Measuring optical phase singularities at subwavelength resolution

Abstract

We will present experimental and theoretical studies of optical fields with subwavelength structures, in particular phase singularities and coherent detection methods with nanometric resolution. An electromagnetic field is characterized by an amplitude, a phase and a polarization state. Therefore, experimental studies require coherent detection methods, which allow one to measure the amplitude and phase of the optical field with subwavelength resolution. We will present two instruments, a heterodyne scanning probe microscope (heterodyne SNOM) and a high resolution interference microscope (HRIM). We will review some earlier work using the heterodyne SNOM, in particular the measurement of phase singularities produced by a 1 µm pitch grating with 10 nm spatial sampling. Using the HRIM we have investigated the intensity and phase distributions (with singularities) in the focal region of microlenses. The measurements are compared with the results calculated by rigorous diffraction theory.

Detecting vortices in superconductors: Extracting one-dimensional topological singularities from a discretized complex scalar field

“…This method reduces the representation of a 3D field to a set of discrete 1D objects. Previously, parts of these techniques have been applied to trace vortices in small-scale 3D type-II superconductor data [18,19] and to find optical vortices in experimentally measured electromagnetic fields [20,21]. However, the target and scale of our application, the techniques for unwrapping the phase locally, the interpolation to more precisely describe the vortex object, the method for rapidly constructing a vortex object from a subgraph, the introduction of a compact and mesh-independent representation, and the general consideration of the computational efficiency of the extraction are unique to our work.…”

High Resolution Interference Microscopy: A Tool for Probing Optical Waves in the Far-Field on a Nanometric Length Scale

“…Other non-periodic structures that were investigated with the HRIM were microlenses [45]. The field distribution in the focal plane of microlenses is strongly modulated by diffraction due to a high N.A.…”

Submicro-optics: big effects on a small scale

“…The same microscope is also capable of measuring the phase distribution per plane i.e. acting as a Mach-Zehnder interferometer 8 . Obtaining highresolution, 3-D phase of a field provides even more information on the nature of the field created by an object.…”