Nanoscale dynamics by short-wavelength four wave mixing experiments

Abstract

Multi-dimensional spectroscopies with vacuum ultraviolet (VUV)/x-ray free-electron laser (FEL) sources would open up unique capabilities for dynamic studies of matter at the femtosecond-nanometer time-length scales. Using sequences of ultrafast VUV/x-ray pulses tuned to electron transitions enables element-specific studies of charge and energy flow between constituent atoms, which embody the very essence of chemistry and condensed matter physics. A remarkable step forward towards this goal would be achieved by extending the four wave mixing (FWM) approach at VUV/soft x-ray wavelengths, thanks to the use of fully coherent sources, such as seeded FELs. Here, we demonstrate the feasibility of VUV/soft x-ray 7

Free-Electron Laser Design for Four-Wave Mixing Experiments with Soft-X-Ray Pulses

“…Subsequently, one of these pulses is directed onto a diffraction grating to obtain two pulses with a small frequency separation. We demonstrate that this approach has all the benefits of the technique discussed in [22,23], but is not sensitive to intrabeam Coulomb scattering and has the advantage of higher x-ray pulse intensity.…”

“…To the best of our knowledge, only two XFEL proposals published to date meet, in principle, the above requirements [22,23]. In [22], current enhanced SASE [24] is combined with echo-enabled harmonic generation [25] to produce two temporally coherent soft-x-ray pulses with a variable time delay, a wide bandwidth (up to ∼10 eV), and frequencies that can be independently tuned over a broad range.…”

“…In [22], current enhanced SASE [24] is combined with echo-enabled harmonic generation [25] to produce two temporally coherent soft-x-ray pulses with a variable time delay, a wide bandwidth (up to ∼10 eV), and frequencies that can be independently tuned over a broad range. This proposal was extended in [23] by adding the third soft-x-ray pulse in a fashion similar to [22] and by explicitly showing how all three pulses can be recombined on a sample with adjustable angles of incidence and variable time delays. Alternatively, the wide bandwidth enables any pulse to be split into two (or more) pulses by employing diffraction gratings.…”

“…Alternatively, the wide bandwidth enables any pulse to be split into two (or more) pulses by employing diffraction gratings. However, inherent to the technique employed in [22,23] is coherent radiation from weakly prebunched electrons that produce relatively low field intensities by FEL standards.…”

“…It should also be emphasized that intrabeam Coulomb scattering of electrons (not analyzed in [22,23]) could potentially limit attainable bunching for the production of high frequency radiation as discussed in [26].…”