High-Harmonic Inverse-Free-Electron-Laser Interaction at 800 nm

We present the first direct observation of a higher-order inverse-free-electron-laser (IFEL) interaction. Interaction at the fourth, fifth, and sixth harmonics is observed from an IFEL operating at 800 nm. The harmonic spacing, relative harmonic strength, and transverse beam overlap of the interaction are all in good agreement with tracking simulations.

Figure 1

Calculated trajectory of beam from the measured fields of the undulator. The oscillation increases the horizontal overlap.

Figure 2

Example data run with 1500 laser on events. The solid curve is the least squares fit to all data points and gives the mean interaction of 18 keV. The dashed curve is the maximum estimate and gives the peak interaction of 25 keV. The width of cross correlation is 2.2 ps rms.

Figure 3

Vertical and horizontal overlap scans. The solid curve is simulation. The horizontal overlap is wider than the vertical due to the horizontal oscillation of the electrons within the undulator.

Figure 4

IFEL gap scan data, with 164 runs total. Comparison to simulation (solid line) shows very good agreement to the shape and spacing of resonance peaks. The harmonic numbers are given next to each peak. Simulation has been rescaled vertically by 0.67 to better visualize overlap.