An exact surface-integral approach for accurate interferometric microscopy of single nanoparticles

Area of Science:

• Optics and Photonics
• Materials Science
• Nanotechnology

Background:

• Accurate optical characterization of nanoscale materials is crucial for advanced applications.
• Traditional methods often rely on approximations, limiting precision.
• Phase-stepping interferometric microscopy offers high sensitivity but requires robust theoretical models.

Purpose of the Study:

• To develop a precise computational method for modeling the optical phase response of single nanowires.
• To enable highly accurate refractive index metrology of nanowires using phase-stepping interferometric microscopy.
• To assess the feasibility of measuring subwavelength nanowires and the robustness of the measurement technique.

Main Methods:

• A 2D half-plane surface-integral equation (SIE) approach was employed to model light scattering.
• The Helmholtz equation was solved exactly, avoiding ray-optic approximations.
• Simulations were performed for nanowires with varying radii and refractive indices under phase-stepping interferometric microscopy conditions.

Main Results:

• The SIE method enables precise refractive index metrology with a potential precision of 7 × 10⁻⁵.
• Nanowires with radii as small as 0.001λ can be measured.
• The method demonstrates robustness against variations in light source characteristics, illumination, and nanowire cross-section shape.

Conclusions:

• The developed SIE approach provides an exact and accurate method for optical phase response modeling of nanowires.
• This technique significantly advances the capabilities of refractive index metrology for nanoscale materials.
• Future work can extend this approach to simultaneous radius and refractive index measurements and arbitrary nanoparticle shapes.