H. Paul Urbach

Near-field read-out of a 50-GB first-surface disc with NA=1.9 and a proposal for a cover-layer-incident, dual-layer near-field system

We present read-out results of a 50 GB disk with a blue laser and a NA=1.9 Solid Immersion Lens in a conventional focus and tracking actuator. Furthermore, we show a light path and a disk design that enable cover-layer incident near field recording on dual-layer disks with a capacity of 300 GB on a double-sided disk.

Calculation of the Rayleigh–Sommerfeld diffraction integral by exact integration of the fast oscillating factor

We describe a numerical method that can be used to calculate the propagation of light in a medium of constant (possibly complex) index of refraction n. The method integrates the Rayleigh-Sommerfeld diffraction integral numerically. After an appropriate change of integration variables, the integrand of the diffraction integral is split into a slowly varying and an (often fast) oscillating quadratic factor. The slowly varying factor is approximated by a spline fit, and the resulting Fresnel integrals are subsequently integrated exactly. Although the method is not as fast as methods involving a fast Fourier transform, such as plane-wave propagation or Fresnel approximation, it is accurate over a greater range than these methods.

Modeling latent-image formation in photolithography, using the Helmholtz equation

A method for simulating latent image formation in a photoresist illuminated by partially coherent light is described. The latent image is calculated by repeatedly solving a boundary-value problem for the Helmholtz equation on a two-dimensional domain, using the finite-element method. The dependence of the developed image on defocus is investigated for the case of high numerical aperture. The obtained results are compared with those predicted by the vertical propagation model and the first-order model.

Near Field Recording on First-Surface Write-Once Media with a NA=1.9 Solid Immersion Lens

We present a single-wavelength near field recording set-up with a blue laser and a NA=1.9 solid immersion lens in a conventional focus and tracking actuator. The most important aspects to realize such a near field recording system are discussed, in particular, gap error signal normalization and correction of chromatic aberration of the objective lens. First recording results demonstrate that the set-up is fully operational.

Optimization of light extraction from OLEDs

In recent years, many methods were developed to improve the efficiency of an OLED. In this paper, we investigate the effects of some main factors contributing to the extraction efficiency. These factors include the polarization of the source, the distance between the source and the metal, and the thickness of the layers. We will also discuss the effect of periodic patterns such as a grating structure.

Thin-film interference effects in photolithography for finite numerical apertures

It is known that the energy coupled into a planar resist film atop a reflective substrate and illuminated from above has an oscillatory dependence on the resist thickness. We consider in detail the remarkable effects produced by oblique waves in the incident illumination for projection optical lithography with finite numerical apertures. A simple discussion reveals how significant corrections to thin-film interference phenomena in photolithography can occur relative to the case of normally incident illumination. Moreover, the criterion for the onset of these corrections is derived and is shown to be closely similar to that for the onset of bulk defocus effects. Rigorous modeling results are then presented, based on a finite element solution of the two-dimensional Helmholtz equation. A simplified oblique-propagation model is also introduced.

Application of nonperiodic phase structures in optical systems.

Wide, nonperiodic stepped phase structures are studied to correct various parameter-dependent wave-front aberrations in optical systems. The wide nature of these phase structures makes them easy to manufacture with sufficient compensation of the wave-front aberrations. Wave-front aberration correction for both continuous and discrete parameter variations are studied. An analytical method is derived for the discrete parameter variations to find the optimal phase structure. Both theoretical and experimental results show that these nonperiodic phase structures can be used to make (1) lenses athermal (defocus and spherical aberration compensated), (2) lenses achromatic, (3) lenses with a large field of view, (4) lenses with a reduced field curvature, and (5) digital versatile disk objective lenses for optical recording that are compatible with compact disk readout.

Resolution Limit of Optical Disc Mastering.

With the increase of the information density on optical discs, it becomes increasingly necessary to improve the quality and the resolution of the optical disc mastering process. The obvious approach is to reduce the size of recorded structures by reducing the λ/ NA ratio of the recorder. Indeed, mastering at UV wavelengths has been put into practice by several companies. This paper deals with an additional route towards higher resolution. It is shown that the combination of improved photoresist processes and better exposure techniques can lead to a clear reduction of the smallest achievable pit size. Combining such techniques with UV mastering, pit lengths below 200 nm should be well within reach of classical optical disc mastering.

Spectral Theory of Resonances in Electromagnetic Gratings

Anomalies in the diffracted efficiencies of periodic gratings often occur near resonances. Using the min-max principle for the eigenvalues of the singular, non-compact, integral operator of the electromagnetic scattering problem, the problem of the existence of resonances is studied and conical incident angles for which resonances exist are constructed.

Superresolution in Far-Field Microscopy

The theoretical possibility of reconstructing images of objects with structured details smaller than the detraction limit was shown already many years ago. By scanning near-field optical microscopy this possibility has been realised. We obtained noise-limited resolution in farfield microscopy. In this paper we discuss the experiment and some of its applications.