Figure 3. Characterization of water environments using hyperspectral stimulated Raman Spectroscopy.

A, SRS microscopy illustration. The pump laser beam and modulated Stokes laser beam are combined and focused onto the sample. When the energy difference between the pump and the Stokes laser matches the vibrational energy (${\mathrm{\omega }}_{\text{vib}}$) of the chemical bond of interest, the vibrational transition is accompanied by stimulated Raman loss (SRL) on the pump beam and stimulated Raman gain (SRG) on the Stokes beam. SRL on the pump beam is detected by the photodiode and extracted by the lock-in amplifier for SRS imaging.

B, Hyperspectral SRS mapping of water heterogeneity in condensates with ratiometric SRS images (I(3250 cm⁻¹) /I(3450 cm⁻¹) shows the relative abundance of tetrahedral water to distorted water. Scale bar, 3 μm.

C, Hyperspectral SRS mapping of water heterogeneity in condensates with ratiometric SRS images (I(3650 cm⁻¹) /I(3450 cm⁻¹) shows the relative abundance of free water to distorted water. Scale bar, 3 μm.

D, Hyperspectral SRS mapping of water heterogeneity in condensates with images shows the averaged OH frequency $<\omega >$ . Scale bar, 3 μm.

E, Quantitative analysis of averaged OH frequency $<\omega >$ for the interfaces of different condensates.

F, Quantitative analysis of averaged OH frequency $<\omega >$ for the dense phase of different condensates. Unpaired T-test shows the p-value.