We decompose the light field in the focal plane of an imaging system into a set of optical eigenmodes. Subsequently,
the superposition of these eigenmodes is identified, that optimizes certain aspects of the imaging process.
In practice, the optical eigenmodes modes are implemented using a liquid crystal spatial light modulator. The
optical eigenmodes of a system can be determined fully experimentally, taking aberrations into account. Alternatively,
theoretically determined modes can be encoded on an aberration corrected spatial light modulator. Both
methods are shown to be feasible for applications. To achieve subdiffractive light focussing, optical eigenmodes
are superimposed to minimize the width of the focal spot within a small region of interest. In conjunction with
a confocal-like detection process, these spots can be utilized for laser scanning imaging. With optical eigenmode
engineered spots we demonstrate enhanced two-point resolution compared to the diffraction limited focus and a
Bessel beam. Furthermore, using a first order ghost imaging technique, optical eigenmodes can be used for phase
sensitive indirect imaging. Numerically we show the phase sensitivity by projecting optical eigenmodes onto a
Laguerre-Gaussian target with a unit vortex charge. Experimentally the method is verified by indirect imaging
of a transmissive sample.
Non-diffracting beams, such as Bessel and Mathieu beams, offer a wide range of potential applications in
the fields of bio-photonics, micromanipulation and spectroscopy. One of the main features of these beams
is their self-healing behavior where the beams reconstruct after an obstacle. Higher order versions of these
beams incorporate non-diffracting optical singularities or vortices propagating together with the beams in a
straight line. Vortices are ubiquitous in many parts of physics and their dynamics, especially their creation
and annihilation processes are very important in fundamental physics. Newly demonstrated Airy beams
represent a different class of non-diffracting beams that do not propagate in a straight line but exhibit
a constant transversal acceleration. The self-healing properties of these Airy beams together with their
transversal acceleration can be used to optically clear entire regions of microparticles. These Airy beams
are created using a spatial light modulator that encodes a cubic phase front on an incident Gaussian beam.
Using the same method and suitable computer generated holograms we are able to generate Airy like beams
that include optical vortices. In this paper, we study the creation and evolution of Airy beam accelerating
vortices from the theoretical and experimental perspective.
Airy beams are of great interest as a result of their unusual characteristics, they are non-diffracting and also
propagate along a parabolic path due to the presence of a transversal acceleration component. In this paper
the generation of a white light Airy beam is presented, an investigation is also carried out to determine
how the properties of an Airy beam change with the wavelength and spatial coherence of the source. A
supercontinuum source is used in conjunction with a spatial light modulator to produce the Airy beams.
The wavelength dependence study of the Airy beam parameters was carried out by inserting interference
filters into the supercontinuum beam path to select each wavelength. The parameters investigated are
the deflection coefficient of the Airy beam, b0, this quantifies the parabolic path traveled by the beam;
the characteristic length, x0, which is related to the lobe spacing, and lastly the aperture coefficient, a0.
The deflection coefficient and the characteristic length were both found to be wavelength dependent. The
aperture coefficient did not alter as a result of wavelength, however it was found to be dependent on the
spatial coherence, and therefore on the M2 value, of the beam. The other parameters, b0 and x0, are
unaffected by the spatial coherence of the source.
The year 2007 witnessed the experimental realization of extraordinary laser beams termed Airy and parabolic
beams. Surprisingly, these beams are immune to diffraction and in addition exhibit transverse acceleration while
propagating. This peculiar property of both Airy and parabolic beams facilitates the clearance of both microparticles
and cells from a region in a sample chamber through particle/cell transport along curved trajectories. We
term this concept "Optically mediated particle clearing" (OMPC) and, alternatively, "Optical redistribution"
(OR) in the presence of a microfluidic environment, where particles and cells are propelled over micrometersized
walls. Intuitively, Airy and parabolic beams act as a form of micrometer-sized "snowblower" attracting
microparticles or cells at the bottom of a sample chamber to blow them in an arc to another region of the sample.
In this work, we discuss the performance and limitations of OMPC and OR which are currently based on a single
Airy beam optionally fed by a single parabolic beam. A possible strategy to massively enhance the performance
of OMPC and OR is based on large arrays of Airy beams. We demonstrate the first experimental realization of
In their pioneering work, Burns et al. [Phys. Rev. Lett. 63, 1233 (1989)] discovered a laser-induced optical
interaction between dielectric microparticles dispersed in water. This interaction occurred in the plane transversal
to the laser beam and, interestingly, induced bound pairs of particles. Accordingly, the observed phenomenon
was termed "transverse optical binding" (TOB). Burns et al. argued that TOB arises from coherently induced
electric dipoles in the microspheres. Indeed, this explanation verified the experimental observation that the
spatial periodicity of the TOB interaction matched the laser wavelength in water. However, relatively little
experimental evidence has been provided, to date, for both the strength and functional dependence of this effect
on the particle distance. In our study, we used an experimental method which allowed us to directly measure
the TOB interaction. As a result, we found that this interaction is surprisingly long-ranged.
Three-body and four-body interactions have been directly measured in a colloidal system comprised of three (or four) charged colloidal particles. Two of the particles have been confined by means of a scanned laser tweezers to a line-shaped optical trap where they diffused due to thermal fluctuations. By means of an additional focused optical trap a third particle has been approached and attractive three-body interactions have been observed. These observations are in qualitative agreement with additionally performed nonlinear Poissson-Boltzmann calculations. Two configurations of four particles have been studied experimentally as well and in both cases a repulsive four-body interaction term has been observed.