The emission of ultrashort thermal x-ray radiation is shown to be controlled by two factors; peak temperature and the population of `cold' electrons. Two experiments are used to illustrate these mechanisms. The first measures the time history of 50 angstroms - 130 angstroms x-rays from ultrashort pulse laser heated solid targets. This experiment is used to illustrate the effect of the peak temperature on the full width at half maximum of the emission. The second experiment measures the dependency of decay time of the 1s<sup>2</sup>(S<sub>0</sub>) - 1s2p(<sup>1</sup>P<sub>1</sub>) transition (He<sub>(alpha</sub> )) emission on target thickness. This is used to infer the effects of unheated material or `cold' electrons on the time history of the x-ray emission.

The investigations of ultrashort (0.4 - 0.6 ps) laser pulse radiation interaction with solid targets have been carried out. The Trident subpicosecond laser system was used for plasma creation. The X-ray plasma emission was investigated with the help of high-resolution spectrographs with spherically bent micra crystals. It is shown that when high contrast ultrashort laser pulses were used for plasma heating its emission spectra could not be explained in terms of commonly used theoretical models and transitions in so called `hollow atoms' must be taken into account for adequate description of plasma radiation.

The soft x-ray emission from plasma on a gold-doped glass target produced by a 130-fs Ti:sapphire laser pulse was studied at a laser intensity range of 10¹⁵ - 10¹⁶ W/cm². To evaluate the effects of gold clusters in glass, we compared gold-doped glass with different gold cluster sizes while keeping the gold densities the same (approximately 0.001 vol%). We found that larger gold clusters led to an increase in soft x-ray emission integrated in the range from 5 to 20 nm. Integrated soft x- ray emission from a gold-doped glass target reached about 50% of that from a 1-micrometers thick gold film target. The gold clusters in glass enhanced the soft x-ray emissions about four times compared with a host glass which contained no gold clusters. The pulse durations of soft x-rays emitted from gold-doped glass targets were measured to be 4 - 7 ps, which were slightly shorter than those from a gold target. Due to the low metal density and high plasma formation threshold, particulate deposition, which is a serious obstacle in applying laser-produced plasma x-rays to practical use, was greatly reduced by the use of a gold- doped glass target. From these points of view, femtosecond laser-produced plasma x-ray emitted from metal-doped glass show promise as an ultrafast soft x-ray source.

Backlighting is extensively used as a diagnostic tool in experiments relative to Inertial Confinement Fusion. Thus, beam and target nonuniformities effects on hydrodynamic instabilities growth and imprinting, shock propagation in solid materials and foil acceleration are studied in planar geometry. Spherical or cylindrical implosions measurements are relative to hydrodynamic instabilities, feedthrough and fuel-pusher mixing, in-flight aspect ratio, implosion velocity, symmetry and peak compression densities. With the laser mega-joule very high laser power and energy will be reached that will give access to new density and temperature domains. Correlatively, diagnostics survivability has to be considered taking the large X-ray, neutron and debris emissions into account. The X-ray induced shocks or neutron induced radioactivity will constitute limitations to measurements inside the target chamber. The experimental program on its route towards ignition and gain will anyway still require backlighters to optimize the targets parameters (the microballoon wall thickness, the ablator nature) and allow the adjustment of not well known quantities as opacities and equations of state.

We present and discuss time resolved spectra (KeV range) of solid density plasmas produced by the interaction of clean high intensity laser pulses (400 fs, 0.53 micrometers light) with solid and foil targets at intensities between 10¹⁸ W/cm² and 10²⁰ W/cm². Results have been obtained with the new PX1 x-ray stream camera which has a temporal resolution of 750 fs in the KeV x-ray range.

Short-pulse laser-produced plasmas look very promising for the generation of sub-picosecond X-rays. By combining several experimental techniques, we have significantly progressed towards a better understanding of ultrafast laser-matter interaction. The X-ray yield is a sensitive function of the electron density gradient scale length of the target plasma. In this work, the scale length has been changed by varying the temporal separation between the main laser pulse and a lower intensity prepulse. X-ray spectroscopic diagnostics of the plasma parameters have been used from the analysis of resonance and dielectronic satellite lines. The angular and energy distribution of suprathermal electrons emitted during the ultrafast laser- plasma interaction have been measured as a function of laser polarization and prepulse delay. Frequency-domain interferometry and optical measurements of the reflected probe pulse have been used to study the velocity and the gradient scale length of the expanding plasma. The K_α emission yield peaks for a scale length where resonant absorption is optimized. Hydrodynamic simulations have been performed to investigate the plasma dynamics and the basic processes which control the X-ray emission duration and intensity. Applications of ultrashort K_α X-rays to the diagnostic of solid plasma conditions and as a source for time-resolved diffraction and spectroscopy of transient chemical, biological or physical phenomena are underway.

