Fig. 5: Signal-to-noise ratio (SNR) of dual-comb photoacoustic spectroscopy.

a Time-domain SNR of the PA signal as a function of averaging time for the VACNTs at an incident optical power of 18 mW (black triangles), paraffin at an incident power of 24 mW (blue diamonds), and PDMS at an incident power of 24 mW (red circles). The solid green lines are fits to the data according to \({\mathrm{SNR}} = {{A}} \times \sqrt \tau\), where τ is the averaging time and A is a fit parameter. b Time-domain SNR of the PA signal for the VACNT target as a function of optical excitation power at a fixed averaging time of 61 s (triangles) and a linear fit to optical excitation power (green line). In these measurements, spectral SNRs are roughly the same as time-domain SNRs. For comparison, a time-domain SNR of 32 for paraffin transforms to a peak spectral SNR of 45. This scaling changes slightly depending on the spectrum. As discussed in Supplementary Note 1, the spectral SNR at optical frequency v is defined as the mean magnitude of the PA response at v divided by the standard deviation of the PA response at v over many repeated measurements.