Shali Xiao

Propagation of the finite energy Airy-Hermite-Gaussian beams in uniaxial crystals orthogonal to the optical axis

Abstract We derive an analytical propagation expression of the finite energy Airy-Hermite-Gaussian beam propagating in a uniaxial crystal orthogonal to the optical axis, and calculate numerical examples to investigate the influences of the propagation distance and the ratio of the extraordinary refractive index to the ordinary refractive index on the beam profile. In addition, we also examine the intensity distribution of the beam propagating in the uniaxial crystals at different observation sections. Our research shows that the initial beam profile of the beam remains nearly invariant for a short propagation distance in the crystal. However, as propagation distance continues to increase, the beam width will gradually enlarge, where the diffusion velocities of the beam in the X and Y directions are different. Moreover, both the ratio of the extraordinary refractive index to the ordinary refractive index and the Hermite order number also strongly affect the beam profile in a uniaxial crystal. Our work may find some potential applications in optical trapping and nonlinear optics involving in the special beam profile.

High resolution X-ray spherically bent crystal spectrometer for laser-produced plasma diagnostics

A new high spectral resolution crystal spectrometer is designed to measure very low emissive X-ray spectra of laser-produced plasma in [EQUATION] nm range. A large open aperture ([EQUATION] (mm)) mica (002) spherically bent crystal with curvature radius [EQUATION] mm is used as dispersive and focusing element. The imaging plate is employed to obtain high spectral resolution with effective area of [EQUATION] (mm). The long designed path of the X-ray spectrometer beam is 980 mm from the source to the detector via the crystal. Experiment is carried out at a 20-J laser facility. X-ray spectra in an absolute intensity scale is obtained from Al laser-produced plasmas created by laser energy of 6.78 J. Samples of spectra obtained with spectral resolution of up to [EQUATION] are presented. The results clearly show that the device is good to diagnose laser high-density plasmas.

SPIRAL PHOTON SIEVES APODIZED BY A BESSEL-LIKE WINDOW

In order to improve the focusing and imaging effects of conventional spiral zone plates (SZPs), we design a new type of spiral photon sieve (SPSs) apodized by a robust Bessel-like window. The design principle and numerical simulation results show that the Bessel-like window has a better modulation effect on the main lobe compression and side suppression of the point spread function (PSF) than other traditional window. Taking advantage of the robustness of Bessel-like windows, the proposed SPS can achieve a higher spatial resolution and lower side lobe noise than the conventional SPS and SZP. The practical effects have also been demonstrated by image experiments on the micropore. Our work may find some potential applications in laser alignment, optical trapping, optical communication and edge enhancement imaging fields.

A new method to calibrate the absolute sensitivity of a soft X-ray streak camera

In this paper, we introduce a new method to calibrate the absolute sensitivity of a soft X-ray streak camera (SXRSC). The calibrations are done in the static mode by using a small laser-produced X-ray source. A calibrated X-ray CCD is used as a secondary standard detector to monitor the X-ray source intensity. In addition, two sets of holographic flat-field grating spectrometers are chosen as the spectral discrimination systems of the SXRSC and the X-ray CCD. The absolute sensitivity of the SXRSC is obtained by comparing the signal counts of the SXRSC to the output counts of the X-ray CCD. Results show that the calibrated spectrum covers the range from 200 eV to 1040 eV. The change of the absolute sensitivity in the vicinity of the K-edge of the carbon can also be clearly seen. The experimental values agree with the calculated values to within 29% error. Compared with previous calibration methods, the proposed method has several advantages: a wide spectral range, high accuracy, and simple data processing. Our calibration results can be used to make quantitative X-ray flux measurements in laser fusion research.

Accumulated-carrier screening effect based investigation for the pixellated CdZnTe radiation detector

Based on the pixellated CdZnTe detector, the radiation imaging experiment for the Rh target X-ray source is accomplished. The experimental results indicate that the response signals of the anode pixels, which distribute over the center irradiated area, are completely shut-off when the tube voltage is 45 kV and the tube current increases to 20 µA. Moreover, the non-response pixel area expands with the increase of the tube current, and the total event count of the CdZnTe detector reduces obviously. Furthermore, the inner electric potential and electric field distributions of the pixellatedCdZnTe detector are simulated based on the Poisson equation. The simulation results reveal that the accumulation of the hole carriers, which resulted from the extremely low drift ability of the hole carrier, leads to a relatively high space-charge-density area in the CdZnTe bulk when the irradiated photon flux increases to 5×105 mm−2 · s−1. And thus, the induced signal screen effect of the anode pixels in the center irradiated area is mainly attributed to the distorted electric field which makes electron carriers drifting toward the high potential area in the CdZnTe crystal instead of the pixelanodes.

