Shensheng Han

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.

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.

Emission from line‐focused laser‐heated multi‐groove target

Line‐shaped plasma was produced by ablating plasma from multi‐groove Aluminum surface of a groove period of 100 μm, on which the direction of groove (50 μm in depth and 50 μm in width) is perpendicular to the focal line of 1.05 μm 120 ps (FWHM) heating laser. Comparison with the results of flat‐slab target, different spatial profiles of electron density and temperature and line emission intensity were found. Enhancement of on‐axis emission of candidate lasing line of Al10+which maybe originate from enhanced GL value were observed.

Space-resolved Spectral Diagnosis of Line-shaped Laser-produced Magnesium Plasmas

Space-resolved spectra of line-shaped laser-produced magnesium plasmas in the normal direction of the target have been obtained using a pinhole crystal spectrograph. These spectra are treated by a spectrum analyzing code for obtaining the true spectra and fine structures of overlapped lines. The spatial distributions of electron temperature and density along the normal direction of the target surface have been obtained with different spectral diagnostic techniques. Especially, the electron density plateaus beyond the critical surface in line-shaped magnesium plasmas have been obtained with a fitting technique applied to the Stark-broadened Ly-α wings of hydrogenic ions. The difference of plasma parameters between those obtained by different diagnostic techniques is discussed. Other phenomena, such as plasma satellites, population inversion, etc., which are observed in magnesium plasmas, are also presented.

An experimental study on the conduction region of nonlocalized absorption laser plasmas

Abstract A spectral diagnostic technique has been used to study the properties of conduction regions of laser plasmas. Electron densities beyond the critical surface have been obtained by fitting the Stark-broadened line wing of hydrogenic ions, and the results are in good agreement with the theoretical mode of planar laser-driven ablation. The electron temperature and flux-limited factor of electron thermal conduction have also been estimated.

Development of short-wavelength coherent XUV light sources at SIOFM

Recent progress on the development of short-wavelength coherent XUV light sources at SIOFM is presented, including the space- and time-resolved observation of short-wavelength lasing by lithium-like Si11+, Ca17+, and Ti19+ ions and H-like F8+ ion, and the theoretical design for new approaches, such as controlled expansion cooling, x-ray pumping and strongly radiative cooling.

Space-resolved electron density measurements using the stark-broadened line wings of hydrogenic ions in line-shaped laser plasmas

A program was developed using the Marquardt algorithm method to fit the Stark‐broadened line wings of hydrogenic ions, which can be conveniently used to measure electron density in laser‐produced plasma. Applications of the method are illustrated using space‐resolved 2p‐1s resonance lines in line‐shaped laser plasmas of Mg slab targets irradiated with different laser intensity. Space‐resolved electron densities higher than the critical density are obtained by fitting the Stark‐broadened line wings with the program.

Soft x‐ray laser of He‐like aluminum ions

With numerical calculations, the plasma conditions, in which the laser gains of 1s3d 1D2 ‐ 1s2p 1P1 transition of He‐like aluminum ions can be produced, have been obtained. The method of radiative cooling used to produce the necessary plasma conditions has also been proposed and simulated.

Recent progress on shorter wavelength recombination X‐ray laser research at SIOFM

We will report recent progress on shorter wavelength recombination X‐ray laser research at SIOFM, including the observation of lasing at 46.8 A of the lithium‐like Ti19+ 4f‐3d transition, which was conducted at LF12 laser facility of SIOFM with Ti slab targets driven by an about 110 ps‐duration FWHM quasi‐Gaussian pulse (λ=1.05 μm). Comparison of long‐pulse (∼900 ps) and short pulse (∼110) driving Li‐like Si and Ca ions and H‐like F ion recombination X‐ray lasers will also be presented.