Fermi is a seeded FEL operating in high-gain harmonic generation mode. The FEL layout is constituted by a modulator and six radiators separated by a dispersive section. The modulator and the radiators can be tuned to the same resonant frequency to set up an asymmetric optical klystron configuration where self-amplified spontaneous emission can be generated and studied. This paper presents the e...

The particle optics code GPT [1] has been applied to study the single pass electron beam interaction with an external laser field in the undulator system of a free electron laser. In particular, this code has been used to simulate the laser electron beam interaction in an optical klystron. Micro-bunching as a result of the interaction of the electron bunch with an electromagnetic pulse is prese...

The simplest high gain free electron laser (FEL) amplifier concept is proposed. A klystron amplifier has the useful property that the various electronic processes take place in separate portions of the amplifier, rather than overlapping as in FEL amplifier with an uniform undulator. The klystron consists of two fundamental parts: succession of 2-3 cascades (modulator), and an output undulator (...

The storage-ring FEL at DELTA has been successfully operated with different filling patterns and temporal structures following the installation of new mirror chambers three years ago. The modulation depth of the opticalklystron spectrum was used to measure the electron energy spread. The measured FEL output power at high beam currents strongly exceeded the predictions of the low-gain model. Thi...

Many high-gain free electron lasers worldwide are planning to incorporate seeding setups into their day-to-day operation. These techniques provide both longitudinal and transverse coherence extended control of the output laser radiation spectral properties. However, wavelength repetition rate strongly depend on properties seed system. With peak power required for successful seeded operation, it...

We propose experimentally simplified schemes of an optically dispersive interface region between two coupled free electron lasers (FELs), aimed at achieving a much broader gain bandwidth than in a conventional FEL or a conventional optical klystron composed of two separated FELs. The proposed schemes can universally enhance the gain of FELs, regardless of their design, when operated in the shor...