Xingtao Wang

Electrochemical fabrication of ordered Bi2S3 nanowire arrays

We have successfully fabricated ordered, well-crystallized Bi2S3 nanowire arrays embedded in the nanochannels of porous anodic aluminium oxide templates by direct current electrodeposition from a dimethylsulfoxide solution containing BiCl3 and elemental sulfur. X-ray diffraction and selected area electron diffraction investigations demonstrate that the Bi2S3 nanowires have an orthorhombic uniform structure. Electromicroscopy results show that the nanowires are quite ordered with diameters of about 40 nm and lengths up to 5 µm. X-ray energy dispersion analysis indicates that the atomic composition of Bi and S is very close to a 2 : 3 stoichiometry. The optical properties of these nanowires were characterized by optical absorption techniques. These studies reveal that the annealed Bi2S3 nanowires have an optical band edge (direct) of about 1.56 eV.

Demonstration of nonlinear-energy-spread compensation in relativistic electron bunches with corrugated structures

High quality electron beams with flat distributions in both energy and current are critical for many accelerator-based scientific facilities such as free-electron lasers and MeV ultrafast electron diffraction and microscopes. In this Letter, we report on using corrugated structures to compensate for the beam nonlinear energy chirp imprinted by the curvature of the radio-frequency field, leading to a significant reduction in beam energy spread. By using a pair of corrugated structures with orthogonal orientations, we show that the quadrupole wakefields, which, otherwise, increase beam emittance, can be effectively canceled. This work also extends the applications of corrugated structures to the low beam charge (a few pC) and low beam energy (a few MeV) regime and may have a strong impact in many accelerator-based facilities.

Polarization switching demonstration using crossed-planar undulators in a seeded free-electron laser

Polarization switching of light sources is required over a wide spectral range to investigate the symmetry of matter. In this paper, we report the first experimental demonstration of the crossed-planar undulators technique at a seeded free-electron laser, which holds great promise for the full control and fast switching of the polarization of short-wavelength radiation. In the experiment, the polarization state of the coherent radiation at the secondharmonic of the seed laser is switched successfully. The experimental results confirm the theory and pave the way for applying the crossed-planar undulators technique for seeded x-ray free-electron lasers.

Single-shot measurement of free-electron laser polarization at SDUV-FEL

In this paper, a division-of-amplitude photopolarimeter (DOAP) for measuring the polarization state of a free-electron laser (FEL) pulse is described. The incident FEL beam is divided into four separate beams, and four Stokes parameters can be measured in a single-shot. In the crossed-planar undulators experiment at the Shanghai deep ultraviolet FEL test facility, this DOAP instrument constructed in house responsed accurately and timely while the polarization-state of fully coherent FEL pulses were switched, which is helpful for confirming the crossed-planar undulators technique for short-wavelength FELs.

Polarization control proposal for Shanghai deep ultraviolet free electron laser

In this paper, a fully coherent radiation option with controllable polarization is proposed for the Shanghai deep ultraviolet free electron laser (FEL) test facility. Intensive start-to-end simulation suggests that the two crossed planar undulators which generate the horizontal and vertical linear polarized FEL, should be placed as close as possible for avoiding the polarization performance degradation of the final combined FEL radiation. With the existence of the phase-shifter between the two crossed radiators. Fourier-Transform-Limited output radiation with 100 nJ order pulse energy, 5 Ps full pulse length and circular polarization degree above 90% could be achieved