The small-gain regime of free-electron lasers without inversion (FELWI) is considered and seeming contradictions with the traditional theory of FEL are resolved. As a result, a generalized Madey's theorem is obtained for the case of a phase shift given to electrons between the two wigglers. It explicitly demonstrates the contribution of interference of radiation from the wigglers. It is shown, by considering the motion in the phase-space, that Liouville's theorem applied to the motion of electrons in a two-dimensional (rather than one-dimensional) real space is consistent with a non-zero integral of the gain over electron energies. These conclusions are crucial for the achievement of orders-of-magnitude improvement in the FEL gain in the case of a large electron energy spread.

The inversionless free electron laser having a drift region consisting of two magnets is analyzed. Performing numerical simulations of electron motion inside wigglers and drift region, we have shown that this system has a positive mean gain over the entire energy distribution of the electron beam. We study the influence of emittance and the spread of electron energies on the gain in small- and high-gain regimes.

An international co-operative project to develop an advanced X-ray source on the basis of Compton backscattering is described. The goal is the re-configuration of the Kharkov Institute of Physics and Technology (KIPT) N-100 storage ring to support the efficient interaction of its electron beam with a high power pulsed-laser cavity. At equilibrium both the electron and X-ray beams’ phase space characteristics are determined by a balance of stochastic photon cooling and emission. In this paper the operating parameters and fundamental spectral and temporal properties of the novel source are summarized and the potential for its development.into an ultra-short pulse source is discussed.

The advantages and challenges of using a powerful x-ray source for the fast ignition of compressed Inertial Confinement Fusion (ICF) targets have been considered. The requirements for such a source together with the optics to focus the x-rays onto compressed DT cores lead to a conceptual design based on Energy Recovery Linacs (ERLs) and long wigglers to produce x-ray pulses with the appropriate phase space properties. A comparative assessment of the parameters of the igniter system indicates that the technologies for building it, although expensive, are physically achievable. Our x-ray fast ignition (XFI) scheme requires substantially smaller energy for the initiation of nuclear fusion reactions than other methods.

In recent months a novel femtosecond X-ray source, the Sub-Picosecond Photon Sourcxe (SPPS), has been commissioned at SLAC. The source consists of moderate-emittance electron bunches extracted from the SLAC Damping Rings, an acceleration through the SLAC 3km linac up to ~28 GeV, compression through an initial compressor chicane followed by further compression through an existing SLAC dogleg in the Final Focus Test Beam (FFTB) tunnel, and generation of X-ray pulses of about the same temporal length (~80 fs) by an APS-built 28 period transverse undulator. In this note we consider the possibility of extending the capabilities of the SPPS to produce femtosecond pulses of arbitrary polarization, which would enable the impulsive excitation and study of ultrafast magnetic phenomena, a field hitherto inaccessible to experimental science. An analysis of the expected performance of the proposed source together with requirements for linac operation are presented.

The dynamical theory of x-ray diffraction is extended in the form of an explicitly time-dependent synthesis of the Takagi-Taupin and eikonal theories of x-ray diffraction. Being based upon microscopic electromagnetism, the theory can describe time dependence on subpicosecond timescales. Several x-ray optical elements are proposed for the subpicosecond manipulation of x-rays.

We have fabricated and tested short focal-length compound refractive lenses (CRLs) composed of micro-bubbles embedded in epoxy. The bubbles were formed in epoxy inside glass capillaries. The interface between the bubbles formed 90 to 196 spherical bi-concave microlenses reducing the overall focal length inversely by the number of lenses. When compared with CRLs manufactured using other methods, the micro-bubble lenses have shorter focal lengths, better imaging, and focusing qualities with higher transmissions and gains for moderate energy x-rays (e.g. 7 - 12 keV). We used beamline 2-3 at the Stanford Synchrotron Radiation Laboratory (SSRL) to measure focal lengths between 100-150 mm and absorption apertures between 90 to 120 μm. Transmission profiles were measured giving, for example, a peak transmission of 27 % for a 130-mm focal length CRL at 8 keV. The focal-spot sizes were also measured yielding, for example, an elliptical spot of 5 x 14-μm² resulting from an approximate 80-fold demagnification of the 0.44 x 1.7 mm² source. The measured gains in intensity over that of unfocused beam were between 9 and 26. Theoretical gain calculations that include spherical aberrations show that these values are reasonable. The micro-bubble technique opens a new opportunity for designing lenses in the 8-9 keV range with focal lengths less than 30-40 mm.

