Biomedical subjects

Noora Tossavainen

Publications and source records attributed to Noora Tossavainen.

3 recordsLinked to original sources

PubMed2006

White LED light coupling into light guides with diffraction gratings.

Radial diffractive gratings are used to couple light of a white LED into a light guide. Theoretical coupling efficiencies are evaluated with rigorous diffraction theory in a pure conical mounting. It is shown that when the refractive index of the grating increases from 1.46 to 2.05 the incoupling efficiency increases from 42% to 63%. Also, with the increasing refractive index the incoupling efficiency is shown to become more nearly uniform over the visible spectrum. Experimental results for the incoupled efficiencies and the color coordinates of the incoupled spectra are introduced for refractive indices n=1.46 and n=1.56.

Journal Article↗

PubMed2006

Diffraction of conic and Gaussian beams by a spiral phase plate.

An analytical expression for the spatial spectrum of the conic wave diffracted by a spiral phase plate (SPP) with arbitrary integer singularity of order n is obtained. Conic wave diffraction by the SPP is equivalent to plane-wave diffraction by a helical axicon. A comparison of the conic wave and Gaussian beam diffraction on a SPP is made. It is shown that in both cases a light ring is formed, with the intensity function growing in proportion to rho(2n) at small values of radial variable rho and decreasing as n(2)rho(-4) at large rho. By use of direct e-beam writing on the resist, a 32 level SPP of the 2nd order and diameter 5 mm is manufactured. By use of this SPP, a He-Ne laser beam is transformed into a beam with phase singularity and ringlike intensity distribution. A four-order binary diffractive optical element (DOE) with its transmittance proportional to a linear superposition of four angular harmonics is also manufactured. With this DOE, simultaneous optical trapping of several polystyrene beads of diameter 5 microm is performed.

Journal Article↗

PubMed2006

Producing illumination-independent additively mixed colors by diffractive optics.

We apply transmission gratings under Littrow incidence to produce polychromatic colors by additive color mixing. Parametric optimization of gratings is employed to produce high efficiency. In addition, we show that the system can yield the same color from a wide variety of spectra; i.e., the system can produce metameric colors.

Journal Article↗