Abstract
We present the promise of generating gigawatt mode-locked multichromatic x rays in a seeded free-electron laser (FEL). We show that, by using a laser to imprint periodic modulation in electron beam phase space, a single-frequency coherent seed can be amplified and further translated to a mode-locked multichromatic output in an FEL. With this configuration the FEL output consists of a train of mode-locked ultrashort pulses which span a wide frequency gap with a series of equally spaced sharp lines. These gigawatt multichromatic x rays may potentially allow one to explore the structure and dynamics of a large number of atomic states simultaneously. The feasibility of generating mode-locked x rays ranging from carbon $K$ edge ($\ensuremath{\sim}284\text{ }\text{ }\mathrm{eV}$) to copper ${L}_{3}$ edge ($\ensuremath{\sim}931\text{ }\text{ }\mathrm{eV}$) is confirmed with numerical simulation using the realistic parameters of the linac coherent light source (LCLS) and LCLS-II. We anticipate that the mode-locked multichromatic x rays in FELs may open up new opportunities in x-ray spectroscopy (i.e. resonant inelastic x-ray scattering, time-resolved scattering and spectroscopy, etc.).
Highlights
Free-electron lasers (FELs) can provide high-power coherent short-wavelength radiation which is enabling forefront science in physics, chemistry, biology, material science, etc
In the x-ray wavelengths, most of the FELs operate in the self-amplified spontaneous emission (SASE) mode [1,2] in which the initial beam shot noise is amplified by several orders of magnitude to gigawatt (GW) and beyond
We have studied a simple scheme to generate modelocked multichromatic x rays in an FEL
Summary
Free-electron lasers (FELs) can provide high-power coherent short-wavelength radiation which is enabling forefront science in physics, chemistry, biology, material science, etc. It may be envisioned that, if the output of an FEL can be tailored to provide x rays which span a wide frequency range covering the absorption edges with multiple sharp lines as those from mode-locked lasers, RIXS may be performed in a single shot with a spectrometer that disperses the incoming and outgoing photons in two orthogonal planes [21]. This may greatly enhance the capability of an x-ray FEL, and may potentially open up new opportunities in x-ray science. The feasibility of generating mode-locked multichromatic x rays ranging from carbon K edge ($ 284 eV) to copper L3 edge ($ 931 eV) is demonstrated with numerical simulation using the realistic parameters of the LCLS and LCLS-II
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