We have measured the intensity profile and transmission of x-rays focused by a series of bi-concave parabolic unit lenses fabricated in lithium and beryllium. For specified focal length and photon energy, lithium and beryllium compound refractive lenses (CRL) have a larger transmission, aperture size, and gain compared to aluminum, epoxy, and kapton CRLs. One Li CRL was composed of 335 bi-concave, parabolic unit lenses, each with an on-axis radius of curvature of 0.95 mm. This Li CRL achieved a 95 cm focal length at 8 keV with an effective aperture of 1 mm, an on-axis (peak) transmission of 26 %, and an on-axis intensity gain of 18.9. The beryllium compound refractive lens was composed of 160 bi-concave unit lenses, each with a radius of curvature of 1.9 mm. The Be CRL achieved two-dimensional focusing at 6.5 keV with a gain of 1.5, peak transmission of 9 %, focal length of 93 cm, and an effective aperture of 600 μm. Based upon the principle of spontaneous emission amplification in an FEL wiggler, coherent x-ray sources are being developed with wavelengths of 1-1.5 Å and source diameters of 50-80 μm, and the Be and Li CRL may be used to provide a small, intense image. For these coherent x-ray source parameters, the large apertures of Be and Li CRLs enable intensity gains of 10⁵ to 10⁶.

We present the optical design of systems for the splitting of the radiation from a FEL at 40 and 10 nm, in the framework of a proposal made fro Elettra Synchrotron (Trieste, Italy) to the Italian Ministry of Education, Universities and Research for the construction and operation of an ultra-high brillance source in the EUV and soft X-ray region. It is important to design systems for the beam-splitting of the EUV radiation, both for having the FEL radiation available simultaneously to several experiments, and for the division and recombination of the beam (pump-probe techniques). We present systems with a grazing-incidence plane grating, which is illuminated by the single FEL beam and gives several output beams (the zero order and the diffracted orders). The grating gives intrinsically a time stretching of the diffracted beam, so time-compensated configurations must be used, i.e. the configurations in which a second grating compensates for the distortion given by the first grating. Different systems are presented: 1) splitting of the primary beam in several secondary beams for different experiments; 2) splitting and recombining of the primary beam in two beams with variable delay from two different directions; 3) splitting and recombining of the primary beam in two beams with variable delay and same direction.

We present the optical design of high-resolution monochromators for the utilization of the radiation from a FEL at 40 and 10 nm, in the framework of a proposal made from Elettra Synchrotron (Trieste, Italy) to the Italian Ministry of Education, Universities and Research for the construction and operation of an ultra-high brillance source in the UV and X region. Since the FEL emission is expected to be highly monochromatic (λ/Δλ≈10000), a monochromator is useful only if able to provide a spectral resolution higher than the intrinsic FEL resolution (λ/Δλ>100000). Two systems are presented: 1) normal-incidence configurations with multilayer-coated optics; 2) grazing-incidence configurations with a plane grating operated in conical diffraction. Normal-incidence configurations have very high spectral resolution, but the spectral band of operation is limited by the multilayer coating, so optics with different coatings have to be used when the FEL is tuned within the spectral region of operation. Configurations in conical diffraction have also very high resolution, high efficiency and a wide spectral band of operation.

