Gu Yuqiu

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.

Deuterium Clusters Fusion Induced by the Intense Femtosecond Laser Pulse

Neutrons (2.45 MeV) from deuterium cluster fusion induced by the intense femtosecond (30 fs) laser pulse are experimentally demonstrated. The average neutron yield 103 per shot is obtained. It is found that the yield slightly increases with the increasing laser spot size. No neutron can be observed when the laser intensity I < 4.3×1015 W/cm2.

Ti X-Ray Laser Shadowgraphy Experiment

An x-ray laser shadowgraphy experiment was conducted on Xingguang-II laser facility in 1996. A multi-layer spherical mirror was used as an imaging element and a high sensitivity CCD camera as a detector. We measured the near-field image of the Ti x-ray laser beam. With a Ti x-ray laser beam as a backlight source, we obtained a clear Cu mesh image, demonstrating the potential as advanced diagnostic measurements to study high density plasmas in inertial confinement fusion research.

Laser-driven flier impact experiments at the SG-III prototype laser facility

Laser-driven flier impact experiments have been designed and performed at the SG-III prototype laser facility. The continuum phase plate (CPP) technique is used for the 3 ns quadrate laser pulse to produce a relatively uniform irradiated spot of 2 mm. The peak laser intensity is 2.7×1013 W/cm2 and it accelerates the aluminum flier with a density gradient configuration to a high average speed of 21.3 km/s, as determined by the flight-of-time method with line VISAR. The flier decelerates on impact with a transparent silica window, providing a measure of the flatness of the flier after one hundred microns of flight. The subsequent shock wave acceleration, pursuing, and decay in the silica window are interpreted by hydrodynamic simulation. This method provides a promising method to create unique conditions for the study of a materials properties.

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.

High-energy ion emission from cooled deuterium clusters in 20 TW laser fields

High-energy ion emission from intense-ultrashort (30fs) laser-pulse- cooled deuterium-cluster (80K) interaction is measured. The deuterium ions have an average energy 20keV, which greatly exceeds Zweibacks expectation [Phys. Rev. Lett. 84 (2000) 2634]. These fast deuterium ions can be used to drive fusion and have a broad prospect.

Performance comparison of the neon-like chromium soft x-ray lasing driven by a double laser pulse with different duration

A comparison has been made of performance of the neon-like chromium soft x-ray lasing at 28.5 nm driven by a double 900 ps pulse at 6 TW/cm2, with that driven by a double 200 ps pulse at similar irradiance. The double 200 ps pulse has been found to be much more efficient to drive x-ray lasing with higher intensity.

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.