Stimulated Raman versus Inverse Raman: Investigating Depletion Mechanisms for Super-Resolution Raman Microscopy

Area of Science:

• Optical microscopy
• Spectroscopy
• Nanotechnology

Background:

• Fluorescence microscopy enables nanoscale biological imaging but faces challenges with fluorescent labels.
• Label-free super-resolution techniques are highly desirable to overcome these limitations.
• Stimulated Raman scattering (SRS) microscopy offers a label-free approach, with stimulated Raman depletion microscopy (SRDM) achieving super-resolution.

Purpose of the Study:

• To conclusively demonstrate the suppression mechanisms in SRDM.
• To contrast super-resolution Raman microscopy approaches on Stokes and anti-Stokes sides.
• To establish inverse Raman scattering (IRS) as a basis for super-resolution imaging.

Main Methods:

• Utilized a toroidally shaped beam to deplete SRS signal at the focal spot edges.
• Monitored depletion of SRS and inverse Raman scattering (IRS) signals across varying depletion powers.
• Investigated four-wave coherent Raman pathways induced by a femtosecond depletion beam.

Main Results:

• Conclusively demonstrated the suppression mechanisms responsible for super-resolution in SRDM.
• Observed additional four-wave coherent Raman pathways upon introduction of the depletion beam.
• Showcased the depletion of IRS signal, validating inverse Raman depletion microscopy (IRDM).

Conclusions:

• SRDM's suppression mechanisms are now clearly understood.
• IRDM is established as a viable super-resolution imaging technique.
• Combined SRDM and IRDM provide versatile, label-free super-resolution imaging across a wide spectral range.