Metallic Nanostructures are giving rise to a great deal of attention from a broad scientific community, ranging from physicist and electrical engineers to biologists. The interest is growing rapidly in finding novel devices for future applications that allow using metallic waveguides for optical signal transmission and processing. In this contribution, we investigate some of the fundamental phenomena that take place in these systems. Also the extraordinary transmission of light though sub-wavelength holes in a metal is investigated, keeping in mind various potential biophotonics applications. In this paper, we demonstrate an optical nano-imaging technique that is particularly well suited to characterize the near-field interaction of light with metallic nanostructures: coherent near-field microscopy. This technique allows the total characterization of the near-field by giving full access to its amplitude and its phase. Its application to the characterization and study of plasmonic nanostructures is illustrated using several systems, the coherent near-field optical measurements of light transmission though sub-wavelength holes drilled in a gold thin film and surface plasmons propagating on a metal film and its interaction at a metal-air interface.
A coherent scanning near-field optical microscope (SNOM) is presented. The set-up employs heterodyne interferometry, allowing measurements of both amplitude and phase of the optical field. Experimental results show polarization effects that reveal important information about the vectorial field conversion by the fiber tip.
Proc. SPIE. 5181, Wave Optics and Photonic Devices for Optical Information Processing II
KEYWORDS: Waveguides, Near field scanning optical microscopy, Near field optics, Femtosecond phenomena, Nanophotonics, Photonic crystals, Near field, Nanostructures, Heterodyning, Light wave propagation
Nanoscale science is playing an increasingly important role in developing future technologies for information systems including computing, telecommunications, display, high-resolution imaging and sensing. Optical and photonic technologies are recognized as enablers in most of these applications. However, construction of artificially engineered nanostructured optical and optoelectronic materials, resonant nanostructures such as photonic crystals, and integrated nanophotonic active and passive devices is one of the most challenging tasks. In order to improve device performance, good characterization tools for structural and functional testing of nanophotonic devices are required. One technique that may be promising for improving visualization, imaging, and characterization tools is based on coherent Near-field Scanning Optical Microscopy (NSOM). This instrument enables quantitative detection of the complex amplitude of the optical near-field of various nanophotonic devices on nanoscale. Amplitude, phase and topography are measured simultaneously by combining an NSOM and a heterodyne interferometer. Its continuous wave (CW) design has been extended with ultra-short femtosecond laser pulses at 1550 μm to investigate phenomena in the optical near field with femtosecond time resolution. The evanescent light of a short pulse has been observed in a waveguide, allowing the investigation of both its spatial and temporal device characteristics.
An electromagnetic field is characterized by an amplitude, a phase and a polarization state. In this paper, we intend to gain an understanding of the interaction of light with microstructures in order to determine their optical properties. Measurements of the amplitude and phase close to gratings are presented using a heterodyne scanning probe microscope. We discuss some basic properties of phase distributions. Indeed, coherent light diffracted by microstructures can give birth to phase dislocations, also called phase singularities. Phase singularities are isolated points where the amplitude of the field is zero. The position of these special points can lead us to information about the structure (shape, surface defects, etc), by comparing with rigorous diffraction calculation using e.g. the Fourier Modal Method (FMM). We present high-resolution measurements of such phase singularities and compare them with theoretical results. Polarization effects have been studied in order to understand the field conversion by the fiber tip.