Mid-Infrared Optical Photothermal Interferometric Microscopy of Substrate-Supported Samples

Area of Science:

• Microscopy
• Spectroscopy
• Optical Physics

Background:

• Existing scattering-based models for optical photothermal mid-infrared (O-PTIR) microscopy are computationally complex for non-spherical samples.
• Accurate interpretation of image contrast in O-PTIR microscopy requires advanced theoretical frameworks.

Purpose of the Study:

• To propose and experimentally validate an interferometry model for O-PTIR microscopy.
• To develop a computationally tractable model for analyzing thin-film samples on substrates.
• To enhance signal-to-noise ratios and information content in O-PTIR measurements.

Main Methods:

• Development of a thin-film interferometry model for O-PTIR microscopy.
• Experimental evaluation of the model using localized, transient heat deposition.
• Analysis of both time-averaged (DC) and photothermally induced (AC) reflectivity changes.
• Comparison of measurements on silicon and calcium fluoride substrates.

Main Results:

• The proposed optical photothermal interferometry analysis (OPTIA) model accurately interprets O-PTIR measurements.
• Absolute thickness of individual Synechocystis colonies was recovered.
• Significant signal-to-noise enhancements were observed on silicon substrates due to interference effects.
• The model predicted and confirmed enhanced contributions from optical interference.

Conclusions:

• The OPTIA model provides a robust method for analyzing O-PTIR data from substrate-supported samples.
• Interference effects can be leveraged to significantly improve O-PTIR measurement sensitivity and information yield.
• This work lays the groundwork for new O-PTIR measurement strategies exploiting native interferometry.