Optical eigenmodes for illumination & imaging
Abstract
This thesis exploits so called “Optical Eigenmodes” (OEi) in the focal plane of
an optical system. The concept of OEi is introduced and the OEi operator approach is outlined, for which quadratic measures of the light field are expressed as
real eigenvalues of an Hermitian operator. As an example, the latter is employed
to locally minimise the width of a focal spot. The limitations of implementing
these spots with state of the art spatial beam shaping technique are explored and
a selected spot with a by 40 % decreased core width is used to confocally scan an
in focus pair of holes, delivering a two-point resolution enhanced by a factor of
1.3.
As a second application, OEi are utilised for fullfield imaging. Therefore they
are projected onto an object and for each mode a complex coupling coefficient
describing the light-sample interaction is determined. The superposition of the
OEi weighted with these coefficients delivers an image of the object. Compared
to a point-by-point scan of the sample with the same number of probes, i.e.
scanning points, the OEi image features higher spatial resolution and localisation
of object features, rendering OEi imaging a compressive imaging modality. With
respect to a raster scan a compression by a factor four is achieved. Compared
to ghost imaging as another fullfield imaging method, 2-3 orders of magnitude
less probes are required to obtain similar images. The application of OEi for
imaging in transmission as well as for fluorescence and (surface enhanced) Raman
spectroscopy is demonstrated.
Finally, the applicability of the OEi concept for the coherent control of nanostructures is shown. For this, OEi are generated with respect to elements on a
nanostructure, such as nanoantennas or nanopads. The OEi can be superimposed in order to generate an illumination of choice, for example to address one
or multiple nanoelements with a defined intensity. It is shown that, compared to
addressing such elements just with a focussed beam, the OEi concept reduces illumination crosstalk in addressing individual nanoelements by up to 70 %. Furthermore, a fullfield aberration correction is inherent to experimentally determined
OEi, hence enabling addressing of nanoelements through turbid media.
Type
Thesis, PhD Doctor of Philosophy
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