In order to address the present difficulty in experimentally generating the relativistic Laguerre-Gaussian laser, primarily due to damage caused to optical modulators, a high-reflectivity phase mirror is applied in the femtosecond petawatt laser system to generate a relativistic hollow laser at the highest intensity of 6.3×10^{19}  W/cm^{2} for the first time. A simple optical model is used to verify that the vortex laser may be generated in this new scheme; using such a relativistic vortex laser, the hollow plasma drill and acceleration are achieved experimentally and proven by particle-in-cell simulations. With the development of the petawatt laser, this scheme opens up possibilities for the convenient production of the relativistic hollow laser at high repetition and possible hollow plasma acceleration, which is important for a wide range of applications such as the generation of radiation sources with orbital angular momentum, fast ignition for inertial confinement fusion, and jet research in the astrophysical environment.

A new spin-dependent deflection mechanism is revealed by considering the spin-correlated radiation-reaction force during laser-electron collision. We found that such deflection originates from the non-zero work done by the radiation-reaction force along the laser polarization direction in each half-period, which is larger/smaller for spin-anti-paralleled/spin-paralleled electrons. The resulted anti-symmetric deflection is further accumulated when the spin-projection onto the laser magnetic field is reversed in adjacent half-periods. The discovered mechanism dominates over the Stern–Gerlach deflection for electrons of several hundreds of MeV and 10 PW-level laser peak power. The results provide a new perspective to study the strong-field QED physics in quantum radiation-reaction regime and an approach to leverage the study of radiation-dominated and strong-field QED physics via particle spins.

The colliding between ultra-relativistic electrons and an ultra-intense laser pulse is a powerful approach to testify the physics in strong-field QED regime. By considering spin-dependent radiation-reaction during laser-electron collision we find anti-symmetric deflection of electrons with different spin states. We revealed that such deflection is induced by the non-zero work done by radiation-reaction force along field polarization-direction in a half-period of phase, which is larger for spin-anti-paralleled electrons and smaller for spin-paralleled electrons. The spin-projection on the magnetic field of an electron gets inversed in adjacent half-periods due to oscillating magnetic field and therefore the deflection due to spin-dependent radiation is accumulated rather than vanishing. The new mechanism provides an extra dimension to observe quantum radiation-reaction effect in the strong-field QED regime by measuring the anti-symmetric distribution.

High brightness gamma rays can be generated by colliding an ultra-intense laser pulse with a high energy electron beam. This collision phenomenon also represents a powerful approach to explore new physics in the exotic strong field Quantum Electro-Dynamics (QED) regime. Here we show that in the cross-collision geometry, there exists a barrier induced by the classical radiation-reaction force that prohibits electrons of arbitrarily high energies to pass. However, such classical barrier vanishes in the QED picture, where electrons can be well reflected (transmitted) in the regimes forbidden by classical theory. This effect can be measured in the up-coming 10–100 PW laser facilities for laser intensities at 2 × 10 23 W cm −2 and electron energies of ~10 2 MeV. The results are capable of identifying the boundaries between classical and QED approaches in the strong field regime and confirming the various models describing this fundamental process.

We propose a new approach based on an all-optical set-up for generating relativistic polarized electron beams via vortex Laguerre-Gaussian (LG) laser-driven wakefield acceleration. Using a pre-polarized gas target, we find that the topology of the vortex wakefield resolves the depolarization issue of the injected electrons. In full three-dimensional particle-in-cell simulations, incorporating the spin dynamics via the Thomas-Bargmann Michel Telegdi equation, the LG laser preserves the electron spin polarization by more than 80% while assuring efficient electron injection. The method releases the limit on beam flux for polarized electron acceleration and promises more than an order of magnitude boost in peak flux, as compared to Gaussian beams. These results suggest a promising table-top method to produce energetic polarized electron beams.

We investigated the effect of a plasma charge separation field on radiation reaction (RR) in laser–plasma interactions. By implementing the plasma field equation developed in one-dimension into the classical Landau–Lifshitz formula, our numerical test-particle modeling revealed distinctive plasma electron dynamics in three regimes: the low density underdense regime, the near-critical density (NCD) regime and the highly overdense one. It is discovered from the electron trajectories and gamma-ray emission that the RR effect is mostly significant at near-critical plasma densities. The underlying mechanism is well interpreted by the theoretical analysis from the perspective of the potential contained in the charge separation field and demonstrated in two dimensional particle-in-cell simulations using the quantum electro-dynamic photon emission approach. Our findings indicate that the NCD plasma is the most efficient medium to leverage RR and generate high-energy and low-divergence gamma-photons.

