Performance of low-coherence and confocal refractometry with reduced index contrast

Area of Science:

• Optical Metrology
• Biomedical Optics

Background:

• Accurate measurement of refractive index and thickness is crucial for optical systems.
• Low refractive index contrast presents challenges for traditional measurement techniques.

Purpose of the Study:

• To evaluate the performance of combined low-coherence and confocal refractometry.
• To assess measurement accuracy under conditions of reduced refractive index contrast.

Main Methods:

• Utilized a fibre-based low-coherence interferometer with a line-scan spectrometer.
• Designed a sample mimicking the eye's on-axis structure with varying sucrose concentrations.
• Simultaneously measured phase and group refractive indices (n_p, n_g) and physical thickness (t).

Main Results:

• The instrument successfully measured refractive index and thickness of transparent components.
• Measurement accuracy decreased with reduced refractive index contrast.
• Accuracy remained better than 0.6% for sucrose concentrations up to 60.3%.

Conclusions:

• Combined low-coherence and confocal refractometry is effective for measuring transparent objects.
• The system demonstrates robust performance even with challenging low refractive index contrast conditions.
• The developed method shows potential for applications requiring precise optical property measurements.