Figure 2.

Vibrational imaging of lipids using coherent Raman scattering. (A) Spontaneous Raman spectra of oleic acid. The red solid line indicates asymmetric stretching vibrational mode of the carbon–hydrogen bond at 2,845 cm-1. (B) Schematic of excitation and detection for coherent Raman scattering. For both coherent anti-Stokes Raman scattering (CARS) and stimulated Raman scattering (SRS)imaging, a characteristic vibrational mode of the CH2 bond in lipids is excited with two incoming photons at the pump (ωp) and Stokes (ωs) frequency. Stimulated Raman loss (SRL) is detected as a loss in the pump intensity and stimulated Raman gain (SRG) is detected as a gain in the Stokes intensity. CARS is detected at the anti-Stokes frequency, ωAS.