Spectroscopic Optical Coherence Tomography for Thin Layer and Foil Measurements

Area of Science:

• Metrology
• Optical Engineering
• Materials Science

Background:

• Standard optical coherence tomography (OCT) systems have limitations in resolving the thickness of very thin layers and foils.
• Accurate thickness assessment is crucial for various applications in materials science and engineering.
• Existing methods often struggle with subsurface layers or layers beneath other materials.

Purpose of the Study:

• To develop and validate a novel OCT-based method for evaluating the thickness of thin layers and foils.
• To assess the feasibility of measuring layer thickness beyond the standard resolution limits of commercial OCT systems.
• To enable thickness measurement of layers located below the surface or covered by other materials.

Main Methods:

• Modeled the OCT system as a two-beam interferometer, incorporating a Fabry-Pérot interferometer within the measurement arm.
• Analyzed the backscattered light from thin layers as multiple beam interference to determine layer parameters.
• Evaluated layer thickness by identifying the minimum interference contrast, validated through experiments with wedge cells and thin foils.

Main Results:

• The developed mathematical model accurately predicts the behavior of thin layers with varying materials, thicknesses, and depths.
• Experimental verification confirmed the model's ability to measure thin film thickness based on interference contrast minima.
• The method successfully determined layer thickness and location, even for subsurface or covered layers.

Conclusions:

• The proposed OCT signal analysis method enhances metrological capabilities, allowing thickness evaluation below system resolution.
• This technique enables the measurement of covered layers and the creation of high-sensitivity thickness maps.
• The findings present a significant advancement for precise thickness assessment in thin films and foils.