi fibers is shown to be more extensive than previously recognized: their nonlinear coupling contributes to the suppression of incoherent dynamics at short pump pulse durations, while it is responsible for non-phase-matched parametric amplification of noise observed in the long pulse regime. We further discuss the dependence of SC coherence on fiber design, and present basic experimental verifications for our findings using single-shot detection of SC spectra generated by picosecond pulses. This work outlines both the further potential as well as the limitations of broadband coherent light source development for applications such as metrology, nonlinear imaging, and ultrafast photonics, among others.

THE PATTERN OF CARDIOVASCULAR COMORBIDITY IN PATIENTS WITH SEVERE FORMS OF PSORIASIS: DATA OF RETROSPECTIVE ANALYSIS OF A HOSPITAL COHORT

Psoriasis (Ps) and psoriatic arthritis (PsA) are, in addition to skin and osteoarticular lesions, accompanied by a variety of comorbidities, primarily cardiovascular diseases (CVDs), which contributes to shorter life expectancy by on an average of 5–7 years. There are scarce data on the prevalence and pattern of CVDs in a Russian cohort of patients with severe forms of Ps and PsA. Obtaining such information can contribute to the elaboration of programs for screening and prevention of CVDs in this patient group. Objective: to study the prevalence and pattern of CVDs in a hospital cohort of patients with severe forms of Ps and PsA. Subjects and methods . Medical records were retrospectively analyzed in 890 patients with severe forms of Ps (mean age, 51.9±11.6 years; mean Ps duration, 11.6±0.6 years); who had been treated at the Branch of the V.G. Korolenko Clinic, Moscow Research and Practical Center of Dermatovenereology and Cosmetology, in 2010 to 2015. The Psoriasis Area and Severity Index (PASI) averaged 49.4±0.5. The frequency of PsA was assessed by the code L40.5; that of SVDs was determined by the registered diagnoses in accordance with the codes of the International Classification of Diseases, 10th edition (ICD-10): hypertension (ICD-10 code I10–I15), coronary heart disease (CHD) (I20–I25), atherosclerosis (I70), and cerebrovascular disorders (I65–I66). Results and discussion. PsA was identified in 303 (34%) patients. There were a total of 516 (59%) patients with CVDs. Hypertension, CHD, atherosclerosis, and cerebrovascular disorders were more frequently recorded in patients with PsA than in those with PsA without arthritis. Conclusion. CVDs are recorded in more than half of the hospital cohort patients with severe forms of Ps. CVDs are more frequently recorded in PsA than in Ps without arthritis. Hypertension among the SVDs is a leader in its frequency in both groups; more than half of the patients were found to have CHD and atherosclerosis; cerebrovascular disorders were less common.

Single-cycle surface plasmon polaritons on a bare metal wire excited by relativistic electrons.

Terahertz (THz) pulses are applied in areas as diverse as materials science, communication and biosensing. Techniques for subwavelength concentration of THz pulses give access to a rapidly growing range of spatial scales and field intensities. Here we experimentally demonstrate a method to generate intense THz pulses on a metal wire, thereby introducing the possibility of wave-guiding and focussing of the full THz pulse energy to subwavelength spotsizes. This enables endoscopic sensing, single-shot subwavelength THz imaging and study of strongly nonlinear THz phenomena. We generate THz surface plasmon polaritons (SPPs) by launching electron bunches onto the tip of a bare metal wire. Bunches with 160 pC charge and ≈6 ps duration yield SPPs with 6–10 ps duration and 0.4±0.1 MV m−1 electric field strength on a 1.5 mm diameter aluminium wire. These are the most intense SPPs reported on a wire. The SPPs are shown to propagate around a 90° bend.

Picosecond green and deep ultraviolet pulses generated by a high-power 100 kHz thin-disk laser.

We report on the generation of the second (515 nm) and fourth (257.5 nm) harmonics from a 100 kHz diode-pumped solid-state laser operating at a wavelength of 1030 nm which uses one Yb:YAG thin disk in the regenerative amplifier and delivers 60 W of the average output power in pulses of 4 ps duration. Thirty-five W in green light and 6 W in deep ultraviolet (DUV) were achieved. The sensitivity of the second harmonic generation efficiency toward the lithium triborate crystal temperature is demonstrated in experiment. The overall conversion efficiency from NIR to DUV of 10% was achieved. The β-barium borate and cesium lithium borate crystals were used as green to DUV convertors and compared regarding the efficiency and spectral bandwidths. The achieved output power is unique for DUV picosecond pulses.

Time-resolved cathodoluminescence microscopy with sub-nanosecond beam blanking for direct evaluation of the local density of states.

We show cathodoluminescence-based time-resolved electron beam spectroscopy in order to directly probe the spontaneous emission decay rate that is modified by the local density of states in a nanoscale environment. In contrast to dedicated laser-triggered electron-microscopy setups, we use commercial hardware in a standard SEM, which allows us to easily switch from pulsed to continuous operation of the SEM. Electron pulses of 80-90 ps duration are generated by conjugate blanking of a high-brightness electron beam, which allows probing emitters within a large range of decay rates. Moreover, we simultaneously attain a resolution better than λ/10, which ensures details at deep-subwavelength scales can be retrieved. As a proof-of-principle, we employ the pulsed electron beam to spatially measure excited-state lifetime modifications in a phosphor material across the edge of an aluminum half-plane, coated on top of the phosphor. The measured emission dynamics can be directly related to the structure of the sample by recording photon arrival histograms together with the secondary-electron signal. Our results show that time-resolved electron cathodoluminescence spectroscopy is a powerful tool of choice for nanophotonics, within reach of a large audience.

Simulations of 10 μm filaments in a realistically modeled atmosphere

We numerically study the formation and propagation dynamics of 10 μm filaments in the atmosphere. We investigate filament formation of multi-Joule 100 fs and 1 ps duration pulses over propagation lengths of 100 m and find that the carrier self-steepening regularization mechanism predicted for 4 μm wavelengths still holds. In our study we include multiple physical effects ignored in the past, such as rotational Raman and avalanche ionization. In addition we incorporate in our simulations the most detailed dispersive model available for atmospheric air, which includes multiple species, such as O2, N2, Ar, CO2, CO, and CH4, for a variety of humidity levels. Results presented here are expected to have a significant impact in the wider field of nonlinear optics where the use of mid-infrared lasers is rapidly growing.