Demonstration of High-Trapping Efficiency and Narrow Energy Spread in a Laser-Driven Accelerator

Laser-driven electron accelerators (laser linacs) offer the potential for enabling much more economical and compact devices. However, the development of practical and efficient laser linacs requires accelerating a large ensemble of electrons together (“trapping”) while keeping their energy spread small. This has never been realized before for any laser acceleration system. We present here the first demonstration of high-trapping efficiency and narrow energy spread via laser acceleration. Trapping efficiencies of up to 80% and energy spreads down to 0.36% ($1\sigma$) were demonstrated.

Figure 1

Model simulation for STELLA showing the microbunching process. (a) $E$-beam energy shift from initial energy versus phase distribution relative to accelerating wave. (b) Energy-phase distribution after energy modulation by the first laser acceleration stage. (c) Energy-phase distribution after traveling through the bunch compressor (chicane). (d) Microbunch longitudinal density distribution of (c).

Figure 2

Schematic layout for the STELLA experiment.

Figure 3

(a) Example of electron energy spectrum for high-trapping efficiency case with the chicane phase delay set for maximum acceleration. The solid curve is data; the histogram (for 5000 electrons) is the model prediction with $1.7\mathrm{T}\mathrm{W}/{\mathrm{c}\mathrm{m}}^2$ driving IFEL2. (b) The energy-phase plot predicted by the model for simulation in (a).

Figure 4

Example of electron energy spectrum for narrow energy spread case with the chicane phase delay set for maximum acceleration. The solid curve is data; the histogram (for 5000 electrons) is the model prediction with $1.3\mathrm{T}\mathrm{W}/{\mathrm{c}\mathrm{m}}^2$ driving IFEL2. The two dips on the data curve designated as fiducial lines are caused by scribe lines on the spectrometer output screen.