Engraving of stainless-steel wires to improve optical quality of closed-loop wire-guided flow jet systems for optical and X-ray spectroscopy.

This paper describes performance enhancement developments to a closed-loop pump-driven wire-guided flow jet (WGJ) for ultrafast X-ray spectroscopy of liquid samples. Achievements include dramatically improved sample surface quality and reduced equipment footprint from 7 × 20 cm to 6 × 6 cm, cost, and manufacturing time. Qualitative and quantitative measurements show that micro-scale wire surface modification yields significant improvements to the topography of the sample liquid surface.

Sub-Millisecond Photoinduced Dynamics of Free and EL222-Bound FMN by Stimulated Raman and Visible Absorption Spectroscopies.

Time-resolved femtosecond-stimulated Raman spectroscopy (FSRS) provides valuable information on the structural dynamics of biomolecules. However, FSRS has been applied mainly up to the nanoseconds regime and above 700 cm, which covers only part of the spectrum of biologically relevant time scales and Raman shifts. Here we report on a broadband (~200-2200 cm) dual transient visible absorption (visTA)/FSRS set-up that can accommodate time delays from a few femtoseconds to several hundreds of microseconds after illumination with an actinic pump.

Implementation of a crossed-slit system for fast alignment of sealed polycapillary X-ray optics.

A new modification of a table-top laser-driven water-jet plasma X-ray source has been successfully implemented and commissioned at the Extreme Light Infrastructure (ELI) Beamlines user facility. In order to preserve the broadband nature of the source for spectroscopic experiments, a polycapillary lens was initially chosen as the focusing element. Generally, polycapillary X-ray optics have a narrow photon acceptance angle and small field of view, making alignment complicated and time-consuming.

Femtosecond-to-nanosecond dynamics of flavin mononucleotide monitored by stimulated Raman spectroscopy and simulations.

Flavin mononucleotide (FMN) belongs to the large family of flavins, ubiquitous yellow-coloured biological chromophores that contain an isoalloxazine ring system. As a cofactor in flavoproteins, it is found in various enzymes and photosensory receptors, like those featuring the light-oxygen-voltage (LOV) domain. The photocycle of FMN is triggered by blue light and proceeds via a cascade of intermediate states.

Time-Resolved Femtosecond Stimulated Raman Spectra and DFT Anharmonic Vibrational Analysis of an Electronically Excited Rhenium Photosensitizer.

Time-resolved femtosecond stimulated Raman spectra (FSRS) of a prototypical organometallic photosensitizer/photocatalyst ReCl(CO)(2,2'-bipyridine) were measured in a broad spectral range ∼40-2000 (4000) cm at time delays from 40 fs to 4 ns after 400 nm excitation of the lowest allowed electronic transition. Theoretical ground- and excited-state Raman spectra were obtained by anharmonic vibrational analysis using second-order vibrational perturbation theory on vibrations calculated by harmonic approximation at density functional theory-optimized structures. A good match with anharmonically calculated vibrational frequencies allowed for assigning experimental Raman features to particular vibrations.

Pyrene, a Test Case for Deep-Ultraviolet Molecular Photophysics.

We determined the complete relaxation dynamics of pyrene in ethanol from the second bright state, employing experimental and theoretical broadband heterodyne detected transient grating and two-dimensional photon echo (2DPE) spectroscopy, using pulses with duration of 6 fs and covering a spectral range spanning from 250 to 300 nm. Multiple lifetimes are assigned to conical intersections through a cascade of electronic states, eventually leading to a rapid population of the lowest long-living excited state and subsequent slow vibrational cooling. The lineshapes in the 2DPE spectra indicate that the efficiency of the population transfer depends on the kinetic energy deposited into modes required to reach a sloped conical intersection, which mediates the decay to the lowest electronic state.

New Insights into the Photophysics of DNA Nucleobases.

We report the results of an extended time-resolved study of DNA nucleobases in aqueous solutions conducted in the deep UV using broad-band femtosecond transient absorption and electronic two-dimensional spectroscopies. We found that the photodeactivation in all DNA nucleobases occurs in two steps: fast relaxation (500-700 fs) from the excited state ππ* to a "dark" state and its depopulation to the ground state within 1-2 ps. Our experimental observations and performed theoretical modeling allow us to conclude that this dark state can be associated with the nπ* electronic state, which is connected to the excited and ground states via conical intersections.

A closed-loop pump-driven wire-guided flow jet for ultrafast spectroscopy of liquid samples.

We describe the design and provide the results of the full characterization of a closed-loop pump-driven wire-guided flow jet system. The jet has excellent optical quality with a wide range of liquids spanning from alcohol to water based solutions, including phosphate buffers used for biological samples. The thickness of the jet film varies depending on the flow rate between 90 μm and 370 μm.