Quantum theory of stimulated Raman scattering microscopy.

Area of Science:

• Spectroscopy
• Microscopy
• Quantum Optics

Background:

• Stimulated Raman scattering (SRS) microscopy visualizes chemical bonds with high sensitivity and speed.
• A rigorous theoretical framework explaining SRS microscopy's advantages over conventional Raman microscopy is lacking.
• Traditional understanding of Raman scattering's weakness is incomplete due to differing light-matter interaction orders.

Purpose of the Study:

• To present a recently developed stimulated response formulation for SRS microscopy.
• To quantitatively explain why and how much SRS microscopy outperforms conventional Raman microscopy.
• To unify spontaneous and stimulated emission and Raman processes.

Main Methods:

• Summarizing the stimulated response formulation, defining the stimulated Raman cross section (σSRS) analogous to Einstein's B coefficient.
• Comparing σSRS with the traditional Raman cross section (σRaman) and linear absorption cross sections.
• Utilizing experimental measurements and quantum electrodynamic theories to support the formulation.

Main Results:

• The stimulated Raman cross section (σSRS) is intrinsically strong, potentially exceeding electronic counterparts.
• A duality in Raman scattering is revealed, where σRaman and σSRS magnitudes differ for the same molecule.
• The formulation unifies four optical processes and predicts absolute signal and detectability in SRS microscopy.

Conclusions:

• SRS microscopy excels in high spatiotemporal regimes, enabling superior chemical bond imaging.
• The new theoretical framework provides quantitative predictions and explains SRS microscopy's high performance.
• This theory is expected to advance both the scientific understanding and technological applications of Raman spectroscopy.