Soft x-ray lasers laboratory devices are now reliable enough that their high brightness and significant coherence can be routinely exploited. This paper will describe some potential uses of such systems to probe, through interferometry diagnostic techniques, large high density plasmas relevant to Inertial Confinement Fusion.

We previously reported 18 nm Schwartzchild microscope by using a laser plasma source. Now we are planning to improve our Nd:YAG laser system and the multilayers mirror of Mo/B4C instead of Mo/Si, for producing shorter wavelength radiation and developing a new soft x-ray imaging setup. To compress the pulse width of the laser, the SBS (Stimulated Brillouin Scattering) cells is available. To short the wavelength to the 4th harmonics of the laser with high as 0.4 J energy per pulse, the hindrance is the low, less than 20%, nonlinear conversion efficiency. In this paper we are going to briefly introduce the new method to overcome the hindrance and the configuration of the SBS cell.

In this paper we describe a low debris laser plasma source with cryogenic CO₂ target developed in our institute, which can emit strong line radiation in EUV region even in water window. In particular the source is a very important candidate radiation source for the future EUV lithography production line.

Spectra from various target materials from a KrF-laser plasma source have been investigated in the extreme UV spectral range between 12 and 17 nm using an off-Rowland grazing-incidence spectrograph. Additional calibration of the yield at 13 nm and measurement of the spatial and temporal characteristics of the plasma has been done using a combination of a multilayer mirror and XUV diode or fiber image carrier system.

We describe the development of a laser-plasma source based on frozen water droplet targets which is essentially debris- free and capable of continuous, high-repetition-rate (> 1 kHz) operation. Created by modest (< 1 J) laser energies, this source produces copious emission at 13 nm and 11.6 nm, the preferred wavelengths for EUV projection lithography, with negligible target operation costs. Extension of this source to other wavelengths is considered.

Time resolved x-ray diffraction and scattering have been applied to the measurement of a wide variety of physical phenomena from chemical reactions to shock wave physics. Interest in this method has heightened in recent years with the advent of versatile, high power, pulsed x-ray sources utilizing laser plasmas, electron beams and other methods. In this article, we will describe some of the fundamentals involved in time resolved x-ray diffraction, review some of the history of its development, and describe some recent progress in the field. In this article we will emphasize the use of laser-plasma as the x-ray source for transient diffraction.

Optical pump, x-ray diffraction probe measurements have been used to study the lattice dynamics of single crystals with picosecond-milliangstrom resolution by employing a table- top, laser-driven x-ray source. The x-ray source, consisting of an approximately 30 fs, 75 mJ/pulse, 20 Hz repetition rate, terawatt laser system and a moving Cu wire target assembly, generates approximately 5 X 10¹⁰ photons (4π steradians s)^-1 of Cu K_α radiation. Lattice spacing changes of as small as 1 X 10^-3 Å in a few picoseconds have been detected, utilizing Bragg diffraction from GaAs single crystals. Enhancement of the diffraction intensity associated with degradation of the crystals during and after the laser irradiation has been observed, likely due to a transition from dynamic to kinematic diffraction.

We present time- and space-resolved XUV spectra of boron and carbon plasmas created by focusing 100-fs laser pulses on a solid target to an intensity of 10¹⁷ W/cm². Emission lines originating from He-like and H-like excited states from n equals 2 to the ionization limit are observed with a spatial resolution of 100 micrometers in the direction normal to the target plane and with a temporal resolution of up to 4 ps. The position of the ionization limited is seen to depend very crucially on the plasma parameters of density and temperature, and is explained through continuum lowering effects. We observed the dynamics of the continuum lowering for plasma slices at different distances from the target, and record a maximum lowering of 40 eV in He-like carbon (10% of the ionization potential) from the disappearance of the 1snp - 1s² line and from the position of the continuum edge.

The physics of laser-plasma interaction and x-ray generation by laser have been extensively investigated as close relevance laser fusion. Efficient conversion to x-rays and controllability of wavelength, pulse width, and geometrical size have given us the high potentiality of applications to wide scientific and technical fields. An efficient high average power laser with a good beam quality is also under development as the key technology for the applications.

