Biomedical Engineering Reference
In-Depth Information
6
Simulation of Aberrations
6.1.
Introduction.........................................................................................83
6.2.
Wavefront.Aberration.Simulation.for.a.Spherical.Object.............84
6.3.
.Modeling.of.an.Oocyte.Cell.and.Comparison.to.
Experimental.Results..........................................................................87
6.4.
Wavefront.Aberration.Simulation.for.a.Cylindrical.
.
Object....................................................................................................90
6.5.
.Optical.Fiber.Simulation.and.Comparison.to.
.
Experimental.Results.......................................................................... 91
Michael Schwertner
confovis GmbH
6.6.
Discussion.and.Conclusion................................................................93
6.1 introduction
It.has.been.suggested.to.correct.for.aberrations.of.the.wavefront.using.adaptive.optics,.as.is.discussed.
in. Chapters. 4,. 7. and. 8. on. adaptive. correction.. here. the. idea. is. to. feed. a. pre-aberrated. wavefront. to.
the. optical. system. that. contains. aberrations. opposite. to. those. generated. within. the. system.. Hence,.
.aberrations.will.cancel.out.and.difraction-limited.imaging.is.accomplished.again..A.standard.adaptive.
optics.system.includes.a.wavefront-sensing.element.and.operates.in.a.closed.loop.to.correct.aberration.
actively.. Another. approach. is. to. use. predictive. aberration. correction,. sometimes. referred. to. as. open.
loop. control.. Here,. the. aberration. conditions. are. inferred. from. secondary. parameters—for. example,.
the.position.of.the.focal.spot.within.the.specimen—and.corrected.accordingly..herefore,.the.simulation.
and.prediction.of.aberrations.is.the.key.to.predictive.correction.
he.efect.of.refractive.index.mismatch.in.luorescence.microscopy.was.irst.theoretically.analyzed.
by.Hell.et.al..(1993)..he.spherical.aberration.components.caused.by.focusing.through.a.layer.of.mis-
matched.refractive.index.can.be.calculated.analytically.if.the.refractive.index.and.thickness.of.each.layer.
is.known.(Török.et.al..1995;.Booth.et.al..1998).
Many. biological. specimens. can. be. approximated. by. cylindrical. or. spherical. object. shapes.
(e.g., cells). of. uniform. refractive. index. or. superpositions. of. several. of. these. structures.. In. this.
chapter,.we.calculate.the.specimen-induced.deformations.of.the.wavefront.for.spherical.and.cylin-
drical.objects..A.ray-tracing.method.is.used.to.obtain.the.pupil.phase.function.and.subsequently.
the.Zernike.mode.content.of.the.wavefront.using.numerical.integration..A.mouse.oocyte.cell.and.
an.optical.fiber.are.modeled.and.the.simulations.are.compared.to.experimental.results..The.inter-
ferometer. setup. used. for. the. direct. measurements. of. the. specimen-induced. aberrations. has. been.
described.in.Chapter.3.
83
