Renzhong Tai

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.

Recent progress in X-ray laser research in JAERI

Recent progress in x-ray laser (XRL) research in Japan Atomic Energy Agency (JAEA) is reviewed. The repetition-rate of the x-ray laser has been improved from each 20 minutes to 10 seconds (0.1 Hz) by installing new driver laser, TOPAZ, which allows us to promote the applications of fully spatial coherent 13.9 nm laser in the wide variety of research fields such as material science, single-shot x-ray holography and atomic physics. In order to improve the present performance of the x-ray lasers, we have investigated the possibilities of the enhancement of the peak brilliance using v-groove target and the generation of circularly polarized x-ray laser under a strong magnetic field. Towards shorter wavelength x-ray lasers, we have investigated several schemes. One is the use of reflection of the light by relativistic plasma mirror driven by laser-wake-field, and the other is photo-pumping scheme using Kα emission from a solid target.

Observation of the Ferroelectric Material with Instantaneous X‐ray Laser Speckles

Picosecond x‐ray speckles experiment has been conducted with a simple setup. The source was a compact silver‐plasma‐based x‐ray laser, with a wavelength of 13.9 nm and pulse duration of 7 ps. The sample was a single crystal of BaTiO3, with ferroelectric multi‐domain structure (a/c domains). The matter correlation function, including statistical information of those randomly distributed scatterers (domains here) within the sample, was extracted by deconvolution of the speckle pattern. The instantaneous x‐ray speckle technique has proved to be particularly efficient to be used to observe fast microscopic‐scale phenomena that are hard to access with other methods currently.

Development of a full spatial coherent x-ray laser at 13.9 nm

We have succeeded in developing a laser-pumped x-ray laser with full spatial coherence at 13.9 nm. A highly directed x-ray laser beam with the divergence of 0.2 mrad was generated from the double target experiment, where a seeding light from the first laser medium was amplified in the second medium. The observed divergence is close to the diffraction limited value within a factor of two. The seeding light was amplified in the second medium without refraction influence and the gain coefficient was about 8 cm-1. The gain region of the second medium was far away from the target surface compared with that of the first medium and located in the considerably low density region. From the measurement of visibility, it was found that the spatial coherent length is longer than the beam diameter.

Progress in X‐Ray Laser Development at JAERI

By traveling wave irradiation with a compact, 2‐beam, 1‐ps, 20‐J CPA Nd‐glass laser dedicated to x‐ray laser research, saturated amplification has been demonstrated in Ni‐like Ag at 13.9 nm and Ni‐like Sn at 12.0 nm. High gain amplification has been also obtained in Ni‐like La at 8.8 nm and with gaseous targets in Ne‐like Ar at 46.9 nm and Ni‐like Xe at 9.98 nm. Generation of highly coherent x‐ray laser is planned by injection seeding of the plasma amplifier. The newly developed 340‐TW Ti‐sapphire laser may enable generating exceedingly high power x‐ray radiation which will be useful for pumping inner‐shell ionization x‐ray lasers.

Coherence properties and applications of a transient collisional excitation type silver soft x‐ray laser at Advanced Photon Research Center

A ∼10J, pico‐second laser pumped transient collisional excitation type silver soft x‐ray laser at 13.9 nm routinely delivers collimated saturated amplification soft x‐ray laser pulses with an energy of 20 μJ at the Advanced Photon Research Center. The soft x‐ray laser pulse contains reasonable spatial coherence length of 0.1 mm at the place 1 m away from the x‐ray laser source. The pulse width and energy are a few ps and a few tens of μJ, which is sufficient for imaging with pico‐second time resolution. We describe the three kinds of subjects including the spatial coherence measurement of the silver x‐ray laser using a multi‐slit array, the wave front division type soft x‐ray interferometer using a Lloyd’s mirror and the measurement of domain size distributions in a single BaTiO3 ferroelectrics crystal at room temperature. As for the interferometer experiment, we have obtained a 50 μm diameter wire image with fringe shifts. As for the speckle measurement, the spatial correlation and the spatial power spec...

Demonstration of Transient Collisional Excitation X‐Ray Lasers in Gases

We have demonstrated a high gain neonlike 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 was measured on the transient collisionally excited 3p 1S0 − 3s 1P1 transition for neonlike argon at 46.9 nm with targets up to 0.45‐cm long. Preliminary result on the nickellike xenon x‐ray laser is also discussed.