Focusing light through spherical interface for subsurface microscopy

Abstract

Focusing and directing lights have numerous applications in most of scientific and technological areas. The first part of this thesis reviews and develops an efficient method based on multipole expansions for studying the focused field of polarized light, including radially-polarized and other important cases. We compare and highlight the differences between our method with the well-known Debye-Wolf diffraction integrals for calculating the field in the focal region. We also decompose a focused beam into a converging beam and a diverging beam and discuss their implications in focusing beyond diffraction limit.

In the second part of this thesis, we give a novel interpretation of the scattering mechanism for particles in a focused beam. Light scattering by a spherical particle represents a classical topic. The generalized Lorenz-Mie theory (GLMT) has been well developed for analyzing the scattering effects. However, the GLMT is not able to account for the multiple reflections inside the scatterer. Through our interpretation, we derive a series for taking into account the multiple reflections in a simple and straightforward way. Our series not only explains the scattering mechanism well but also helps to solve the boundary conditions at a spherical interface rigorously.

Solid immersion microscopy (SIM) provides a high spatial resolution and optical collection efficiency, which are the most desirable properties of nearly all optical systems. The SIM has been developed and improved both theoretically and experimentally for the last 3 decades. Recently, it is becoming more and more important in identifying faulty locations in integrated circuits that, as predicted by the well-known Moore's law, are getting smaller and denser. In the third part of this thesis, we study the SIM both theoretically and experimentally. Theoretically, we form a rigorous analytical model for studying the focal field of the SIM and correct errors of the existing models. Experimentally, we manipulate binary masks and polarization of light to resolve gratings consisting of 120-nm-wide lines, spaced 120 nm apart, using 1342nm wavelength laser.