Size and Refractive Index Determination of Single Polystyrene Spheres

Area of Science:

• Optical physics
• Materials science
• Nanotechnology

Background:

• Accurate characterization of dielectric spheres is crucial for various scientific and industrial applications.
• Mie theory provides a theoretical framework for understanding light scattering from particles.

Purpose of the Study:

• To develop and validate a precise method for determining the radius and refractive index of dielectric spheres.
• To assess the accuracy and identify sources of error in light scattering measurements for particle characterization.

Main Methods:

• Measuring the angular intensity of polarized light scattered from dielectric spheres.
• Fitting experimental data to Mie theory calculations using least-squares methods.
• Utilizing a He-Cd laser (λ=441.6 nm) for illumination and analyzing particles with radii from 117-1175 nm.

Main Results:

• Determined sphere radii with a precision of 0.2% and accuracy of 0.9% for a 457 nm particle.
• Obtained refractive indices within 1% of the bulk value (1.615).
• Identified angular scattering discrepancies as the primary error source, which was mitigated by calibration.

Conclusions:

• Light scattering measurements combined with Mie theory offer a highly accurate technique for dielectric sphere characterization.
• The developed method provides reliable determination of particle radius and refractive index, surpassing manufacturer specifications.
• Calibration of the scattering angle is critical for maximizing measurement precision and accuracy.