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We have proposed and developed a new hybrid microscopy system using a soft x-ray microscope and a fluorescence microscope imaging the same biological cells at the nearly same time. Combining the powerful advantages such as high spatial resolution of the soft x-ray microscope and the accurate organelle identification of the fluorescence microscope, we can observe fine structures of the cellular organelles in live hydrated biological cells in situ. Staining the cells with several fluorescent dyes such as Mito-tracker, Phalloidin, and DAPI, the soft x-ray images of the cells have been directly compared with the fluorescent images and the cellular organelles such as mitochondria, actin filaments, and chromosomes in the soft x-ray images have been clearly identified. Since the soft x-ray microscope has higher spatial resolution than that of the fluorescence microscope, not only shape of the cellular organelles but also the fine structures of the cellular organelles of the live biological cells have been clearly observed for the first time.

Ultra thin gold films having a thickness of 20-30 nm are favorable laser plasma targets for a soft x-ray microscopy, because the ultra thin films emit intense soft x-rays at the wavelength of water window region from the rear side with respect to the surface irradiated with short pulse laser. Using rear side emissions, the distance between the x-ray source and the specimens can be reduced so that the x-ray flux on specimens increases. In addition, the microscope system can be designed to be compact when the specimen holder and x-ray source are combined in one piece. In the present study, the biological specimen holder combined with a gold ultra thin film plasma target has been developed for a contact-type soft x-ray microscope. This x-ray microscope system needs not any x-ray optics such as a condenser and/or an objective optics which causes a decrease in x-ray photons for imaging. Specimen holder equipped with the plasma target keeps biological specimens at wet condition in vacuum. In this study, x-ray images of hydrated living cells (MH-S mouse alveolar macrophage cell line) have been obtained successfully by use of the newly developed specimen holder. These experimental results reveal that the soft x-ray image can be taken safely. Specimen holder combined with plasma x-ray source will be a key component of a compact soft x-ray microscope using in a laboratory.

X-ray flash imaging by contact microscopy with a highly intense laser-plasma x-ray source was achieved for the observation of wet biological cells. The exposure time to obtain a single x-ray image was about 600 ps as determined by the pulse duration of the driving laser pulse. The x-ray flash imaging makes it possible to capture an x-ray image of living biological cells without any artificial treatment such as staining, fixation, freezing, and so on. The biological cells were cultivated directly on the surface of the silicon nitride membranes, which are used for the x-ray microscope. Before exposing the cells to x-rays they were observed by a conventional fluorescent microscope as reference, since the fluorescent microscopes can visualize specific organelles stained with fluorescent dye. Comparing the x-ray images with the fluorescent images of the exact same cells, each cellular organelle observed in the x-ray images was identified one by one and actin filaments and mitochondria were clearly identified in the x-ray images.

The paper is devoted to experimental and theoretical studies of ablation of condensed matter by optical (OL),extreme ultraviolet (EUV) and X-ray lasers (XRL). Re sults obtained at two dierent XRL are compared. The“rst XRL is collision Ag-plasma laser with pulse duration L = 7 ps and energy of quanta h =89.3 eV, whilethe second one is EUV free electron l aser (EUV-FEL) and has parameters L =0.3 ps and energy of quanta 20.2eV. It is shown that ablation thresholds for these XRL at LiF dielectric are approximately the same. A theory ispresented which explains slow growth of ablated mass w ith ”uence in case of XRL as a result of transition fromspallative ablation near threshold to evaporative ablation at high ”uencies. It is found that the metal irradiatedby short pulse of OL remains in elastic state even in hig h shear stresses. Material strength of aluminum at veryhigh deformation rates V/V 10 9 s 1 is de“ned.Keywords: Short pulse laser ablation, EUV and X-ray laser ablation of LiF, material strength de“ned in laserexperiment

Observation of soft x-ray emissions from laser produced plasmas using ultra thin film targets has been carried out. Au ultra thin films deposited on silicon nitride membranes were irradiated with a high contrast Nd:glass laser pulses. The spectral properties of emitted soft x-rays were monitored with an x-ray spectrograph from the membrane side. The observed emission intensities had a clear dependence on the Au film thickness. The results suggest that most of the laser energy irradiated is absorbed by the Au films and few of the energy goes into the silicon nitride membranes, which means an efficient laser energy deposition to the ultra thin Au film target and a high energy conversion rate from laser to x-rays.

This paper gives an overview of recent progress of laser-driven plasma x-ray lasers in Japan Atomic Energy Agency (JAEA). Fully spatial coherent plasma x-ray laser (XRL) at 13.9 nm with 0.1 Hz repetition rate has been developed using new driver laser system TOPAZ, and the succeeding optimization of the pumping condition has realized more efficient generation of the coherent x-ray pulse. The 0.1 Hz XRL is now routinely used in the wide variety of the application experiments: The highlights of these applications are the study of fluctuation in the atomic structure of ferroelectric substances under the phase transition using the double XRL probe beam technique and the construction of new x-ray laser interferometer to observe nano-scale dynamics of materials.

To widen the field of application of the x-ray laser, higher repetition rate of the x-ray laser is needed. Moreover, the study on effective generation of x-ray laser by optimizing pumping conditions is very important in order to achieve the high repetition rate. At Japan Atomic Energy Agency (JAEA), we have been developing a new type of high repetition rate x-ray laser driver using zigzag slab amplifier for high repetitive x-ray lasing and an OPCPA (Optical Parametric Chirped Pulse Amplification) preamplifier for optimizing x-ray lasing conditions instead of a regenerative amplifier. We are now studying the optimization of pumping conditions for efficient x-ray lasing by the use of pump laser with very high pulse contrast from the OPCPA preamplifier. And we are planning to perform applications using the high repetition rate x-ray laser such as x-ray holography.

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 each0 minutes to0 seconds (0.1 Hz) by installing new driver laser, TOPAZ, which allows us to promote the applications of fully spatial coherent3.9 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.

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.

We review our recent progress in the development of transient x-ray lasers and of their application to plasma diagnostic. The first observation of C-ray laser emission at the new PHELIX-GSI facility is reported. This TCE X-ray laser will be a promising tool for heavy-ion spectroscopy. We then present the main results obtained at the LULU-CPA facility with a compact high-resolution X-UV imaging device. This device was used to investigate the spatial source structure of the Ni-like silver transient X-ray laser under different pumping conditions. The key-role of the width of the background laser pulse on the shape of the emitting aperture is demonstrated. Finally the imaging device was used as an interference microscope for interferometry probing of a laser-produced plasma. We describe this experiment performed at APRC-JAERI.

We proposed a method to generate highly spatial coherent x-ray laser, in which high order harmonics was used as a seed light of a laser-produced x-ray amplifier. In this case, the intensity and the spatial coherence of the output x-ray depended on the harmonic conversion efficiency and the spectral and spatial coupling efficiencies between the harmonics and the lasing line. Based on the present x-ray lasers using a transient collisional-excitation (TCE) scheme, we investigated the values of these efficiencies, which were needed to realize a high spatial coherence. For this purpose we constructed a Ti:Sapphire laser system in which the central wavelength and the spectral bandwidth were tunable, and we conducted a preliminary experiment. The neon-like Ti x-ray laser at a wavelength of 32.4 nm was taken as an example, and harmonics at the same wavelength was generated using Ar gas target under the conditions that the central wavelength of 810 nm and the pulse duration of 1 ps. The experimental result showed that the characteristics of the harmonics were good enough to use as a seed light of x-ray lasers.