Yuichi Kozawa 교수

To generate a radially polarized laser beam we designed and fabricated a new Brewster optical element that consists of convex and concave conical prisms. The lateral surface of the convex conical prism was coated with a dielectric multilayer (SiO2 and Ta2O5) to enhance polarization selectivity. By combining two prisms we obtained a conical Brewster prism without beam divergence owing to refraction. A radially polarized TEM01* (R-TEM01*) mode laser beam was demonstrated when this prism was used i

The phenomenon of superoscillation produces oscillations that are faster than the fastest Fourier component of a system, potentially forming a local “hot spot” with a size below the diffraction limit. We show that a radially polarized Laguerre–Gaussian mode has the inherent ability to form superoscillation spots simply by controlling the incident beam size. We investigate this in detail, both numerically and experimentally. Our numerical simulations predict that lateral resolutions close to 100 

Single-beam optical trapping of micrometer-sized dielectric particles is experimentally demonstrated using radially and azimuthally polarized beams. The axial and transverse optical trapping efficiencies of glass and polystyrene beads suspended in water are measured. The radially polarized beam exhibited the highest trapping efficiency in the axial direction due to the p polarization of the radial polarization on the particle surface. On the other hand, the azimuthally polarized beam had a highe

The intensity distributions near the focal point for radially polarized laser beams including higher-order transverse modes are calculated based on vector diffraction theory. For higher-order radially polarized mode beams as well as a fundamental mode (R-TEM01*) beam, the strong longitudinal component forms a sharper spot at the focal point under a high-NA focusing condition. In particular, double-ring-shaped radially polarized mode (R-TEM11*) beams can effectively reduce the focal spot size bec

The intensity distributions of a tightly focused radially polarized beam that has a double-ring-shaped transverse mode pattern were calculated based on vector diffraction theory. The distribution of the longitudinal component near the focus varied drastically with the degree of truncation of the incident beam by a pupil. When the ratio of the pupil radius to the beam radius was approximately 1.3, the longitudinal component disappeared at the focal point, owing to destructive interference. This d

We demonstrate that the lateral resolution of confocal laser scanning microscopy is dramatically improved by a higher-order radially polarized (HRP) beam with six concentric rings. This beam was generated simply by inserting liquid crystal devices in front of an objective lens. An HRP beam visualized aggregated 0.17 μm beads individually and is also applicable to biological imaging. This method can extend the capability of conventional laser scanning microscopes without modification of the syste

A concentrically patterned photonic crystal mirror with polarization selectivity fabricated by the autocloning technique was used for the generation of radially and azimuthally polarized beams from an Nd:YAG laser cavity. By adopting the photonic crystal mirror as the output coupler of the cavity, both radially and azimuthally polarized beams were obtained with similar output power as that of an unpolarized beam generated by a conventional, non-polarization-selective output coupler.

We consider the formation of a small focal spot, which has been reported in [J. Opt. Soc. Am. A 24, 1793 (2007)], by separating a higher-order radially polarized Laguerre-Gaussian beam into two parts: a Bessel-like multi-ring part and an annular part. The latter forms a dominant small spot of longitudinal electric field component near the focus, while the former mainly contributes to a weak annular pattern of radial component.

The spatial resolution characteristics in confocal laser scanning microscopy (LSM) and two-photon LSM utilizing a higher-order radially polarized Laguerre-Gaussian (RP-LG) beam are numerically analyzed. The size of the point spread function (PSF) and its dependence on the confocal pinhole size are compared with practical LSM using a circularly polarized Gaussian beam on the basis of vector diffraction theory. The spatial frequency response in terms of the optical transfer function (OTF) is also

We demonstrate second-harmonic generation from a (110)ZnSe crystal for focused, axially symmetric polarized beams. Distinctive distributions in polarization and intensity accompanying transverse mode conversion to higher-order Hermite-Gaussian or Laguerre-Gaussian modes are observed. A longitudinal electric field generated by a radially polarized beam is verified by the variation in the intensity distribution.

Dark-spot formation is demonstrated by calculating electric-field distribution near the focus produced by focusing higher-order transverse-mode vector beams with radial and azimuthal polarizations in addition to Laguerre-Gaussian beams with linear and circular polarizations. The size of the dark spot in the radial direction varies from one beam to another, but the size in the axial direction is almost the same. The radially polarized TM02-mode beam is predicted to form a dark spot solely by an a

The longitudinal electric field produced by focusing a radially polarized beam is applied in confocal laser scanning microscopy by introducing a higher-order transverse mode, combined with a technique of polarization conversion for signal detection. This technique improves signal detection corresponding to the longitudinally polarized field under a small confocal pinhole, enabling full utilization of the small focal spot characteristic of the longitudinal field. Detailed numerical and experiment