Refractive effects in coherent anti-Stokes Raman scattering microscopy

Area of Science:

• Chemical Imaging
• Optical Microscopy
• Spectroscopy

Background:

• Coherent Anti-Stokes Raman Scattering (CARS) microscopy offers high sensitivity and 3D resolution for vibrational imaging.
• CARS signal detection is known to be influenced by sample size and shape.
• The impact of refractive index mismatches on CARS signals requires further investigation.

Purpose of the Study:

• To investigate the effects of refractive index mismatches on CARS signals.
• To analyze the influence of surrounding medium's refractive index on backward- and forward-detected CARS signals.
• To understand how index mismatches affect signal localization within the sample.

Main Methods:

• Theoretical modeling using geometrical and wave optics.
• Experimental measurement of backward-CARS and forward-CARS (F-CARS) signals.
• Utilizing polystyrene beads of varying diameters in different refractive index solvents.

Main Results:

• Refractive index mismatches generate a backward-reflected F-CARS signal that typically dominates the detected backward signal.
• Simulations confirm that index mismatches alter the intensity of both forward- and backward-detected CARS signals.
• Signal maxima for forward- and backward-detected CARS occur at different positions along the optical axis when index mismatches are present.

Conclusions:

• Refractive index mismatches are a critical factor influencing CARS signal detection and interpretation.
• Understanding these mismatches is essential for accurate vibrational imaging with CARS microscopy.
• The findings provide insights into optimizing CARS microscopy for chemical species analysis.