The diffraction of x-rays in crystalline materials is governed by the amplitudes of the Fourier transform of the electron density, commonly called the structure factors. A change in these amplitudes can be induced by a high-power laser and can lead to a number of interesting effects, like a sweep of the beam propagation direction that could be used for a device for time-resolved x-ray detection that bears some similarity to a streak camera and can potentially reach few-femtosecond resolution. Another effect that becomes relevant on subpicosecond timescales is the generation of frequency-shifted x-rays, which could be used in Mossbauer spectroscopy, or for the concentration of x-ray photons into a narrow energy band. Even small changes in the structure factors can produce a large effect through coherent interaction with the x-rays in a large crystalline volume. A theoretical treatment, based on the Takagi-Taupin theory of dynamical diffraction, is presented.

Our recent developments are described regarding a novel synchronization architecture based on all optical method to achieve precise timing synchronization in a large and complex X-ray beam system. There are several key technologies in this approach, and the recent achievement is a precise synchronization of two independent mode-locked Ti:sapphire laser oscillators with an optical phase-locked loop. The cross correlation of two femtosecond lasers was measured for the relative timing jitter as small as 28 fs.

Progress in ultrafast xray science demands a new generation of high time-resolution x-ray detectors. We discuss an xray and laser cross-correlation technique which could serve as a basis for a femtosecond xray detector. The cross- correlation technique is based on visible-laser-induced modifications to x-ray photoelectron spectra.

A free electron laser for the XUV spectral range is currently under test at the TESLA Test Facility at DESY. High gain has been demonstrated below 100nm wavelength, and it is expected that the FEL will provide intense, sub-picosecond radiation pulses with photon energies up to 200eV. Thin film optical elements required for this facility are currently being developed by the X-ray optics group of the GKSS research center near Hamburg. Sputter-deposited coatings have been prepared for the use as total reflection X-ray mirrors for FEL beam optics. Coatings of low Z elements with the lowest possible absorption and high reflectivity have been investigated. Silicon substrates have been coated with carbon using different deposition conditions. The films were investigated using the soft X-ray reflectometer at the HASYLAB beamline G1. The measurements show that the reflectivity of the films is typically 90% at energies below 200eV and a grazing incidence angle of 4 degrees. The optical constants of these coatings obtained from the reflectivity measurements and are in agreement with tabulated values. The deposition parameters have been optimized resulting in argon contamination free films with near-theoretical performance. Preliminary investigations concerning the heat resistance of the films were also carried out.

Free electron lasers have the promise of producing extremely high-intensity short pulses of coherent, monochromatic radiation in the 1-10 keV energy range. For example, the Linac Coherent Light Source at Stanford is being designed to produce an output intensity of 2x10¹⁴ W/cm² in a 230 fs pulse. These sources will open the door to many novel research studies. However, the intense x-ray pulses may damage the optical components necessary for studying and controlling the output. At the full output intensity, the dose to optical components at normal incidence ranges from 1-10 eV/atom for low-Z materials (Z<14) at photon energies of 1 keV. It is important to have an understanding of the effects of such high doses in order to specify the composition, placement, and orientation of optical components, such as mirrors and monochromators. Doses of 10 eV/atom are certainly unacceptable since they will lead to ablation of the surface of the optical components. However, it is not precisely known what the damage thresholds are for the materials being considered for optical components for x-ray free electron lasers. In this paper, we present analytic estimates and computational simulations of the effects of high-intensity x-ray pulses on materials. We outline guidelines for the maximum dose to various materials and discuss implications for the design of optical components.

