Biomedical Engineering Reference
In-Depth Information
wavefronts..Only.very.few.data.points.of.the.experimental.data.were.afected.since.the.iber.was.not.hori-
zontally. aligned,. only. a. very. narrow. range. of. positions. in. respect. to. the. iber. axis. show. the. efect,. and.
wavefront.measurements.were.recorded.on.a.rather.coarse.grid.corresponding.to.steps.of.about.9.μm.
6.6 Discussion and conclusion
Ray-tracing.simulations.of.the.specimen-induced.aberrations.caused.by.cylindrical.and.spherical.objects.
were.performed..Simulation.examples.for.focusing.into.a.spherical.object.at.diferent.depths.were.given..
A.sphere.of.refractive.index.1.35.immersed.in.water.can.be.regarded.as.a.very.simple. model.of.a.cell.
within.a.water-based.sample..One.has.to.be.aware.that.the.simulations.are.carried.out.for.a.wavefront.
propagating.through.the.whole.sample—as.this.is.the.case.for.our.interferometric.wavefront.measure-
ment. setup.. A. confocal. microscope. works. in. epi-mode. and. the. luorescence. excitation. and. emission.
beams.propagate.between.the.objective.lens.and.the.focal.spot.only..herefore,.the.simulation.results.
are.strictly.equivalent.to.the.epi-mode.only.in.case.the.focus.is.set.to.the.bottom.or.top.of.the.sample.
Simulations.for.a.mouse.oocyte.cell.and.an.optical.iber.were.calculated.and.compared.to.experimen-
tal.results.obtained.by.interferometric.wavefront.measurements..he.Zernike-mode.data.from.the.ray.
tracing.are.in.good.agreement.with.the.measured.experimental.data.for.both.the.modeled.samples;.the.
characteristic.features.of.the.Zernike.amplitude.distribution.across.the.ield.of.view.were.reproduced.
by. the. simulation.. Furthermore,. an. approximation. of. the. diference. in. refractive. index. between. the.
biological.cell.and.the.embedding.medium.and.the.focal.position.was.inferred.from.the.simulation.due.
to.the.best.approximation.found.for.the.experimental.data.
Again,.the.simulations.showed.that.the.aberrations.can.be.described.by.a.relatively.low.number.of.Zernike.
modes..his.means.that.it.is.suicient.in.adaptive.optics.systems.to.correct.for.a.small.number.of.modes.only.
A.limitation.of.the.current.ray-tracing.model.is.the.assumption.of.a.straight.propagation.of.the.rays..his.
approximation.holds.for.small.and.rather.smooth.variations.of.the.refractive.index.and.is.justiied.for.the.
samples.under.investigation..he.relative.diferences.in.refractive.index.of.about.2%.were.rather.small,.but.
values.of.that.magnitude.are.expected.for.biological.samples.embedded.in.water-based.solutions.
Acknowledgement
It.is.noted.that.these.results.have.also.been.presented.in.the.publication.Schwertner.et.al..(2004a).
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