High temporal and spectral resolution of stimulated x-ray Raman signals with stochastic free-electron-laser pulses

Abstract

The chaotic nature of x-ray free-electron-laser pulses is a major bottleneck that has limited the joint temporal and spectral resolution of spectroscopic measurements. We show how to use the stochastic x-ray field statistics to overcome this difficulty by correlation signals averaged over independent pulse realizations. No control is required over the spectral phase of the pulse, enabling immediate application with existing, noisy x-ray free-electron-laser pulses. The proposed stimulated Raman technique provides the broad observation bandwidth and high time-frequency resolution needed for the observation of elementary molecular events. A model is used to simulate chaotic free-electron-laser pulses and calculate their correlation properties. The resulting joint temporal/spectral resolution is exemplified for a molecular model system with time-dependent frequencies and for the RNA base Uracil passing through a conical intersection. Ultrafast coherences, which represent a direct signature of the nonadiabatic dynamics, are resolved. The detail and depth of physical information accessed by the proposed stochastic signal are virtually identical to those obtained by phase-controlled pulses.

24 pages, 13 figures

References in corpus (4)

• Coherent control with a short-wavelength Free Electron Laser
• Attosecond Pulse-shaping using a seeded free-electron laser
• Nonlinear optical spectroscopy of single, few, and many molecules; nonequilibrium Green's function QED approach
• Resonance fluorescence in ultrafast and intense x-ray free-electron-laser pulses