Generation of a Self-Chirped Few-Cycle Optical Pulse in a FEL Oscillator

Abstract

We study the generation of a self-chirped optical pulse in a free-electron laser (FEL) oscillator. In a high-gain FEL oscillator, the frequency chirp is induced in the slippage region as a result of superradiant FEL resonance, and this time-frequency correlation evolves continuously into a few-cycle regime, if the optical cavity length is perfectly synchronized to the electron bunch interval. Numerical simulations based on the slowly evolving wave approximation and experimental results are presented.

High power coupled midinfrared free-electron-laser oscillator scheme as a driver for up-frequency conversion processes in the x-ray region

“…Furthermore, as was demonstrated in Ref. [29], the FEL interaction induces a frequency chirp in the generated spike, making further compression of the pulse duration possible while bringing the pulse width ultimately down to a few cycles. Along with the mentioned high extraction efficiency, the generation of ultrashort (< 10 cycles) spikes is an additional factor provided by the presented high-gain FEL oscillator operated at perfect synchronism towards achieving high peak intensities ($10 14 Watts=cm 2 focused to a spot size of $100 m) that are sufficient to drive the envisaged up-frequency conversion processes at long mid-IR wavelengths.…”

“…An important aspect in our approach is that both oscillators are driven in a single spike modus realized in a short pulse high-gain FEL oscillator with perfectly synchronized optical cavity length ( $ zero cavity detuning) where the cavity round-trip time of the optical pulse equals the electron bunch interval [27][28][29][30]. In this regime that is dominated by high FEL gain, low cavity loss and optical pulse-electron beam slippage effects, the radiation stored in the cavity evolves into an ultrashort, intense spike while keeping a self-similar shape following the saturation.…”

“…The experimental results reported in Refs. [27][28][29] have been realized by employing a superconducting rf-linac driven short pulse high-gain FEL oscillator in a ''perfectly'' synchronized cavity to generate few-cycle ultrashort, high peak power radiation at $20 m. Involving significantly shorter electron bunches ( z $ 100 fs) and shorter radiation wavelengths in the mid-IR, a more challenging synchronization of a few femtoseconds is required in order to ensure a stable operation in the presented FEL modus. The latter is feasible with the advent of new synchronization techniques elaborated in x-ray FEL facilities for time resolved experiments that utilize femtosecond to attosecond pulses [7,35], with the tremendous development that took place in recent years in monitoring and stabilizing the synchronization between the subsystems involved in an FEL device to reduce time arrival jitter budget down to a femtosecond time scale [36,37].…”

Deep saturated Free Electron Laser oscillators and frozen spikes

“…An insightful analysis on this point can also be found in [12]. This is just a qualitative statement, a more detailed study in analytical terms will be presented elsewhere.…”

Nanocontrol of single dense energetic electron sheet in a chirped pulse with critical relativistic intensity

“…Such pulses are used to generate intense femtosecond pulses in solid-state laser systems, which is called chirped pulse amplification [20]. With current technology, the chirp of an intense pulse can be adjusted with great flexibility [21,22]. The normalized spectral bandwidth of a few-cycle laser pulse can extend to a few tens of percents [23].…”