Refractive index measurements of multiple layers using numerical refocusing in FF-OCT

Area of Science:

• Optical Physics
• Metrology
• Materials Science

Background:

• Refractive index (RI) and thickness are critical material properties.
• Measuring these properties in multilayered samples can be challenging.
• Full Field Optical Coherence Tomography (FF-OCT) offers non-invasive imaging capabilities.

Purpose of the Study:

• To develop and demonstrate a novel method for measuring the RI and thickness of individual layers in multilayered samples.
• To utilize numerical refocusing in FF-OCT for this purpose.
• To validate the method's accuracy and reliability.

Main Methods:

• Employing numerical refocusing by adjusting the image sensor plane in FF-OCT.
• Calculating sample shift and comparing it with actual shift to determine layer RI.
• Extracting layer thickness simultaneously with RI measurement.
• Preparing multilayered samples with varying materials and refractive indices.

Main Results:

• Accurate measurement of refractive indices for oils ranging from 1.2977 to 1.3857, with agreement within 0.205% of reported values.
• Successful extraction of oil RI and physical thickness from multilayered stacks with average errors of 0.065% and 0.990%, respectively.
• Demonstrated capability to measure properties of individual layers within complex stacks.

Conclusions:

• The proposed numerical refocusing method in FF-OCT is effective for precise RI and thickness determination of layers in multilayered samples.
• This technique offers a significant advancement for material characterization in various scientific and industrial applications.
• The method shows high accuracy and robustness even with complex sample structures.