Margaret Doyle

Lawrence Berkeley National Laboratory

ABSTRACT

Amplified Spontaneous Emission (ASE), otherwise known as Stimulated X-Ray Emission (S-XES), has helped build a baseline for nonlinear x-ray spectroscopic techniques. Not only has it been shown to amplify spectra by over four orders of magnitude, but bandwidths below the natural 1s core-hole lifetime broadening have been observed in the onset of stimulated emission from Mn solutions. In ASE, the transition with the largest dipole moment gets amplified first. Only upon saturation do less intense transitions become enhanced. In order to study weaker but more chemically sensitive transitions, a seed pulse may be deployed through seeded S-XES. Having a seed with good spatio-temporal overlap with the pump pulse allows for specific chemical transitions to be selected and amplified, thus allowing for access to better chemical sensitivity and control over the final states.  A SASE seed pulse has been used for such a seeded experiment at LCLS. However, since SASE radiation from an XFEL is stochastic in nature, pulse-to-pulse fluctuations are the norm. As a result, only a small percentage of the photons from the seed contribute to creating the seeded XES signal. A monochromatic seed pulse would give a user even finer control over the selected states and resulting spectra. We extended this investigation at SACLA in January of 2020, during which SACLA's two-color mode with self-seeding capabilities was used to generate a monochromatic, tunable seed pulse.

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