Abstract
Generation of few-cycle optical pulses in free-electron laser (FEL) oscillators has been experimentally demonstrated in FEL facilities based on normal-conducting and superconducting linear accelerators. Analytical and numerical studies have revealed that the few-cycle FEL lasing can be explained in the frame of superradiance, cooperative emission from self-bunched systems. In the present paper, we review historical remarks of superradiance FEL experiments in short-pulse FEL oscillators with emphasis on the few-cycle pulse generation and discuss the application of the few-cycle FEL pulses to the scheme of FEL-HHG, utilization of infrared FEL pulses to drive high-harmonic generation (HHG) from gas and solid targets. The FEL-HHG enables one to explore ultrafast science with attosecond ultraviolet and X-ray pulses with a MHz repetition rate, which is difficult with HHG driven by solid-state lasers. A research program has been launched to develop technologies for the FEL-HHG and to conduct a proof-of-concept experiment of FEL-HHG.
Highlights
Oscillators and Its Application to Bonifacio and his colleagues first suggested that free-electron laser (FEL) may be operated in the superradiant regime, in which the radiated peak power is proportional to the squared electron number, Ne2, from self-bunched systems [1]
Evolution of few-cycle FEL pulses was experimentally confirmed in FELIX, JAERI-FEL, and other short-pulse FEL oscillators
From analytical and numerical studies, it was found that the few-cycle FEL lasing in the short-pulse FEL oscillators is explained in the frame of superradiance, cooperative emission from self-bunched systems, and superradiance in high-gain FEL amplifiers
Summary
Oscillators and Its Application to Bonifacio and his colleagues first suggested that free-electron laser (FEL) may be operated in the superradiant regime, in which the radiated peak power is proportional to the squared electron number, Ne2 , from self-bunched systems [1]. In the superradiance FEL, a periodical bunching structure is self-organized in the electron beam traversing an undulator and the bunched beam emits cooperative radiation. Superradiance is observed in short-pulse FEL oscillators, where a periodical bunching structure is self-organized after the recursive interaction of the electron bunches and the optical pulse to emit cooperative radiation in the slippage region. The research program established for developing basic technologies and conducting a proof-of-principle experiment for the FEL-HHG is presented
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