This PDF file contains the front matter associated with SPIE Proceedings Volume 7451, including the Title Page, Copyright information, Table of Contents, and Conference Committee listing.

Life science and biology have advanced with the progress of microscope technology. A strong desire of life scientists is to observe live cells with high spatial resolution. The development of soft x-ray microscopy using a special wavelength called the water window started in the 1970s in order to fulfill this desire. However, the photon fluxes realized so far are still insufficient for this application. Here, we demonstrate the generation of a coherent water window x-ray by extending the plateau region of high-order harmonics under a neutral-medium condition. The observed maximum harmonic photon energy attained are 300 eV and 450 eV in Ne and He, respectively. Our proposed generation scheme, combining a 1.6 mm laser driver and a neutral Ne gas medium, is efficient and scalable in output yields of the water window x-ray. This powerful concept is expected to boost the development of soft x-ray microscopes based on high-order harmonics.

Two novel schemes for efficient x-ray laser generation from laser-produced plasma and capillary discharge-driven plasmas are described. The combination of nano-structured targets with the high energy ultrashort pulse lasers can result in the generation of laser-produced plasmas that could lead to high brightness sources of incoherent multi-KeV radiation and x-ray lasers of short pulse duration at shorter wavelengths. The generation of 0.5-1 keV x-ray laser radiation from a Ni-like U plasma created using excitation from a Petawatt laser is analyzed. The efficient excitation of capillary discharge plasmas in micro-capillary discharge channels is discussed.

The phase compensation of the negatively chirp of the attosecond pulse train is demonstrated experimentally. By adding a weak second harmonic laser field, the phase compensation can be negatively chirp or positively chirp at different time delay, which support a new way to generate the strong transform-limited attosecond pulse.

We report new advances in the development of high repetition rate table-top soft x-ray lasers. We have extended the gain-saturated operation of these lasers to 10.9 nm demonstrating a 1 Hz repetition rate laser operation in Ni-like tellurium with an average power of 1 microwatt. In a separate development we have demonstrated the first all-diodepumped soft x-ray laser. Lasing was achieved in the 18.9 nm line of Ni-like molybdenum in a plasma heated by a compact all-diode-pumped Yb:YAG laser. The solid state pump laser produces 8.5 ps pulses with up to 1 J energy at 10 Hz repetition rate. This diode-pumped laser has the potential to greatly increase the repetition rate and average power of soft x-ray lasers on a significantly smaller footprint. These compact soft X-ray lasers offer new scientific opportunities in small laboratory environments.

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.

Stable and reliable operation of a nickel-like molybdenum transient collisional soft x-ray laser at 18.9 nm demonstrated and studied with a 10Hz Ti:sapphire laser system proves the suitability of the double-pulse non-normal incidence pumping geometry for table-top high repetition soft x-ray lasers and broadens the attractiveness of x-ray lasers as sources of coherent radiation for various applications. X-ray laser emission with pulse energies well above 1 μJ is obtained for several hours at 10Hz repetition-rate without re-alignment under optimized double pumping pulse parameters including energy ratio, time delay, pulse duration and line focus width.

Laboratory based X-ray lasers (XRL) exhibit a broad application potential in material sciences, imaging, spectroscopy and laser plasma diagnostics if two main issues are solved: a stable, well defined output of the system and a high repetition rate for fast data acquisition. During the last few years using the grazing incidence pumping (GRIP) scheme an pump energy level as low as 1 J was demonstrated for saturated XRL operation. This pump energy could be provided in principle even by commercially available Ti:Sa laser systems. However, the repetition rate of these systems is limited to 10 Hz and the output stability of the XRL follows that of the pumping laser. To overcome this situation a dedicated high repetition rate XRL pumping laser will be introduced here. This concept is based on a fully diode pumped solid state laser using thin Yb:YAG disks as active material. In this paper we report about the first phase of the project aimed at a high average power XRL user station based on the GRIP scheme.

In this paper we present the perspectives of the development of the XUV laser sources using High-power laser facilities. We focus our paper on the present statuts of the LASERIX facility and especially its role in the development of the XUV laser sources considering the French "Institut de la Lumière Extrême" (ILE) and the potential European project Extreme Light Infrastructure (ELI).

