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Rafael Abela: Experimental Demonstration of a Soft X-Ray Self-Seeded Free-Electron Laser

February 26, 2015
 

The Linac Coherent Light Source has added a self-seeding capability to the soft x-ray range using a grating monochromator system 

The construction of x-ray free-electron lasers (FELs) driven by self-amplified spontaneous emission (SASE) has pushed the brightness of x-ray sources by a remarkable 10 orders of magnitude [1,2]. Despite the relatively monochromatic output (typically bandwidth is on the order of 0.2%–0.5% of the fundamental energy), many types of experiments benefit from even narrower bandwidth; the ability to target and measure fine energy structure in combination with femtosecond pulse length enables new opportunities in time-resolved x-ray spectroscopy.

Ratner, D., Abela, R., Amann, J., Behrens, C., Bohler, D., Bouchard, G., Bostedt, C., Boyes, M., Chow, K., Cocco, D., Decker, F.J., Ding, Y., Eckman, C., Emma, P., Fairley, D., Feng, Y., Field, C., Flechsig, U., Gassner, G., Hastings, J., Heimann, P., Huang, Z., Kelez, N., Krzywinski, J., Loos, H., Lutman, A., Marinelli, A., Marcus, G., Maxwell, T., Montanez, P., Moeller, S., Morton, D., Nuhn, H.D., Rodes, N., Schlotter, W., Serkez, S., Stevens, T., Turner, J., Walz, D., Welch, J., and Wu, J. (2015) Experimental Demonstration of a Soft X-Ray Self-Seeded Free-Electron Laser. Phys Rev Lett 114, 054801 (10.1103/PhysRevLett.114.054801)


Figure 1. Schematic of the SXRSS system (not to scale). Shot noise from randomly distributed electrons generates 1–5 μJ
of relatively wide bandwidth SASE radiation in the first string of undulators (grey line). The seeding monochromator, consisting of a
grating (G), three mirrors (M1;M2;M3), and an adjustable slit, selects a small bandwidth (green line) while the electron chicane directs the electron bunch around the monochromator and resets the electron beam to shot noise. Finally, the overlap diagnostics (BOD10 and BOD13) coalign electrons and monochromatic x rays in the second half of the FEL. Pulse energies are shown for a nominal electron bunch with a charge of 150 pC, and duration of 100 fs, but other parameter ranges are also possible.


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