Theory of mid-infrared absorption microspectroscopy: II. Heterogeneous samples.

Area of Science:

• Spectroscopy
• Microscopy
• Optical Physics

Background:

• Fourier transform infrared (FT-IR) spectroscopic imaging integrates optical microscopy with vibrational spectroscopy.
• Data in FT-IR imaging can be influenced by optical setup, sample shape, and material properties.
• A quantitative model is needed to predict these dependencies.

Purpose of the Study:

• To develop a theoretical framework for predicting sample-induced optical and spectral distortions in FT-IR spectroscopic imaging.
• To establish a quantitative understanding of how sample morphology and optical properties influence recorded data.

Main Methods:

• Combined rigorous coupled wave analysis (RCWA) with models for sampling geometry and sample structure.
• Systematically explored the interplay of morphology and dispersion using varied sample complexities.
• Quantified spectral distortions predicted by the model.

Main Results:

• Developed a theory relating recorded FT-IR imaging data to sample spectral and physical properties.
• Demonstrated the dependence of detected optical intensity on spatial sample structure.
• Experimentally validated the theory using a microfabricated photoresist polymer standard.

Conclusions:

• The developed framework provides a basis for understanding sample-induced distortions in spectroscopic IR microscopy and imaging.
• Enables more accurate interpretation of FT-IR imaging data from heterogeneous samples.
• Facilitates the correction of spectral distortions caused by sample morphology.