Focusing an x-ray free electron laser (XFEL) pulse into a gas target, a plasma of transiently core excited ions can be created within a few fs, building a pathway to an inner-shell keV x-ray laser. Varying the XFEL parameters, a wide variety of pulse structures can be created with comparable peak-intensities to XFELs: isolated pulses of subfs duration, trains of pulses with increased temporal coherence, and trains of fs pulses of different wavelengths. We present self-consistent gain and amplification calculations, tailored to predict first experiments on lasing in neon pumped by the Linac Coherent Light Source at Stanford.

We present collective Thomson scattering with soft x-ray free electron laser radiation as a method to track the evolution of warm dense matter plasmas with ~200 fs time resolution. In a pump-probe scheme an 800 nm laser heats a 20 μm hydrogen droplet to the plasma state. After a variable time delay in the order of ps the plasma is probed by an x-ray ultra violet (XUV) pulse which scatters from the target and is recorded spectrally. Alternatively, in a self-Thomson scattering experiment, a single XUV pulse heats the target while a portion of its photons are being scattered probing the target. From such inelastic x-ray scattering spectra free electron temperature and density can be inferred giving insight on relaxation time scales in plasmas as well as the equation of state. We prove the feasibility of this method in the XUV range utilizing the free electron laser facility in Hamburg, FLASH. We recorded Thomson scattering spectra for hydrogen plasma, both in the self-scattering and in the pump-probe mode using optical laser heating.

We report on the x-ray absorption of Warm Dense Matter experiment at the FLASH Free Electron Laser (FEL) facility at DESY. The FEL beam is used to produce Warm Dense Matter with soft x-ray absorption as the probe of electronic structure. A multilayer-coated parabolic mirror focuses the FEL radiation, to spot sizes as small as 0.3μm in a ~15fs pulse of containing >10¹² photons at 13.5 nm wavelength, onto a thin sample. Silicon photodiodes measure the transmitted and reflected beams, while spectroscopy provides detailed measurement of the temperature of the sample. The goal is to measure over a range of intensities approaching 10¹⁸ W/cm². Experimental results will be presented along with theoretical calculations. A brief report on future FEL efforts will be given.

The evolution of the transmission of extreme ultra-violet (EUV) light from a germanium backlighter through heated thin iron targets has been measured at laser irradiances of about 8×10¹⁶ W cm^-2. A rapid increase in transmission from 0 to 30% in 20 ps was observed. A two dimensional radiation hydrodynamics model was used to simulate the heating of the plasma and the transmission of EUV light as a function of time. The tamped iron targets were heated up to an average electron temperature of about 55 eV and a mass density of approximately 0.6 g cm^-3. The transmission measurements are in reasonable agreement with modelling results. The experimental layout is similar to an X-ray laser experiment and therefore, for relatively low plasma temperatures, these kinds of experiments can be done in combination with X-ray laser experiments, giving transmission data for a range of wavelengths rather than a single X-ray laser wavelength.

Collective x-ray Thomson scattering allows measuring plasmons, i.e electron plasma oscillations (Langmuir waves). This is manifest in the appearance of spectrally up- and down-shifted spectral features in addition to the Rayleigh signal. The ratio of the up- and down-shifted signals is directly related to detailed balance, allowing to determine the plasma temperature from first principles. The spectral shift of the plasmon signals is sensitive to temperature and electron density. We discuss the experimental considerations that have to be fulfilled to observe plasmon signals with x-ray Thomson scattering. As an example, we describe an experiment that used the Cl Ly-α x-ray line at 2.96 keV to measure collective Thomson scattering from solid beryllium, isochorically heated to 18 eV. Since temperature measurement based on detailed balance is based on first principles, this method is important to validate models that, for example, calculate the static ion-ion structure factor S_ii(k).

We describe recent advances in the demonstration of table-top full field microscopes that use soft x-ray lasers for illumination. We have achieved wavelength resolution and single shot exposure operation with a very compact 46.9 nm microscope based on a desk-top size capillary discharge laser. This λ=46.9 nm microscope has been used to captured full field images of a variety of nanostructure systems and surfaces. In a separate development we have demonstrated a zone plate microscope that uses λ=13.2 nm laser illumination to image absorption defects in a extreme ultraviolet lithography (EUVL) mask in the same geometry used in a 4x demagnification EUVL stepper. Characterization of the microscope's transfer function shows it can resolve 55 nm half period patterns. With these capabilities, the λ=13.2 nm microscope is well suited for evaluation of pattern and defect printability of EUVL masks for the 22 nm node.

