Fig. 2: CAHRS spectra of PNA solution.

a, b Raw observed spectra from PNA solution (red lines) and neat chloroform solvent (black lines). c, d Intensity-corrected spectra of PNA solution by dividing the raw spectra of PNA solution by those of neat chloroform. e, f Spontaneous HR spectra of the PNA solution. Spectral ranges of a, c, and e are around 1350 cm⁻¹, and b, d, and f are around 850 cm⁻¹. In the CAHRS measurements, the powers of the ω₁ and ω₂ lights were 60 and 5 mW, the exposure times were 1 s, and 10 exposures were averaged. In the spontaneous HR measurements, the power of the excitation light was 50 mW, the exposure time was 10 s, and 10 exposures were averaged.