A compact laser plasma accelerator (CLAPA) that can stably produce and transport proton ions with different energies less than 10 MeV, $<1\%$ energy spread, several to tens of pC charge, is demonstrated. The high current proton beam with continuous energy spectrum and a large divergence angle is generated by using a high contrast laser and micron thickness targets, which later is collected, analyzed and refocused by an image-relaying beam line using a combination of quadrupole and bending electromagnets. It eliminates the inherent defects of the laser-driven beams, realizes precise manipulation of the proton beams with reliability, availability, maintainability and inspectability (RAMI), and takes the first step towards applications of this new generation of accelerator. With the development of high-rep rate Petawatt (PW) laser technology, we can now envision a new generation of accelerator for many applications in the near future soon.

A comprehensive study of charge diagnostics is conducted to verify their validity for measuring electron beams produced by laser plasma accelerators (LPAs). First, a scintillating screen (Lanex) was extensively studied using subnanosecond electron beams from the Advanced Light Source booster synchrotron, at the Lawrence Berkeley National Laboratory. The Lanex was cross calibrated with an integrating current transformer (ICT) for up to the electron energy of 1.5 GeV, and the linear response of the screen was confirmed for charge density and intensity up to $160\mathrm{pC}/{\mathrm{mm}}^2$ and $0.4\mathrm{pC}/(\mathrm{ps}{\mathrm{mm}}^2)$, respectively. After the radio-frequency accelerator based cross calibration, a series of measurements was conducted using electron beams from an LPA. Cross calibrations were carried out using an activation-based measurement that is immune to electromagnetic pulse noise, ICT, and Lanex. The diagnostics agreed within $\pm 8\%$, showing that they all can provide accurate charge measurements for LPAs.

In order to implement radiotherapy based on a laser accelerator, it is necessary to precisely control the spatial distribution and energy spectrum of the proton beams to meet the requirements of the radiation dose distribution in the three-dimensional biological target. A compact laser plasma accelerator has been built at Peking University, which can reliably generate and transport MeV-energy protons with a specified energy onto the irradiation platform. In this paper, we discuss several technologies for the accurate control of a laser-accelerated proton beam with large divergence angle and broad energy spread, including the determination of the beam source position with micron accuracy, a tuning algorithm for the transport line which we refer to as “matching-image-point two-dimensional energy analysis” to realize accurate energy selection, and the control of beam distribution uniformity. In the prototype experiment with low energy protons and 0.5-Hz irradiation rate, a tailored energy deposition is demonstrated, which shows the potential feasibility of future irradiation based on laser-accelerated proton beams.

Ultra-short untraintense laser interacting with solid targets can produce significant electromagnetic pulses (EMPs), which are strongly pertinent to laser and target parameters. In this study, EMPs' generation due to pulsed laser (30 fs, ${6\times 10}^{19}$ W/cm²) irradiating aluminum foils are recorded and analyzed. The experimental results indicate a pre-ablation pulse (200 ps, ${1\times 10}^{12}$ W/cm²) that tends to enhance the electromagnetic emission inside the target chamber and the diagnostic cavity. The largest EMP signal is obtained when the pre-ablation pulse is incident on the target at 100 ps prior to the main laser beam. Meanwhile, the frequencies of EMPs are broadened up to 2 GHz in the diagnostic cavity in the 100 ps delayed case, indicating that EMPs with higher frequencies can be generated if the most energetic electrons are accelerated. The simulating results verify expansion of the pre-plasmas induced by the pre-ablation laser, which is beneficial to lift both the energy and quantity of hot electrons escaping from the target, accounting for the ehancement of EMPs. The resulting conclusions offer a new avenue to generate intense EMPs, which can be potentially used in nondestructive examination, high-power microwave source, and energy transfer.

When an ultra-intense relativistic laser is irradiated on a solid target, terahertz (THz) pulses can be generated by coherent transition radiation when the laser-driven electron beams cross the rear surface of the target. The radiation energy depends on the number and energy of the electrons. By introducing a milli-joule picosecond ablation laser pulse, an underdense preplasma with a scale length of micrometers is generated at the front surface of the target. Electron beams with more charge and higher energy can be produced during the interaction between the following main laser pulse and the preplasma, which enhance the THz radiation and affect the radiation angle. Two dimensional particle-in-cell simulations demonstrate the improvement of electron beams and a nearly tenfold enhancement of THz radiation energy is observed.

We report systematic studies of laser-driven proton beams produced with micrometer-thick solid targets made of aluminum and plastic, respectively. Distinct effects of the target materials are found on the total charge, cutoff energy, and beam spot of protons in the experiments, and these are described well by two-dimensional particle-in-cell simulations incorporating intrinsic material properties. It is found that with a laser intensity of 8 × 10¹⁹ W/cm², target normal sheath acceleration is the dominant mechanism for both types of target. For a plastic target, the higher charge and cutoff energy of the protons are due to the greater energy coupling efficiencies from the intense laser beams, and the larger divergence angle of the protons is due to the deflection of hot electrons during transport in the targets. We also find that the energy loss of hot electrons in targets of different thickness has a significant effect on the proton cutoff energy. The consistent results obtained here further narrow the gap between simulations and experiments.