Interplay of the chirps and chirped pulse compression in a high-gain seeded free-electron laser

Abstract

In a seeded high-gain Free-electron Laser (FEL), where a coherent laser pulse interacts with an ultra-relativistic electron beam, the seed laser pulse can be frequency chirped, and the electron beam can be energy chirped. Besides these two chirps, the FEL interaction introduces an intrinsic frequency chirp in the FEL even if the above mentioned two chirps are absent. In this paper we examine the interplay of these three chirps. The problem is formulated as an initial value problem, and solved via a Green function approach. Besides the chirp evolution, we also give analytical expressions for the pulse duration and bandwidth of the FEL, which remains fully longitudinally coherent in the high gain exponential growth regime. Because the chirps are normally introduced for a final compression of the FEL pulse, some conceptual issues are discussed. We show that in order to get a short pulse duration, an energy chirp in the electron beam is necessary.

Isolated few-cycle radiation from chirped-pulse compression of a superradiant free-electron laser

“…It was also suggested to use a chirped electron pulse to generate self-amplified chirped radiation, which is then filtered to seed a downstream self-amplified-spontaneousemission (SASE) FEL [2]. Wu et al [3,4] pointed out that manipulating frequency and energy chirps in both the seed radiation and drive beam, respectively, to an FEL allows generation of attosecond few-cycle pulses.…”

Self-Amplified Spontaneous Emission Free-Electron Laser with an Energy-Chirped Electron Beam and Undulator Tapering

“…6 has a standard deviation of 1.45 nm. It likely results from the contribution of a partially nonlinear chirped radiation field spike [31]. A Fourier limited pulse with the same width would have a rms duration of $50 fs and a peak power of about 2 GW.…”

Exponential growth, superradiance, and tunability of a seeded free electron laser

“…Exponential growth and superradiance regimes exist in a high-gain free electron laser (FEL). For a seeded FEL, in the exponential growth regime, the seed power is exponentially amplified; the pulse duration, the frequency bandwidth, and the frequency chirp are modified [1,2,3,4]. The exponential growth stops when the FEL induced energy spread gets too large compared to the FEL Pierce parameter ρ [5,6].…”

“…To analyze the start-up of a seeded FEL amplifier we use the coupled set of Vlasov and Maxwell equations which describe the evolution of the electrons and the radiation field [12,13,14]. The seeded FEL can be described by an integral representation of the initial seed, A(θ , 0), convoluting with the FEL Green function [2]. The FEL electric field is written as E(t, z) = A(θ , Z)e i(θ −Z) with A(θ , Z) being the slow varying envelope function.…”

“…The FEL electric field is written as E(t, z) = A(θ , Z)e i(θ −Z) with A(θ , Z) being the slow varying envelope function. The evolution is [2] A…”