Field-Resolved Optical Precision Metrology

Prof. Ioachim Pupeza

Email: ioachim.pupeza@rptu.de
Phone: +49 631 205-2315

Prof. Pupeza's group develops techniques for infrared field-resolved spectroscopy (IR-FRS) of molecular vibrations, aiming to approach the ultimate sensitivity and precision limits set by the nature of light. In close collaboration with biologists and physicians, we translate the results of this fundamental research in the field of photonics into novel tools and technologies for addressing biomedical questions. These include high-throughput IR-FRS flow cytometry, high-resolution FRS spectroscopy of gases, and sub-wavelength IR-FRS microscopy of living systems. Ioachim Pupeza holds a chair of Experimental Physics at the RPTU in Kaiserslautern, and leads research groups at the Leibniz-IPHT and Fraunhofer ITWM.

A waveform-stable, few-cycle infrared pulse (upper beam) is focused onto a microfluidic chip through which cells flow at high speed. Upon transmission through the microfluidic chip, the pulse interacts with a cell, and the excitation is followed by the coherent response of the sample (lower beam). This "infrared fingerprint" carries quantitative information on both the chemical composition, and the geometry of the cell. Field-resolved spectroscopy (FRS) reads this fingerprint on the level of the oscillating electric field of light. Due to its unparalleled sensitivity and linear detection dynamic range, FRS allows for label-free infrared fingerprinting of cells in their native, aqueous state at high speed for the first time.
Image: privat

Research Areas

At heart of our experimental setups lies the generation of few-cycle, high-power, waveform-stable infrared pulses. We target high pulse repetition rates (> 10 MHz) affording short measurement times and, thus, improved statistics. Our IR radiation sources are based on intra-pulse difference-frequency generation [1,2,3,4], and have reached world records in terms of brilliance for broadband coherent sources. Further development envisages the coverage of the entire molecular fingerprint region with powerful, few-cycle pulses.

The optical waveforms associated with the response of matter to the excitation with these waveforms are measured via electro-optic sampling (EOS) involving their nonlinear mixing with an ultrashort gate pulse in a crystal. Our group has pioneered EOS with powerful, short-wave mid-IR gate pulses [1]. This enables record photon detection efficiencies over bandwidths spanning more than one octave in the molecular fingerprint region [5]. Because the electric-field strength scales with the square root of the number of photons, this implies an unprecedented measurement sensitivity of within one order of magnitude from the ultimate limit for – potentially single-cycle – optical electric fields.

In close collaboration with the Jena University hospital, and within the Excellence Cluster "Balance of the Microverse", we are exploring the first applications of these novel techniques to unmet medical needs, such as theranostics of life-threatening infections.

Link to the Laboratory for Lightwave Metrology at the TU KaiserslauternExternal link

[1] Pupeza et al., Nature Photon. 9, 721 (2015).
[2] Pupeza et al., Nature 577, 52 (2020).
[3] Butler et al., Opt. Lett. 44, 1730 (2019).
[4] Butler et al., J. Phys: Photonics 1, 044006 (2019).
[5] Hofer et al., Opt. Express 33, 1 (2025).