Generation of coherent two-color pulses at the two adjacent harmonics in a seeded free-electron laser

TL;DR

This paper proposes a novel method for generating coherent two-color pulses at adjacent harmonics in a seeded free-electron laser, enabling precise control of pulse timing for advanced optical applications.

Contribution

A new scheme using a tilted electron beam and transverse gradient undulator to produce two-color pulses at adjacent harmonics in a HGHG FEL.

Findings

Numerical simulations confirm the scheme's feasibility in the EUV waveband.

The pulse separation can be controlled on the order of hundreds of femtoseconds.

The method enables simultaneous generation of two coherent pulses at adjacent harmonics.

Abstract

The growing requirements of pump-probe techniques and nonlinear optics experiments greatly promote the studies of two-color free-electron lasers (FELs). We propose a new method to generate coherent two-color pulses in a high-gain harmonic generation (HGHG) FEL. In this scheme, an initial tilted electron beam is sent though the modulator and dispersive section of an HGHG FEL to generate the bunching at harmonics of the seed laser. Then a transverse gradient undulator (TGU) is adopted as the radiator and in such radiator, only two separated fractions of the tilted beam will resonate at two adjacent harmonics of the seed laser and are enabled to emit the coherent two-color pulses simultaneously. The time separation between the two pulses are on the order of hundreds of femtoseconds, and can be precisely controlled by varying the tilted amplitude of the electron beam and/or the transverse gradient of the TGU radiator. Numerical simulations confirm the validity and feasibility of this scheme in the EUV waveband.