Echo-enabled harmonic generation free electron laser

Abstract

In this paper, we systematically study the echo-enabled harmonic generation (EEHG) free electron laser (FEL). The EEHG FEL uses two modulators in combination with two dispersion sections that allow one to generate in the beam a high harmonic density modulation starting with a relatively small initial energy modulation of the beam. After presenting an analytical theory of the phenomenon, we address several practically important issues, such as the effect of incoherent synchrotron radiation in the dispersion sections, and the beam transverse size effect in the modulator. Using a representative realistic set of beam parameters, we show how the EEHG scheme enhances the FEL performance and allows one to generate a fully (both longitudinally and transversely) coherent radiation. As an example, we demonstrate that 5 nm coherent soft x rays with GW peak power can be generated directly from the 240 nm seeding laser using the proposed EEHG scheme.

Mode-locked multichromatic x rays in a seeded free-electron laser for single-shot x-ray spectroscopy

“…Finally, it is worth mentioning that several existing schemes [40][41][42][43][44] that use external seeding and a fewcycle infrared laser to generate an isolated attosecond pulse can be extended to generate attosecond pulse train with multiple sharp frequency lines if the few-cycle infrared laser is replaced with an ordinary multiple-cycle laser. For instance, in Ref.…”

“…For instance, in Ref. [41], an isolated attosecond x-ray pulse with central wavelength at 1 nm and FWHM pulse width of 20 attosecond was generated. If a train of 20 attosecond pulse is generated using multiple-cycle Ti: sapphire laser, then in the frequency domain there will be $50 sharp lines equally separated by 1.5 eV.…”

“…Currently, both self-seeding [3][4][5][6] and external seeding [7][8][9][10][11][12][13][14] are under active study for generation of fully coherent x rays. Nonetheless, such seeded FELs nominally only provide one frequency line, i.e., a fully coherent output at a specific frequency determined by the monochromator, or the seed laser frequency and the harmonic number.…”

Echo enabled harmonic generation free electron laser in a mode-locked configuration

“…There is therefore considerable interest in developing high-brightness, X-ray attosecond duration pulses that would allow the study of these ultra-fast atomic and molecular processes. This letter proposes a method of achieving this by combining the two previously unrelated FEL methods of Echo Enabled Harmonic Generation (EEHG) [10,11] and the Mode-Locked Optical Klystron (MLOK) [12].…”

Comparison of short pulse generation schemes for a soft x-ray free electron laser

“…Several schemes have recently been proposed for the production of short pulse radiation using high-gain free electron lasers (FELs), the majority of which use a fewcycle optical laser pulse to modulate the electron energy or trajectory in a small section of the bunch. This can be applied as an extension of the enhanced self-amplification of spontaneous emission or echo-enabled harmonic generation based schemes, in which energy modulation is used in combination with magnetic chicanes to enhance the local current density [1][2][3]. Other schemes selectively amplify the radiation emitted by the maximum energy-offset portion of the bunch in several stages [4,5], or alternatively the radiation from this portion can be selected after saturation in a single stage undulator using a monochromator [6].…”