Abstract
We describe a transient absorption (TA) spectroscopy system in the ultraviolet (UV) spectral range, for the study of the ultrafast optical response of biomolecules. After reviewing the techniques for the generation and characterization of ultrashort UV pulses, we describe the experimental setup of our ultrabroadband UV TA spectrometer. The setup combines sub-20-fs UV pump pulses tunable between 3.35 and 4.7 eV, with broadband white-light-continuum probe pulses in the 1.7–4.6 eV range. Thanks to the broad tunability of the pump pulses in the UV spectral range, the extremely high temporal resolution and the broad spectral coverage of the probe, this TA system is a powerful and versatile tool for the study of many biomolecules. As an example of its potential, we apply the TA spectrometer to track ultrafast internal conversion processes in pyrene after excitation in the UV, and to resolve an impulsively excited molecular vibration with 85-fs period.
Highlights
Since the development of mode-locked laser sources [1], ultrafast optical spectroscopy has provided invaluable insight into the light-triggered dynamical processes in many different systems of interest for physics, materials science andchemistry [2,3]
This paper describes our recent efforts at developing an ultrafast transient absorption (TA) spectroscopy system in the UV with high temporal resolution for the study of the ultrafast optical response of biomolecules
) essentially flat: the corresponding temporal spectral phases of the pulses, retrieved by 2DSI, which are intensity profiles, shown as solid lines in Figure 4b–d, reveal sub-20-fs pulses, with a FWHM duration where Si(λpr) is the signal measured by the spectrometer at a given probe wavelength for the i-th laser very close to that of the corresponding TL pulses: 16.2
Summary
Since the development of mode-locked laser sources [1], ultrafast optical spectroscopy has provided invaluable insight into the light-triggered dynamical processes in many different systems of interest for physics, materials science and (bio)chemistry [2,3]. TA typically works in a stroboscopic fashion, using two synchronized pulses, the pump and the probe. The pump pulse is resonant with a transition of the system under study, triggering a photoinduced process whose time course is followed by measuring the absorption change of the time-delayed probe pulse, which should ideally be as broadband as possible in order to deliver the maximum amount of spectroscopic information on the system [6,7,8,9]. The time resolution of TA spectroscopy is determined by the so-called instrumental response function (IRF). In TA spectrometers with relatively narrow-band (>100 fs duration) transform-limited (TL) pump and probe pulses, the IRF is the cross-correlation of the intensity profiles of pump and probe pulses [10]
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