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Laminar and blazed type holographic varied-line-spacing spherical gratings for use in a versatile soft x-ray flat-field spectrograph attached to an electron microscope are designed, fabricated, and evaluated. The absolute diffraction efficiencies of laminar (or blazed) master and replica gratings at 86.00° incidence evaluated by synchrotron radiation show over 5% (or 8%) in the 50–200 eV range with the maxima of 22% (or 26%–27%). Also the resolving power evaluated by a laser produced plasma source is in excess of 700 at the energy near the K emission spectrum of lithium (∼55??eV) for all gratings. Moreover, the K emission spectrum of metallic Li with high spectral resolution is successfully observed with the spectrograph attached to a transmission electron microscope.

A line pair for a resonant photo-pumping x-ray-laser scheme is proposed in which the wavelength matching between the aluminum Kα⊂2 line (λ = 0.833 95 nm) and the 2p6-(2p1/2,4d3/2)1 transition of the neonlike zinc ions (λ = 0.834 00 nm) is used. The population kinetics code of the neonlike zinc ions in plasma under irradiation of the aluminum K α line shows that substantial amplification gain can be generated in the transition of (2p1/2,3p1/2)0-(2p1/2,4d3/2)1 at a wavelength of 3.5 nm. We also investigate the experimental arrangement of this scheme, which implies that this scheme is feasible with the present ultra-short-pulse-laser technology. [ABSTRACT FROM AUTHOR]

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.

We have developed a soft x-ray laser (SXRL) interferometer capable of the single-shot imaging of nano-scaled structure dynamics. The interferometer consisted of the reflection optics including double Lloyd's mirrors and focusing optics, and the interference fringes are produced on the detector surface. The depth and lateral resolutions of the interferometer were about 1 nm and 1.8 m, respectively. By using this interferometer, the initial stage (~50 ps) of the ablation process of the Pt surface pumped by a 70 fs Ti:Sapphire laser pulse was observed. The expansion speed of the surface estimated from the result (34 nm/50 ps) indicated that the nano-bubble structures were formed in the initial stage of the ablation. In order to observe the detailed dynamics, the temporal synchronization between the pump and probe pulses was improved to be 3 ps by adopting a portion of the SXRL and pump beams as the time fiducials, to which the pump and probe timing was adjusted by using the x-ray streak camera.

We demonstrate in-line phase-contrast imaging of nanothickness foils by using a relatively large, polychromatic, debris-free femtosecond-laser-driven cluster-based plasma soft x-ray source, and a high-resolution, large dynamic range LiF crystal detector. The spatial coherence length of radiation in our setup reached a value of 5 μm on the sample plane, which is enough to observe phase-contrast enhancement in the images registered by the detector placed only a few hundred micrometers behind the object. We have developed a tabletop soft x-ray emission source, which emits radiation within a 4π sr solid angle, and which allows one to obtain contact and propagation-based phase-contrast imaging of nanostructures with 700 nm spatial resolutions. This advance could be of utility for metrology applications.

We attempted the first measurement of the spectral width of the nickel-like molybdenum x-ray laser (${\lambda}\;=\;18.895\;nm$) by use of a high-resolution spectrometer in order to determine the strength of the magnetic field required for the generation of a circularly polarized x-ray laser. The spectral width was measured to be ${\Delta}{\lambda}\;=\;18\;m{\AA}$ under the substantial lasing condition. The magnetic field required for the generation of a circularly polarized x-ray laser was 40 T. The splitting of the x-ray laser line was clearly obtained under 15 T external magnetic field. The strength of the magnetic field estimated from the splitting of the x-ray laser line was large compared with the external magnetic field. It implies that there might be an alternative mechanism for enhancement of the magnetic field in the gain medium plasma.

We have improved a highly coherent x-ray laser at 13.9 nm using an oscillator-amplifier configuration. To improve a high-brilliance x-ray laser, we adopted traveling wave pumping for the amplifier target and rotated the amplifier target 3-4 mrad in the counterclockwise direction. Thereby, a seed x-ray laser can be amplified by medium plasma of the amplifier target with a high gain coefficient. The amplified x-ray laser has the output energy of ~1.3 μJ, corresponding to a large photon flux of 6.5×10^10 photons/pulse and a high peak brilliance of 5×10^26 photons/(s⋅mm^2⋅mrad^2⋅ 0.01% bandwidth).

