Envelope and waveguide methods: a comparative study of PbF(2) and CeO(2) birefringent films

Area of Science:

• Materials Science
• Optical Engineering
• Thin Film Physics

Background:

• Optical characterization of thin films relies on models to interpret measurements.
• Isotropic models assume uniform optical properties in all directions.
• Microstructure of deposited films can deviate from ideal isotropic behavior.

Purpose of the Study:

• To investigate the validity of the isotropic optical model for thin films.
• To compare optical characterization methods for thin films.
• To determine the optical properties of obliquely deposited cerium oxide (CeO2) films.

Main Methods:

• Characterization of low-birefringence lead fluoride (PbF2) coatings.
• Comparison of envelope and prism-coupler waveguide methods.
• Optical analysis of obliquely deposited CeO2 coatings (58.3°).
• Application of uniaxial and biaxial optical models.

Main Results:

• Agreement between envelope and waveguide methods was achieved for PbF2 under the isotropic assumption.
• The isotropic model failed for obliquely deposited CeO2 coatings.
• Consideration of film microstructure improved correlation between TE and TM modes for thickness.
• Refractive indices from envelope and waveguide methods were consistent when accounting for microstructure.

Conclusions:

• The microstructure of obliquely deposited films significantly impacts optical properties.
• Advanced optical models (uniaxial, biaxial) are required for accurate characterization of anisotropic films.
• Accurate determination of refractive indices requires consideration of film anisotropy.