Laser assisted emittance exchange: Downsizing the x-ray free electron laser

A technique is proposed to generate electron beam with ultralow transverse emittance through laser assisted transverse-to-longitudinal emittance exchange. In the scheme a laser operating in the TEM10 mode is used to interact with the electron beam in a dispersive region and to initiate the emittance exchange. It is shown that with the proposed technique one can significantly downsize an x-ray free electron laser (FEL), which may greatly extend the availability of these light sources. A hard x-ray FEL operating at 1.5 Å with a saturation length within 30 meters using a 3.8 GeV electron beam is shown to be practically feasible.

Figure 1

Schematic of the laser assisted emittance exchange.

Figure 2

Phase space evolution in the emittance exchanger with CSR effect included (gold particles are marked by red color): (top left) $x^{\prime }$ vs $x$ at the entrance to the exchanger; (top right) $x^{\prime }$ vs $z$ at the entrance to the exchanger; (bottom left) $x^{\prime }$ vs $z$ after interaction with the TEM10 laser; (bottom right) $\gamma$ vs $x$ after interaction with the TEM10 laser.

Figure 3

Phase spaces after EE beam line (gold particles are marked by red color): (top left) $x^{\prime }$ vs $x$; (top right)$\gamma$ vs $z$; (bottom left) $x$ vs $z$; (bottom right) $x$ vs $\gamma$.

Figure 4

Power vs $z$ in the undulator for the soft x-ray FEL at 1.5 nm (blue curve) and hard x-ray FEL at 1.5 Å (red curve); the inset plot shows three typical snapshots of the power profile at 15 m for the 1.5 nm FEL.