Optimization of azimuth angle settings in polarizer-compensator-sample-analyzer off-null ellipsometry.

Area of Science:

• Optical Physics
• Materials Science
• Surface Science

Background:

• Ellipsometry is a powerful technique for characterizing thin films and surfaces.
• Off-null intensity measurements in ellipsometry are sensitive to sample property variations.
• Azimuth angle settings critically influence measurement sensitivity and data interpretation.

Purpose of the Study:

• To investigate the dependence of azimuth angle settings on off-null intensity changes in ellipsometry.
• To derive expressions for optimizing azimuth angles for maximum sensitivity to sample property variations.
• To validate derived approximations and optimization strategies using numerical and experimental data.

Main Methods:

• Derivation of a closed-form expression for null condition azimuth angles.
• Approximation of off-null light intensity near null for small changes in reflection coefficients.
• Development of expressions for optimal azimuth angles yielding maximum intensity change.
• Numerical simulations and experimental verification using porous silicon gas sensors.

Main Results:

• Off-null intensity changes near null are primarily governed by ellipsometric parameters tan psi and A.
• Optimal azimuth angles maximize the intensity change for specific sample property variations.
• Sensitivity optimization is dependent on the ellipsometric parameter tan psi.
• Experimental results confirm the validity of derived approximations and optimization methods.

Conclusions:

• Optimized azimuth angle settings are essential for maximizing sensitivity in ellipsometric measurements.
• The derived expressions provide a framework for selecting optimal angles for diverse sample characterization.
• This approach is particularly valuable for applications like gas sensing where subtle sample changes occur.