Development and applications of nonlinear optical spectroscopy: 16th ECONOS/36th ECW meeting in Jena (Germany)

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 16th ECONOS conference and 36th CARS workshop were held in Jena, Germany, on April 2–5, 2017, chaired by Jürgen Popp and Michael Schmitt (Leibniz Institute of Photonic Technology [IPHT], Institute of Physical Chemistry of the Friedrich Schiller University Jena, and Abbe Center of Photonics). Altogether, 100 participants shared their research in oral sessions and poster sessions and participated in lively discussions and social activities. After a welcome reception and a keynote lecture entitled “New Advances in Molecular Spectroscopic Imaging” by Ji-Xin Cheng on Sunday afternoon, the regular scientific program began on Monday morning at the Abbe Center of Photonics. Seven invited talks were given during the course of the conference, followed by contributed oral presentations, and a poster session. The social event constituted a guided tour at Leuchtenburg Castle and the conference dinner at the historic restaurant of the castle. This special section of the Journal of Raman Spectroscopy constitutes a selection of six papers presented at ECONOS/ECW 2017. Due to the broad scope of the conference, the papers cover a broad range of methods and their applications to a variety of systems. Applications of nonlinear optical spectroscopy traditionally cover all states of matter, which is also reflected in this special issue. Hosseinnia et al.1 present rotational CARS of gaseous ethane with an emphasis on concentration measurements in mixtures with nitrogen. They show that the spectra of ethane and nitrogen partially overlap. In order to allow a meaningful evaluation, a novel Fourier analysis approach was developed permitting the determination of relative concentrations and temperatures. Another study related to gas phase and combustion diagnostics is authored by Marrocco.2 He extended his theoretical model not only to allow the investigation of effects caused by the temporal laser profile but also to include chirp. The comparison of his analytical model with experimental data shows a good agreement except for some limitations imposed by deviations of the nonresonant CARS signal from the Gaussian structure assumed in the model. Vereshchagin et al.3 studied the nature of the cubic and cascaded quadratic nonlinear responses in a KTiOPO4 crystal, when it is pumped with picosecond pulses. They observed a variety of linear and nonlinear optical phenomena, which can be utilized in frequency conversion, for instance. Lanin et al.4 investigated nonlinear effects for quantum memory applications. CARS is shown to provide a versatile spectroscopic protocol for the optical interrogation of broadband quantum memories based on long-lived coherent phonons in solids. They utilized a frequency-tunable Stokes field to map the broadband pump wave packet into a memory based on coherently driven optical phonons of diamonds. The probe field was then applied with a variable delay time to read out the coherence driven by the pump and Stokes fields yielding information about the state of the phonon memory. In addition, the conference covered a variety of nonlinear optical microspectroscopy application. Zada et al.5 presented stimulated Raman scattering microscopy as a potential tool for the analysis of microplastics particles. They performed test measurements to identify five different polymer types in microplastics extracted from environmental or consumer product samples. A major advantage of using stimulated over spontaneous Raman microscopy was found to be the thousand-fold higher speed of mapping. This led to the conclusion that SRS can be an efficient method for monitoring microplastics in the environment. Fabelinski et al.6 demonstrate epi-surface-enhanced coherent anti-Stokes Raman scattering (SECARS) microimaging of Au-nanoparticle-bound organic reporter molecules. Their method utilizes surface-enhanced Raman scattering (SERS)-active metamaterial junctions, which are based on nanoparticles spread over a nanostructured CeO2 faceted dielectric film, deposited on an Al sublayer. The results show that the molecules/Au–NP conjugates immobilized on the surface provide strong SECARS signals without deteriorating the conjugates. An excellent chemical contrast was found for biochemically relevant target molecules. 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. We would like to thank all the delegates, presenters of talks and posters, helpers in the background, and sponsors, which made the 2017 ECONOS/ECW meeting in Germany an enjoyable and memorable event. Special thanks to the Editor-in-Chief of the Journal of Raman Spectroscopy, Larry Nafie, for making this special section possible and, of course, to all the authors and reviewers of the papers for their invaluable contribution.