Method of an enhanced self-amplified spontaneous emission for x-ray free electron lasers

We describe a technique by which an energy modulation of electrons via interaction with a laser pulse in a wiggler magnet is used for a significant increase of the electron peak current prior to entering a long self-amplified spontaneous emission (SASE) free electron laser undulator. This results in a reduction of the gain length for the SASE process and a modification of the structure of the output x-ray radiation. It also temporally links the output x-ray pulse to the initial laser pulse, thus providing an opportunity for accurate synchronization between the laser pump pulse and x-ray probe pulse for pump-probe experiments.

Figure 1

A schematic of ESASE x-ray FEL.

Figure 2

(a) Longitudinal phase space after the chicane showing microbunching of electrons and an enhanced electron density. Only a part of the WS equivalent to one optical cycle at the laser wavelength is actually shown. (b) The histograms of the energy distribution of electrons after the chicane taken along the lines $a,b,c$ in (a).

Figure 3

Normalized peak current (a) and energy spread (b) versus distance within the microbunch. The dots show computer simulation results while the solid line was obtained with Eqs. (6, 7).

Figure 4

Gain length at various distances within the microbunch calculated using fitting formula from Ref. 18.

Figure 5

Energy and peak current modulations produced in interaction with a few-cycle laser pulse. Only a part of the electron bunch affected by the interaction is shown.