A compact capillary discharge table top soft X ray laser was used for a table top photolithography tool using different approaches: holographic printing, interferometric lithography and coherent Talbot self imaging. Large areas, of the order of millimeter square, with periodic and arbitrary patterns were printed in a photoresist in short exposure times. The proof of principle of the lithographic technique achieved the expected ~100 nm resolution.

The mechanisms responsible for an increase in collimation of laboratory plasma jets with higher atomic number was studied using soft x-ray laser interferometry and 2D model simulations. Dense plasma jets (Ne~ 10²⁰ cm^-3) were produced by irradiating V-shaped grooves of different materials (C, Al, and Cu) with 120 ps Ti:Sa laser pulses at peak intensities of 1 x 10¹² W cm^-2. High contrast soft x-ray interferograms of these plasmas were generated by combining a Mach-Zehnder interferometer that uses diffraction gratings as beam-splitters and a 46.9 nm table-top capillary discharge laser probe. A significant increase in jet collimation was observed for the higher Z materials. Simulations performed with the radiation hydrodynamic code HYDRA attribute differences in jet collimation to an increased radiation cooling of the higher Z jets.

The PHELIX laser at the GSI Helmholtz center for heavy-ion research is dedicated to provide high energy, ultra-intense laser pulses for experiments in combination with energetic ion beams. Development of x-ray lasers is targeting a number of applications in this context, including x-ray laser spectroscopy of highly-charged ions, and Thomson scattering diagnostics of heavy-ion driven plasmas. Recent developments centered on the application of a novel double-pulse pumping scheme under GRIP-like, non-normal incidence geometry for both the pre- and the main pulse for transient pumped Ni-like lasers. This scheme considerably simplifies the set-up, and provides a very stable pumping situation even at low pump energies close to the lasing threshold. The technique was scaled to pulse energies above 100 J for the pumping of shorter wavelength x-ray lasers. In addition, a slightly tunable high-harmonic source using a split-off beam from the Nd:Glass pre-amplifier of PHELIX was developed as a seeding source.

Nearly four decades ago H-like and He-like resonantly photo-pumped laser schemes were proposed for producing X-ray lasers. However, demonstrating these schemes in the laboratory has proved to be elusive. One challenge has been the difficulty of finding an adequate resonance between a strong pump line and a line in the laser plasma that drives the laser transition. Given a good resonance, a second challenge has been to create both the pump and laser plasma in close proximity so as to allow the pump line to transfer its energy to the laser material. With the advent of the X-FEL at LCLS we now have a tunable X-ray laser source that can be used to replace the pump line in previously proposed laser schemes and allow researchers to study the physics and feasibility of photo-pumped laser schemes. In this paper we model the Na-pumped Ne X-ray laser scheme that was proposed and studied many years ago by replacing the Na He-α pump line at 1127 eV with the X-FEL at LCLS. We predict gain on the 4f - 3d transition at 231 Å. We also examine the feasibility of photo-pumping He-like V and lasing on the 4f - 3d transition at 38.7 Å, which would be within the water-window. In addition we look at the possibility of photo-pumping Ne-like Fe and creating gain on the 4d - 3p transition at 53 Å and the 3p - 3s transition at 255 Å.

We report on gain-saturated operation of the 4d → 4p, J = 0-1, 11.4-nm soft-x-ray laser line in Ni-like antimony (Sb) at a pump energy of only 2.5 J. The driving laser used was a 1054-nm Nd:glass CPA laser system with a pulse duration of 7 ps (FWHM). The pump beam was focused with a tilted on-axis parabolic mirror in a grazing-incidence (GRIP) pumping configuration at a grazing angle of 45°. For this angle, the length of the line focus attains a value of 19.6 mm (FWHM) for the 120-mm beam diameter used in these experiments. In addition, the excitation velocity of the intrinsic traveling wave increases to 1.41c and results in a temporal mismatch of ~20 ps at the output end of the target. As a consequence, care must be taken in interpreting the usual gain measurements (intensity-vs.-target length). A novel method to distinguish the different effects causing roll-off based on the second derivative of the intensity curve will be discussed.