Experiments to develop high photon energy x-ray sources were carried out on the Nova laser. Ten laser beams delivered approximately 39 kJ of energy in 2 ns into a Be cylinder filled with Xe gas. The conversion efficiency into x-rays > 4 keV was measured to be 5 - 15%, which is the highest measured in this photon regime for laser-produced plasmas. The temporal dependence of the x-ray emission indicates that the bulk of the emission is emitted in the first half of the 2 ns pulse. A set of diagnostics were fielded to image the volume in emission as well as provide spectra to measure conversion efficiency.

Leading edge research in molecular dynamics, photoelectron spectroscopy, surface interactions and radiobiology has pushed forward the requirement for intense, pulsed, tunable sources of vacuum ultraviolet radiation. Presently, only synchrotron radiation sources are sufficiently bright for these applications. A bright, continuously tunable VUV beamline capable of delivering in excess of 10¹³ photons/sec/cm²/1nm BW 100 nm, 50 Hz repetition rate (BW equals (Delta) (lambda) /(lambda) is the bandwidth) to the sample, has been constructed on a plasma source generated by a high repetition rate, picosecond KrF excimer laser system.

Several novel approaches to collimating x-rays have been proposed in the last few years. Although some show promise as collimators for point x-ray sources, little work has so far been done on their integration with laser plasmas. Here we discuss their potential and possible applications.

Prospects for utilization of laser produced plasma x-ray source in diagnostic radiology are discussed with special emphasis on application in non-invasive coronary artery angiography and low dose high resolution mammography.

A large volume non-conventional XeCl excimer laser (HERCULES) emitting long pulses (from 10 ns up to 120 ns at a wavelength of 308 nm) has been used to drive a soft x-ray plasma source. The x-rays pulse duration and the energy conversion efficiency in different spectral regions have been measured; x-rays emission lasting up to 100 ns has been obtained in the 70 eV region. The dependence of x-ray pulse duration on the size of the laser spot is discussed. The x- ray source can be operated both in vacuum and in helium at atmospheric pressure. This allows irradiating over a large area both for contact microscopy of living specimens (up to 1 mm² windows) and for radiobiology (up to some cm² windows). The experimental results obtained for these two applications as well as for radiographic images of living insects are discussed.

For the study of future nm devices, electronic and chemical states must be observed with nm resolution, and a photoelectron microscope is strongly desired to be developed. A compact system for in-house analysis can be realized with a laser-plasma x-ray source. Experimental results confirm that an x-ray photoelectron microscope with a laser-plasma can become a powerful tool with potential spectrum acquisition time comparable to that with a synchrotron source. Reported are high energy resolution photoelectron spectra for Si revealing the existence of surface states, and 2-D mapping with resolution of 60 micrometers demonstrating that simultaneous detection of multi-elements by the time-of-flight energy analysis is powerful in obtaining a reliable mapping. High electron detection efficiency of the system with a pulse source is discussed to be essentially important for nm resolution.

A hot and dense plasma can be produced by high-power laser irradiation of a high-pressure gas puff target. The plasma emits strong x-ray radiation in low photon-energy range (soft x-rays and XUV radiation) and is considered to be used as a debrisless laser-produced x-ray source. It was shown that the laser-irradiated gas puff plasma is an ideal source for the high-resolution spectroscopic studies of complex spectra of the multicharged ions. This paper reports our investigations of x-ray spectra of heliumlike argon and neonlike krypton ions. The gas puff targets were created with the use of a specially designed high-pressure solenoid valve operating at a backing pressure up to 15 at and quipped with a sonic-type circular nozzle of 0.5 mm in diameter. Parameters of the gas puff targets were measured using x-ray shadowgraphy and laser interferometry. To irradiate the gas puff targets we have used a Nd:glass laser, which generates 10 J pulses in 1 ns FWHM. The laser beam was focused onto the gas puff target perpendicularly in respect to the flow of gas using an aspherical lens. The diameter of a laser beam in the focus were about 100 micrometers , what ensured the radiation power density to be of order of 10¹⁴ W/cm². To measure x-ray spectra emitted by a laser-irradiated gas puff target we have used a simple focusing crystal spectrographs with a mica crystal curved into a spherical surface of radius R equals 100 mm. The spectra were recorded on Kodak RAR 2495 x-ray commercial film. The high resolving power of the spectrograph of about (lambda) /(Delta) (lambda) equals 10000 permitted high-precision wavelength spectral measurements. The measured x-ray spectra have the small spectra width of the observed lines associated with the low expansion velocity of the laser- irradiated gas puff plasma. Dielectronic sodiumlike satellites to neonlike krypton resonance lines have measured for the first time. High-resolution spectra of heliumlike argon were also obtained. The measured spectra have been used for diagnosing the plasma parameters.

