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High-Intensity Coherent Nonlinear Optics

Periodic Reporting for period 2 - HICONO (High-Intensity Coherent Nonlinear Optics)

Reporting period: 2017-10-01 to 2019-09-30

Laser-based, photonic technologies exhibit a major key technology of the 21st century, with a large impact in a vast range of high-end optics applications. Extension of the range of such scientific and commercial laser applications requires a constant expansion of the accessible regimes of laser operation. Concepts from nonlinear optics, in particular driven with ultra-fast lasers, provide all means to achieve this goal. However, nonlinear optics typically suffer from efficiencies well below unity, e.g. if high-order processes are involved or if the driving laser pulse intensities must be limited below damage thresholds (e.g. in nonlinear microscopy of living cells, or nonlinear spectroscopy of combustion processes in engines). Thus, we require methods to enhance nonlinear optical processes. The field of “coherent control” provides techniques to manipulate laser-matter interactions. The basic idea is to use appropriately designed light-matter interactions to steer quantum systems towards a desired outcome, e.g. to support nonlinear optical processes. HICONO aimed at novel methods for coherent control, applied to support high-intensity ultra-fast nonlinear optics. This established novel and efficient types of light sources, e.g. to generate extreme-ultraviolet radiation, ultra-broad spectra or intense attosecond laser pulses. HICONO introduced novel concepts for ultra-fast spectroscopy and microscopy, and stimulated novel developments in laser technology, e.g. to provide novel ultra-fast light sources or new devices to characterize ultra-fast light pulses. HICONO involved three scientific work packages: (WP1) “Coherent control of high-intensity frequency conversion” deals with the development, implementation and investigation of coherent control scenarios to steer frequency conversion, driven by high-intensity laser pulses. (WP2) “High-intensity nonlinear spectroscopy and microscopy” deals with implementations and applications of high-intensity nonlinear optical processes in spectroscopy and microscopy, e.g. to monitor ultra-fast chemical dynamics by high-harmonic generation, and to develop novel variants of coherent harmonic microscopy. (WP3) “Ultra-short pulse measurement and characterization” deals with enabling technologies to precisely measure and characterize complex light fields.
The 6 academic and 2 industry teams in HICONO conducted a broad variety of fundamental experimental studies to coherently control high-intensity frequency conversion driven by high-intensity laser pulses, applications of such processes to nonlinear ultrafast spectroscopy and microscopy, as well as development of commercially relevant enabling technologies. The investigations aimed at spatial resolutions down to the size of a single molecule, and temporal resolutions down to the attosecond regime. The findings already lead to 14 publications (additional papers in preparation, submitted, or in press), a novel demonstration device for ultra-precise distance measurement, and a novel commercial device for characterization of ultra-fast laser pulses. Some specific highlights in the research projects of the individual teams are: TUDA combined resonance enhancements and quasi-phase matching to improve the brightness of frequency conversion processes towards vacuum-ultraviolet (VUV) radiation in a gas-filled capillary. Moreover, the team developped novel variants of nonlinear third-harmonic microscopy enabling higher contrast and/or larger signal yield. Nonlinear microscopy enables imaging of otherwise fully transparent optical samples. IC generated VUV pulses with a high efficiency from laser-ablation plumes, and also conducted related investigations on harmonic generation from liquids, which we found to be an advantageous alternative medium. The team developped a target system with unique capabilities, i.e. stable flow in vacuum and liquid sheets with thickness down to the micrometer regime. With the setup IC demonstrated harmonics reaching large photon energies beyond 30 eV. The findings drive laser light sources towards sufficiently intense pulses at ever shorter wavelengths and higher resolutions. ICFO achieved a breakthrough imaging the three-dimensional atomic-scale arrangement of molecular systems, by applying laser-induced electron self-diffraction. The latter enables imaging of molecular reactions with accuracies down to the size of a single molecule and the ultra-fast time scale of molecular motion. This serves to understand and finally control chemical reactions towards desired outcomes. QUB worked on generating high harmonic radiation using the unique JETI200 laser system, which operates at very high pulse intensities. UOXF developed and successfully implemented new approaches to measure and characterize complex, ultra-fast light pulses by space-time interferometry. Such devices are an essential component of any technology involving ultra-short laser pulses, and, hence, also of commercial potential. Moreover, UOXF achieved a first implementation of high harmonic generation in a gas-filled hollow core photonic crystal fiber to provide a bright ultra-fast light source. The industry team LUPH extended the possibilities of an ultra-precise distance sensor, i.e. to increase the data rate by electro-optical modulation (EOM). The investigations lead to a new prototype for improved distance measurements, which is of commercial relevance for a multitude of optics applications, where precise distance information down to the range of one nanometer is required. The findings will lead to an improved version of the commercially available LUPHOSCAN device soon. The industry team FTL successfully developped a novel, commercial device for temporal characterization of few cycle, mid-infrared laser pulses. This is required in any laser technology applying such pulses. With the trade name FROZZER the device is now already part of the commercially available product portfolio of FTL.
As the above examples of the research highlights in the HICONO teams indicate, the network already proceeded well beyond the state-of-the-art of ultra-fast laser physics and nonlinear optics. This is also mirrored by the many papers published or submitted to peer-reviewed scientific journals and development of two commercially relevant technologies for optics industry. Potentially, there are also options to commercially exploit the findings in HICONO to improve nonlinear microscopy and measurement of ultra-fast light pulses. The scientific developments in HICONO are of relevance to high-technology optics applications in physics, chemistry, medicine, and engineering. In the broader sense of a socio-economic impact, HICONO contributed to the strongly expanding and fast growing field of photonic technologies by training of young researchers with appropriate skills to exploit the concepts of high-intensity laser technologies, laser-based control, and applied nonlinear optics.
typical laser setup HICONO