Tim Schönwald has successfully completed his MSc in our group at RPTU. The thesis, titled “Numerical and Experimental Study of Noise Mitigation Techniques toward Quantum-Limited Grating- and Fourier-Transform Infrared Spectroscopy”, investigates sensitivity and dynamic-range limits of infrared spectroscopy in theory and experiment.
In the frame of his thesis, developed a 1-µm Fourier-transform infrared (FTIR) setup that combines balanced homodyne signal amplification with numerical lock-in detection, achieving near shot-noise-limited balanced detection. The system is capable of detecting signals at the few-photon level while simultaneously maintaining a linear detection dynamic range of 13 orders of magnitude in signal power. To validate and contextualize these findings beyond the scope of the laboratory, a noise-aware digital twin model—building on Maximilian Högner’s implementation—was extended to accurately reproduce the experimental setup, thereby supporting and explaining the observed results.
Balanced homodyne detection (BHD) setup schematic and laboratory photograph. The system comprises the main BHD beamline and a delay-calibration interferometer, which is split off before sample attenuation to provide an unattenuated reference waveform for numerical lock-in detection.
In parallel, a balanced grating-based single-shot spectrometer was developed using a femtosecond-pulsed laser and a segmented photodiode array. This setup demonstrated signal-to-noise improvement through detector-segmentation-based balancing and investigated non-linear spectral broadening in fused silica plates, paving the way for future implementations of time-domain pulse compression and nonlinear-optics-based spectroscopy techniques.
Tim will continue as a PhD student with the Laboratory for Lightwave Metrology. His research will focus on extending these findings into the mid-infrared spectral region, where many fundamental molecular vibrations occur and where quantum-limited detection promises particularly high impact for chemical and biomedical sensing. His work will address the development and implementation of novel single-shot electro-optic sampling (EOS) techniques, enabling the direct probing of ultrafast field dynamics. By combining broadband mid-infrared generation with EOS-based detection, the research aims to capture transient processes on femtosecond timescales, providing a powerful platform for advancing both fundamental studies of light-matter interaction and future applications in real-time spectroscopy and molecular diagnostics.