Conference Agenda

Dual-comb spectroscopy combining key advantages of fast, broadband and accurate measurements has been established in the infrared as a method for the investigation of a variety of samples, more recently for the field studies of atmospheric gases with kilometer-scale absorption path lengths.

We could recently extend the application capabilities of field-deployed dual comb spectroscopy by developing a portable dual-comb spectrometer operating in the visible spectral region for atmospheric monitoring of NO2, a pollution gas of major importance. In combination with a multi-pass approach through the atmosphere, an interaction path length of almost a kilometer is reached while achieving both advanced spatial resolution (90 m) and high detection sensitivity (5 ppb).

By transposing DCS into the UV spectral region, the highly energetic UV photons can be exploited to drive electronic and rovibronic transitions in molecular (gas) species. We realized UV dual comb spectroscopy using two broadband ultraviolet frequency combs centered at 871 THz and covering a spectral bandwidth of 35.7 THz. We obtain rotational state-resolved absorption spectra of formaldehyde, a prototype molecule with high relevance for laser spectroscopy and environmental sciences in 100 µs of measurement time.

The experimental investigation of chemically and biologically relevant dynamics induced by visible or ultraviolet (UV) light requires high temporal resolution and spectroscopic techniques capable of resolving the complexity of these processes. Time-resolved photoelectron spectroscopy has proven to be a key tool for the study of these dynamics, but most studies have been conducted with a limited temporal resolution of about 100 fs. Furthermore, typical schemes employ a deep-UV probe, which limits the observation window and leads to spectrally congested traces. In this work, we present a UV pump – extreme-UV probe beamline with sub-20 fs temporal resolution, unambiguously characterized by an in-situ photoelectron cross-correlation measurement. As an example of the capability of the setup, we show a time-resolved investigation of the non-adiabatic dynamics of acetylacetone. The extreme temporal resolution allows us to resolve the passage through the first conical intersection and to identify the coherently excited vibrational modes.

Traditional amplifier-based pump-probe systems offer versatility but are often limited by their complexity and low measurement speeds, particularly when probing samples that require low excitation fluences and high sensitivities. To circumvent this limitation, we introduce a pump-probe system that leverages a novel 60 MHz single-cavity dual-comb oscillator and an ultra-low noise supercontinuum enabled by polarization maintaining all-normal dispersion fiber. The presented system can operate in equivalent time sampling mode (also known as asynchronous optical sampling) or in arbitrary optical delay generation mode. This dual-mode operation facilitates a broad range of time-resolved studies. We have employed this system to study the non-fullerene electron acceptor Y6, a compound of significant interest in solar cell development, revealing its response at various probe wavelengths with ultra-high sensitivity. The results demonstrate the system's potential to advance the field of ultrafast spectroscopy

We report an unexpected result of the anisotropy of the nonlinear optical response of carbon nanotubes, inherent to their chirality. Using a model based on the resolution of the semiconductor Bloch equations, we theoretically demonstrate that, upon irradiation with an intense linearly polarized laser pulse along the axial direction, chiral nanotubes exhibit an oscillating azimuthal current that is absent in achiral species. This current induces a magnetic field parallel to the axis of the nanotube that radiates like a loop antenna.

ADASOPS pump-probe spectroscopy is a multi-timescale technique that is spreading rapidly especially in the field of biomolecule dynamics. Based on slight variations of the laser repetition rate, it is simple to implement and can cover a time range extending from a hundred femtoseconds to a millisecond or more. We have studied the energy fluctuations associated with this approach and have proposed a method for overcoming any instabilities.