A new Förster resonance energy transfer (FRET) concept for a multichromophoric organic sensitizer in a dye-sensitized solar cell is presented based on a phenyl base body that accommodates the separately linked donor and acceptor moieties. The whole assembly is attached to the surface of a ZnO nanorod electrode via a carboxylic anchor group. FRET activity was demonstrated with UV-VIS measurements, and the charge separation dynamics at the inorganic/organic interface were analyzed with fs transient absorption and terahertz pump/probe for the precursors and fully assembled FRET units.
An ultrafast x-ray streak camera is under development at LBNL for application primarily to studies of ultrafast magnetization dynamics. In initial work, a temporal resolution of 900fs in accumulative mode at 5 KHz has been achieved. These results and methods currently being developed to improve the resolution and repetition rate are resented. One of the primary limits to temporal resolution is caused by the finite energy width of the electron distribution from the photocathode. The positive time of flight dispersion with energy in the accelerating region of the camera can be countered by introduction of downstream optics that give negative time of flight dispersion with energy, leading to an approximate overall cancellation of this temporal aberration. Initial results of an end-to-end simulation model using the full photoelectron distribution are presented.
The spin dynamics of ferromagnetic thin films following an excitation by ultrashort 100-fs near-infrared laser pulses has recently received much attention. Here, a new approach is described using x-ray magnetic circular dichroism to investigate demagnetization and magnetization switching processes. In contrast to magneto-optical measurements, x-ray dichroism has the advantage of determining separately the spin and orbital components of the magnetic moment. The relatively low time resolution of the synchrotron x-ray probe pulses (80 ps FWHM) is overcome by employing an ultrafast x-ray streak camera with a time resolution of < 1 ps. A description of the experimental setup including the x-ray/IR laser pulse synchronization and the streak camera is given.