Schematic of the synchronization and delay control of the laser pulses with respect to the x-ray pulses. The laser is shown operating at 6.52 MHz (78.2 MHz ÷ 12) to match the x-rays in the standard 24 bunch mode. The light gray pulses separated by 12.8 ns illustrate other oscillator pulses that could be chosen for coarse delay of the laser relative to the x-ray pulses.
Experimental arrangement for the time-resolved XAS measurement of NiTMP in toluene.
Data acquisition scheme using a single 4.2 mA bunch to record laser-on/laser-off data at 135 kHz. Electronic gates are used to distinguish counts from x-ray pulses from a selected bunch and also those from x-ray pulses that are overlapped with the laser pulses.
(a) XAS fluorescence yield at the Ni K edge from NiTMP solvated in toluene, collected in a single scan in one hour. Shown are the laser excited (solid curve) and ground state (dashed curve) spectra. The ground state spectrum was collected from all x-ray pulses but the laser-on and so has been divided by 47 to be compared with the laser excited spectrum. The laser repetition rate was 135.8 kHz. The x-rays probed 50 ps after the laser pulse. The laser power was 0.7 W corresponding to 5 μJ/pulse. The inset shows the 1s → 4p and 1s → 3d edge features. (b) Difference spectrum between the laser excited and ground state spectra shown in the top panel.
Time evolution of the 1s → 4p z resonance of the T1 laser excited state of NiTMP (8.34 keV). The ratio of the singlet laser-on and laser-off counts is plotted. The solid line is a fit of a Gaussian function (accounting for the 94 ps FWHM x-ray pulse) convoluted with an exponential decay function. The fit gives a decay time of 186 ± 10 ps for the T 1 state. The data were collected at 135.8 kHz and the laser power was 0.7 W.
Laser-on/laser-off ratio at the 1s → 4p z resonance of the T 1 laser excited state of NiTMP (8.34 keV) as a function of the laser fluence. The laser was focused to a FWHM spot size of 60 × 60 μm2.
Normalized absorption coefficient, μ, as a function of x-ray energy for the pre-edge 1s → 3d features of the ground and excited states of NiTMP in solution. The extracted excited state spectrum (open circles) was fit (solid line) to a sum of two Gaussians (dashed) and an arctangent (dashed) background. The Gaussian fits to the (8.3339 keV) and (8.3315 keV) resonances show a splitting of 2.4 eV. The ground state spectrum (filled circles and line) with a single peak at 8.3330 keV is shown for comparison. The Gaussian plots are offset by .01 for clarity. The data was collected at 135.8 kHz. The x-rays probed 50 ps after the laser excitation. The laser power was 0.7 W.
Available power and pulse energy at the fundamental, second, and third harmonics in the 10 ps operational mode at selected repetition rates.
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