Transport of ultraintense laser-driven relativistic electrons in dielectric targets

Ultraintense laser-driven relativistic electrons provide a way of heating matter to high energy density states related to many applications. However, the transport of relativistic electrons in solid targets has not been understood well yet,especially in dielectric targets. We present the first detailed two-dimensional particle-in-cell simulations of relativistic electron transport in a silicon target by including the field ionization and collisional ionization processes. An ionization wave is found propagating in the insulator, with a velocity dependent on laser intensity and slower than the relativistic electron velocity. Widely spread electric fields in front of the sheath fields are observed due to the collective effect of free electrons and ions. The electric fields are much weaker than the threshold electric field of field ionization. Two-stream instability behind the ionization front arises for the cases with laser intensity greater than 5 × 1019W/cm^2 that produce high relativistic electron current densities.

Generation and application of high-contrast laser pulses using plasma mirror in the SULF-1PW beamline

The plasma mirror system was installed on the 1 PW laser beamline of Shanghai Superintense Ultrafast Laser Facility[SULF]for enhancing the temporal contrast of the laser pulse.About 2 orders of magnitude improvement on pulse contrast was measured on picosecond and nanosecond time scales.The experiments show that high-contrast laser pulses can significantly improve the cutoff energy and quantity of proton beams.Then different target distributions are assumed in particles in cell simulations,which can qualitatively assume the expansion of nanometer-scale foil.The high-contrast laser enables the SULF-1PW beamline to generally be of benefit for many potential applications.

Relativistic Electromagnetic Soliton in Electron-Positron-Ion Plasma

Considering the limiting weak nonlinearity, we obtained the solution of the coupled equations describing the interaction of ultraintense laser with cold transparent multicomponent plasma. It was indicated that the ions tend to accumulate at the center of the soliton and have large velocity when we consider the mobile ions in the multicomponent plasma, which shows that the result is different from that of the Berezhiani＇s analysis. The change of proportion of ions in the plasma has effects on the amplitude of vector potential and the maximum velocity of the soliton.

Acceleration of 60 MeV proton beams in the commissioning experiment of the SULF-10 PW laser

We report the experimental results of the commissioning phase in the 10 PW laser beamline of the Shanghai Superintense Ultrafast Laser Facility(SULF).The peak power reaches 2.4 PW on target without the last amplifying during the experiment.The laser energy of 72±9 J is directed to a focal spot of approximately 6μm diameter(full width at half maximum)in 30 fs pulse duration,yielding a focused peak intensity around 2.0×10^(21)W/cm^(2).The first laser-proton acceleration experiment is performed using plain copper and plastic targets.High-energy proton beams with maximum cut-off energy up to 62.5 MeV are achieved using copper foils at the optimum target thickness of 4μm via target normal sheath acceleration.For plastic targets of tens of nanometers thick,the proton cut-off energy is approximately 20 MeV,showing ring-like or flamented density distributions.These experimental results reflect the capabilities of the SULF-10 PW beamline,for example,both ultrahigh intensity and relatively good beam contrast.Further optimization for these key parameters is underway,where peak laser intensities of 10^(22)-10^(23)w/cm^(2)are anticipated to support various experiments on extreme field physics.

Fabrication of large-area uniform carbon nanotube foams as near-critical-density targets for laser–plasma experiments

Carbon nanotube foams(CNFs)have been successfully used as near-critical-density targets in the laser-driven acceleration of high-energy ions and electrons.Here we report the recent advances in the fabrication technique of such targets.With the further developed floating catalyst chemical vapor deposition(FCCVD)method,large-area(>25 cm^(2))and highly uniform CNFs are successfully deposited on nanometer-thin metal or plastic foils as double-layer targets.The density and thickness of the CNF can be controlled in the range of 1−13 mg/cm^(3)and 10−200µm,respectively,by varying the synthesis parameters.The dependence of the target properties on the synthesis parameters and the details of the target characterization methods are presented for the first time.

Laser scaling for generation of megatesla magnetic fields by microtube implosions

Microtube implosions are a novel scheme to generate ultrahigh magnetic fields of the megatesla order.These implosions are driven by ultraintense and ultrashort laser pulses.Using two-and three-dimensional particle simulations where megatesla-order magnetic fields can be achieved,we demonstrate scaling and criteria in terms of laser parameters,such as laser intensity and laser energy,to facilitate practical experiments toward the realization of extreme physical conditions,which have yet to be realized in laboratories.Microtube implosions should provide a new platform for studies in fundamental and applied physics relevant to ultrahigh magnetic fields.

Accurate electron beam phase-space theory for ionization-injection schemes driven by laser pulses

After the introduction of the ionization-injection scheme in laser wake field acceleration and of related high-quality electron beam generation methods,such as two-color and resonant multi-pulse ionization injection(Re MPI),the theory of thermal emittance has been used to predict the beam normalized emittance obtainable with those schemes.We recast and extend such a theory,including both higher order terms in the polynomial laser field expansion and non-polynomial corrections due to the onset of saturation effects on a single cycle.Also,a very accurate model for predicting the cycle-averaged distribution of the extracted electrons,including saturation and multi-process events,is proposed and tested.We show that our theory is very accurate for the selected processes of Kr^(8+→10+) and Ar^(8+→10+),resulting in a maximum error below 1%,even in a deep-saturation regime.The accurate prediction of the beam phase-space can be implemented,for example,in laser-envelope or hybrid particle-in-cell(PIC)/fiuid codes,to correctly mimic the cycle-averaged momentum distribution without the need for resolving the intra-cycle dynamics.We introduce further spatial averaging,obtaining expressions for the whole-beam emittance fitting with simulations in a saturated regime,too.Finally,a PIC simulation for a laser wakefield acceleration injector in the Re MPI configuration is discussed.

Large temporal window and high-resolution single-shot cross-correlator with two separate measurement channels

In strong-field physics experiments with ultraintense lasers,a single-shot cross-correlator(SSCC)is essential for fast optimization of the pulse contrast and meaningful comparison with theory for each pulse shot.To simultaneously characterize an ultrashort pulse and its long pedestal,the SSCC device must have both a high resolution and a large temporal window.However,the resolution and window in all kinds of single-shot measurement contradict each other in principle.Here we propose and demonstrate a novel SSCC device with two separate measurement channels:channel-1 for the large-window pedestal measurement has a moderate resolution but a large window,while channel-2 for the ultrashort pulse measurement has a small window but a high resolution;this allows the accurate characterization of the pulse contrast in a single shot.A two-channel SSCC device with a 200-fs resolution and 114-ps window has been developed and tested for its application in ultraintense lasers at 800 nm.