We suggest a new class of high-flux renewable optics, in particular, for the use at the X-ray free electron laser, LCLS, which is under discussion now. The size of optical elements we have in mind is from a fraction of a square centimeter to a few square centimeters. We suggest that working fluid be pressed through a porous substrate (made, e.g., of fused capillaries) to form a film, a few tens to a hundred microns thick. After the passage of an intense laser pulse, the liquid film is sucked back through the substrate by a reversed motion of the piston, and formed anew before the next pulse. The working surface of the film is made flat by capillary forces. We discuss the role of viscous, gravitational, and capillary forces in the dynamics of the film and show that the properly made film can be arbitrarily oriented with respect to the gravitational force. This makes the proposed optics very flexible. We discuss effects of vibrations of the supporting structures on the quality of optical elements. Limitations on the radiation intensity are formulated. We show how the shape of the film surface can be controlled by electrostatic and magnetic forces, allowing one to make parabolic mirrors and reflecting diffraction gratings.

In this work we describe new kind of refractive lens for focusing of high flux X-ray radiation of next generation X-ray sources. It is proposed to create such lens driving relatively low electric currents inside evacuated capillary made of low-Z material. The numerical simulations show that during the 0.1 - 3 microsecond(s) , 2-6 kA current pulse, the wall sustained stable capillary discharge plasma forms a concave density profile with almost parabolic index of refraction. Compared to solid materials, the plasma is able to sustain 2-3 order of magnitude larger doze ~100 eV/atom and can operate at larger fluxes and specifically in the relatively long wavelength region 1-4 keV where solid materials have dramatically larger absorption. For radiation sources similar to LCLS, the plasma lens can be placed right at the exit of undulator and deliver 3-4 orders of magnitude larger fluxes in the focal spot.

The rapid development of laser technology and related progress in research using lasers is shifting the boundaries where laser based sources are preferred over other light sources particularly in the XUV and x-ray spectral region. Laser based sources have exceptional capability for short pulse and high brightness and with improvements in high repetition rate pulsed operation, such sources are also becoming more interesting for their average power capability. This study presents an evaluation of the current capabilities and near term future potential of laser based light sources and summarizes, for the purpose of comparison, the characteristics and near term prospects of sources based on synchrotron radiation and free electron lasers. Conclusions are drawn on areas where the development of laser based sources is most promising and competitive in terms of applications potential.

The Linac Coherent Light Source (LCLS) is a 1.5 to 15 A- wavelength free-electron laser (FEL), currently proposed for the Stanford Linear Accelerator Center (SLAC). The photon output consists of high brightness, transversely coherent pulses with duration <300 fs, together with a broad spontaneous spectrum with total power comparable to the coherent output. The output fluence, and pulse duration, pose special challenges for optical component and diagnostic designs. We discuss some of the proposed solutions, and give specific examples related to the planned initial experiments.

TESLA is the project to build a superconducting linear collider for particle physics and an X-ray free-electron laser (XFEL) laboratory. The XFEL operates in the high-gain self-amplified spontaneous emission mode and peak brilliances of the order 10³⁵,photons/(smm²mrad²0.1%bw) corresponding to 10¹² photons in a 100 femtosecond X-ray pulse have been calculated. The covered wavelength range extends from 25 to 0.85A. To obtain SASE FEL radiation at these wavelengths the electron accelerator must fulfill extreme requirements with respect to emittance and bandwidth. The paper describes the technical realization of the XFEL laboratory, introduces the properties of XFEL photon beams and gives an overview of the scientific applications of XFEL radiation.

The Spring-8 Compact SASE Source (SCSS) is a high peak- brilliance soft X-ray free electron laser project. It has been funded in April 2001, aiming to generate first light in 2003 at VUV region, and ultimately 3.6 nm in water-window in 2005. Combination of the high-gradient C-band accelerator and in-vacuum short-period undulator realizes a SASE-FEL facility to generate soft X-ray within 100 m machine length. SCSS will provide six order of magnitude peak-brilliance enhancement compared to the current third-generation sources at 3~20 nm range.

We have analyzed the evolution and the interaction dynamics of secondary cascade electrons generated by a single Auger electron in diamond and in amorphous carbon. The elastic mean free path was calculated as a function of impact energy, using the muffin-tin potential approximation, while the differential mean free path and the inelastic mean free path were estimated from two different optical models as a function of the impact energy. A Monte-Carlo model for describing the time evolution of the cascade was constructed, and numerical simulations were performed. The results show that the maximal average ionization rate caused by a single Auger electron corresponds to about $20$ to $40$ ionization events in a macroscopic sample. These electrons are liberated within 100 fs, following the Auger emission.

