Extended Data Figure 1: Apparatus of SRS microscopy.
A narrow-band pump laser (5–6 ps pulse width) and an intensity-modulated Stokes laser (fixed at 1,064 nm, 6-ps pulse width) are temporally and spatially synchronized before collinearly focused onto cell samples. When the energy difference between the pump photons and the Stokes photons matches the vibrational frequency (ωvib) of the targeted chemical bonds, the chemical bonds are efficiently excited to the vibrational excited state. For each transition, a photon in the pump beam is annihilated (stimulated Raman loss) and a photon in the Stokes beam is created (stimulated Raman gain). A lock-in detection scheme is used to sensitively measure the intensity loss of the pump beam (that is, stimulated Raman loss).