We investigate the precession of electron spins during beam-driven plasma-wakefield acceleration based on density down-ramp injection by means of full three-dimensional (3D) particle-in-cell (PIC) simulations. A relativistic electron beam generated via, e.g., laser wakefield acceleration, serves as the driving source. It traverses the prepolarized gas target and accelerates polarized electrons via the excited wakefield. We derive the criteria for the driving beam parameters and the limitation on the injected beam flux to preserve a high degree of polarization for the accelerated electrons, which are confirmed by our 3D PIC simulations and single-particle modeling. The electron-beam driver is free of the prepulse issue associated with a laser driver, thus eliminating possible depolarization of the prepolarized gas due to ionization by the prepulse. These results provide guidance for future experiments towards generating a source of polarized electrons based on wakefield acceleration.

We investigated laser proton acceleration in the bubble regime when radiation reaction (RR) effects become non-negligible. By using particle-in-cell simulations, it is shown that in addition to the bubble field, the RR trapped electrons form another charge-separation field, leading to fast acceleration of the background protons at the early stage. However, for insufficient laser intensities, the reduced bubble field and acceleration length originating from the laser depletion by gamma-photon emission do not allow for trapping and further acceleration of the protons. The final proton energy is significantly smaller than the one when RR is not considered. This effect can be mitigated by tuning the peak laser intensity (hence the pulse duration) for certain laser energy and plasma density. By increasing the laser intensity (shortening the pulse duration), we found that protons pre-accelerated by the RR-induced charge separation field gain enough momenta such that they are picked-up by the bubble field and continuously accelerated. In this case, the bubble field is also strong enough to trap protons located in the bubble front. Eventually, two groups of protons are effectively accelerated, resulting in a bump in the proton spectrum. These results can be used to design the future proton acceleration experiments in upcoming 100 PW laser facilities.

An approach is proposed to directly measure the relativistic laser pulse duration. In the scheme, two identical high-intensity laser pulses are irradiated on a thin plasma target symmetrically in V-shape. High order harmonics carrying the information of two incident pulses are generated in different directions during the nonlinear interaction process. The direction of the third harmonic can be predicted from the theoretical analysis and its intensity in this direction can be recorded as an autocorrelation function of the delay time between the incident pulses. Then, the pulse duration which is 70% of the full width at half maximum of the autocorrelation curve can be obtained. This approach has been verified by particle-in-cell simulations and the error is 3.7% for a 30 fs relativistic laser pulse as an example.

Micro-structures are advantageous in manipulating the laser intensity and laser-driven high energy electron sources. Both effects benefit acceleration of high energy protons by ultra-intense laser pulses. We investigate the enhancement on proton cut-off energy and yield induced by micro-wire-array structure via particle-in-cell simulation. Our simulations reveal that the abundant energetic electrons originating from the structures are essential for sequential proton acceleration. We find that this effect becomes active only when the laser pulse intensity reaches a = 2. The proton energies are further optimized by designing structures of different featured sizes. The results suggest two distinctive regimes, where the electron number is significantly enhanced by using short and dense arrays, while the long and sparse arrays are more efficient in increasing the cut-off beam energies. When combining both patterns, we see that the compound target contains features from both the long array and the short array, comparing to flat interfaces. These results will guide future experiments utilizing three-dimensional micro-engineered targets.

With the development of femtosecond laser technology and wide applications of polymethyl methacrylate (PMMA),the research on optical properties of PMMA has become a hot spot.Filamentation phenomenon appears in the process of transparent materials by femtosecond laser.Generation principles of self-focusing and filamentous are analyzed.One of the most important characteristics of laser beam is polarization state.Linearly polarized light,circularly polarized light,radially polarized light and angularly polarized light can be controlled by the combination of spatial light modulator,1/2 wave plate and 1/4 wave plate.Generated polarized light with energy of 1 μJ is used in the line processing on PMMA,and then the comparative analysis is conduct on the length and initial position of filamentation under different polarized light.Experimental results show that linearly polarized light and circularly polarized light result in filamentation with short length,and filamentation position of linearly polarized light is close to the incident plane.Radially polarized light and azimuthally polarized light result in long length,and the distance of filamentation position to the incident plane is long.

Polarization state is one of the important characteristics of the laser beam,and the polarization states will affect the drilling quality on the flexible circuit board (FPC).A theoretical calculation method for damage threshold of FPC material with polyimide as substrate was presented,and the way of obtaining four polarization states (linear,circular,radial and azimuthal) is proposed by combining a liquid crystal spatial light modulator,a half-wave plate and a quarter-wave plate.The damage threshold of the flexible circuit board processed by the 800 nm femtosecond laser is calculated to be 25.44 J/cm2 through drill-ing experiments of different processing energy.Experiments with different polarization states were also done on the condition of the same energy and the same sample.The experimental results show that the radial polarization and angular polarization have better roundness and bigger diameter.