A New Method for Determining the Optical Constants of Highly Transparent Solids

Area of Science:

• Materials Science
• Optical Physics
• Spectroscopy

Background:

• Accurate optical constants are crucial for transparent substrates used in various applications.
• Existing methods like ellipsometry (EM) and double optical pathlength transmission method (DOPTM) have limitations in measuring weak absorption indices and resolving solution ambiguities.

Purpose of the Study:

• To present a novel combined technique (DOPTM-EM) for precise optical constant determination of highly transparent substrates.
• To overcome the deficiencies of individual DOPTM and EM methods, particularly for weak absorption indices.

Main Methods:

• A hybrid approach combining ellipsometry (EM) for initial optical constant estimation.
• Utilizing the double optical pathlength transmission method (DOPTM) with EM-derived values as initial inputs for gradient-based inverse method.
• Simultaneous retrieval of refractive and absorption indices without Kramers-Kronig relation.

Main Results:

• The DOPTM-EM successfully determined optical constants for polycrystalline BaF₂, CaF₂, and MgF₂.
• Accurate measurement of refractive and absorption indices was achieved across a broad spectral range (0.2-14 µm).
• The method ensures retrieval of unique, true optical constants by resolving ambiguities present in DOPTM alone.

Conclusions:

• The combined DOPTM-EM technique provides a robust solution for accurate optical constant measurement of highly transparent materials.
• This method enhances precision, especially in the transparent spectral region where absorption indices are weak.
• The developed technique facilitates broader research and application development involving transparent substrates.