We present a microfluidic platform for the generation, characterization and optical manipulation of monodisperse oil droplets in water with equilibrium interfacial tensions on the order of 0.1-1μN/m. An oil-in-water emulsion containing the surfactant Aerosol OT, heptane, water and sodium chloride under conditions close to the microemulsion phase transition was used. Through active control of the emulsion salinity and temperature, our microfluidic platform offers the unique capability of tuning the interfacial tension of droplets in the range of 1μN/m to few mN/m according to the operation required. Upon collection in a separate observation chamber, droplets were characterized by using video microscopy-based measurement of thermally-induced capillary waves at the droplet interface. Holographic optical tweezers were used to manipulate the droplets and construct 3D nanofluidic networks consisting of several droplets connected by stable oil threads a few nanometers across.
We discuss the design, implementation and performance of a novel platform for the production and optical control of
ultra-low interfacial tension droplets in the 1-10 micron regime. A custom-designed, integrated microfluidic system
allows the production of oil-in-water emulsion droplets of controllable size. This provides an optimised physical
platform in which individual droplets are selected, trapped and shaped by holographic optical tweezers (HOTs) via
extended optical landscaping. The 3D structure of the shaped droplet is interrogated by a combination of conventional
brightfield imaging and fluorescent structured-illumination sectioning. We detail the problems and limitations of closed-loop holographic control of droplet shape.
The Centre for Advanced Instrumentation (CfAI) of Durham University (UK) has recently successfully completed the
development of 24 Integral Field Units (IFUs) for the K-band Multi-Object Spectrometer (KMOS). KMOS is a second
generation instrument for ESO’s Very Large Telescope (VLT) which is due for delivery during the summer of 2012. The
KMOS IFU is based on the Advanced Image Slicer Concept developed by the CfAI and previously successfully
implemented on the Gemini Near-InfraRed Spectrograph and JWST NIRSpec. Each IFU contains 14 channels which
have to be accurately aligned. In addition, all 24 IFUs have to be co-aligned requiring the accurate alignment of an
unprecedented grand total of 1152 optical surfaces. In this paper we describe how this has been achieved through the use
of complex monolithic multi-faceted metal mirror arrays, which were fabricated in-house by means of freeform diamond
machining. We will summarise the results from the metrology performed on each of the optical components and describe
how these were integrated and aligned into the system. We will also summarise the results from the system level
acceptance tests, which demonstrate the excellent performance of the IFUs. Each of the 24 IFUs is essentially diffraction
limited across the entire field (Strehl ratios ~ 0.8) with throughput predictions (based on measurements of the surface
roughness) rising from 86% at a wavelength of 1 micron to 93% at 2.5 micron. We believe that this level of performance
has not previously been achieved in any image slicing IFU and showcases the potential of the current state-of-the-art
We present the results of a study on Dual-Stage Deformable Mirrors using Zonal Bimorph Deformable Mirror (ZBDM)
technology. A high density 'tweeter' DM has been assembled onto a lower density, high dynamic range 'woofer' DM to
generate an integrated mirror which offers both high resolution and dynamic range simultaneously. Such a device has the
potential to significantly simplify the design of astronomical Adaptive Optics (AO) systems. The latest developments are
presented, including the fabrication of a small scale demonstrator.
This paper will focus on the metrology of multiple complex surfaces that are to be integrated into the KBand Multi-
Object Spectrograph (KMOS). KMOS is a multi-field astronomical spectrograph designed for integration with the 8.2m
diameter European Southern Observatory Very Large Telescope (VLT). There are 1080 separate optical surfaces in the
design, many of them complex freeform surfaces. Optical surfaces were manufactured in aluminium by precision
freeform diamond machining. This flexible technique allows the fabrication of extremely complex surfaces with an
accuracy of better than 15 nm RMS over a 20 mm aperture, giving the designer great freedom in generating powerful
and unorthodox designs. However, the complexity of these freeform surfaces poses a challenge to their accurate
characterisation. This paper will discuss in detail the metrology of a specific freeform component in the instrument. The
form of these complex astigmatic surfaces was measured using spherical wavefronts by adapting a tilted Twyman-Green
Interferometer arrangement. There are eight separate designs for this type of component, each with a different orientation
and magnitude of astigmatism. Careful mechanical fixturing is essential to align the astigmatic axis to the test set up.
The impact of mechanical tolerances on measurement uncertainty will be discussed in detail.
