Depth profiles in confocal optical microscopy: a simulation approach based on the second Rayleigh-Sommerfeld...

Area of Science:

• Optical Microscopy
• Spectroscopy
• Materials Science

Background:

• Confocal Raman microscopy is a powerful tool for chemical analysis.
• Accurate depth profiling is crucial for understanding material properties.
• Existing methods can be limited by optical effects like refractive index mismatch.

Purpose of the Study:

• To develop a theoretical framework for recovering intensity depth profiles in transparent samples using confocal optical microscopy.
• To accurately model the response function of a confocal Raman microscope, accounting for optical aberrations.
• To enable precise reconstruction of chemical species distribution within samples.

Main Methods:

• Utilized the second Rayleigh-Sommerfeld diffraction integral and scalar wave optics.
• Incorporated refractive index mismatch between sample and objective lens medium.
• Employed an iterative multi-fitting scheme (conjugate gradient and Brent algorithm) for simultaneous depth profile fitting.

Main Results:

• The developed model accurately describes the effect of refractive index mismatch on Raman signals.
• The method achieved discrepancies lower than 3% when compared to experimental measurements.
• Successfully retrieved beam waist, signal amplitude, and sample surface position.

Conclusions:

• The theoretical procedure provides an accurate method for Raman depth profiling in transparent samples.
• This work is a significant step towards solving the inverse problem in micro-Raman depth profiling.
• The framework is amenable to simple numerical implementation for reconstructing chemical profiles.