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A new laser chirping prescription is derived by means of the phase-stationary method for an incident Gaussian laser pulse in conjunction with a Liénard-Wiechert calculation of the scattered radiation flux and spectral brilliance. This particularly efficient laser chirp has been obtained using the electric field of the laser and for electrons and radiation on axis. The frequency modulation is somewhat reduced with respect to that proposed in the previous literature, allowing the application of this procedure to lasers with larger values of the parameter a0. Numerical calculations have been performed using mildly focused and narrow bandwidth laser pulses, confirming a larger efficiency of the chirp prescription here introduced. The chirp efficiency has been analysed as a function of the laser parameter and focusing. [ABSTRACT FROM AUTHOR]

A seeded FEL driven by a linac based on super conducting cavities, generating 108–1010 coherent photons per shot at 2–5 keV with 0.2–1 MHz of repetition rate, can address the need of a source devoted to fine analysis of matter using the linear spectroscopy technique. The seeding scheme described hereafter is a multi-stage cascade upshifting the radiation frequency by a factor 20–40. The x-ray range can be achieved with a seed constituted by a coherent flash in the extreme ultraviolet range provided by an FEL oscillator operating at 12–14 nm. The whole chain of x-ray generation is described by means of start-to-end three-dimensional simulations. [ABSTRACT FROM AUTHOR]

We present a new, more nuanced understanding of non-linear effects in inverse Compton sources. Deleterious non-linear effects can arise even at low laser intensities, a regime previously viewed as linear. After laying out a survey of non-linear phenomena which degrade the effectiveness of inverse Compton sources, we discuss two powerful techniques designed to avoid these non-linearities. Starting with the known technique of non-linear longitudinal chirping of the laser pulse in the high laser field regime, we show that the simple stretching of the laser pulse, while keeping the energy constant, can significantly increase the spectral density of the scattered radiation in many operating regimes. Our numerical simulations show that combining these two techniques avoids detrimental non-linearities and improves the performance of inverse Compton sources over an order of magnitude. [ABSTRACT FROM AUTHOR]

We present a new method for computation of radiation spectra in the non-linear regime of operation of inverse Compton sources characterized by high laser intensities. The resulting simulations agree well with the experiments. Increasing the laser intensity changes the longitudinal velocity of the electrons during their collision, leading to considerable non-linear broadening in the scattered radiation spectra. The effects of such ponderomotive broadening are so deleterious that most inverse Compton sources either remain at low laser intensities or pay a steep price to operate at a small fraction of the physically possible peak spectral output. This ponderomotive broadening can be reduced by a suitable frequency modulation (also referred to as "chirping", which is not necessarily linear) of the incident laser pulse, thereby drastically increasing the peak spectral density. This frequency modulation, included in the new code as an optional functionality, is used in simulations to motivate the experimental implementation of this transformative technique. [ABSTRACT FROM AUTHOR]