In stereo displays, binocular disparity creates a striking impression of depth. However, such displays
present focus cues-blur and accommodation-that specify a different depth than disparity, thereby
causing a conflict. This conflict causes several problems including misperception of the 3D layout,
difficulty fusing binocular images, and visual fatigue. To address these problems, we developed a
display that preserves the advantages of conventional stereo displays, while presenting correct or
nearly correct focus cues. In our new stereo display each eye views a display through a lens that
switches between four focal distances at very high rate. The switches are synchronized to the
display, so focal distance and the distance being simulated on the display are consistent or nearly
consistent with one another. Focus cues for points in--between the four focal planes are simulated by
using a depth-weighted blending technique. We will describe the design of the new display, discuss
the retinal images it forms under various conditions, and describe an experiment that illustrates the
effectiveness of the display in maximizing visual performance while minimizing visual fatigue.
Liquid crystal (LC) adaptive optical elements are described, which provide an alternative to existing micropositioning
technologies in optical tweezing. A full description of this work is given in . An adaptive LC prism supplies tip/tilt
to the phase profile of the trapping beam, giving rise to an available steering radius within the x-y plane of 10 μm.
Additionally, a modally addressed adaptive LC lens provides defocus, offering a z-focal range for the trapping site of
100 μm. The result is full three-dimensional positional control of trapped particle(s) using a simple and wholly
electronic control system. Compared to competing technologies, these devices provide a lower degree of controllability,
but have the advantage of simplicity, cost and light efficiency. Furthermore, due to their birefringence, LC elements
offer the opportunity of the creation of dual optical traps with controllable depth and separation.
Interferometric techniques are attractive in wavefront sensing because they give a direct measure of the phase, which means they are useful for use with a piston-only wavefront corrector (such as a liquid crystal spatial light modulator, or some MEMS mirrors). We describe a novel method of implementing a common-path phase-shifting point diffraction interferometric wavefront sensor. The sensor simultaneously gives two phase-shifted outputs which can be used to drive a phase-only wavefront corrector. The device can also give a null output which can be used to calibrate any scintillation.
We present and demonstrate a technique for producing a high-speed variable focus lens using a fixed birefringent lens and a ferroelectric liquid crystal cell as a polarization switch. A calcite lenses with ordinary and extraordinary focal lengths of 109mm and 88mm respectively, was used to demonstrate focus switching at frequencies of up to 3kHz. Two identical lenses and a single liquid crystal were also used to demonstrate zoom.
We report on work on producing phase-only polymer-dispersed liquid crystals for use in spatial light modulators for adaptive optics. The aim is to assess the magnitude of the achievable phase shifts and the associated slew rate. We describe our methodology of producing devices and present our initial results.
We report on our work on producing liquid crystal switchable modal lenses and their use in a compound lens system in order to produce variable focus/zoom lenses. We describe work on producing a high power lens, and present theoretical work on off-axis phase modulation in a liquid crystal lens which is important in order to be able to carry out a complete optical design of a liquid crystal lens.
An adaptive lens, which has variable focus and is rapidly controllable with simple low-power electronics, has numerous applications in optical telecommunications devices, 3D display systems, miniature cameras and adaptive optics. The University of Durham is developing a range of adaptive liquid crystal lenses, and here we describe work on construction of modal liquid crystal lenses. This type of lens was first described by Naumov  and further developed by others [2-4]. In this system, a spatially varying and circularly symmetric voltage profile can be generated across a liquid-crystal cell, generating a lens-like refractive index profile. Such devices are simple in design, and do not require a pixellated structure. The shape and focussing power of the lens can be controlled by the variation of applied electric field and frequency. Results show adaptive lenses operating at optical wavelengths with continuously variable focal lengths from infinity to 70 cm. Switching speeds are of the order of 1 second between focal positions. Manufacturing methods of our adaptive lenses are presented, together with the latest results to the performance of these devices.
In this paper we review progress towards making a liquid crystal spatial light modulator (LC-SLM) which has all the desired specifications required for (astronomical) adaptive optics (AO). Our work at Durham is currently focused on developing modal LCs, as they have some key advantages over conventional LC-SLMs. A modal LC-SLM is a device whose optical properties more closely resemble a deformable facesheet mirror than a conventional LC-SLM which are pixelated. Therefore they have a Gaussian, rather than a piston-only, influence function.