Development of high-repetition-rate laser pump/x-ray probe methodologies for synchrotron facilities

We describe our implementation of a high repetition rate (54 kHz-6.5 MHz), high power (> 10 W), laser system at the 7ID beamline at the Advanced Photon Source for laser pump/x-ray probe studies of optically driven molecular processes. Laser pulses at 1.06 mu m wavelength and variable duration (10 or 130 ps) are synchronized to the storage ring rf signal to a precision of similar to 250 fs rms. Frequency doubling and tripling of the laser radiation using nonlinear optical techniques have been applied to generate 532 and 355 nm light. We demonstrate that by combining a microfocused x-ray probe with focused optical laser radiation the requisite fluence (with < 10 mu J/pulse) for efficient optical excitation can be readily achieved with a compact and commercial laser system at megahertz repetition rates. We present results showing the time-evolution of near-edge x-ray spectra of a well-studied, laser-excited metalloporphyrin, Ni(II)-tetramesitylporphyrin. The use of high repetition rate, short pulse lasers as pump sources will dramatically enhance the duty cycle and efficiency in data acquisition and hence capabilities for laser-pump/x-ray probe studies of ultrafast structural dynamics at synchrotron sources. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3615245]