Research on a logarithmically bent Laue crystal analyzer for X-ray monochromatic backlight imaging

A new logarithmically bent Laue imaging crystal analyzer (LBLICA) was proposed to obtain the monochromatic image of plasmas and exhibited a great potential for application in the Inertial Confinement Fusion experiment over a large field of view (FOV) and with a high spatial resolution. The imaging geometry of the LBLICA has been discussed. According to the Bragg condition and the equation of the logarithmic spiral, the key image parameters of the crystal analyzer, including the system magnification, the spatial resolution, and the FOV, have been analyzed theoretically. An experiment has been performed with a Cu target X-ray tube as a backlighter to backlight a mesh grid consisting of 50-μm Cu wires, and the monochromatic image of the grid has been obtained with a spatial resolution of approximately 30 μm.

Transient x-ray diffraction to measure the dynamic response of shocked lithium fluoride single crystal

Transient x-ray diffraction, also called time-resolved x-ray diffraction and dynamic x-ray diffraction, is one novel diagnostic technique for probing shocked solids. It can provide direct information about microscopic mechanisms governing shock-induced deformation and structural changes at atomistic scales with nanosecond and picoseconds resolution, and lately, it has become possible to measure the structure of transients with sub-picoseconds and sub–Angstrom resolution with the development of ultrafast lasers which can produce femtosecond electron and x-ray pulses in the form of characteristics emission lines as well as x-ray continua in the keV range. In this paper, we detect and measure directly the dynamic response of lithium fluoride single crystal shocked compressed by laser irradiation in SHENGUANG II. In our experiments, high-intensity lasers irradiated a thin Cu foil to generate helium-like rays as x-ray source. Film (IP--image plate) recorded x rays diffracted from multiple lattice planes both perpendicular and oblique angles to the shock loading direction [100]. We gained the diffraction signals of the lattice planes (200) shocked and unshocked, what’s more, other lattices (113), (1-13). The positions of the diffraction lines associated with the (200) lattice plane indicated compression of the lattice along [100] direction by 13%. In the experiment, a large-angle detector consists of two films-one rectangular in shape,one triangular in shape that are positioned to record x rays diffracted from a shocked single crystal nearly within a full π steradian. The experiment shows that transient x-ray diffraction can diagnose the dynamical response of solid with higher resolution.

Study of X-ray imaging with toroidally bent crystal

We developed a focusing imager with a toroidally bent crystal imager. The imager can be used in X‐ray imaging of laser fusion experiments. This article discusses the focusing properties of toroidally bent crystal in Bragg geometry. Simulations of spatial resolution for toroidally bent crystals with different conditions including source size and detector position were done using the ray‐tracing method. The applicable conditions for optimized two‐dimensional (2D) imaging of X‐ray source are proposed. Toroidally bent crystal of mica with curvature radius 290 mm in the meridional plane and 190 mm in the sagittal plane is used as imaging element in the experiments. The high‐quality visible 2D X‐ray image was obtained with the imaging plate due to the high collection efficiency of the bent crystal imaging system. It is demonstrated that the toroidally bent mica crystal could be used in X‐ray imaging. By analyzing the image information of the sagittal direction, we find out that the toroidal crystal imager has spatial resolution about 34 µm.

Intensifying process of polarization ef fect within pixellated CdZnTe detectors for X-ray imaging

The intensifying process of polarization effect at room temperature in a pixellated Cadmium zinc telluride (CdZnTe) monolithic detector is studied. The process is attributed to the increase in build up space charges in the CdZnTe crystal, which causes an expansion of the space charge region under the irradiated area. The simulations of electric potential distributions indicate that the distorted electric potential due to the high X-ray flux is significantly changed and even deteriorated due to increasing space charges within the irradiated volume. An agreement between the space charge distribution and electric potential is discussed.

Detection of the X-ray spectra of imploding neon Z-pinch with elliptically bent mica crystal spectrometer

A wide variety of X-ray and extreme ultraviolet diagnostics are being developed to study on Yang accelerator. An elliptically bent crystal spectrometer is designed with a focal length of 1350 mm. A mica crystal with an interplanar spacing of 1.984 nm bent onto an elliptical substrate with eccentricity of 0.9485 is used. The crystal analyzer covers the Bragg angle range from 30° to 60°. The mica crystal can efficiently reflect radiation in multiple orders, covering the entire spectral range from 0.1 to 1.73 nm except for a gap from 0.86 to 1.0 nm. The application experiment is performed on Yang accelerator using the bent mica crystal analyzer. Spectra of neon-puff Z-pinch plasmas are recorded with a X-ray film, showing the H-like and the He-like lines of neon. Each spectrum has been identified and used for the wavelength calibration, and most of the line radiation is contained in the He-α and the L-α lines. The experimental results have demonstrated that the spectral resolution approximates 379.