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Femtosecond pump/supercontinuum-probe spectroscopy: Optimized setup and signal analysis for single-shot spectral referencing
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Image of FIG. 1.
FIG. 1.

Setup for transient absorption. Multifilament supercontinuum generation extends the probe range from the visible into the uv to , but it requires optics for a 6° full solid angle at the source. Mirror objectives allow spot size in the sample cell and upon entrance into two spectrographs. Apertures and slits are avoided after the BS (for notations see text).

Image of FIG. 2.
FIG. 2.

Specifications of the Schwarzschild objective, as optimized by ray tracing.

Image of FIG. 3.
FIG. 3.

Sample cell of variable optical path length . While the solution is flown through slowly, the cell is oscillated at its resonance frequencies (ca. 20 Hz) in the two directions orthogonal to the optical axis.

Image of FIG. 4.
FIG. 4.

Acquisition sequence and corresponding data package for a fixed delay position. considered in the reference and sample spectrograph, , corresponding readout. During a sequence the plate is not moved.

Image of FIG. 5.
FIG. 5.

Correlation between reference and sample reads , at the pixel considered, for 500 events like in Fig. 6. Black points: same continuum shot, registered in parallel by the two spectrographs. The regression line through the origin, with slope or optimal quotient , is also shown. Gray points: successive continuum shots, registered by the sample spectrograph only.

Image of FIG. 6.
FIG. 6.

Parent distribution for the data in Fig. 5 (black contours at , , 0.3, 0.9 of the peak) sampling the deviation of the slope. (Along gray lines the corresponding . corresponds approximately to the long axis).

Image of FIG. 7.
FIG. 7.

Change of optical density between events 0 (“pump off”) and (“pump on”) but with the pump beam physically blocked. This baseline (black) has rms noise of across the full pixel range (wavelengths 277–660 nm). The same standard error for is obtained from regression analysis at each pixel individually (gray band between ). The baseline from consecutive shots is shown for comparison (gray line); the improvement of S/N by single-shot referencing is for this experiment.

Image of FIG. 8.
FIG. 8.

Optical spectra of the H33258/DNA complex in an aqueous solution, stationary (a) (solid lines) and transient (b) and (c) after femtosecond laser excitation (parallel pump-probe polarization). The evolution in (c) reflects that of stimulated emission which is strictly related to spontaneous fluorescence from the excited ligand H33258.

Image of FIG. 9.
FIG. 9.

Transient absorption trace at 405 nm (black line in lower panel (b) and its description by a global fit with three convoluted exponentials (green) and Gaussian functions (red, see text). The residuals from this description are shown in the upper panel (a). The gray band/dashed lines represent the range for 68/99.7% confidence.

Image of FIG. 10.
FIG. 10.

Femtosecond stimulated Raman scattering spectra of aqueous FAD (inset, with diphosphate) constructed from five partial spectra (see text) for the electronic ground state (bottom), and for the state 0.5 ps after actinic excitation at 475 nm (top). The Raman pump at 523 nm was resonant with the and transitions, leading to dispersive line shapes. Middle: in the difference spectrum most of the population background has been canceled, and the noise becomes visible.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Femtosecond pump/supercontinuum-probe spectroscopy: Optimized setup and signal analysis for single-shot spectral referencing