The development in the field of X-ray laser and its applications at c-FAST is discussed in detail. First of all the recent progress in understanding of seeding X-ray laser with harmanics is presented. On the other hand, analysis of the kinetic processes by numerical simulations shows their dependence on the pump laser pulse structure. The latter cleary supports the thesis that multi-pulse pump schemes are more efficient that those based on two or single laser pump pulse. Finally such applications as coherent diffraction imaging and photoelectron spectroscopy constitute basis for practical use of X-ray lasers.

Neutral Al_mC_n clusters are investigated both experimentally and theoretically for the first time. Single photon ionization through 193 nm, and 46.9 nm lasers is used to detected neutral cluster distributions. Al_mC_n clusters are generated through laser ablation of a mixture of Al and C powders pressed into a disk. An oscillation of the VIEs of Al_mC_n clusters is observed in the experiments. The ionization energies of Al_mC_n clusters change as a function of the numbers of Al and C atoms in the clusters. Theoretical density functional theory and ab initio calculations are carried out to explore the structures, ionization energies, and molecular orbitals of the Al_mC_n clusters. C=C bonds are favored for the lowest energy structures for Al_mC_n clusters. Based on calculations of HOMOs (highest occupied molecular orbitals) of Al_mC_n clusters we find that the ionization energies of these clusters do not simply depend on open or closed shell valence electron configurations, but also depend on the electronic structure details of the clusters. The calculational results provide good and consistent explanations of the experimental observations, and are consistent with them.

The LASERIX facility provides coherent and short soft x-ray beams for scientific applications. The beams are generated through high intensity laser interaction with matter using two different schemes, plasma based soft x-ray lasers, and high order laser harmonic generation. We describe in this communication the present status of the facility. The LASERIX beamtime has been recently opened to external users. We present two typical experiments performed in that context with the facility. The first one is dedicated to the fundamental study of the plasma based soft x-ray laser, whereas the second uses the existing beam to study irradiation induced dammage in DNA samples. We present also the development performed on the soft x-ray laser source to improve its stability and high repetition rate operation.

We present recent calculations performed with the Maxwell-Bloch COLAX code. We investigate several features of transient X-ray lasers pumped with grazing incidence geometry and operated either with or without seeding by a highorder harmonics pulse. We show that the spontaneous emission source term included in the code accounts well for the speckle patterns observed in near-field and far-field images of the amplification of spontaneous emission (ASE) beams. Our calculations confirm the predictions of a simpler model based on the properties of spatial and temporal coherence of the source. We study the role of varying the level of the harmonic pulse seeded in the X-ray laser plasma. We show that the amplification factor and the contrast with respect to the ASE background cannot be maximized simultaneously. Finally we describe a recent upgrade of the code in which a time-dependent description of the populations of the lasing states has been implemented. This more rigorous treatment allows us to investigate the small-scale temporal behaviour of seeded X-ray lasers. The new version of the COLAX code was recently tested and preliminary results will be presented.

A model of the frequency and temporal variation of laser output incorporating the lifetime of stimulated emission and gain narrowing effects is shown to predict the minimum pulse durations possible with injection seeded amplification. We show that pulse durations significantly shorter than 1 ps will be difficult to achieve with plasma based x-ray lasers because of the narrow spectral bandwidth and long lifetime of the population inversion.

High-harmonic-seeded x-ray laser became an important issue in x-ray laser development due to the possibility to obtain a highly coherent and polarized soft x-ray source. We performed theoretical investigations into amplification of high harmonic pulses in an x-ray lasing medium by using a model based on Maxwell-Bloch equations. From the theoretical works, we analyze characteristics of energy extraction and temporal profile of output pulse. In addition, preliminary experimental results and ongoing experiments related the harmonic-seeded x-ray lasers are reported.

