Quantum Fourier Transform Infrared Spectroscopy: Evaluation, Benchmarking and Prospects

Abstract: Sensing with undetected photons has enabled new, unconventional approaches to Fourier transform infrared (FTIR) spectroscopy. Leveraging properties of non-degenerated entangled photon pairs, mid-IR information can be accessed in the near-IR spectral domain to perform mid-IR spectroscopy with silicon-based detection schemes. Here, we address practical aspects of vibrational spectroscopy with undetected photons using a quantum-FTIR (QFTIR) implementation. The system operates in the spectral range from around $3000~\mathrm{cm}^{-1}$ to $2380~\mathrm{cm}^{-1}$ (detection at around $12500~\mathrm{cm}^{-1}$) and possesses only $68~\mathrm{pW}$ of mid-IR probing power for spectroscopic measurements with a power-dependence of the signal-to-noise ratio of $1.5\cdot 10^{5}~\mathrm{mW}^{-1/2}$. We evaluate the system's short- and long-term stability and experimentally compare it to a commercial FTIR instrument using Allan-Werle plots to benchmark our QFTIR implementation's overall performance and stability. In addition, comparative qualitative spectroscopic measurements of polymer thin films are performed using the QFTIR spectrometer and a commercial FTIR with identical resolution and integration times. Our results show under which conditions QFTIR can practically be competitive or potentially outperform conventional FTIR technology.