The diffraction of femtosecond x-ray pulses by crystals will play a central role in the development of the optics of x-ray free-electron lasers (XFELs). Making use of Fourier analysis, we calculate the temporal dynamical diffraction of an incident delta function by single- and double- symmetric Bragg crystal monochromators. The time-dependent intensity of ultrashort XFEL pulses diffracted by perfect crystals is discussed. Our simulations show modifications in the time structure of incident 8 keV, 280-fs-duration, microbunched XFEL pulses after diffraction by the crystal optics. Finally, we investigate the statistical fluctuations of the time-integrated intensity from shot to shot.

The temporal coherence properties of the X-ray pulse from a Free Electron Laser (FEL) will be altered during the process of dynamical diffraction from a perfect crystal. We present simulations of this process based on time-dependent dynamical diffraction theory. In addition, we present simulations of the diffraction of chirped X-ray pulses, demonstrating methods of pulse recompression by use of strained crystals.

Several laboratories are now in the process of designing and constructing coherent x-ray sources, and application of these beams for radiography and material studies is facilitated by having appropriate optical components to provide collimation or focusing. Control of x-rays can be achieved by employing elements that perform refraction, diffraction or reflection, as exemplified by a lens, grating or mirror, respectively. Of course, the maximum intensity of minimum image size that is obtainable from any of these elements is determined by diffraction effects. Using the parameters of the Liinac Coherent Light Source (LCLS) being studied at the Stanford Synchrotron Radiation Laboratory (SSRL), x-ray optical components can increase the beam intensity approximately eight orders of magnitude and provide submicron images. Performance comparisons are made between the zone plate, the phase zone plate, the compound refractive lens, the Fresnel compound refractive lens, and the parabolic mirror.

We present a method for generating femtosecond duration x-ray pulses using a single-pass free-electron laser (FEL). This method uses an energy-chirped electron beam to produce a frequency-chirped x-ray pulse through self-amplified spontaneous emission (SASE). After the undulator we consider passing the radiation through a monochromator. The frequency is correlated to the longitudinal position within the pulse, and therefore, by selecting a narrow bandwidth, a short temporal pulse will be transmitted. The short pulse radiation is used to seed a second undulator, where the radiation is amplified to saturation. In addition to short pulse generation, this scheme has the ability to control shot-to-shot fluctuations in the central wavelength due to electron beam energy jitter. We present calculations of the radiation characteristics produced by a chirped-beam two-stage SASE-FEL, and consider the performance of the chirped-beam two-stage option for the Linac Coherent Light Source (LCLS).

As unique beamlines in the third-generation synchrotron facilities, a 25-m undulator beamline and a one-kilometer beamline were constructed and started in operation at SPring-8. The design and performance of the 25-m undulator beamline are presented. To diagnose the coherence properties of x-rays, an x-ray intensity interferometer was developed at the beamline. The correlation technique was applied to determining the interference condition with a bicrystal interferometer. High-quality synthetic diamond crystals are being developed for XFEL monochromator crystal.

A unique X-ray source, of exceptional brightness and with pulse widths as low as 30 fs rms, has been proposed at the Stanford Linear Accelerator Center. Named the Sub-Picosecond Photon Source (SPPS), the facility takes 30 Gev bunches from the linac and compresses them in three stages to achieve peak currents of 30 kA in the Final Focus Test Beam (FFTB) beamline. The existing FFTB can accommodate an undulator of up to 10 m in length which will deliver ~10⁸ 1.5 A photons per pulse in a 0.1% bandwidth with a peak brightness of ~10²⁵ photons/sec/mm²/mrad²/0.1% BW, in a pulse width of ~80 fs FWHM. The short electron bunches are also ideal for plasma and wakefield studies as well as providing abundant R&D possibilities for verifying short bunch behavior in the future Linac Coherent Light Source (LCLS).