Aidi Qian

Evolution of spectrally discriminated spatial uniformity of line‐shaped plasmas

A space‐resolved soft x‐ray (SXR) transmission grating spectrometer and a SXR streak camera are used to investigate the evolution of spectrally discriminated spatial uniformity of line‐shaped plasmas produced by uniform laser illumination in line focus. It is found that the spatial nonuniformity of SXR emissions and ion turbulence occur during optical laser’s heating. Various instabilities can be excited due to the long scale length in line‐shaped plasmas to produce the phenomenon.

Space‐ and time‐resolved investigation of short wavelength x‐ray laser in Li‐like Ca ions

We have demonstrated the soft x‐ray amplification for lithium‐like Ca17+ 4f‐3d transition at 57.7 A with 900 ps, 1.05 μm drive laser pulse. The spatial distribution of the gain coefficient and temporal history of the lasing line emissions were also obtained.

Soft X-ray amplification by Li-like Al10+ and Si11+ ions in recombining plasmas

Experimental studies of soft X-ray lasers were carried out on the six-beam laser facility and the LF 12 laser facility of SIOM. Using a home-made one-dimensional spatially resolved grazing incidence grating spectrograph, XUV amplification has been observed in Li-like aluminum and silicon ions, by irradiation of slab targets with a line-focused laser. Based on time-integrated measurement, gain coefficients are 3.1 cm−1 for the 105.7 Å 5f−3d transition in Li-like Al ions, and 1.5 cm−1 and 1.4 cm−1 for the 88.9 Å 5f−3d and the 87.3 Å 5d−3p transitions in Li-like Si ions, respectively. The maximum gain × length products (GL) are about 2.5.

Spatial uniformity and its time evolution of linear laser plasmas

The effect of laser illumination conditions on the uniformity of the linear laser plasmas produced is investigated with time-integrated and time-resolved soft x-ray diagnostics. Evident nonuniformities along the line focus resulting from nonuniform laser intensity distributions have been observed with a conventional simple line-focusing technique. Specifically, the nonuniformity of higher charge-state ions is more remarkable than that of lower ones. A uniform linear plasma can be obtained with a new line-focusing technique that produces uniform laser illumination. Nonuniformities under uniform laser illumination are found to occur primarily in the laser heating period. Further development of time-matched and spatial uniform line-focused laser illumination will produce more uniform linear plasmas.

Laser plasma x‐ray emission studies using a pinhole transmission grating spectrometer

The powerful diagnostic capabilities of the pinhole transmission grating spectrometer (PTGS) have been utilized in studying laser plasma soft x‐ray (SXR) emission and the following results are presented: (1) Studies of the SXR emission from C, Al, SiO2, Cu, Se, Mo, Sn, Er, W, and Au targets irradiated by a 1.06‐μm laser beam with average power density 5×1014 W/cm2 and 300 ps duration indicate the strong dependence of the SXR emission on the atomic number Z. (2) Comparative experiments of Al or Au plasma SXR emission show that changes of the laser intensity have a more remarkable influence on low‐Z plasma SXR emission than on high Z’s. (3) Experiments on target configurations (foil, multilayer, and half‐cylindrical‐groove target) reveal that the foil target is least effective for short‐wavelength SXR emission, while the half‐cylindrical target not only converges the plasma in the groove region, but also most effectively enhances the short‐wavelength SXR emission or increases the electron temperature therei...

Filamentation and jets in line-focused laser-produced plasmas

Abstract In line-focused laser-produced plasma experiments on planar and cylindrical targets, we have observed the line-focused laser beam breakup into filaments as well as small-scale plasma jet-like structures. These phenomena might become obstacles in achieving optimum X-ray lasing in the type of experiments using line-focused laser-produced plasmas as a gain medium.

Studies of Recombination X-Ray-Laser Gain and Gain-Medium Uniformity

The time evolution of the uniformity of the line-shaped X-ray-laser gain medium and the spatial characteristics of the recombination X-ray-laser gains of the Li-like ions are studied using long (∼900 ps) and short (∼100 ps) laser pulses.

An alternative method for gain determination of recombination X-ray lasers

Abstract An improved method was proposed for gain determination of recombination X-ray lasers. The axial line intensity ratio of the lasing emission to an optically thin spontaneous emission is used to overcome the intensity fluctuations caused by shot-to-shot randomness in laser conditions. With this method, the gain of the Li-like Si 4f-3d lasers at 13.0 nm was measured, which is in agreement with theoretical simulations.

Time and space resolved studies of recombination x-ray lasers

Abstract A novel experimental technique of time- and space-resolved X-ray diagnostics has been developed by coupling a stigmatic flatfield grating spectrometer to a soft X-ray streak camera to study the dynamics of recombination X-ray lasers. Time and space characteristics of Li-like Si X-ray lasers have been investigated and some interesting results have been obtained. Preliminary results with CaF2 target are given.

Optical diagnostics of line-focused laser-produced plasmas

To find out homogeneous line-shaped plasma as a gain mediuni of soft Xray lasers produced by linefocused lasers the hydrodynamic characteristics and forms of harmonic and X-ray emission profiles of the plasma colunu-is have been studied with optical diagnostic equipments such as the five-frame laser probing diagnostic system the micrographic diagnostic systems and the spectral resolved Xray pinhole camera. Some experimental results are given and the emphasis is put on those of the halfcylindricalgroove shell targets. The results show that the halfcylindrical groove shell target may be favorable for soft X-ray laser research. 1 .