We present the characterization of an ultrafast x-ray streak camera based on a new bilamellar x-ray tube. This camera, named FX1, has been tested in static (imaging) and dynamic (sweep) mode with several continuous and pulsed sub-picosecond UV and X-ray sources. The FX1 camera was designed to overcome some limitations observed with the PX1 camera which has been used previously at INRS to achieve high resolution sub-picosecond time resolved spectroscopy of ultrafast laser produced plasmas. Line Spread Function measurements indicated a strong improvement of the static image contribution to the temporal resolution compared to the PX1 camera performances [Rev. Sci. Instr. 71, 3627, 2000]. Furthermore a much higher dc extraction field can now be sustained at the photocathode-acceleration slit region. The FX1 camera has been successfully operated in various experimental conditions. An upper limit of the temporal response of the FX1 has been measured in the keV x-ray range in single shot mode with a laser-based x-ray source (2keV) having a duration (FWHM) of 1.4 ps. The FX1 camera has also been coupled to photoconductive switches and testesd in accumulation mode [Rev. Sci. Instr. 73, 1617, 2002] with VUV light produced with the 1 kHz Ti:sapphire laser of the CELIA. A newly assembled test-bench is now currently used at INRS for the characterisation of streak cameras in both single-shot and accumulation mode with the 10Hz Ti:sapphire laser of INRS.

We demonstrated that the shot-to-shot timing jitter of a streak camera is reduced to 30 fs when it is triggered by a standard kilohertz laser with 1.2% RMS fluctuation. Such small jitter was obtained by improving the response time of deflection plates and the rise-time of a ramp pulse generated by a photoconductive switch, and by operating the photoconductive switch at the optimum working condition. The temporal resolution of the x-ray streak camera operating in accumulation mode is better than 600 femtosecond that is not limited by the timing jitter.

When an atom is ionized by an x-ray pulse in the presence of a laser field,the drift velocity of photoelectrons shows the phase dependence on the dressing field.We show how to use this effect to characterize single attosecond x-ray pulses.(i)Attosecond streak camera - the distortion of the photoelectron spectra induced by the laser field is used to map the temporal shape of the x-ray pulse to the photoelectron spectra.(ii) Attosecond SPIDER (spectral phase interferometry for direct electric-field reconstruction) - the spectral shearing interferometry of photoelectrons is used to directly retrieve the spectral phase of the x-ray pulse from the photoelectron spectra.

The performance of CsI photocathodes has been characterized for use with grazing incidence soft x-rays. The total electron yield and pulsed quantum efficiency from a CsI photocathode has been measured in a reflection geometry as a function of photon energy (100 eV to 1 keV), angle of incidence and the electric field between the anode and photocathode. The total electron yield and pulsed quantum efficiency increase as the x-ray penetration depth approaches the secondary electron escape depth. Unit quantum efficiency in a grazing incidence geometry is demonstrated. A weak electric field dependence is observed for the total yield measurements; whilst no significant dependence is found for the pulsed quantum efficiency. Theoretical predictions agree accurately with experiment.

Timing synchronization between two independent Ti:sapphire mode-locked lasers has been developed for Laser-Compton X-ray generation. The lasers operated at different repletion frequencies of 119 MHz and 2856 MHz. The two lasers were actively synchronized with a phase-locked loop at a frequency of 2856 MHz. Fluctuation of the optical sum-frequency intensity was measured, and timing jitter was obtained. The rms timing jitter between the lasers was below 5 fs for several tens of seconds. The fluctuation was measured with a maximum observation bandwidth of 300 kHz. To improve long-time stability, a sum-frequency signal was fed back with a slow loop bandwidth, achieving long time operation for 1 hour with 5 fs synchronization.

A new photon-counting area detector, based on parallel-plate gas amplification with a resistive anode and remote readout electrode is described. The detector is sealed and has sensitive area of 14x14 cm². The detector is unique in its ability to achieve high gain at high counting rates. A local counting rate >10e⁵ counts/mm2-sec has been achieved at a gain of 10⁵ in a radiation-hard, non-polymerizing gas mixture. The global readout rate is limited by the delay line and electronics to <10⁶ counts/sec but more sophisticated readout schemes should allow this rate to be increased by more than an order of magnitude. The operating characteristics of the detector are described and preliminary x-ray diffraction data are presented.

Due to the planar construction of present x-ray streak tubes significant off-center defocusing is observed in both static and dynamic images taken with one-dimensional resolution slits. Based on the streak tube geometry curved photocathodes with radii of curvature ranging from 3.5 to 18 inches have been fabricated. We report initial off-center focusing performance data on the evaluation of these "improved" photocathodes in an X-ray streak camera and an update on the theoretical simulations to predict the optimum cathode curvature.