We experimentally demonstrate the amplification of optical-field-ionization soft x-ray lasers in an optically preformed plasma waveguide for pure xenon, krypton, and argon gases, respectively. The lasing photon number of Ni-like Kr laser at 32.8 nm generated in waveguide is dramatically enhanced by about three orders of magnitude in comparison to that without plasma waveguide, resulting in a photon number of 8×10¹⁰ and an energy conversion efficiency of 2×10^-6 with a pump pulse of just 235 mJ. In addition to the 46.9 nm main lasing line for Ne-like argon, the 45.1 and 46.5 nm lasing lines are also observed, indicative of the strong enhancement effect and the large gas density in the plasma waveguide. With this technique multispecies parallel x-ray lasing is also demonstrated in a Kr-Ar mixed-gas waveguide. By seeding optical-field-ionization plasma with high harmonic signals, 32.8-nm Kr laser output can be further improved to produce brighter and better collimated x-ray laser beams. Comparing with the same laser seeded only with spontaneous emission, seeding with high harmonics yields much smaller divergence, enhanced spatial coherence, and controlled polarization. With the illumination of high-brightness 32.8-nm x-ray laser pulses, single-shot x-ray digital holographic microscopy with an adjustable field of view and magnification is demonstrated successfully. The ultrashort x-ray pulse duration combined with single-shot capability offers great advantage for flash imaging of delicate samples.

Plasma-based seeded soft x-ray lasers have the potential to generate high-energy, highly coherent, short pulse beam. Due to their high density, plasmas created by interaction of intense laser with solid target should store the highest amount of energy density among all plasma amplifiers. However, to-date output energy from seeded solid amplifiers remains as low as 60 nJ. We demonstrated that careful tailoring of the plasma shape is crucial for extracting energy stored in the plasma. With 1 mm wide plasma, energy as high as 22 μJ in sub-ps pulse is achievable. With such tailored plasma, gain and pumping efficiency has been increased by nearly a factor of 10 as compared to the narrower plasma amplifiers studied previously and here.

Samples of plasmid DNA were irradiated with pulsed 18.9 nm radiation originating from a Mo X-ray laser (XRL) pumped in GRIP configuration at the LASERIX facility. Up to 21 000 pulses were delivered with a repetition rate of 10 Hz and average pulse energy of 200 nJ. Radiosensitization by two different platinum compounds (platinum terpyridine chloride (PtTC) and platinum nanoparticles) were investigated. SSB and DSB yields were measured using agarose gel electrophoresis. The occurrence of single and double strand breaks not present in controls having undergone the same treatment except for the XRL irradiation can be seen as a clear effect of the XRL irradiation. This confirms the role of direct effects in DNA damages as previously seen with low energy ions and electrons (1) (2). In addition we demonstrate a DNA breaks enhancement in the presence of platinum. No difference of enhancement was seen between these two radiosensitizers.

Planar parabolic refractive lenses are one important kind of compound refractive lenses which are used in the third generation synchrotron radiation sources as an x-ray focusing device. In order to test the influence of the number of the individual lens on the transmission and gain, a set of 30 micro-focusing planar parabolic lenses with different number (from 1 to 30) of the individual lens was designed, which had equal apertures of 250 μm and equal focal length of 30 cm at 8.05 keV. The parameters of the lenses were optimized for performing focusing test at x-ray diffractometer (XRD). The optical simulation was completed by ray tracing by the commercial program of ZEMAX. The radius of curvature at the tip of the parabola ranged from 1.23 μm to 37 μm and the theoretical transmission from 43.3 % to 33.2 %. The theoretical width of focal line was about 3.4 μm. Ultra violet lithography was used to fabricate the planar lenses from SU-8 photoresist which thickness was 224 μm. Measured dimension of lenses is coincident with the theoretical one. Focusing properties of the lenses were studied both at XRD and at U7B beamline at the National Synchrotron Radiation Laboratory (NSRL) at the energy of 8.05 keV. The detector was a Peltier-cooled, 1380 x 1030 format (6.45 x 6.45 μm² pixels) charge coupled device with a fiber-optic-coupled scintillator (Photonic Sciences Ltd., "X-ray Fast Digital Imager"). The width of focal line was about 27.4 μm with a gain of 7.17 for N=8 lenses which was achieved in the NSRL. The reasons for the big difference between theoretical values and measured ones were discussed.

A focusing test of hard x-rays has been done using spherical compound refractive lens which was composed of 123 biconcave microlenses with a size of 200 μm in diameter. Each microlens was formed by the epoxy between two bubbles which were injected into an epoxy-filled glass capillary. The focal length of the lens was 114 mm at 8 keV. The optical simulation was completed by ray tracing by the commercial program of ZEMAX. The estimated size of focal spot was 17.2 μm. The focusing experiment has been achieved at U7B beamline in the National Synchrotron Radiation Laboratory (NSRL) at the energy of 8 keV. The measured focal spot size (FWHM) was 33.3x65.9 μm² (VxH).

