Laser Spectroscopy with extreme Resolution
Birgitta Schultze-Bernhardt
Institut für Materialphysik & Institut für Experimentalpysik
16:15 - 17:15 Tuesday 20 October 2020 TUG P2 Video: https://cloud.tugraz.at/index.php/s/N9dJNRF2AR5qB57 Link to discussion at 5 pm
Light-matter-interaction is a key ingredient to atomic and molecular physics, condensed matter physics and electrical engineering. It sheds light onto the consistency of matter, it is exploited for the investigation of physical properties of any substance and it can be utilized to initiate, monitor and even control chemical reactions. If the latter involve the excitation of electrons, the processes under scrutiny often occurs on the femtosecond (10$^{-15}$ s) or even attosecond (10$^{-18}$ s) time scale. Those ultrafast dynamics can best be resolved in real time by (laser) pulses that are shorter than the studied process itself – making ultrashort laser pulses on the femtosecond and even attosecond level highly desirable. Simultaneously, ultrashort pulses come with a broad spectral bandwidth, providing large spectral coverage for the acquisition of absorption properties of a system under scrutiny.
One recent spectroscopic technique harnessing ultrashort laser pulses is called dual comb spectroscopy. It combines high spectral resolution with broad spectral coverage and short measurement times. In the recent years, the young spectroscopic method has proven its capabilities in molecular spectroscopy in different spectral regions ranging from the visible across the infrared spectral region into the THz domain. It has recently been extended to nonlinear hyperspectral imaging via Raman spectroscopy [1, 2]. So far, the ultraviolet spectral region has not yet been conquered although many molecular gasses, especially of astrophysical and environmental relevance, have strong and congested absorption characteristics in this range (few examples: NO$_2$, CO, SO$_2$, HCHO). Our latest efforts on expanding dual comb spectroscopy via nonlinear frequency up-conversion into the (extreme) ultraviolet (XUV) region will be presented [3]. XUV radiation accesses also ultrafast electron dynamics that can be resolved in real time by attosecond pump-probe spectroscopy [4-6]. A recent experiment shows the unprecedented combination of transient absorption and time-resolved ion spectroscopy providing a detailed picture of ionization dynamics in highly excited atoms [7].
By combining the two innovative methods of dual comb and pump probe spectroscopy, an unparalleled combination of high spectral (femtometer) and high temporal (femtosecond) resolution will be achieved for the first time. We envisage this next-level spectroscopy platform to become a prime tool for the kinematically complete and fully state resolved exploration of virtually all photo-induced processes. That includes biological and technological light-to-energy conversion, catalytic atmospheric reactions and the photochemistry of sight.
References:
[1] T. Ideguchi, S. Holzner, B. Bernhardt, G. Guelachvili, N. Picqué and T. W. Hänsch, Nature 502, 355 (2013)
[2] T. Ideguchi, B. Bernhardt, G. Guelachvili, T.W. Hänsch and N. Picqué, Vol. 37, 4498 (2012)
[3] V. Schuster, C. Liu, R. Klas, P. Dominguez, J. Rothhardt, J. Limpert and B. Bernhardt, available at https://arxiv.org/abs/2006.03309 (2020)
[4] X. Li, B. Bernhardt, A. R. Beck, E. R. Warrick, Adrian N. Pfeiffer, M. J. Bell, D. J. Haxton, C. W. McCurdy, D. M. Neumark and S. R. Leone, J. Phys. B: At. Mol. Opt. Phys. 48, 125601 (2015)
[5] B. Bernhardt, A. R. Beck, X. Li, E. R. Warrick, M. J. Bell, D. J. Haxton, C. W. McCurdy, D. M. Neumark and S. R. Leone, Physical Review A 89, 023408 (2014)
[6] A. R. Beck, B. Bernhardt, E. R. Warrick, M. Wu, S. Chen, M. B. Gaarde, K. Schafer, D. M. Neumark and S. R. Leone, New J. Phys. 16, 113016 (2014)
[7] K. Hütten, M. Mittermair, S. Stock, R. Beerwerth, V. Shirvanyan, J. Riemensberger, A. Duensing, R. Heider, M. Wagner, A. Guggenmos, S. Fritzsche, N. M. Kabachnik, R. Kienberger and B. Bernhardt, Nature Communications 9, 719 (2018)
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