Measuring the complex field scattered by single submicron particles

Marco A C Potenza,Tiziano Sanvito,Alberto Pullia

doi:10.1063/1.4935927

Abstract

We describe a method for simultaneous measurements of the real and imaginary parts of the field scattered by single nanoparticles illuminated by a laser beam, exploiting a self-reference interferometric scheme relying on the fundamentals of the Optical Theorem. Results obtained with calibrated spheres of different materials are compared to the expected values obtained through a simplified analytical model without any free parameters, and the method is applied to a highly polydisperse water suspension of Poly(D,L-lactide-co-glycolide) nanoparticles. Advantages with respect to existing methods and possible applications are discussed.

Highlights

Methods for characterizing physical properties of nanoparticles are of increasing importance for research and industry
We describe a method for simultaneous measurements of the real and imaginary parts of the field scattered by single nanoparticles illuminated by a laser beam, exploiting a self-reference interferometric scheme relying on the fundamentals of the Optical Theorem
In the rest of the paper, we present an analytical model describing the system without any free parameters and show experimental results obtained with calibrated spheres of different materials, comparing the complex fields recovered from the experimental data to rigorous Mie theory calculations

Summary

INTRODUCTION

Methods for characterizing physical properties of nanoparticles are of increasing importance for research and industry. Traditional optical methods for measuring the size of single particles are based on the fundamentals of light scattering, typically the dependence of the scattering cross section Csca upon the particle radius a and the wavelength λ. The extinction cross section Cext, which gives the total power removed by both scattering and absorption, can be obtained just by measuring the reduction of the incoming light beam when the particle lies across its path. This is done through another class of instruments that is commercially available, the Single Particle Obscuration Sensor (SPOS).[2]. The reliability of the system when operating with polydisperse samples, we report experimental results obtained with a suspension of Poly(D,L-lactide-co-glycolide) nanoparticles

SINGLE PARTICLE EXTINCTION AND SCATTERING

Fundamentals of the method

Measuring the complex field

Validation of the particle position in the beam

EXPERIMENTAL RESULTS

CONCLUSIONS