Shoujun Wang

X-ray astronomy in the laboratory with a miniature compact object produced by laser-driven implosion

It has been suggested that the extreme states of matter generated by high-intensity lasers could allow conditions similar to those in the vicinity of black holes to be studied in the lab. The observation of striking similarities between the X-ray spectra emitted by a laser-driven laboratory plasma and those measured from two high-mass binary star systems suggests such potential has been realized.

Intergrowth Bi2WO6–Bi3TiNbO9 ferroelectrics with high ionic conductivity

This work was supported by the Ministry of Science and Technology of China through 973-Project under Grant No. 2002CB613307.

Opacity Studies of Silicon in Radiatively Heated Plasma

Measurements of the opacity of silicon at high temperature and high density are reported. A silicon dioxide foam was heated by eight nanosecond laser beams while a backlighter X-ray source was produced with a picosecond laser. Absorptions of the 1-2 transitions of Si XII through Si VI were observed in the wavelength range from 6.6 to 7.1 A. The experimental results are simulated with theoretical calculations under local thermodynamic equilibrium using a detailed level accounting model and can be reproduced in general when the effects of the oxygen in the SiO2 are taken into account.

Strong terahertz radiation from air plasmas generated by an aperture-limited Gaussian pump laser beam

Terahertz radiation generated by focusing the fundamental laser pulse and its second harmonic into ambient air strongly saturates with increasing pump laser energy. We demonstrate a simple method to control the Gaussian pump laser beam to improve the output of terahertz radiation with an adjustable aperture. With the optimal aperture-limited pump laser beams, the terahertz wave amplitudes can be enhanced by more than eight times depending on the pump laser parameters than those of aperture-free cases.

Directional modulation of visual responses of pretectal neurons by accessory optic neurons in pigeons

The nucleus lentiformis mesencephali and the nucleus of the basal optic root in birds, homologous to the nucleus of the optic tract and the terminal nuclei of the accessory optic tract in mammals, are involved in optokinetic nystagmus. The present study provides the first electrophysiological evidence that reversible blockade of the pigeon nucleus of the basal optic root by lidocaine can change visual responsiveness of pretectal neurons in a direction-dependent manner. Thirty pretectal cells examined were classified as unidirectional (80%), bidirectional (10%) and omnidirectional (10%) cells according to their directional selectivity. Among the unidirectional cells, seven cells changed firing rates in all directions of motion, 11 changed visual responses only in the preferred directions and six others did not change their responsiveness during lidocaine. Most of the bidirectional cells changed firing rates in the temporonasal direction, and two-thirds of the omnidirectional cells showed these changes in all directions. Thirteen lidocaine administration sites were marked within the nucleus of the basal optic root and 19 recording sites were marked within the nucleus lentiformis mesencephali. This histological verification indicates that the effects of lidocaine blockade in the accessory optic nucleus on the directional selectivity and visual responsiveness of pretectal cells appear to be related, to some extent, to the location of drug injections in the nucleus of the basal optic root. This study has found that visual neurons in the nucleus of the basal optic root, which predominantly prefer vertical and backward motion, could modulate the directional selectivity and visual responsiveness of neurons in the nucleus lentiformis mesencephali, which mainly prefer horizontal motion. It is conceivable that both nuclei work together in coordination and in competition during optokinetic nystagmus.

Energy penetration into arrays of aligned nanowires irradiated with relativistic intensities: Scaling to terabar pressures

Nanowire arrays heated by laser pulses of relativistic intensity open a path to extreme energy densities and pressures. Ultrahigh-energy density (UHED) matter, characterized by energy densities >1 × 108 J cm−3 and pressures greater than a gigabar, is encountered in the center of stars and inertial confinement fusion capsules driven by the world’s largest lasers. Similar conditions can be obtained with compact, ultrahigh contrast, femtosecond lasers focused to relativistic intensities onto targets composed of aligned nanowire arrays. We report the measurement of the key physical process in determining the energy density deposited in high-aspect-ratio nanowire array plasmas: the energy penetration. By monitoring the x-ray emission from buried Co tracer segments in Ni nanowire arrays irradiated at an intensity of 4 × 1019 W cm−2, we demonstrate energy penetration depths of several micrometers, leading to UHED plasmas of that size. Relativistic three-dimensional particle-in-cell simulations, validated by these measurements, predict that irradiation of nanostructures at intensities of >1 × 1022 W cm−2 will lead to a virtually unexplored extreme UHED plasma regime characterized by energy densities in excess of 8 × 1010 J cm−3, equivalent to a pressure of 0.35 Tbar.

Single-shot soft x-ray laser linewidth measurement using a grating interferometer.

The linewidth of a 14.7 nm wavelength Ni-like Pd soft x-ray laser was measured in a single shot using a soft x-ray diffraction grating interferometer. The instrument uses the time delay introduced by the gratings across the beam to measure the temporal coherence. The spectral linewidth of the 4d1S0-4p1P1 Ni-like Pd lasing line was measured to be Δλ/λ=3×10(-5) from the Fourier transform of the fringe visibility. This single shot linewidth measurement technique provides a rapid and accurate way to determine the temporal coherence of soft x-ray lasers that can contribute to the development of femtosecond plasma-based soft x-ray lasers.

K-shell x-ray emission enhancement via self-guided propagation of intense laser pulses in Ar clusters

K-shell x-ray at about 3 keV emitted from Ar clusters irradiated by 110 mJ 55 fs intense laser pulses is studied. The x-ray flux is optimized by moving the nozzle away from the focus of the laser pulse. The total flux of K-shell x-ray photons in 4pi reaches a maximum of 4.5x10(9) photons/shot with a conversion efficiency of 2.5x10(-5) when the nozzle displacement is 2 mm and a long plasma channel is observed by a probe beam.

Characteristic measurements of silicon dioxide aerogel plasmas generated in a Planckian radiation environment

The temporally and spatially resolved characteristics of silicon dioxide aerogel plasmas were studied using x-ray spectroscopy. The plasma was generated in the near-Planckian radiation environment within gold hohlraum targets irradiated by laser pulses with a total energy of 2.4 kJ in 1 ns. The contributions of silicon ions at different charge states to the specific components of the measured absorption spectra were also investigated. It was found that each main feature in the absorption spectra of the measured silicon dioxide aerogel plasmas was contributed by two neighboring silicon ionic species.

Efficient picosecond x-ray pulse generation from plasmas in the radiation dominated regime

The efficient conversion of optical laser light into bright ultrafast x-ray pulses in laser created plasmas is of high interest for dense plasma physics studies, material science, and other fields. However, the rapid hydrodynamic expansion that cools hot plasmas has limited the x-ray conversion efficiency (CE) to 1% or less. Here we demonstrate more than one order of magnitude increase in picosecond x-ray CE by tailoring near solid density plasmas to achieve a large radiative to hydrodynamic energy loss rate ratio, leading into a radiation loss dominated plasma regime. A record 20% CE into hν>1  keV photons was measured in arrays of large aspect ratio Au nanowires heated to keV temperatures with ultrahigh contrast femtosecond laser pulses of relativistic intensity. The potential of these bright ultrafast x-ray point sources for table-top imaging is illustrated with single shot flash radiographs obtained using low laser pulse energy. These results will enable the deployment of brighter laser driven x-ray sources at both compact and large laser facilities.