Frequency conversion of intense, ultra-short laser pulses is an efficient way to extend the accessible wavelength regime of lasers towards the extreme-ultraviolet (XUV), i.e., wavelengths well below 100 nm. Such XUV pulses are of relevance to obtain high spatial resolution, as it is important for laser-based lithography and microscopy, or to obtain large temporal resolution by combining broad XUV spectra to super-short attosecond (as) pulses. However, the conversion efficiency of higher-order harmonic generation processes is usually very low. Hence, we apply techniques based on coherent light-matter interactions to control and improve the conversions efficiency, e.g., by constructive quantum interferences on multi-photon excitation pathways, preparation of atomic superposition states at maximal coherence, or generation of laser-dressed states and controlled laser-induced Stark shifts, to drive excited atomic states into multi-photon resonance with the laser field. Beyond the objective to improve frequency conversion of intense, ultra-short laser pulses, the investigations tackle also a basic scientific question in the research field: Where are the limits of coherent-adiabatic light-matter interactions via atomic resonances, which initially were developed and meant for applications at low intensities? How far can we increase the laser intensities towards (or beyond) the electric field which binds the electrons in the atom, and still exploit resonances and quantum coherences, mediated via such resonances?
Selected References
Frequency up-conversion of intense, ultrashort laser pulses at maximal atomic coherence
F. Cipura, P. Ackermann, and T. Halfmann
Physical Review A, 102 033730 (2020)
DOI: 10.1103/PhysRevA.102.033730
Resonantly enhanced harmonic generation via dressed states with large Autler–Townes splittings
F. Cipura and T. Halfmann
J. Opt. Soc. Am. B 36, 10 2777-2784 (2019)
DOI: 10.1364/JOSAB.36.002777
Phase-matched harmonic generation in gas-filled waveguides in the vicinity of a multiphoton resonance
Patric Ackermann, Xavier Laforgue, Mario Hilbig, Maximilian Schilder, and Thomas Halfmann
J. Opt. Soc. Am. B 35, 2 468-480 (2018)
DOI: 10.1364/JOSAB.35.000468
Strong quantum interferences in frequency up-conversion towards short vacuum-ultraviolet radiation pulses
P. Ackermann, A. Scharf, and T. Halfmann
Phys. Rev. A 89, 063804 (2014)
DOI: 10.1103/PhysRevA.89.063804
Resonantly-enhanced harmonic generation in Argon
P. Ackermann, H. Münch and T. Halfmann
Opt. Expr. 20, 13824 (2012)
DOI: 10.1364/OE.20.013824
