Controlled transition to different proton acceleration regimes:Near-critical-density plasmas driven by circularly polarized few-cycle pulses

A controlled transition between two different ion acceleration mechanisms would pave the way to achieving different ion energies and spectral features within the same experimental set up,depending on the region of operation.Based on numerical simulations conducted over a wide range of experimentally achievable parameter space,reported here is a comprehensive investigation of the different facets of ion acceleration by relativistically intense circularly polarized laser pulses interacting with thin near-critical-density plasma targets.The results show that the plasma thickness,exponential density gradient,and laser frequency chirp can be controlled to switch the interaction from the transparent operating regime to the opaque one,thereby enabling the choice of a Maxwellian-like ion energy distribution with a cutoff energy in the relativistically transparent regime or a quasi-monoenergetic spectrum in the opaque regime.Next,it is established that a multispecies target configuration can be used effectively for optimal generation of quasi-monoenergetic ion bunches of a desired species.Finally,the feasibility is demonstrated for generating monoenergetic proton beams with energy peak atℰ≈20–40 MeV and a narrow energy spread ofΔℰ/ℰ≈18%–28.6%confined within a divergence angle of∼175 mrad at a reasonable laser peak intensity of I0≃5.4×10^(20)W/cm^(2).

Investigation of wire-array Z-pinches by laser probing diagnostics

Laser diagnostics provides powerful tools for the investigation of dense Z-pinches.In this paper,wire-array Z-pinches are investigated at the 1 MA Zebra generator using laser diagnostics at different wavelengths coupled with x-ray diagnostics.Plasma dynamics during the ablation,implosion,and stagnation stages are observed by multiframe diagnostics.Cascading and nonprecursor implosions are studied in wire arrays.Ultraviolet diagnostics allows deep penetration into the Z-pinch plasma at stagnation.End-on probing reveals the complicated structure of the precursor.Strong magnetohydrodynamic instabilities are found in a dense pinch hidden in the trailing plasma.Small-scale instabilities are seen in the Z-pinch plasma with micrometer resolution.Probing of the pinch from four directions shows asymmetrical trailing plasma in some configurations of wire arrays.Faraday rotation diagnostics reveals the magnetic fields and the current distribution in the plasma of the precursor and Z-pinch.Redistribution of current in the trailing plasma is seen during kink and sausage instabilities in the stagnation stage.The formation of micropinches and hot spots in the Z-pinch is analyzed with coupled laser and x-ray diagnostics.Different laser diagnostics allow the study of Z-pinch plasmas in all stages,including fast dynamics and instabilities.

Dimethylammonium iodide stabilized bismuth halide perovskite photocatalyst for hydrogen evolution

Metal halide perovskites have emerged as novel and promising photocatalysts for hydrogen generation.Currently,their stability in water is a vital and urgent research question.In this paper a novel approach to stabilize a bismuth halide perovskite[(CH_(3))_(2)NH_(2)]_(3)[Bil_(6)](DA_(3)Bil_(6))in water using dimethylammonium iodide(DAI)without the assistance of acids or coatings is reported.The DA3Bil6 powder exhibits good stability in DAI solutions for at least two weeks.The concentration of DAI is found as a critical parameter,where the I^(-)ions play the key role in the stabilization.The stability of DA3Bil6 in water is realized via a surface dissolution-recrystallization process.Stabilized DA3Bil6 demonstrates constant photocatalytic properties for visible light-induced photo-oxidation of I^(-)ions and with PtCI4 as a co-catalyst(Pt-DA_(3)Bil_(6)),photocatalytic H2 evolution with a rate of 5.7μmol·h^(-1)from HI in DAI solution,obtaining an apparent quantum efficiency of 0.83%at 535 nm.This study provides new insights on the stabilization of metal halide perovskites for photocatalysis in aqueous solution.

Targets for high repetition rate laser facilities:needs,challenges and perspectives

A number of laser facilities coming online all over the world promise the capability of high-power laser experiments with shot repetition rates between 1 and 10 Hz. Target availability and technical issues related to the interaction environment could become a bottleneck for the exploitation of such facilities. In this paper, we report on target needs for three different classes of experiments: dynamic compression physics, electron transport and isochoric heating, and laser-driven particle and radiation sources. We also review some of the most challenging issues in target fabrication and high repetition rate operation. Finally, we discuss current target supply strategies and future perspectives to establish a sustainable target provision infrastructure for advanced laser facilities.

