Huajing Tang

ENHANCEMENT OF X-RAY LASING DUE TO WAVEFRONT CORRECTION OF LINE-FOCUSING OPTICS WITH A LARGE-APERTURE DEFORMABLE MIRROR

Intense x-ray laser radiation at 7.92 nm in nickel-like neodymium has been achieved by improving the line-focusing pattern using a large-aperture deformable mirror. A deformable mirror of 40 cm diameter with hexagonally arranged 37 mechanical actuators has been developed. The wavefront aberration due to a cylindrical lens used for line focusing has been corrected with the deformable mirror to produce a line-focusing pattern of uniform narrow width and uniform intensity distribution. The intensity of the x-ray laser beam has increased six times due to the improvement of the line-focusing pattern.

Characterization and optimization of a laser-produced x-ray source with a gas puff target

Soft x-ray emission from plasmas produced using a laser- irradiated gas puff target have been investigated. The use of the gas puff targets, created by pulsed injection of high- density gas from a solenoid valve through a nozzle, eliminates the production of debris associated with solid targets. To improve the gas puff target two approaches have been used: (1) cooling of the valve with liquid nitrogen to increase condensation of gas and (2) formation of the target by injection of gas in gas surrounding the nozzle output using the double nozzle setup. The gas puff targets created with these two approaches were characterized with x-ray backlighting method using laser-produced x-ray source. Laser pulses of 1 ns time duration with energy up to 10 J from a Nd:glass laser and of either 0.9 ns or 10 ns time duration with energies up to 0.7 J from a Nd:YAG laser were used to produce plasmas. Emissions in the soft x-ray range from laser- produced gas puff plasmas were studied for various gases. Significant improvement of x-ray production from the double stream gas puff target has been observed.

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.

Intense Nickel-like Neodymium X-Ray Laser at 7.9 nm with a Double-Curved-Slab Target

We have demonstrated triple-pulse lasing combined with an X-ray mirror with 4 pumping pulses in Ni-like Nd at 7.9 nm. Intense triple-pulse X-ray laser radiation has been generated with a double-curved-slab target, which was irradiated with laser pulses of quasi-traveling wave configuration, using cylindrical lens arrays for uniform pumping. An order of magnitude higher X-ray laser pulse energy was observed along the forward-traveling wave direction compared to the backward-traveling wave direction. Output energy in the forward direction was estimated to be ~40 µJ.

Generation of intense x-ray laser radiation at 8 nm in Ni-like Nd ions

Results of the joint experiment between ILE Japan and NLHPLP/IAPCM China are reported. New optics for improved line focusing, a cylindrical lens array and a deformable mirror, were used in irradiation of x-ray laser targets. Double-pass amplification at 7.9 nm has been demonstrated. Strong lasing at 7.9 nm with approximately 100 (mu) J output energy has been obtained in Ni-like Nd ions by quasi-traveling wave pumping of double targets.

Development and applications of X‐ray lasers at LSAI/LIXAM

We present an overview of our research activity achieved since the last X‐ray laser Conference in Saint‐Malo. Our research program involves the development of laser‐pumped collisional X‐ray lasers under different regimes of irradiation, and the use of these sources for applications. The work presented involves a number of French and international collaborations and was carried out at different pump laser facilities: LULI (Ecole Polytechnique), LOA (ESNTA) in France; Rutherford Laboratory in U.K; PALS in Czech Republic.

Development of intense short-wavelength Ni-like soft x-ray lasers toward the water window

We report experimental results on Ni-like x-ray laser at the wavelength as short as 4.4 nm. The performance of x-ray lasing pumped by various types of pulse trains which were composed of 100 ps pulses was investigated with a double slab targets which were placed in series to double the gain length. Two opposing laser beams irradiated the double targets with a suitable time difference for quasi traveling wave pumping. The well collimated double target amplification was successfully demonstrated with two beam irradiation for Yb and Hf lasing at 5.0 nm and 4.7 nm whose gain length products were 11 and 6, respectively. The Ni- like lasing line of Ta have been observed at 4.5 nm. Based on these results, we will report the suitable pumping condition for the saturated water window x-ray lasers.

X-ray laser research in JAERI-Kansai

The nickel-like silver x-ray laser in the transient collisional-excitation scheme is demonstrated. The gain coefficient, the intensity ratio to the background signal, the beam divergence and the size of the gain region are investigated.

Characterization of laser-produced gas-puff plasmas for soft x-ray projection lithography

We characterize a laser produced gas puff plasma for soft x- ray generation. Strong emissions at 11.4 nm wavelength region was observed, using krypton and xenon gas puff targets irradiated by a 0.7J/8ns Nd:YAG laser. Space resolved x-ray spectra measurement indicated that the source size depends on the Rayleigh length and the gas density profile. A channeling effect for larger tare size which is connected with the thermal focusing has been observed.

Uniform line focus and multitarget coupling for the creation of near-water-window nickel-like x-ray laser

To obtain high gain saturated amplification soft x-ray lasing output, uniform and long amplification medium must be created by focusing and target set-up technology. We report on the cylindrical lens array and multi target coupling system for creating uniform line focus. Through these methods, serial x-ray lasing with the wavelength towards the wavelength of water window are obtained on the GekkoXII Nd glass laser facility in ILE, Osaka, University.