Biomedical subjects

Sjoerd Stallinga

Publications and source records attributed to Sjoerd Stallinga.

6 recordsLinked to original sources

PubMed2007

Compact system description for systems comprising a tilted plane parallel plate.

A paraxial model describing the astigmatism generated by a plane-parallel plate is derived. This model fits the framework of the 4x4 matrix formalism that Arsenault used to describe cylindrical lenses. The framework including this new model is used to build a compact system description of a plane-parallel plate combined with a cylindrical lens, from which several imaging properties are derived. Calculation results are compared with ray-trace simulation results and measurements. Both the ray-trace and the experimental results are in excellent agreement with the calculated results.

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PubMed2006

Energy and momentum of light in dielectric media.

The conservation of energy, linear momentum, and angular momentum of the electromagnetic field in linear dielectric media with arbitrary dispersion and absorption is studied in the framework of an auxiliary field approach in which the electric and magnetic fields are complemented by a material field. This material field depends on a continuous variable omega, and describes harmonic motions of the charges with eigen frequency omega. It carries an electric dipole moment and couples as such to the electric field. The equations of motion of the model are equivalent to Maxwell's equations in an arbitrary dispersive and absorbing dielectric and imply that several quantities are conserved. These quantities may be interpreted as the energy, momentum, and angular momentum of the total system, and can be viewed as the sum of the corresponding quantities of the field and matter subsystems. The total momentum turns out to be equal to the Minkowski momentum plus a dispersive contribution. The total energy and total momentum of a wave packet both travel with the group velocity, while the ratio of total momentum and total energy is given by the phase velocity.

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PubMed2005

Finite conjugate spherical aberration compensation in high numerical-aperture optical disc readout.

Spherical aberration arising from deviations of the thickness of an optical disc substrate from a nominal value can be compensated to a great extent by illuminating the scanning objective lens with a slightly convergent or divergent beam. The optimum conjugate change and the amount and type of residual aberration are calculated analytically for an objective lens that satisfies Abbe's sine condition. The aberration sensitivity is decreased by a factor of 25 for numerical aperture values of approximately 0.85, and the residual aberrations consist mainly of the first higher-order Zernike spherical aberration term A60. The Wasserman-Wolf-Vaskas method is used to design biaspheric objective lenses that satisfy a ray condition that interpolates between the Abbe and the Herschel conditions. Requirements for coma by field use allow for only small deviations from the Abbe condition, making the analytical theory a good approximation for any objective lens used in practice.

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PubMed2005

Compact description of substrate-related aberrations in high numerical-aperture optical disk readout.

Optical disks are read out by focusing a beam of high numerical aperture (NA) through the substrate. Deviations of the thickness from the nominal value result in spherical aberration; tilting the substrate results in coma. Exact analytical expressions for the rms aberration per micrometer thickness mismatch (for spherical aberration) and per degree tilt (for coma) are derived. The paraxial estimates for these sensitivities proportional to NA4 (spherical aberration) and NA3 (coma) underestimate the exact values by a factor of approximately 2 for the value NA = 0.85, corresponding to the new Blu-ray disk format. Expansion of the aberration function in Zernike aberrations shows that the exact aberration functions are well described by the lowest-order Zernike spherical aberration (A40) and coma (A31) term for all but the very highest NA values.

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PubMed2004

Light distribution close to focus in biaxially birefringent media.

The effect of focusing into a biaxially birefringent medium on the light distribution in the focal region of a high-NA optical system is investigated with the Debye approach to vectorial diffraction theory. Attention is limited to media with small birefringence. The electric field in the focal region is the sum of the field of the two polarization eigenmodes of the biaxially birefringent medium. Both modes are generally astigmatically aberrated, are defocused with respect to each other, and have a polarization field that is nonuniform over the pupil. The diffraction integrals are calculated numerically on the basis of an expansion of the field close to focus in terms of partial waves.

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PubMed2004

Strehl ratio for focusing into biaxially birefringent media.

The Strehl ratio for focusing into biaxially birefringent media with small birefringence is investigated. An analytical expression for the Strehl ratio as a function of the polarization and birefringence parameters is derived in the paraxial limit from a generalization of the scalar aberration theory. The expression agrees well with results of a numerical calculation.

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