Biomedical subjects

Hanna Lajunen

Publications and source records attributed to Hanna Lajunen.

3 recordsLinked to original sources

PubMed2004

High-efficiency broadband diffractive elements based on polarization gratings.

A method is introduced for designing paraxial-domain diffractive elements working over a broad frequency range. The method is based on space-variant manipulation of the state of polarization by form-birefringent binary diffractive structures. It is shown that any scalar phase transmission function can be realized by use of such polarization-modulating structures and that at least in some cases it is even possible to exceed the scalar paraxial-domain upper bounds of diffraction efficiency over a broad frequency band.

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PubMed2004

Overall coherence and coherent-mode expansion of spectrally partially coherent plane-wave pulses.

The modal theory for spectrally partially coherent nonstationary plane waves is introduced. The theory is first developed in the space-frequency domain and then extended to the space-time domain. Propagation properties of the coherent modes are analyzed. The concept of the overall degree of coherence is extended to the domain of nonstationary fields, and it is shown that the overall degree of coherence of partially coherent plane-wave pulses is the same in the space-frequency and space-time domains. The theory is applied to the recently introduced concept of spectrally Gaussian Schell-model plane-wave pulses.

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PubMed2003

Simulation of light propagation by local spherical interface approximation.

A new local elementary interface approximation is introduced for the modeling of wave propagation through interfaces between homogeneous media. The incident wave and the surface profile are approximated locally by a spherical wave and a spherical surface, respectively. The wave field travels through the modulated structure according to the laws of geometrical optics, being refracted by the surface and propagating to the output plane locally as a geometric spherical wave. Diffraction theory is applied to propagate the field from the output plane onwards. We provide comparisons of the method with the thin-element approximation, the local plane-wave and interface approach, and rigorous diffraction theory using a sinusoidal surface-relief grating as an example. We illustrate the power of the new method by applying it to the analysis of a diffractive beam splitter.

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