Fig. 1: Basic principles and experimental setup of the single-photon DC-GIS scheme.

a Sketch of the basic principles of single-photon DC-GIS. The dual-comb signal with a time-domain duration of \(\Delta T\) is composed of a series of evenly spaced teeth in the radio frequency, which can be converted into a dual-comb spectrum by performing a Fourier transform (FT) operation. A series of mode-resolved spectral patterns form a dual-comb matrix to sequentially interrogate sample molecules. Then, a single-photon avalanche diode (SPAD) is used to detect the discrete photon signal and count the photon number of different dual-comb patterns after sample absorption. The response spectrum of the sample can be directly reconstructed from the dual-comb matrix measured in the reference arm and the photon-counting signal by ghost-imaging calculation. b Experimental setup of single-photon DC-GIS. The output of the seed continuous-wave (CW) laser is modulated by a single electro-optic modulator (EOM) to generate a dual-comb time-domain interference signal, which can directly generate a dual-comb source. An arbitrary waveform generator (AWG), which outputs different dual-comb waveforms, is used to drive the EOM generating different dual-comb spectral patterns. A tunable optical filter (TOF) is employed to avoid aliasing. The signal is split into two beams: one is directly incident on a fast photodetector (PD) as the reference signal, while the other is detected by a SPAD after passing through a variable attenuator (VA) and the sample. The data streams from the PD and the SPAD are digitized and recorded synchronously by a data-acquisition card (AlazarTech, ATS9350) for DC-GIS reconstruction.