Peixiang Lu

Study of Ne- and Ni-like x-ray lasers using the prepulse technique

Recent studies of lasing in Ne- and Ni-like ions on the Asterix IV iodine laser [H. Baumhacker et al. Appl. Phys. B 61, 325 (1995)] using the prepulse technique are reviewed. Experimental evidence shows that beam refraction is the main factor for the lack of lasing in low-Z elements, as well as the J=0−1 vs J=2−1 anomaly in Ne-like ion lasers when there is no prepulse. It is shown that the role of the prepulse in enhancing the J=0−1 lasing line in Ne-like ion is to produce a larger and more homogeneous plasma. The measurement of lasing on the J=0−1, 3p−3s transition in Ne-like Mn, V, Sc, Ca, K, Cl, S, and Si using the prepulse technique is reviewed. Wavelengths of these lasers range from 22 to 87 nm with gain lengths between 7 and 12. The drive energy for S was scaled down to 20 J. The experiment demonstrating the 12 nm lasing on the J=0−1, 4d−4p transition in Ni-like Sn is also reviewed.

Development of a pumping laser system for x-ray laser research

A two-beam chirped-pulse-amplification Nd:glass laser system dedicated to x-ray laser research is described. Each beam provides an output energy of 20 J with a typical pulse duration of 1.3 ps. A prepulse of variable duration is generated by use of a novel, to our knowledge, optical system. A reflection optical system, comprised of an off-axis parabolic mirror and a spherical mirror, produces a line focus with 6-mm length and 165-microm width without chromatic aberration. By use of this pumping laser system, the nickel-like silver x-ray laser at a wavelength of 13.9 nm has been demonstrated.

Self-photopumped neonlike x-ray laser

We propose a new x-ray laser mechanism that uses radiation from the strongest 3d ? 2p Ne-like resonance line in an optically thick plasma to radiatively drive population from the Ne-like ground state to the 3d state, which then lases to two 3p states. Collisional mixing of the 3p states with nearby 3s and 3d states depopulates the lower laser states. Modeling is presented for this mechanism in Ne-like Ar, and in experiments we observe one potential 3d ? 3p lasing transition at 45.1 nm in Ne-like Ar.

Lasing in neonlike sulphur and silicon

Abstract We report lasing in neonlike sulphur and silicon using the prepulse technique on the Asterix iodine laser. In sulphur, lasing is observed at 60.1 and 60.8 nm on the 3d 1 P 1 -3p 1 P 1 and 3p 1 S 0 -3s 1 P 1 transitions, respectively. The drive energy for the 60.8 nm laser was scaled down to ∼ 20 J. In silicon, lasing at 87.4 nm on the 3p 1 S 0 -3s 1 P 1 transitions was observed.

Two-dimensional near-field images of the neonlike germanium soft-x-ray laser

We present what are believed to be the first two-dimensional near-field images of the neonlike germanium x-ray laser obtained with multilayer imaging mirrors. The Asterix iodine laser, with a low-intensity prepulse 5.23 ns before the main pulse, was used to irradiate germanium slab targets. We observe a large difference in the spatial dependence of the J = 0-1 and J = 2-1 lines of germanium, with the J = 2-1 emission peaking farther away from the target surface. The prepulse level is also observed to have a significant effect on the spatial dependence of the germanium laser lines. A great deal of structure is observed in the near-field images, particularly in the J = 0-1 emission.

Relative merits of using curved targets and the prepulse technique to enhance the output of the neon-like germanium X-ray laser

Abstract We present a series of experiments using germanium slab stargets with either flat or curved surfaces which are illuminated by a low intensity prepulse before the main optical drive pulse of the 1.315 μm Asterix iodine laser. By varying the radius of curvature of the target surface and the size of the prepulse we show the relative merits of these two effects on improving the output of the neon-like germanium 3p 1 S 0 →3s 1 P 1 lasing transition at 196 A. While the curved targets do improve the laser output at 196 A, the use of the prepulse technique is shown to be much more important in increasing the laser output. We also discuss the relative effect on the other two important germanium laser lines at 232 and 236 A.

Demonstration of a transient-gain nickel-like xenon-ion x-ray laser

We demonstrate a high-gain nickel-like xenon-ion x-ray laser, using a picosecond-laser-irradiated gas-puff target. The elongated x-ray laser plasma column was produced by irradiation of the gas-puff target with line-focused double picosecond laser pulses with a total energy of 18 J in a traveling-wave excitation scheme. Strong lasing at 9.98 nm was observed, and a high gain coefficient of 17.4 cm(-1) was measured on the transient collisionally excited 4d-4p , J=0-1 transition for nickel-like xenon ions with target lengths as great as 0.45 cm. A weak nickel-like lasing line at a shorter wavelength of 9.64 nm was also observed, with a gain coefficient of 5.9 cm(-1) .

Spatial Coherence Measurement of 13.9 nm Ni-like Ag Soft X-Ray Laser Pumped by a 1.5 ps, 20 J Laser

In this paper, we report the first measurement of the time-integrated spatial coherence of the Ni-like Ag X-ray laser at 13.9 nm pumped by a 1.5 ps, 20 J Nd glass laser, in which the transient collisional excitation (TCE) pumping scheme is realized. The time-integrated complex coherence factor (CCF) of the X-ray laser has been determined from partially coherent diffraction patterns of a multislit array placed 1 m away from the X-ray laser source. The transverse coherence lengths in the directions horizontal and vertical to the Ag target surface are estimated respectively to be within 110 µm to 140 µm at a position 1 m from the X-ray laser source. We tried to explain the profile of the CCF with a quasi-monochromatic incoherent source model with various profiles.

NEAR FIELD IMAGING OF THE TRANSIENT COLLISIONAL EXCITATION Ni-LIKE Ag X-RAY LASER

The spatial profile of the transient collisional excitation Ni-like Ag X-ray laser in various plasma lengths was observed using the near field imaging method. The gain region was the size of 50 μm and 30–50 μm distant from the target surface. The shapes of the gain region were crescent shape or consisted of two spots.

Demonstration of a transient high gain soft X-ray laser for neon-like argon

We have demonstrated a high gain neon-like argon ion X-ray laser using a gas puff target. The elongated X-ray laser plasma column was produced by irradiating the gas puff target with line-focused double picosecond laser pulses with a total energy of 9 J in a travelling-wave excitation scheme. Strong lasing was observed, and a high gain coefficient of 18.7 cm-1 and a narrow beam divergence of less than 3.7 mrad were measured on the transient collisionally excited 3p1S0-3s1P1 transition for neon-like argon at 46.9 nm with targets up to 0.45 cm long.