Instantaneous mapping of coherently coupled electronic transitions and energy transfers in a photosynthetic complex using angle-resolved coherent optical wave-mixing

Angle-resolved coherent wave mixing using a 4 fs ultra-broad bandwidth laser

We demonstrate angle-resolved coherent (ARC) wave mixing using 4 fs light pulses derived from a laser source that spans 550-1000 nm. We believe this to be the shortest pulse duration used to date in coherent multi-dimensional spectroscopy. The marriage of this ultra-broad band, few-cycle coherent source with the ARC technique will permit new investigations of the interplay between energy transfers and quantum superposition states spanning 8200  cm^-1. We applied this configuration to measurements on the photosynthetic low light (LL) complex from Rhodopseudomonas palustris in solution at ambient temperature. We observe bi-exponential population dynamics for energy transfer across 5500  cm^-1 (0.65 eV), which we attribute to energy transfer from the Q_x transition of bacteriochlorophylls to the B850 pigment of the complex. We believe for the first time, to the best of our knowledge, we demonstrate that ARC maps can be recorded using a single laser pulse.

Two-dimensional x-ray correlation spectroscopy of remote core states

Nonlinear all-X-ray signals that involve large core-atom separation compared to the X-ray wavelengths may not be described by the dipole approximation since they contain additional phase factors. Expressions for the rotationally averaged 2D X-ray photon echo signals from randomly oriented systems that take this position-dependent phase into account for arbitrary ratio between the core separation and the resonant wavelength are presented. Application is made to the Se K-edge of a selenium dipeptide system.

Controlling stimulated coherent spectroscopy and microscopy by a position-dependent phase

We study the role of geometry dependent phase shifts in stimulated coherent spectroscopy, a special class of heterodyne optical spectroscopy techniques. We generalize the theoretical description of stimulated spectroscopy to include spatial phase effects, and consider the measured material response for several representative excitation and detection configurations. Using stimulated Raman scattering microscopy as an example, we show that different components of the material response are measured depending the position of the object in focus. We discuss the implications of the position dependent phase in stimulated coherent microscopy and point out a detection configuration in which its effects are minimized.