Two-dimensional Fourier transform spectroscopy in the ultraviolet with sub-20 fs pump pulses and 250–720 nm supercontinuum probe

Abstract

Experimental realizations of two-dimensional (2D) electronic spectroscopy in the ultraviolet (UV) must so far contend with a limited bandwidth in both the excitation and particularly the probe frequency. The pump bandwidth is at best 1500 cm −1 (full width at half maximum) at a fixed wavelength of 267 nm or 400 cm −1 for tunable pulses. The use of a replica of the pump pulse as a probe limits the observation of photochemical processes to the excitation region and makes the disentanglement of overlapping signal contributions difficult. We show that 2D Fourier transform spectroscopy can be conducted in a shaper-assisted collinear setup comprising fully tunable UV pulse pairs and supercontinuum probe spanning 250-720 nm. The pump pulses are broadened up to a useable spectral coverage of 2000 cm −1 (25 nm at 316 nm) by self-phase modulation in bulk CaF 2 and compressed to 18 fs. By referencing the white light probe and eliminating pump stray light contributions, high signal-to-noise ratios even for weak probe intensities are achieved. Data acquisition times as short as 4 min for a selected population time allow the rapid recording of 2D spectra for photolabile biological samples even with the

Spectral lineshapes in nonlinear electronic spectroscopy

“…The experimental spectrum is taken from ref. 19. computations of the high-lying excited state manifold to dynamics simulations in molecular systems.…”

“…The homogeneous broadening G = g + 1/T e is affected by two contributions, a lifetime broadening with a relaxation rate constant 1/T e = 1/85 fs (corresponds to a 125 cm À1 Lorentzian bandwidth), which accounts for the decay from the bright L a state to the dark L b state, 19,46 and a pure dephasing rate constant g which accounts for signal decay due to solute-solvent interactions.…”

“…Notably, 2D optical spectroscopy, which is now state of the art in the infrared regime, is becoming accessible in the Vis and UV region [11][12][13][14][15][16][17][18] and has recently been coupled to supercontinuum probing. 19 The beauty of supercontinuum probing resides in its ability to resolve multiple ESA transitions and track their evolution over time. This is a crucial requirement for electronic spectroscopy, as we have shown in previous studies that the most characteristic ESA and SE signals can exhibit shifts of several thousands of cm À1 during the dynamics.…”

“…1), obtained by pumping at the frequency of the bright electronic transition to the second excited state S 2 around 32 000 cm À1 and utilizing a supercontinuum probe in the region 16 000-38 000 cm À1 after a waiting time of 1 ps. 19 The spectrum is characterized by a vibronic progression of ground state bleach (GSB) peaks and several well-resolved ESA bands. Using the introduced approach we simulate the 2D spectra of pyrene for waiting times t 2 = 0 and t 2 = 1 ps.…”

Probing deactivation pathways of DNA nucleobases by two-dimensional electronic spectroscopy: first principles simulations

“…Furthermore, the temporal evolution of the SE and ESA often span over a large spectral range. 2D time-resolved spectroscopy utilizing broadband probe pulses disentangles spectrally and resolves temporally the fingerprints of the individual de-excitation channels [40][41][42] . In this work we employ geometry optimizations in the excited state and probe the higher excited manifold f and the ground state g at the obtained stationary points, while keeping the pump pulse pair in resonance with the singly excited state manifold e at the Franck-Condon (FC) point.…”