High-spectral-resolution quantum Fourier-transform infrared spectroscopy with pulsed laser excitation

Quantum infrared spectroscopy (QIRS), which uses quantum interference of the generation processes of photon pairs, enables infrared spectroscopy using visible light sources and detectors. Until recently, continuous wave (cw) lasers with a narrow linewidth have been used for excitation in most QIRS experiments. Although the use of pulsed laser pumping is attractive, it has been expected that the inherent finite linewidth of pulsed lasers may degrade the spectral resolution of QIRS. Here, we show that this is not always true. The theoretical analysis shows that the resolution of quantum Fourier transform infrared (QFTIR) spectroscopy is not affected by the linewidth of the pump laser. To verify this, we construct an experimental setup for QFTIR spectroscopy using both cw and pulsed laser excitation under the same experimental conditions. High-resolution spectra are successfully obtained for a silicon parallel plate and an acetylene gas cell as samples using a pulsed pump laser with a finite linewidth, and no resolution degradation is observed compared to the case of cw pumping. These results will open up the use of QFTIR spectroscopy using visible light sources and detectors in novel applications including high-speed time-resolved infrared spectroscopy, which will be beneficial for various fields including physics, chemistry, and environmental science.