A perspective on high photon flux nonclassical light and applications in nonlinear optics

Nonclassical light sources have a vital role in quantum optics as they offer a unique resource for studies in quantum technology.However,their applicability is restricted by their low intensity,while the development of new schemes producing intense nonclassical light is a challenging task.In this perspective article,we discuss potential schemes that could be used towards the development of high photon flux nonclassical light sources and their future prospects in nonlinear optics.

Sub-50 fs pulses at 2050 nm from a picosecond Ho:YLF laser using a two-stage Kagome-fiber-based compressor

The high-energy few-cycle mid-infrared laser pulse beyond 2μm is of immense importance for attosecond science and strong-field physics.However,the limited gain bandwidth of laser crystals such as Ho:YLF and Ho:YAG allows the generation of picosecond(ps)long pulses and,hence,makes it challenging to generate few-cycle pulse at 2μm without utilizing an optical parametric chirped-pulse amplifier(OPCPA).Moreover,the exclusive use of the near-infrared wavelength has limited the generation of wavelengths beyond 4μm(OPCPA).Furthermore,high harmonic generation(HHG)conversion efficiency reduces dramatically when driven by a long-wavelength laser.Novel schemes such as multi-color HHG have been proposed to enhance the harmonic flux.Therefore,it is highly desirable to generate few-cycle to femtosecond pulses from a 2μm laser for driving these experiments.Here,we utilize two-stage nonlinear spectral broadening and pulse compression based on the Kagome-type hollow-core photonic crystal fiber(HC-PCF)to compress few-ps pulses to sub-50 fs from a Ho:YLF amplifier at 2μm at 1 kHz repetition rate.We demonstrate both experimentally and numerically the compression of 3.3 ps at 140μJ pulses to 48 fs at 11μJ with focal intensity reaching 10^(13)W/cm^(20.Thereby,this system can be used for driving HHG in solids at 2μm.In the first stage,the pulses are spectrally broadened in Kagome fiber and compressed in a silicon-based prism compressor to 285 fs at a pulse energy of 90μJ.In the second stage,the 285 fs pulse is self-compressed in air-filled HC-PCF.With fine-tuning of the group delay dispersion(GDD)externally in a 3 mm window,a compressed pulse of 48 fs is achieved.This leads to a 70-fold compression of the ps pulses at 2050 nm.We further used the sub-50 fs laser pulses to generate white light by focusing the pulse into a thin medium of YAG.

Relativistic electron acceleration by surface plasma waves excited with high intensity laser pulses

The process of high energy electron acceleration along the surface of grating targets(GTs)that were irradiated by a relativistic,high-contrast laser pulse at an intensity I=2.5×10^20 W/cm^2 was studied.Our experimental results demonstrate that for a GT with a periodicity twice the laser wavelength,the surface electron flux is more intense for a laser incidence angle that is larger compared to the resonance angle predicted by the linear model.An electron beam with a peak charge of∼2.7 nC/sr,for electrons with energies>1.5 MeV,was measured.Numerical simulations carried out with parameters similar to the experimental conditions also show an enhanced electron flux at higher incidence angles depending on the preplasma scale length.A theoretical model that includes ponderomotive effects with more realistic initial preplasma conditions suggests that the laser-driven intensity and preformed plasma scale length are important for the acceleration process.The predictions closely match the experimental and computational results.

High-Flux 1ookHz Attosecond Pulse Source Driven by a High-Average Power Annular Laser Beam

High-repetition rate attosecond pulse sources are indispensable tools for time-resolved studies of electron dynamics,such as coincidence spectroscopy and experiments with high demands on statistics or signal-to-noise ratio,especilly in the case of solid and big molecule samples in chemistry and biology.Although with the high-repetition rate lasers,such attosecond pulses in a pump-probe configuration are possible to achieve,until now,only a few such light sources have been demonstrated.Here,by shaping the driving laser to an annular beam,a 100 kHz attosecond pulse train(APT)is reported with the highest energy so far(51 pl/shot)on target(269 pJat generation)among the high-repetition rate systems(>10 kHz)in which the attosecond pulses were temporally characterized.The on-target pulse energy is maximized by reducing the losses from the reflections and filtering of the high harmonics,and an unprecedented 19%transmission rate from the generation point to the target position is achieved.At the same time,the probe beam is also annular and low loss of this beam is reached by using another holey mirror to combine with the APT.The advantages of using an annular beam to generate attosecond pulses with a high-average power laser are demonstrated experimentally and theoretically,The effect of nonlinear propagation in the generation medium on the annular-beam generation concept is also analyzed in detail.