We present a novel x-ray streak tube design that uses a modest extraction field at the photocathode, axial time-of-flight dispersion compensation, and transverse energy selection to achieve better-than-100-fs time resolution.

An ultra fast, sub-picosecond resolution streak camera has been recently developed at the LLNL. The camera is a versatile instrument with a wide operating wavelength range. The temporal resolution of up to 300 fs can be achieved, with routine operation at 500 fs. The streak camera has been operated in a wide wavelength range from IR to x-rays up to 2 keV. In this paper we briefly review the main design features that result in the unique properties of the streak camera and present its several scientific applications: (1) Streak camera characterization using a Michelson interferometer in visible range, (2) temporally resolved study of a transient x-ray laser at 14.7 nm, which enabled us to vary the x-ray laser pulse duration from ~2-6 ps by changing the pump laser parameters, and (3) an example of a time-resolved spectroscopy experiment with the streak camera.

We present a new x-ray detection technique based on optical measurement of the effects of x-ray absorption and electron hole pair creation in a direct band-gap semiconductor. The electron-hole pairs create a frequency dependent shift in optical refractive index and absorption. This is sensed by simultaneously directing an optical carrier beam through the same volume of semiconducting medium that has experienced an xray induced modulation in the electron-hole population. If the operating wavelength of the optical carrier beam is chosen to be close to the semiconductor band-edge, the optical carrier will be modulated significantly in phase and amplitude. This approach should be simultaneously capable of very high sensitivity and excellent temporal response, even in the difficult high-energy xray regime. At xray photon energies near 10 keV and higher, we believe that sub-picosecond temporal responses are possible with near single xray photon sensitivity. The approach also allows for the convenient and EMI robust transport of high-bandwidth information via fiber optics. Furthermore, the technology can be scaled to imaging applications. The basic physics of the detector, implementation considerations, and preliminary experimental data are presented and discussed.

We describe a gated microchannel plate (MCP) based Quantitative X-ray Imager (QXI) developed by Los Alamos National Laboratory (LANL) and measure some of its performance characteristics. Such imagers use propagating electrical pulses along microstrips on the MCP to quickly gate on and off portions of the strip and hence provide fast framing capability (typically 100 ps frames with up to 1 ns time coverage). Three issues have been quantitatively studied using the QXI and another similar but older LANL gated x-ray framing camera, the GXI-T: QXI pulse shapes generated by its pulse-forming modules: GXI-T optical pulse widths as a function of incident UV energy on the microchannel plate: and the modulation transfer function (MTF) of the QXI intensifier.

The design, construction and implementation of a large format gated x-ray camera (LFC) for the LANL inertial confinement fusion/ radiation physics program is described. The active area of the detector is 105 mm x 105 mm using three 35 mm x 105 mm microchannel plates (MCP), that are proximity focused to a monolithic P-43 phosphor screen. Gating of the six independent, 13 mm, tall electrical microstriplines, deposited on the MCP, is accomplished by six individually biased and delayed high-voltage electrical pulses. The electrical gating pulse is continuously adjustable from 200 ps to 1300 ps, yielding optical shutters of 80 ps to 1000 ps. All electrical functions are computer controlled and monitored. Images are created on the striplines by conventional x-ray pinhole image techniques and recorded by film or a 4096 x 4096 CCD camera that is fiberoptically coupled to the back of the phosphor screen. Construction is complete and the instrument is now operated on a routine basis at local and remote laser facilities. Detailed characterization of the camera is in progress.

The Linac-based Ultrafast X-ray source (LUX) is a proposed recirculating linear accelerator for the purpose of producing intense, tunable, high repetition rate ultrafast x-ray pulses. An angle-time or position-time correlation is induced in the electron bunches by a dipole-mode RF cavity. Undulators and wigglers are sources of synchrotron radiation. Asymmetrically-cut crystals are used as optical elements of an x-ray pulse compression scheme. X-ray pulse durations of 50-100 fs are obtained over a range of photon energies from 2 to 12 keV. An undulator beamline consists of a collimating mirror, two asymmetric crystals and Kirkpatrick-Baez mirrors and provides compressed, monochromatic and focused x-rays for time-resolved experiments.