The coherent beam wave field transformation is considered in the case of slanting illumination of a reflection mask. The parabolic wave equation is used to find the resulting field evolution in free space and after transmission by an ideal lens. Possible applications are lensless imaging, coherent X-ray diffraction imaging (CXDI), X-ray optics and X-ray laser based lithography and reflection microscopy, and high resolution X-ray topography.

K-alpha x-ray sources from laser produced plasmas provide completely new possibilities for x-ray phase-contrast imaging applications. By tightly focusing intense femtosecond laser pulses onto a solid target, K-alpha x-ray pulses are generated through the interaction of energetic electrons created in the plasma with the bulk target. In this paper, we present a continuous and efficient Mo K-alpha x-ray source produced by a femtosecond laser system operating at 100 Hz repetition rate with maximum pulse energy of 110 mJ before compression. The source has x-ray conversion efficiency greater than 10^-5 into K-alpha line emission. In preparation for phase contrast imaging applications, the size of the resultant K-alpha x-ray emission spot has been also characterized. The source exhibits sufficient spatial coherence to observe phase contrast. We observe a relatively small broadening of the K-alpha source size compared to the size of the laser beam itself. Detailed characterization of the source including the x-ray spectrum and the x-ray average yield along with phase contrast images of test objects will be presented.

A soft x-ray reflectometer with laser produced plasma source has been designed, which can work from wavelength 8nm to 30 nm and has high performance. Using the soft x-ray reflectometer above, the scattering light distribution of silicon and zerodur mirrors which have super-smooth surfaces could be measured at different incidence angle and different wavelength. The measurement when the incidence angle is 2 degree and the wavelength is 11nm has been given in this paper. A surface scattering theory of soft x-ray grazing incidence optics based on linear system theory and an inverse scattering mathematical model is introduced. The vector scattering theory of soft x-ray scattering also is stated in detail. The scattering data are analyzed by both the methods above respectively to give information about the surface profiles. On the other hand, both the two samples are measured by WYKO surface profiler, and the surface roughness of the silicon and zerodur mirror is 1.3 nm and 1.5nm respectively. The calculated results are in quantitative agreement with those measured by WYKO surface profiler, which indicates that soft x-ray scattering is a very useful tool for the evaluation of highly polished surfaces. But there still some difference among the results of different theory and WYKO, and the possible reasons of such difference have been discussed in detail.

We present an experimentally simple technique for the measurement of electron density gradients in dense laser plasmas (the plasma region of electron density up to 10²⁴ cm^-3 can be investigated with the use of available XRLs). The distortion of the XRL wave-front caused by the gradients of the electron density is measured using Talbot pattern deformation. The plasma probed by the XRL is imaged on the CCD plane, then a 2D grating is put in front of the chip so that the Talbot plane of this grating fits on the CCD. The compromise between the spatial resolution and the sensitivity for the given wavelength of the probe must be set within the grating design. The main advantages of this method are low requirements on spatial coherence of the probing beam as well as the simple alignment, which are the main difficulties of interferometry using radiation of XRLs.

We report on the results of an experiment using the TARANIS laser system at Queen's University, Belfast (QUB) to pump Ni-like X-Ray Lasers (XRLs) in the GRazing Incidence Pumped (GRIP) configuration. The system uses a long 1.2ns pulse to create a pre-plasma at the correct ionization stage, and a short, ~800fs pulse to produce a population inversion. Strong lasing has been observed for Ni-ions of Mo and Ag. Mo exhibited gain on two laser lines, at 18.9nm and 22.6nm, whilst only a single line, at 13.9nm, has been observed for Ag. The growth curves for both elements are presented. The curve for Ag indicates that saturation has not been achieved. Saturation like behaviour is seen for Mo but the small signal gain and poor fit to the Linford formula indicate that the roll-off is attributable to some effect other than gain saturation. Axial non-uniformity in the gain and mis-match between the ASE group velocity and the traveling-wave excitation are discussed as possible explanations for the shape of the Mo growth curve. Results of an initial application to characterize image plate as a soft x-ray detector are presented and, finally, further possible applications, in particular the potential for the XRL to be used as a photon source for Thomson scattering, are investigated.