Nanosecond flash x-ray microscopy of living biological specimens is demonstrated with subcellular spatial resolution. Single shot images, produced by a compact laser- plasma x-ray source optimized for maximum image contrast, are captured before radiation processes can affect the specimen.

Saccharomyces Cerevisiae yeast cells were irradiated using the soft X-ray laser-plasma source at Rutherford Laboratory. The aim was to produce a selective damage of enzyme metabolic activity at the wall and membrane level (responsible for fermentation) without interfering with respiration (taking place in mitochondria) and with nuclear and DNA activity. The source was calibrated by PIN diodes and X-ray spectrometers. Teflon stripes were chosen as targets for the UV laser, emitting X-rays at about 0.9 keV, characterized by a very large decay exponent in biological matter. X-ray doses to the different cell compartments were calculated following a Lambert-Bouguet-Beer law. After irradiation, the selective damage to metabolic activity at the membrane level was measured by monitoring CO₂ production with pressure silicon detectors. Preliminary results gave evidence of pressure reduction for irradiated samples and non-linear response to doses. Also metabolic oscillations were evidenced in cell suspensions and it was shown that X-ray irradiation changed the oscillation frequency.

The use of a high energy laser source for soft x-ray contact microscopy is discussed. Several different targets were used and their emission spectra compared. The x-ray emission, inside and outside the Water Window, was characterized in detail by means of many diagnostics, including pin hole and streak cameras. Up to 12 samples holders per shot were exposed thanks to the large x-ray flux and the geometry of the interaction chamber. Images of several biological samples were obtained, including Chlamydomonas and Crethidia green algae, fish and boar sperms and Saccharomyces Cerevisiae yeast cells. A 50 nm resolution was reached on the images of boar sperm. Original information concerning the density of inner structures of Crethidia green algae were obtained.

The technique based on Moire deflectometry with soft x-ray laser beam has been demonstrated by the research group of D. Ress in the research of plasma produced by laser. We apply this method to visualize the flow field in diesel combustion chamber, and it is also a new application in the world. When a beam of collimated light passes through the flow field, the index-of-refraction gradient in the plasma bends the rays through an angle. A Moire pattern is created when a probe beam is passed through a pair of rotationally offset (angle (theta) ) 1D rulings consisting of evenly spaced opaque and transmissive stripes. By measuring the fringe shift we can get the information of flow field.

A comparison of the uniformity of the soft and hard x-ray emissions from planar gold foils irradiated by OMEGA laser beams has been performed. A normal-incidence microscope with two multilayer coated mirrors formed 2D images at a wavelength of 48.3 angstroms (257 eV energy). The X5.8 magnified images were recorded by a gated framing camera at various times during the 3 nsec laser pulse. A pinhole camera imaged the x-ray emission in the energy range > 2 keV. On a spatial scale of 10 micrometers , it was found that the soft x-ray images at 257 eV were quite uniform and featureless. In contrast, the hard x-ray images in the energy range > 2 keV were highly nonuniform with numerous features of size 100 - 150 micrometers .

A toroidal crystal spectrometer was designed with the purpose of measuring the aluminum K-absorption edge shift, in the wavelength range around 7.9 angstroms, in highly compressed matter. The expected shift is about 100 mA (approximately 20 eV). The x-ray reflected from the crystal are focused onto a streak camera slit of 16 mm high and 100 micrometers width, to obtain a time resolved spectrum. High resolution value and dispersion of about 1 angstrom/16 mm on the detection window is hence required. A crystal with a toroidal surface is used to enhance the focusing power in the spatial dimension as in the spectral one. Numerical simulations are performed by means of 1D and 2D codes for the determination of the crystal characteristics like the dimension and the curvature radius with respect to the geometric constraints. Some results will be presented concerning the obtained spectra.

