Multiplicative and subtractive focal volume engineering in coherent Raman microscopy

Area of Science:

• Nonlinear optics
• Microscopy
• Spectroscopy

Background:

• Coherent Anti-Stokes Raman Scattering (CARS) microscopy enables vibrational imaging.
• Controlling excitation volumes is crucial for high-resolution CARS applications.
• Nonlinear excitation volumes often limit imaging fidelity.

Purpose of the Study:

• To investigate the reduction of nonlinear excitation volumes using phase-only masks.
• To explore the impact of excitation field manipulation on CARS imaging.
• To assess the potential for enhanced resolution and particle characterization.

Main Methods:

• Performing rigorous calculations for nonlinear excitation volumes.
• Utilizing phase-only masks to condition pump and Stokes driving fields.
• Employing multiplicative and subtractive operations on excitation fields.
• Using a tunable optical bottle beam for the Stokes field.
• Implementing phase-sensitive detection.

Main Results:

• Achieved effective reduction of the excitation volume width by a factor of 1.5 in the focal plane.
• Observed rapid sidelobe growth hindering further focal volume reduction for imaging.
• Demonstrated selective information retrieval from sub-divisions of the excitation volume.
• Showcased an apparent resolution improvement by a factor of 3 for isolated nanoparticles.
• Accurately determined the size of sub-diffraction-limited particles.

Conclusions:

• Phase-only masks offer a viable method for reducing CARS excitation volumes.
• Phase-sensitive detection provides enhanced resolution and metrology capabilities for nanoscale imaging.
• The engineered excitation volumes are suitable for specific imaging applications, particularly nanoparticle analysis.