The use of optics in the fields of nano-technology, telecommunication and
medicine has been growing exponentially in recent years. Application of liquid
crystals within optics has been a growing trend from flat screen displays to
variable focus lenses in a digital versatile discs.
One area of the recent developments within optics has been the development of
two-photon fluorescence microscopy and high-density three-dimensional optical
data storage. In such applications, where a light beam has to be focused deep
within the volume of bulk media, aberrations are introduced. The most dominant
aberration is spherical aberration which results from the mismatch in refractive
indices of the immersion and recording media. The aim of this thesis is to design a
liquid crystal lens for dynamic tube length compensation of the spherical
aberration.
Liquid crystal phase plates are used in everyday liquid crystal displays (LCDs)
such as mobile phones and calculators. The technologies required to manufacture
a liquid crystal phase plate are well understood. However, an application like
three-dimensional data storage requires different properties in the liquid crystal
phase plate, which are investigated in this thesis. To fabricate our liquid crystal
phase plate we used ZLI-5049-000 from MERCK as the liquid crystal medium,
with poly-vinyl alcohol (PVA) and Indium Tin Oxide (ITO) providing the
insulating and conducting layers, respectively. It has been demonstrated that
vacuum vapour deposition can be used to coat a glass substrate with ITO.
However, in order for the ITO coating to be conductive a method is developed
where the substrate is heated to 300oC before, during and after the coating.
Similarly, a method has been developed for producing a uniform 10 μm coating of
PVA on top of the ITO.
In order to produce a liquid crystal lens with the properties required to compensate
for spherical aberration an investigation into the properties of the liquid crystals is
first conducted. A liquid crystal phase plate described in chapter 3 is characterised
to determine the effect of the rubbing direction of the insulating layer and the
effective refractive index change with applied voltage. It has been demonstrated
that an effective change in refractive index of 0.11 can be achieved with 30 volts
applied across the ITO electrodes.
Based on the characterisation of the liquid crystal phase plate four different liquid
crystal lens designs have been proposed and tested. The lens designs are based
upon convergent and divergent lenses with different refractive index lens
substrates. It is determined that a liquid crystal lens with a divergent lens substrate
with a refractive index of 1.785 can be used to effectively compensate for
spherical aberration. This has been confirmed experimentally by using the liquid
crystal lens in a two-photon confocal microscope and measuring a increase in
detected intensity at a depth below the surface of a sample.
The research conducted in this thesis shows the ability to dynamically compensate
for spherical aberration introduced by a mismatch in the refractive indices
between the immersion and sample mediums. It has also been demonstrated that
new methods for fabricating the conductive and insulating layers are suitable for
producing a liquid crystal lens. A liquid crystal lens based on the research in this
thesis could be used in three-dimensional data storage or microscopy applications.
| Identifer | oai:union.ndltd.org:ADTP/216609 |
| Date | January 2006 |
| Creators | Ashraf, Mujahid Al Islam, n/a |
| Publisher | Swinburne University of Technology. Faculty of Engineering and Industrial Sciences |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://www.swin.edu.au/), Copyright Mujahid Al Islam Ashraf |
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