In the present paper we are demonstrated achievement of high spatial resolution for x-ray spectrum of plasma produced by 20 mJ, high-repetition 120 fs laser using a Bragg-Fresnel linear zone plate structure on the mica crystal surface. We had also measured x-ray spectra near resonance line of He_(alpha ) of Mg XI with simultaneously high spectral (up to (lambda) /(Delta) (lambda) equals 10000) and spatial ((Delta) x equals 10 micrometers ) resolution from plasma, heated by such laser, using spectrograph with spherical bent crystal. We demonstrated the important role of inner-shell excitation mechanism for low confinement parameters and propose new excitation channels from highly populated excited states (Li-like and Be-like satellite levels). The collision excitation cross sections for these processes do not decrease with principal quantum number. These channels can be also subject to electron beam excitation. It was shown also the big role of transient effects for Rydberg- Satellites due to a strong three-body recombination into high n-states in the cooling phase. Total spectra simulations are in rather close agreement with experimental results. New 3d¹⁰4 - 3d⁹4l6f spectral features of Cu-like barium, previously observed as unresolved transition arrays, are resolved at first time in present paper and enabling plasma diagnostics which were not possible before. The plasma electron density and temperature are found to be in the ranges: N_e equals 5 X 10²¹ - 10²² cm^-3 and kT_e equals 100 - 50 eV, respectively. The generation of intense, collimated monochromatic x-ray beams ((lambda) approximately 9.5 angstroms) results are presented too.

A new pumping scheme named exploding pumping is proposed for realizing recombination x-ray lasers with high excitation efficiency. In the new scheme, a very thin membrane is employed as a target and it is heated instantaneously before the plasma starts to move by a high peak power sub- picosecond pumping laser. In the scheme, the plasma heating efficiency is improved by being free from heat conduction loss to bulk, and by suppressing the energy loss to hydrodynamic motion. Inertia of the mass delays the start of the plasma motion and gives sufficient time for full ionization. Owing to the extreme thinness of the initial high density plasma, only a few micrometers expansion leads to great reduction of the density and cools down rapidly to produce large gain. Efficient heating of a membrane plasma is confirmed in experimentally observed x-ray spectra and charge collector signals. It is discussed that the most serious problem for realizing water window x-ray lasers is conventional ablation pumping is density gradient which causes refraction of x-rays and limits gain length. The new pumping scheme can solve this refraction problem. The density profile of the expanding plasma in this scheme is fairly uniform because all material expand explosively and because no mass is supplied during the expansion. According to a numerical simulation, 3.34-nm water window of gain length product of 10 will be realized with the 6 J/ 0.3 ps laser irradiation. Longer wavelength x-ray lasers around 13- nm will be realized with a few J/ a few ps pulse pumping. The key technology in the new pumping scheme is suppression of pre-pulse. The effect of pre-pulse is experimentally observed, and means for pre-pulse suppression is discussed.

The response of photographic film to X-rays from laser- plasma is of practical interest. Film is often used for the ultimate detection of x-rays in crystal and grating spectrometers and in imaging instruments such as pinhole cameras largely because of its high spatial resolution (approximately 1 - 10 microns). Characteristic curves for wavelengths--3 nm and 23 nm are presented for eight x-ray films (Kodak 101-01, 101-07, 104-02, Kodak Industrex CX, Russian UF-SH4, UF-VR2, Ilford Q plates and Shanghai 5F film). The calibrations were obtained from the emission of laser-produced carbon plasmas and a Ne-like Ge X-ray laser.

Fabrication of 3D terahertz waveguide components is demonstrated using a novel x-ray micromachining process with integral and embedded x-ray masks. 1 nm x-rays generated by a laser-plasma source are used to expose chemically amplified resist. A repeated exposure and development technique shortens the total x-ray exposure time to 10 min to obtain the required 48 micrometers high structures. A 2.5 THz waveguide cavity is fabricated in gold by electroplating the above resist microstructure.

A new x-ray imaging system based on spherically curved crystals has been developed. It is designed and used for diagnostics of targets ablatively accelerated by the Nike KrF laser. Applications of this instrument include spectroscopy with one-dimension of spatial resolution and two-dimensional monochromatic self-imaging and backlighting. The imaging system with various crystals of mica and quartz is used for plasma diagnostics of the main target and for characterization of potential backlighters. A spherically curved quartz crystal (2d equals 6.687 angstroms, R equals 200 mm) is used to produce monochromatic backlit images with the He- like Si resonance line (1865 eV) as the source of radiation. The spatial resolution of the x-ray optical system is 1.7 micrometers in selected places and 2 - 3 micrometers over large area. Time resolved backlit monochromatic images of CH planar targets driven by the Nike facility have been obtained with 6 - 7 micrometers spatial resolution.