Mechanisms of T cell organotropism

F.M.M.-B. is supported by the British Heart Foundation, the Medical Research Council of the UK and the Gates Foundation

Faraday-rotation imaging by near-field optical microscopy

Lacoste T, Huser T, Heinzelmann H. Faraday-rotation imaging by near-field optical microscopy. Zeitschrift für Physik B Condensed Matter. 1997;104(2):183-184.Scanning near-field optical microscopy with polarization modulation (PM-SNOM) has been applied to image the surface of a yttrium-iron-garnet (YIG) film. Lock-in detection of the phase of the transmitted light directly gives the magnitude of the Faraday rotation angle

Contrast enhancement using polarization-modulation scanning near-field optical microscopy (PM-SNOM)

Lacoste T, Huser T, Prioli R, Heinzelmann H. Contrast enhancement using polarization-modulation scanning near-field optical microscopy (PM-SNOM). Ultramicroscopy. 1998;71(1-4):333-340.Polarization contrast scanning near-field optical microscopy (SNOM) provides information on the orientation of molecules and molecular aggregates on surfaces. Other than in transmission or fluorescence SNOM, the control of polarization demands for SNOM probes having extinction ratios better than 20:1 in at least two perpendicular polarization directions. Most common SNOM probes consist of tapered and metal-coated fiber tips. While the birefringence of fibers can be compensated, the tapering often exhibits depolarizing effects that make good qualitative or even quantitative measurements difficult. In an attempt to improve the quality of the apertures, we have modified metal-coated fiber probes with a focused ion beam (FIB). As an example of investigations where a very good polarization control is needed, we present and discuss polarization-modulation SNOM (PM-SNOM) measurements on dye crystals. The modulation of the direction of linearly polarized light and the use of lock-in techniques allows the simultaneous detection of absorption together with magnitude and orientation of optical anisotropy. (C) 1998 Elsevier Science B.V. All rights reserved

Scanning near-field optical microscopy of cholesteric liquid crystals

Huser T, Lacoste T, Heinzelmann H, Kitzerow HS. Scanning near-field optical microscopy of cholesteric liquid crystals. The Journal of Chemical Physics. 1998;108(18):7876-7880.We have studied glasslike cholesteric liquid crystals by means of scanning near-field optical microscopy. A periodic modulation of the optical polarization was used in order to achieve an optical contrast due to the birefringence of the liquid crystal. Variation of the cholesteric pitch indicates an optical resolution of approximate to 200 nm for a wavelength of 633 nm. (C) 1998 American Institute of Physics

Scanning Near-Field Optical Microscopy (SNOM) and its Application in Mineralogy

Gutmannsbauer W, Huser T, Lacoste T, Heinzelmann H, Güntherodt HJ. Scanning Near-Field Optical Microscopy (SNOM) and its Application in Mineralogy. SCHWEIZERISCHE MINERALOGISCHE UND PETROGRAPHISCHE MITTEILUNGEN. 1995;75(2):259-264.Scanning near-field optical microscopy (SNOM) is a member of the family of scanning probe microscopes. It combines the high three dimensional resolution of a scanning force microscope with the contrast mechanisms of an optical microscope. An optical resolution beyond the diffraction limit can be achieved. We show the first application of this technique in the field of mineralogy, and we point out its future potential

Observation and analysis of near-field optical diffraction

Huser T, Novotny L, Lacoste T, Eckert R, Heinzelmann H. Observation and analysis of near-field optical diffraction. JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION. 1999;16(1):141-148.We present an experimental study of near-field optical interactions between an optical probe and sample objects with different dielectric properties. The interaction strongly affects the radiation emitted at angles beyond the critical angle of total internal reflection in the substrate (the forbidden light regime). Such an effect has been predicted theoretically. Our experimental data show that if a conducting object is close to the optical probe, p-polarized optical fields are deflected away from the object. On the other hand, s-polarized fields are deflected toward dielectric objects. The experimental results show good qualitative agreement with numerical simulations. The described effects have a strong influence on image formation in scanning near-field optical microscopy and thus have to be taken into account for image analysis. (C) 1999 Optical Society of America [S0740-3232(99)02201-2]

Instrumental developments and recent experiments in near-field optical microscopy

Heinzelmann H, Lacoste T, Huser T, Güntherodt HJ, Hecht B, Pohl DW. Instrumental developments and recent experiments in near-field optical microscopy. Thin Solid Films. 1996;273(1-2):149-153.Recent advances in the understanding of light propagation in small dimensions as well as in instrumentation make scanning near-field optical microscopy (SNOM) a very promising tool for studying optical phenomena on a nanometer scale. In this talk, we will demonstrate experiments carried out with the recently developed tunneling near-field optical microscope. We found superior image contrast, as compared with images taken with conventional aperture SNOM, along with the high resolution commonly achieved with fiber probes. This work was motivated by the theoretical investigations presented in Dr. Pohl's talk. We will further describe two recently built instruments. The first is a scanning tunneling optical microscope combined with a scanning force microscope. The second instrument is an aperture-type SNOM mounted on the sample stage of a conventional inverted optical microscope. Of particular interest to us is imaging with polarization contrast. One of the goals is to study liquid-crystal films which have been micropatterned with the help of a force microscope tip. These samples are promising as waveguides and potential electro-optical devices. Additionally, they represent very convenient test samples for polarization SNOM