Zhao Zong-Qing

Laser-driven proton acceleration using a conical nanobrush target

A conical nanobrush target is proposed to improve the total proton energy-conversion efficiency in proton beam acceleration and investigated by two-dimensional particle-in-cell (2D-PIC) simulations. Results indicate a significant enhancement of the number and energies of hot electrons through the target rear side of the conical nanobrush target. Compared with the plain target, the field increases several times. We observe enhancements of the average proton energy and total laser-proton energy conversion efficiency of 105%. This enhancement is attributed to both nanobrush and conical configurations. The proton beam is well collimated with a divergence angle less than 28{sup Degree-Sign }. The proposed target may serve as a new method for increasing laser to proton energy-conversion efficiency.

Efficient laser absorption and enhanced electron yield in the laser-target interaction by using a cone-nanolayer target

A cone-nanolayer target that combines the advantages of the conical and layered geometries for electron acceleration in laser-target interaction is proposed. Two-dimensional particle-in-cell (PIC) simulations show that the cone-nanolayer target can enhance laser absorption and electron yield. With suitable choice of the laser and target parameters, the cone-nanolayer target can be a controllable source of hot electrons at desired energy ranges.

Effect of inner-surface roughness of conical target on laser absorption and fast electron generation

The effect of inner-surface roughness of conical targets on the generation of fast electrons in the laser—cone interaction is investigated using particle-in-cell simulation. It is found that the surface roughness can reduce the fast-electron number (in the energy range E > 1 MeV) and energy, as compared to that from a cone with smooth inner wall. A scaling law for the laser reflectivity based on the vacuum-heating model is derived. Both theory and simulation indicate that laser reflection increases with the height-to-width ratio of the periodic inner surface structure and approaches that of a smooth cone as this ratio becomes zero.

Numerical simulation for all-optical Thomson scattering X-ray source

Energy spectra, angular distributions, and temporal profiles of the photons produced by an all-optical Thomson scattering X-ray source are explored through numerical simulations based on the parameters of the SILEX-I laser system (800 nm, 30 fs, 300 TW) and the previous wakefield acceleration experimental results. The simulation results show that X-ray pulses with a duration of 30 fs and an emission angle of 50 mrad can be produced from such a source. Using the optimized electron parameters, X-ray pulses with better directivity and narrower energy spectra can be obtained. Besides the electron parameters, the laser parameters such as the wavelength, pulse duration, and spot size also affect the X-ray yield, the angular distribution, and the maximum photon energy, except the X-ray pulse duration which is slightly changed for the case of ultrafast laser—electron interaction.

Time-Resolved Radiography using Chirp-Pulse Proton Beams

Protons accelerated by the target normal sheath acceleration (TNSA) mechanism have a wide energy spectrum and are called chirp-pulse protons. The numerical simulation of chirp-pulse proton radiography in an implosion process with single shot is carried out using the Monte Carlo method. Two different methods are proposed. The first method, proton framing radiography, uses a stack of radiochromic film layers as the detector. Each layer deposits protons with energy corresponding to the Bragg peak, which can record the transient state of the implosion process. The second method, proton streak radiography, uses an external magnetic field to deflect protons. Different energies correspond to different times. By using a slit before the magnetic field, one-dimensional spatial resolution and temporal resolution can be obtained. This method is more suitable for the diagnosis of the implosion process.

Design of Elliptical Reflection Zone Plate for Monochromatization of the Ultrafast Betatron Radiation at Low Energy Band

The elliptical reflection zone plate is a kind of optical element in soft x-ray and x-ray ranges and has focusing and dispersion properties. Compared with a transmission zone plate, the required dispersion orders can be easily separated from zeroth order diffraction. It is fabricated on a bulk substrate and does not have much difficulty in the fabrication process. We design a 1000-zone off-axis elliptical reflection zone plate for the monochromatization of the ultrafast betatron radiation at the low energy band, at the designed wavelength of 2.478nm (500 eV) which is an important spectral part of the betatron radiation, with high spatial resolution, high spectral resolution. Moreover, we simulate the designed reflection zone plate properties. The simulation results show that the spatial resolutions in the spatial direction and the spectral direction are 6.4 μm and 7.3 μm (full width half maximum), respectively, and the spectral resolution reaches up to 496 for the well aligned point source system, which is in good agreement with the theoretical predictions. In addition, we discuss some factors influencing the spectral and spatial resolution, such as the zone number, zone area and the incidence wavelength. The elliptical reflection zone plate also has potential applications in investigating x-ray fluorescence spectra and other fields.

New terahertz dispersive device for single-shot spectral measurements of terahertz pulse

A new terahertz dispersive device designed for single-shot spectral measurements of broadband terahertz pulses is proposed. With two-dimensional quasi-randomly distributed element design, the device exhibits approximately the dispersive property of single-order diffraction in far field. Its far-field diffraction pattern is experimentally verified employing a continuous terahertz source centered at 2.52 THz and a pyroelectric focal-plane-array camera, which is in good agreement with the numerical result. The device provides a new approach for direct single-shot spectral measurements of broadband terahertz waves.

An improved deconvolution method for X-ray coded imaging in inertial confinement fusion

In inertial confinement fusion (ICF), X-ray coded imaging is considered as the most potential means to diagnose the compressed core. The traditional Richardson—Lucy (RL) method has a strong ability to deblur the image where the noise follows the Poisson distribution. However, it always suffers from over-fitting and noise amplification, especially when the signal-to-noise ratio of image is relatively low. In this paper, we propose an improved deconvolution method for X-ray coded imaging. We model the image data as a set of independent Gaussian distributions and derive the iterative solution with a maximum-likelihood scheme. The experimental results on X-ray coded imaging data demonstrate that this method is superior to the RL method in terms of anti-overfitting and noise suppression.