Optical coherence refractometry

Area of Science:

• Optical Physics
• Materials Science

Background:

• Interferometric refractometry typically measures group index, limiting applications for scattering or soft materials.
• Surface-dependent measurements can introduce errors in refractive index determination.
• Noncontact and in situ measurement methods are desirable for many material characterization applications.

Purpose of the Study:

• To introduce a novel refractometry technique for measuring the phase refractive index of plane parallel samples.
• To enable bulk refractive index measurements of scattering and soft materials.
• To provide a noncontact and in situ compatible method for refractive index determination.

Main Methods:

• Utilized a low coherence interferometer at multiple angles of incidence.
• Adapted interferometric principles to measure phase refractive index instead of group index.
• Applied the technique to pure silica and a highly scattering resin slab.

Main Results:

• Successfully measured the phase refractive index of plane parallel samples, including scattering materials.
• Demonstrated the technique's capability for bulk, non-surface-dependent measurements.
• Compared results with standard critical angle refractometry, showing good agreement.

Conclusions:

• The novel low coherence interferometry approach enables accurate phase refractive index measurement of challenging scattering and soft samples.
• This technique offers a significant advancement over traditional methods, providing noncontact and in situ measurement capabilities.
• The method is validated by successful application to diverse materials like silica and resin slabs.