Biomedical subjects

Yaoju Zhang

Publications and source records attributed to Yaoju Zhang.

5 recordsLinked to original sources

PubMed2007

Optical intensity distribution of a plano-convex solid immersion mirror.

Ignoring the effect of the small aperture, we deduce the optical field distribution of the so-called plano-convex solid immersion mirror with a small aperture on the apex (PC-SIM) by using the vector diffraction theory. The simulation results show that a PC-SIM, like a solid immersion lens (SIL), can achieve high resolution. Unlike the SIL, the PC-SIM can effectively reduce the spreading of the spot size with increasing distance from the interface. The size and intensity of the spot are related not only to the refractive index of the solid immersion medium but also to the structure parameter of the PC-SIM. The size of a spot smaller than a quarter wavelength can be obtained simply by optimizing the structure parameter of a PC-SIM but not by decreasing the size of the small aperture.

Journal Article↗

PubMed2006

Optical data storage system with a planoellipsoidal solid immersion mirror illuminated directly by a point light source.

A new solid immersion mirror called the planoellipsoidal (PE) solid immersion mirror (SIM) for the near-field optical storage is proposed and developed. The PE SIM has a small aperture on the apex of the ellipsoidal surface. The intensity distribution of the transmitted field is calculated by using the vector diffraction theory. Compared with a conventional solid immersion lens (SIL), the proposed PE SIM has the following features. A PE SIM replaces three optical elements of the collimator, objective, and SIL in a conventional SIL optical storage system, so that the optical system equipped with the PE SIM is not only simple in its assembly but is also effective in making an optical head unit. The PE SIM obtains light from a point light source and focuses it directly on the recording layer, which may be useful for a compact optical data storage system. The convex ellipsoidal surface of the PE SIM can reduce the risk of the SIM touching the surface of the recording medium. In addition, the spreading of the spot size with the increase of distance is very small in the PE SIM.

Journal Article↗

PubMed2006

Design of high-performance supersphere solid immersion lenses.

Two types of novel solid immersion lens are designed and investigated theoretically using the vector diffraction theory. The advantages of these so-called high-performance supersphere solid immersion lenses (HPSILs) are that they can improve the Strehl ratio of the focused spot and increase the focal depth of near-field optical systems. Both the spot size and the sidelobe intensity are not increased, however, compared with those of the standard Weierstrass solid immersion lens. These HPSILs will be useful for near-field optical data storage and photolithography.

Journal Article↗

PubMed2006

Theoretical study of near-field optical storage with a solid immersion lens.

Both the reflection inside a hemisphere solid immersion lens (SIL) and the reflection inside the gap between the SIL and the optical recording medium are considered. The near-field SIL imaging theory for high numerical aperture is developed by using the vector diffraction and thin-film optics. Numerical results show that the spot size, Strehl ratio, and sidelobe intensity have an oscillatory behavior with the change of thickness of the air gap, which results from the interference effect of the transmitted field. We find that for smaller spot size, the Strehl ratio is smaller but the sidelobe intensity is larger. A certain thickness of air gap is useful for optical storage, which is less than 63 nm for the system in the simulated examples.

Journal Article↗

PubMed2005

Vector propagation of radially polarized Gaussian beams diffracted by an axicon.

On the basis of the vectorial Rayleigh diffraction integrals and stationary-phase method, the analytic expression describing the vectorial field distribution of radially polarized Gaussian beams diffracted by an axicon is derived. The theoretical analysis and simulation calculation show that the radial component of the diffraction field is the propagation-invariant first-order Bessel beam when the radially polarized Gaussian beam illuminates the axicon. However, the longitudinal component possesses no such behavior because of its intrinsic r dependence, and its central intensity is the maximum. The longitudinal component is related to the open angle and index of the axicon, which has to be considered when the open angle and index are large. For a small open angle and index, the longitudinal component can be neglected, and the scalar approximation is valid.

Journal Article↗