Development and Applications of Nonlinear Optical Spectroscopy: 21st ECONOS/41st ECW Meeting in Vienna (Austria)

The joint conference of the European Conference on Nonlinear Optical Spectroscopy (ECONOS) and European CARS Workshop (ECW) covers all theoretical and experimental aspects of nonlinear optical spectroscopy and microscopy. Topics include Coherent anti-Stokes Raman scattering (CARS) spectroscopy and microscopy and other forms of coherent Raman scattering, other approaches to the detection of nonlinear optical responses in time and frequency domain, and investigations of the physical and chemical processes defining the spectral signatures in different nonlinear media. Also, emerging analytical techniques and their applications in biomedical research, material science, and engineering are discussed. The 21^st ECONOS conference and 41^st CARS workshop were held in Vienna, Austria, on April 21–24, 2024, chaired by Ellen Backus and Oliver Heckl (University of Vienna). Altogether, 90 participants shared their research in oral sessions and poster sessions and participated in lively discussions and social activities. The first session already took place on Sunday afternoon starting with an invited talk entitled “Optical-optical double-resonance spectroscopy using a frequency comb probe—broadband precision measurements of molecular hot-band transitions” by Aleksandra Foltynowicz of Umeå University followed by contributed talks and a welcome reception. The main scientific program began on Monday morning in the historic Kardinal König Haus in Vienna. Another four invited talks were given during the course of the conference, embedded in the agenda of contributed oral presentations and a poster session. The main social event was the memorable conference dinner at the historic restaurant Heurigen Zahel.

This special section of the Journal of Raman Spectroscopy constitutes a selection of three papers presented at ECONOS/ECW 2024. Due to the broad scope of the conference, the papers cover a broad range of methods and their applications to a variety of systems.

Vergari et al. [1] dedicated their contribution to a very fundamental issue, that is, the representation of nonlinear optical interactions in diagrammatic schemes. Such schemes are essential in the understanding and communication of complicated nonlinear optical phenomena. After reviewing the common Feynman diagrams, Liouville pathways, and the Albrecht notation, the authors suggest that the limitations of the conventional approaches can be overcome by a field-type modification of the Albrecht notation that combines the simplicity of the energy-level representation with the more elaborated diagrams.

Raveesh et al. [2] studied time-domain femtosecond rotational coherent Raman scattering for diagnostic purposes. Experiments in air and pure nitrogen show selectivity and temperature sensitivity in the recorded fs-RCRS temporal scans. A theoretical model is capable of predicting experimental data with good agreement for temporal scans recorded at room temperature and elevated temperature. Moreover, single-shot thermometry is proposed through a dual-probe approach.

Vereshchagin et al. [3] study the spatial localization of surface-enhanced Raman scattering (SERS) over nanostructured self-assembled silver films using confocal Raman microscopy. A series of systematic experiments was carried out in order to unravel the complex signal enhancement phenomena. They observed characteristic space scales exceeding the characteristic scales of inhomogeneities in the substrate nanostructure, which was explained by the interplay of excitation, scattering, and localization of hybrid plasmon-polariton waves under conditions of a real optical scheme, taking the morphology and structure of the silver films into account.

This ECONOS/ECW special section highlights the continuous progress in the area of nonlinear optical spectroscopy and its applications across the science and engineering disciplines. The enthusiasm and creativity of the scientific community as well as the rapid development of novel and improved experimental equipment will ensure an exciting future of nonlinear spectroscopy research.

Ellen H. G. Backus¹, Oliver H. Heckl²

Local organizers

Johannes Kiefer³

Guest editor