Delbert Hansen

Evanescent imaging with induced polarization by using a solid immersion lens

Image contrast enhancement, high lateral resolution, and height information are obtained with induced polarization evanescent imaging using a solid immersion lens. Experiments are conducted by imaging features on a patterned Si substrate. Imaging theory is used to predict optimum orientation of high-spatial-frequency samples, and a topographical image is derived from the induced polarization image through a calibration procedure. A numerical aperture of 1.5 is used in the experiment. Height accuracy of +/-2 nm is demonstrated with a known sample.

Characterization of a novel focusing/tracking technique with increased feedthrough immunity for optical-disk applications: the double-astigmatic method

The astigmatic-focusing/push-pull tracking-error detection method is an elegant and sensitive optical servo technique. Unfortunately the formation of error signals far from either line focus of the astigmat (for relaxing alignment tolerances and broadening the servos acquisition range) gives rise to undesired diffraction effects in the focus servo channel owing to track crossings of the pregrooved disk by the optical stylus, especially if certain aberrations are present. These undesired effects are given several names: pattern noise, optical servo cross talk, and feedthrough. By combining two astigmatic lenses and their associated detectors, one can configure a differential variant of the astigmatic technique. This double-astigmatic method greatly reduces pattern noise caused by the presence of spurious astigmatism oriented with its line foci at ±45° to the disk tracks. In this paper we present numerical modeling and experimental data that demonstrate the effectiveness of this focusing/tracking technique in feedthrough suppression.

Polarization holograms for source-mask optimization

A new technique is introduced to replace DOEs that are used for illumination in lithographic projectors with polarization computer generated holograms (PCGHs) that produce both arbitrary intensity and arbitrary polarization state in the illumination pupil. The additional capability of arbitrary polarization state adds an additional degree of freedom for source-mask optimization. The PCGHs are similar in design and construction to DOEs, but they incorporate polarizationsensitive elements. Three experiments are described that demonstrate different configurations of PCGHs deigned to produce a tangentially polarized ring. Measurements of ratio of polarization and polarization orientation indicate that all three configurations performed well. Experimetns are performed with visible (λ = 632.8nm) light.

Polarization synthesis by computer-generated holography using orthogonally polarized and correlated speckle patterns

An interlaced polarization computer-generated hologram (PCGH) is designed to produce specific irradiance and polarization states in the image plane. The PCGH produces a tangentially polarized annular pattern with correlated speckle, which is achieved by a novel application of the diffuser optimization method. Alternating columns of orthogonal linear polarizations illuminate an interlaced PCGH, producing a ratio of polarization of 88% measured on a fabricated sample. The demonstrated technique can be applied to designs for arbitrary irradiance and polarization states in the image plane.

Square-wave retarder for polarization computer-generated holography

An etched calcite square-wave retarder is designed, fabricated, and demonstrated as an illuminator for an interlaced polarization computer-generated hologram (PCGH). The calcite square-wave retarder enables alternating columns of orthogonal linear polarizations to illuminate the interlaced PCGH. Together, these components produce a speckled, tangentially polarized PCGH diffraction pattern with a measured ratio of polarization of 84% and a degree of linear polarization of 0.81. An experimental alignment tolerance analysis is also reported.

Hyper-NA imaging with solid-immersion optics and induced polarization imaging

Solid immersion lens (SIL) is used in microscopic systems for hyper numerical aperture (NA) imaging. The NA of the SIL microscope can be larger than 2 by using the high refractive index SIL. In this paper, examples of hyper-NA (NA>1.4) imaging are illustrated, including a normal SIL microscope for imaging samples like CPU chips, photomasks which have no cover layer and a special SIL microscope for imaging samples like Blu-Ray optical discs which have cover layer to protect the pattern. In both cases, good contrast images can be achieved by minimizing the system aberration. At the end, characteristics of induced polarization imaging (imaging through crossed polarizers) and a twostep solid immersion lens using Gallium Phosphide (GaP) (NA~2) are discussed.

Optical data destruction system: device design and test results

An optical data destruction system using a high power laser beam is introduced. The system exposes data marks on optical media to a focused high power line beam. The exposure changes the physical and optical properties of the data marks and surrounding layers, making retrieval of the data impossible. Maintaining the focused laser beam on a data layer is achieved by a focus servo using a diffractive optical element (DOE). The system performance is evaluated from a number of destruction experiments on CD-Recordable (CD-R) and CD-ReWritable (CD-RW).