Research at the Laboratory for Lightwave Metrology

Prof. Dr. Ioachim Pupeza
Leibniz-Institut für Photonische Technologien

Analogue gravity experiments with light in optical fibres

The outstanding control over the individual oscillations of the electromagnetic field of light, afforded by optical-phase-stabilized modelocked laser systems, has enabled manifold breakthroughs in science and technology. This talk will give an overview over the contributions of our research group to this field.

We will first address electric-field-resolved spectroscopy (FRS) in the infrared (IR) molecular fingerprint region [1]. Trains of few-cycle mid-IR pulses with identically repeating optical waveforms can be obtained via intrapulse difference-frequency generation driven by powerful, ultrashort near-IR laser pulses in suitable nonlinear crystals. Employing electro-optic sampling [2] to record their transient electric fields confirms the temporal reproducibility of these waveforms down to the (sub-)attosecond range [3]. In addition, electro-optic sampling affords a combination of detection sensitivity, linear dynamic range and bandwidth unprecedented in molecular spectroscopy [4]. These results constitute crucial steps toward infrared (non-)linear spectroscopy of solids, liquids, and gases at the ultimate limits set by the nature of light. In particular, we will address biomedical applications of these spectroscopic techniques which are currently being prepared in our group, including high-throughput infrared flow cytometry and breath analysis by infrared FRS at the intensive-care unit.

The second part of the talk will survey our work in the field of femtosecond enhancement cavities (EC). ECs are passive optical resonators, in which the power of laser light can be increased by several orders of magnitude by means of interferometric coupling. This technique is used for manifold purposes, reaching from high-sensitivity molecular spectroscopy, over high-power cavity-enhanced nonlinear optics to the realization of compact sources of high-photon-energy coherent x-rays via inverse Compton scattering. We will report on the power scaling of pulsed enhancement cavities to the multi-MW regime [5], the generation of temporal dissipative EC solitons [6], and applications of high-finesse ECs in FRS of gases [7].

[1] I. Pupeza, M. Huber, M. Trubetskov, W. Schweinberger, S. A. Hussain, C. Hofer, K. Fritsch, M. Poetzlberger, L. Vamos, E. Fill, T. Amotchkina, K. V. Kepesidis, A. Apolonski, N. Karpowicz, V. Pervak, O. Pronin, F. Fleischmann, A. Azzeer, M. Žigman, and F. Krausz, "Field-resolved infrared spectroscopy of biological systems," Nature 577, 52–59 (2020).
[2] I.-C. Benea-Chelmus, J. Faist, A. Leitenstorfer, A. S. Moskalenko, I. Pupeza, D. V. Seletskiy, and K. L. Vodopyanov, "Electro-optic sampling of classical and quantum light," Optica 12, 546 (2025).
[3] S. A. Hussain, C. Hofer, M. Högner, W. Schweinberger, T. Buberl, D. Bausch, M. Huber, F. Krausz, and I. Pupeza, "Sub-attosecond-precision optical-waveform stability measurements using electro-optic sampling," Sci Rep 14, 20869 (2024).
[4] C. Hofer, D. Bausch, L. Fürst, Z. Wei, M. Högner, T. P. Butler, M. Gebhardt, T. Heuermann, C. Gaida, K. S. Maiti, M. Huber, E. Fill, J. Limpert, F. Krausz, N. Karpowicz, and I. Pupeza, "Linear field-resolved spectroscopy approaching ultimate detection sensitivity," Opt. Express 33, 1 (2025).
[5] H. Carstens, N. Lilienfein, S. Holzberger, C. Jocher, T. Eidam, J. Limpert, A. Tünnermann, J. Weitenberg, D. C. Yost, A. Alghamdi, Z. Alahmed, A. Azzeer, A. Apolonski, E. Fill, F. Krausz, and I. Pupeza, "Megawatt-scale average-power ultrashort pulses in an enhancement cavity," Optics Letters 39, 2595 (2014).
[6] N. Lilienfein, C. Hofer, M. Högner, T. Saule, M. Trubetskov, V. Pervak, E. Fill, C. Riek, A. Leitenstorfer, J. Limpert, F. Krausz, and I. Pupeza, "Temporal solitons in free-space femtosecond enhancement cavities," Nature Photon 13, 214–218 (2019).
[7] P. Sulzer, M. Högner, A.-K. Raab, L. Fürst, E. Fill, D. Gerz, C. Hofer, L. Voronina, and I. Pupeza, "Cavity-enhanced field-resolved spectroscopy," Nat. Photon. 16, 692–697 (2022).