We describe a new technique that incorporates polarization modulation into near-field scanning optical microscopy (NSOM) for nanometer scale polarimetry studies. By using this technique, we can quantitatively measure the optical anisotropy of materials with both the high sensitivity of dynamic polarimetry and the high spatial resolution of NSOM. The magnitude and relative orientation of linear birefringence or linear dichroism are obtained simultaneously. To demonstrate the sensitivity and resolution of the microscope, we map out stress-induced birefringence associated with submicrometer defects at the fusion boundaries of SrTiO3 bicrystals. Features as small as 150 nm were imaged with a retardance sensitivity of approximately 3 x 10(-3) rad.

We use a near-field scanning optical microscope to study optical transmission through a two-dimensional triangular photonic crystal. Spatial variations in the intensity of light coupled through the sample depend on the photon energy and the numerical aperture of the collection optics. We discuss the relationship between the observed dependence and the local structure of the optical modes in the crystal. Features in the data arising from modes with Fourier components inside and outside the first Brillouin zone can be distinguished by this technique. ͓S0163-1829͑97͒09816-0͔With the invention of photonic devices, the ability to frequency select and direct light on microscopic length scales is rapidly becoming a reality. One device that has recently attracted much interest is a periodic dielectric structure called a photonic crystal. 1 Spatial periodicity in this device leads, for instance, to coupling of the electromagnetic field modes of neighboring dielectric waveguides. This results in a nontrivial dispersion relation between the energy and wave vector of the allowed modes, i.e., a photonic band structure. Photonic crystals can be designed to transmit or reflect light in a specific range of frequencies, 1 and their properties are tunable by, for example, modification of their periodicity or index of refraction. Defect structures could be designed to introduce impurity bands not only in selected energy ranges, but also in spatial positions. The first demonstration of bandstructure effects in photonic crystals was in the mm-wave regime. 2 Since this proof of principle, much research effort has concentrated on making structures for visible and nearinfrared light. 1 Recently, photonic band-structure effects in the near-infrared and visible have been measured 3 in twodimensional ͑2D͒ photonic crystals made from nanochannel glass ͑NCG͒ arrays. 4 Photonic crystals have been studied by measuring bulk optical properties such as attenuation and transmission, and band-structure calculations have been used to model and predict these properties. 1 A more detailed understanding can be obtained by studying the microscopic properties such as the local density of photon states and electromagnetic mode structure. Here we demonstrate the use of a transmissionmode near-field scanning optical microscope ͑NSOM͒ to measure directly the spatial variations of light coupled through the sample. The resulting optical intensity distributions depend in part on the local mode structure in the photonic crystal.For a photonic device to be useful at optical frequencies, its lattice spacing must be of the same order as the optical wavelength ͑͒. Measuring optical properties within a unit cell therefore requires resolution higher than that provided by conventional, far-field, diffraction-limited techniques. In near-field scanning optical microscopy ͑also NSOM͒, optical resolution can be better than /10, 5 limited not by but rather by the size of the subwavelength aperture used as a probe. In the study of photonic materials, NSOM has been used to me...

We describe a non-contact, non-optical distance feedback control system for scanning probe microscopes that detects the surface damping of a vibrating probe. The feedback signal is derived from an electrical impedance change in a dithering piezoelectric element with attached scanning tip. The system incorporates an arbitrary-impedance bridge that maximizes detection sensitivity of the surface damping-induced impedance change as the tip approaches and interacts with the sample. In addition, an auxiliary circuit greatly improves reliability by making the feedback signal insensitive to the phase of the impedance change. The complete detection network can sense changes of −80 to −100 dB down to the level of 1 μV in a bandwidth of ≳1 kHz. The feedback system has demonstrated topographic height sensitivity of ∼0.5 Å and dynamic range of ≳60 dB.

Using near-field scanning optical microscopy (NSOM), we observe an inhomogeneous distribution of submicron-sized structural defects at the fusion boundary of polished SrTiO3 bicrystal substrates. Both NSOM and scanning force microscopy show that these substrate defects cause the grain boundary of a YBa2Cu3O7 thin film grown on the bicrystal to wander up to a micron in the film. These structural defects are shown to correlate qualitatively with the electrical characteristics of grain-boundary Josephson junctions patterned on the YBa2Cu3O7 film.

While near-field scanning optical microscopy (NSOM) can provide optical images with resolution much better than the diffraction limit, analysis and interpretation of these images is often difficult. We present a theory of imaging with transmission NSOM that includes the effects of tip field, tip/sample coupling, light propagation through the sample and light collection. We apply this theory to analyze experimental NSOM images of a nanochannel glass (NCG) array obtained in transmission mode. The NCG is a triangular array of dielectric rods in a dielectric glass matrix with a two-dimensional photonic band structure. We determine the modes for the NCG photonic crystal and simulate the observed data. The calculations show large contrast at low numerical aperture (N A) of the collection optics and detailed structure at high N A consistent with the observed images. We present calculations as a function of N A to identify how the NCG photonic modes contribute to and 1 determine the spatial structure in these images. Calculations are presented as a function of tip/sample position, sample index contrast and geometry, and aperture size to identify the factors that determine image formation with transmission NSOM in this experiment.