Report
Teaser, summary, work performed and final results
Periodic Reporting for period 2 - COCONIS (Coherent multidimensional spectroscopy of controlled isolated systems)
Teaser
Light harvesting in photosynthesis and photovoltaics still lack a detailed understanding of elementary processes. In organic photovoltaics central questions deal with the design of hetero structures with high efficiencies in the light-to-energy conversion and specific...
Summary
Light harvesting in photosynthesis and photovoltaics still lack a detailed understanding of elementary processes. In organic photovoltaics central questions deal with the design of hetero structures with high efficiencies in the light-to-energy conversion and specific electronic properties adopted to an application. Since on the molecular level the underlying processes are governed by quantum mechanical effects, one can exploit the corresponding quantum mechanical wave properties on the atomic level to characterize materials. A powerful method doing this is Multidimensional Coherent Electronic Spectroscopy (MCES). However, when isolating fundamental molecular structures in the gas phase, this technique was, so far, not sensitive enough. In this project, a combination of different specific new experimental approaches are put forward to develop methods for MCES, sensitive enough to probe isolated molecular structures. At these building blocks, MCES can map out the energetics and the coupling between all contributing energy levels of a molecular structure and in this way relate the properties of the components to the functioning of excitation and electron transfer. The project aims at demonstrating MCES experiments in the gas phase and study molecular structures relevant for light harvesting. In general, a fundamental understanding of light-induced processes of light-harvesting materials can be instrumental finding new avenues in the design of optimized materials for photovoltaic devices. Photovoltaics or, in general, optoelectronics, on the other hand, will play a decisive role generating and distributing energy in the future.
Work performed
The main goal of the ERC project is the development of new experimental approaches to study fundamental ultrafast and many-body phenomena in well-controlled model systems with novel time-resolved spectroscopy techniques. These experiments pose great experimental challenges and require unique combinations of technologies to overcome these barriers. As such, the first part of the funding period was mainly dedicated to the development of new, unconventional methodologies. Related to that, an advanced optical setup of nested interferometers combined with high repetition-rate femtosecond lasers and a molecular beam machine has been setup. All components have been tested and characterized, providing already valuable information on the applied techniques. Moreover, wave packet interferometry experiments performed with parts of the setup have revealed long-range dipole interactions in extremely dilute systems. We were able to explore dipolar interactions in extreme regions of phase space, so far inaccessible by other methods These results may have important implications in many fields of many-body physics, ranging from ultracold ensembles to biomolecular aggregates and our new highly sensitive method may contribute in these fields to reveal subtle cooperative effects.
The completed setup for 2-dimensional spectroscopy was first tested on atomic samples in a gas cell, before successfully performing the worldwide first experiments on a doped helium nanodroplet beam at millikelvin temperatures. The application of multidimensional spectroscopy to the well-controlled sample revealed many high-resolution details and allowed us to deduce a conclusive picture of the coherent and incoherent ultrafast dynamics of the system. With this experimental demonstration, we achieved a major milestone in our ERC project and a long-standing goal in coherent multidimensional spectroscopy.
Furthermore, new data acquisition schemes and detection types in nonlinear spectroscopy have been developed. We have built a unique experimental apparatus, facilitating 2D spectroscopy measurements with three different types of detection: photoelectron and ion-mass spectrometry as well as fluorescence detection. We established a specialized undersampling technique which permits high lock-in data recovery performance even at very low signal rates, and also engineered an advanced digital signal processing scheme including software-based multichannel lock-in detection to facilitate real-time analysis of data. Finally, we extended the method of phase-modulated nonlinear spectroscopy into the extreme ultraviolet spectral range, using the free-electron laser FERMI as light source. As demonstration example, we probed for the first time the electronic dephasing of a core-shell transition in real time.
Final results
The project has already achieved unprecedented sensitivity and spectral resolution in 2-Dimensional Spectroscopy demonstrated at alkali molecules attached to helium nanodroplets. Since in the formation of even complex organic molecular structures the number densities are very similar when compared to the systems probed so far, we expect that during the further course of the project specifically synthesized complexes can be probed and compared with respect to light-induced processes.
The first experiments on the manipulation of XUV femtosecond pulses from the free-electron laser FERMI have demonstrated the possibility of coherent spectroscopy at XUV or even X-ray light sources without the direct manipulation of XUV/X-ray light pulses. Until the end of the project, experiments are expected even using XUV table-top HHG laser sources for coherent spectroscopy with a time resolution in the attosecond range. This would open new perspectives for the numerous scientific groups operating these kind of light sources in their laboratories. In the XUV energy range, unprecedented spatial resolution can be gained by addressing inner-shell resonances of individual atoms in a molecular compound and attosecond time resolution can be achieved with ultrashort attosecond pulse generation.
Replacing the complex and costly lock-in hardware needed for the acquisition and analysis of phase-modulated data by digital data processing and specific algorithms is a further goal of the project. We are already at the stage, successfully testing systems in a post-processing fashion. A digital online processing of the experimental data seems to be feasible and is expected to be realized until the end of the project.