Optimization ofs-Polarization Sensitivity in Apertureless Near-Field Optical Microscopy

It is a general belief in apertureless near-field microscopy that the so-calledp-polarization configuration, where the incident light is polarized parallel to the axis of the probe, is advantageous to its counterpart, thes-polarization configuration, where the incident light is polarized perpendicular to the probe axis. While this is true for most samples under common near-field experimental conditions, there are samples which respond better to thes-polarization configuration due to their orientations. Indeed, there have been several reports that have discussed such samples. This leads us to an important requirement that the near-field experimental setup should be equipped with proper sensitivity for measurements withs-polarization configuration. This requires not only creation of effective s-polarized illumination at the near-field probe, but also proper enhancement of s-polarized light by the probe. In this paper, we have examined thes-polarization enhancement sensitivity of near-field probes by measuring and evaluating the near-field Rayleigh scattering images constructed by a variety of probes. We found that thes-polarization enhancement sensitivity strongly depends on the sharpness of the apex of near-field probes. We have discussed the efficient value of probe sharpness by considering a balance between the enhancement and the spatial resolution, both of which are essential requirements of apertureless near-field microscopy.

Cold Atoms in a Hollow Mirror Trap

We present a novel and simple vapour-cell magneto-optical atom trap in a pyramidal and a conical hollow mirror cavity. A single laser beam having modulation sidebands at microwaves is used for cooling, trapping and repumping of rubidium atoms. When the laser is circularly polarized and sent into the hollow region, three pairs of counterpropagating beams are automatically produced therein, having the same polarization configuration as in the conventional six beam magneto-optical trap. The precooled atom sources thus produced may be used to obtain much colder and denser atoms for study of their quantum statistical properties.