A chirped pulse amplification laser with zigzag slab Nd:glass amplifiers dedicated to x-ray laser research is described. The laser provides a 1.6 ps duration pulse with ∼7 J energy at a repetition rate of 0.1 Hz. In the power amplifier system, laser light is amplified in a two-step manner: The first step is image-relayed multipass amplification up to ∼1 J with a 10 mm × 10 mm beam. The second step is double-pass amplification up to >10 J with a 10 mm × 90 mm beam. By using this laser system, the saturated amplification of the Ni-like Ag laser at a wavelength of 13.9 nm has been successfully demonstrated.

The anisotropy of electron energy distribution in oxygen plasmas produced by a high intensity laser was investigated by using polarization spectroscopy. An ultra-short pulsed laser with a pulse duration of 66.5 fs and a power density of $1 {\times} 10^17/ W/$\textrm{cm}^2$$ was used. At this power density and pulse duration, the plasma was generated predominantly by optical field ionization. The degree of polarization of OVI 1s$^2$2p$^2$p2- 1s$^2$4d$^2$D$^{0}$ (J = 1/2-3/2 and 3/2-5/2) transition line at 129.92 $\AA$ was measured. O VI 1s$^2$2p$^2$P$^2$ -1s$^2$4s$^2$S$^2$ (J = 1/2-1/2 and 3/2-1/2) transition line at 132.26 $\AA$ was used to calibrate the sensitivity of the optical system. The dependencies of the degree of polarization on the initial gas density and on the laser polarization were investigated. When the laser polarization was changed from a linear to a circular polarization, the degree of polarization was decreased. When the initial gas density was increased, the degree of polarization was decreased.

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 15-μm 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.

We demonstrate the potential of a hydrothermal method-grown ZnO as a high-spatial resolution imaging device for in-situsoft X-ray laser diagnostics by characterizing the exciton emission patterns. By plotting the emission pattern radii at each position, we estimated the evolution of the beam radius around the focal point. The beam profile of the Ni-like Ag ion plasma laser was estimated from the waist radii as 29 and 21 μm, the divergence angle as 7.2 and 11 mrad and the $M^{2}$ factor as 47 and 50 in the horizontal- and vertical-axis, respectively. Spatial resolution of the magnifier was estimated to be 6 μm and is expected to improve by optimizing the optics of the magnifier and using a telescope. Our results would enhance the use of ZnO as an imaging device that would play a crucial role in the development and application of soft X-ray light sources.

A tabletop ultra-bright, debris-free femtosecond-laser-driven cluster-based plasma soft X-ray source, which emits more than $10^{12}$ photons/(sr$\cdot$pulse) in the spectral range 1--10 nm within a $4\pi$ sr solid angle was developed. Using such source in combination with a high dynamic range LiF crystal soft X-ray detector allows obtaining contact and propagation-based phase-contrast images of nanostructures with 700 nm spatial resolutions in a wide field of view. It was demonstrated that the high precision of used techniques enable distinguishing inhomogeneity of measured intensities of ultrathin foils in the order of $\pm 3$%. All of this opens a new approach for PBPC imaging and metrology of full areas of free-standing or mesh-supported nano-thickness foils, or other nanostructures.

A molybdenum slab target was irradiated by double pulses of a line-focused chirped-pulse-amplification Nd:glass laser. A probe beam was injected in the plasma in the longitudinal direction, and we found that the probe beam was guided in the plasma with the plasma length of up to 4.3 mm at the time of 0.8–1.5 ns after the peak of the second pulse. Comparison with hydrodynamics code implied that the electron-density dip or flat region was formed, which was favorable for the efficient soft x-ray lasing under the coupling of the seed x-ray and the x-ray amplifier.

We demonstrate an x-ray laser at a wavelength of 13.9 nm with a beam divergence of 0.2 mrad, which is 1.8 times the diffraction limit. The x-ray laser is generated with two gain media; the seed x-ray pulse from the first medium is amplified in the second medium. The effect of refraction on x-ray propagation is reduced by spatially and temporally controlling the injection of the seed x-ray to the second medium.

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.

A simplified flash-lamp pumped high-average-power Nd:YAG nanosecond laser system based on a master oscillator power amplifier platform was developed toward outside laser remote sensing. The performance of the laser system was demonstrated, obtaining 4 J output pulse energy with a 50 Hz operating frequency. Thermal lens effects were compensated for by using only simple image relays and up to 97% of the laser energy could be contained in the focal spot. The developed laser system was constructed using only components suitable for operation under outside conditions.

Ablation dynamics of tungsten irradiated with a 70 fs laser pulse is investigated with X-ray interferometry and X-ray imaging using a 13.9 nm soft X-ray laser of 7 ps pulse duration. The evolution of high-density ablation front of tungsten (i.e., W) is presented. The ablation front expands to ∼120??nm above the original target surface at 160 ps after femtosecond-laser irradiation with an expansion speed of approximately 750??m/s. These results will provide important data for understanding ablation properties of W, which is a candidate material of the first wall of magnetic confinement fusion reactors.

While it has been expected that X-ray laser will be widely applied to biomedical studies, this has not been achieved to date and its biological effects such as DNA damage have not been evaluated. As a first step for its biological application, we developed a culture cell irradiation system, particularly designed for a plasma-driven soft X-ray laser pulse, to investigate whether the soft X-ray laser is able to induce DNA double strand breaks (DSBs) in living cells or not. The human adenocarcimona cell line A549 was irradiated with the soft X-ray laser at a photon energy of 89 eV and the repair focus formation of the DSBs was assessed by immunofluorescence staining with antiphosphorylated DNA-PKcs (p-DNA-PKcs), ATM (p-ATM) and γ-H2AX antibody. The p-DNA-PKcs, ATM, and γ-H2AX foci were clearly identified after soft X-ray laser irradiation. Furthermore, the increase in the X-ray laser shot number, even from a single shot, results in the increase in p-DNA-PKcs foci. These results are the first evidence that the 89 eV soft X-ray laser is able to induce DSB in living cells. Our study demonstrated that this irradiation system is a useful tool for investigating the radiobiological effect of soft X-ray laser.

Using the x-ray lasers as amplifiers of ultrashort x-ray pulses has been investigated as a scheme for ultimate light sources. For successful implementation, the characteristics of the scheme should be taken into account in designing the amplifiers. In this paper, the basic physics and characteristics of the scheme were analyzed by using the Maxwell-Bloch equations incorporating time-dependent gain, random spontaneous emission, atomic level degeneracy, and radiation polarization. The variation of the pulse parameters such as energy, bandwidth, pulsewidth, and polarization were explained based on a simple mechanism of pulse growth and also compared to that in the conventional x-ray lasers. These results should be the basic information for a practical implementation of the scheme.

Using the recombination plasma scheme, we investigated the amplified spontaneous emissions (ASE) from lithium-like aluminum plasmas produced by multipulse laser irradiation. Three types of multipulse waveforms of Nd-glass laser beam were treated. We measured the time-integrated intensities of the 3d-4f (15.5 nm) and the 3d-5f (10.6 nm) lines of lithium-like aluminum ions for 2.5-cm-long and 1.25-cm-long plasmas. The effective time-averaged gains estimated from these time-integrated intensities varied with the multipulse waveforms. Using a hydrodynamic simulation, we discussed the time history of plasma parameters in the recombining plasma. We concluded that the modifying multipulse waveform contributed to the effective time-averaged gain by maintaining the helium-like ion density until the gain was generated.

A 30-mm long aluminum slab target was irradiated by a line-focused Nd; glass laser light. The relative intensity of the 3d2D-4f2Flaser line (15.4 nm) of the lithiumlike aluminum ions was measured. In this experiment, we put a Mo/Si multilayer mirror on the opposite side of the spectrometer to construct a half cavity. With the use of this mirror, the intensity of the 15.4 nm line became 1.8 times larger than the case without the mirror.