The nitrogen-vacancy (NV) centre in diamond gained popularity as a probe for nanoscale sensing applications in research thanks to the array of sensing modalities available and the bio-compatibility of the material itself, however the utility of NV sensing is limited by the lack of suitable strategies to control them spatially. By confining single nanodiamonds using an optical tweezers (OT) we are able to combine the sensing opportunities of the NV centre with the precision control of position and orientation afforded by OT. This work is an investigation of the interaction of the trapping laser with the spin-based photoluminescence of the NV centre, further it is a demonstration of an all-optical sensing protocol which eliminates the spin depolarisation effects of the trapping laser and allows for NV spin relaxometry in an optically trapped nanodiamond. This relaxometry protocol can determine spin lattice relaxation times on the order of ms and requires relatively low trapping powers < 50 mW, making it particularly applicable to biological systems.
Optically Trapped Probe Microscopy (OTPM) is an emerging imaging technique using optically trapped objects as near-field probes, able to sense a variety of local effects by utilizing different probe materials and geometries. However, the quest for super-resolution in OTPM presents an almost insurmountable barrier; the ever-present stochastic Brownian motion of the trapped object, which serves to geometrically broaden the acquired signal and degrade resolving capacity. A reduction of Brownian motion can be achieved through active trap control or increased laser power, but these approaches carry increased system costs and complexities, or could jeopardize the life-safe nature of IR optical trap experiments. In this poster, we present a post-processing solution to the Brownian motion problem; by splitting measurements into microsecond-length integrations and simultaneously measuring the position of the trapped probe, deconvolution of the effect of Brownian motion on transmitted signal is possible. We conduct an experimental and simulated investigation into this post-processing, and are able to reduce the noise and increase resolution of a variety of excitation patterns in a trapped nanodiamond fluorescence microscope.
In the following study we investigate the dynamics of high aspect ratio nanowires held in a single gradient force optical trap in an overdamped environment. Power spectrum analysis performed on the stochastic trajectory of the optically trapped nanowires indicate that the motion of these nanowires shows characteristics of underdamped motion, where a broad resonance peak is present in the power spectrum of amplitude fluctuations under certain conditions. The resonance occurs when the nanowires are trapped at a height of 50 μm from the cover slip of the sample chamber. The emergence of a resonance peak in the power spectrum could be attributed to the non-conservative motion of nanowires being nonspherical, thus creating a bias towards cyclic motion as examined theoretically by Simpson and Hanna .
We present a study of the trapping properties of Au nanorods of different aspect ratios in an optical tweezers and comparison with other characterization techniques like transmission electron microscope (TEM) imaging and dynamic light scattering (DLS). This study provides information on the dynamics and orientation of Au nanorods inside an optical trap based on a time study of their localised surface plasmon resonance (LSPR) features. The results indicate that the orientation of the Au nanorods trapped in our optical tweezers varies with time and LSPR spectra can provide information on the angle of the nanorod with respect to the direction of propagation of the trapping laser.
In this paper we demonstrate the possibility of modifying porous silicon (PSi) particles with surface chemistry and
immobilizing a biopolymer, gelatin for the detection of protease enzymes in solution. A rugate filter, a one-dimensional
photonic crystal, is fabricated that exhibits a high-reflectivity optical resonance that is sensitive to small changes in the
refractive index. To immobilize gelatin in the pores of the particles, the hydrogen-terminated silicon surface was first
modified with an alkyne, 1,8-nonadiyne via hydrosilylation to protect the silicon surfaces from oxidation. This
modification allows for further functionality to be added such as the coupling of gelatin. Exposure of the gelatin
modified particles to the protease subtilisin in solution causes a change in the refractive index, resulting in a shift of the
resonance to shorter wavelengths, indicating cleavage of organic material within the pores. The ability to monitor the
spectroscopic properties of microparticles, and shifts in the optical signature due to changes in the refractive index of the
material within the pore space, is demonstrated.
We present a novel method for spatial mapping of the luminescent properties of single optically trapped semiconductor
nanowires by combing dynamic optical tweezers with micro-photoluminescence. The technique involves the use of a
spatial light modulator (SLM) to control the axial position of the trapping focus relative to the excitation source and
collection optics. When a nanowire is held in this arrangement, scanning the axial position of the trapping beam enables
different sections of the nanowire axis to be probed. In this context we consider the axial resolution of the luminescence
mapping and optimization of the nanowire trapping by spherical aberration correction.
Solar cell efficiency can be increased by adding a rear layer that captures unabsorbed low-energy
photons and combines their energy to emit higher-energy photons. This concept has been demonstrated
for silicon solar cells using erbium-doped phosphors. Here we investigate the possibility of enhancing
intra-4f up-conversion processes within band-edge slow light modes in photonic crystals. We discuss
the potential efficiency enhancement realizable one-dimensional erbium-doped porous silicon photonic
crystals and present preliminary investigations into these interactions in a real structure.
We report on the dynamics of micro-photoluminescence of single InP semiconductor nanowires trapped in a gradient
force optical tweezers. Nanowires studied were of zinc blende, wurtzite or mixed phase crystal poly-types and ranged in
length from one to ten micrometers. Our results show that the band-edge emission from trapped nanowires exhibits a
quenching of the initial intensity with a characteristic time scale of a few seconds and an associated spectral red shift is
also observed in the mixed phase nanowires.
We present results describing the behavior of optically trapped airborne particles, both solid and liquid. Using back focal
plane interferometry we measure characteristic power spectra describing the position fluctuations within the trap. We
show it is easy to transfer between an over and under damped regime by either varying the trapping power or the
distance into the medium the beam is focused. The results assist in the understanding of airborne tweezers and it is hoped
having under damped systems could lead to exploring analogies in many areas of fundamental physics.
In the following paper we explore the dynamics of single colloidal particles and particle aggregates in a counterpropagating
cavity-enhanced evanescent wave optical trap. For this study we make use of Fabry-Perot like cavity modes
generated in a prism-coupled resonant dielectric waveguide. The advantage of using this type of optical structure is that
there is an enhancement in the electric field of the evanescent at the sample surface that may be used to achieve greater
coupling to colloidal particles for the purposes of optical micromanipulation. We demonstrate an order of magnitude
increase in the optical forces acting on micrometer sized colloidal particles using cavity enhanced evanescent waves,
compared with evanescent wave produced by conventional prism-coupling techniques. The combination of the enhanced
optical interaction and the wide area illumination provided by the prism coupler makes it an ideal geometry for studying
the collective dynamics of many particles over a large area. We study the different type of ordering observed when
particles of different sizes are accumulated at the centre of this novel optical trap. We find that for large particles sizes
(greater than 2μm), colloid dynamics are primarily driven by thermodynamics, whilst for smaller particles, in the range
of 200-600nm, particles ordering is dictated by optical-matter interactions. We suggest a qualitative model for the
observed optically induced ordering occurs and discuss how these results tie in with existing demonstrations of twodimensional
In the following paper we show that near-field optical manipulation can be greatly increased through the use of cavity enhanced evanescent fields. This approach utilises a resonant dielectric structure and a prism coupler to produce Fabry- Perot like cavity modes at a dielectric-fluid interface, which can be utilised in optical manipulation. Using this structure we show a ten-times increase in the optical interaction of micrometer-sized colloids compared with the standard evanescent wave configuration. In addition, stable accumulation and ordering of large-scale arrays of colloids is demonstrated using two counter propagating cavity enhanced evanescent fields. We believe that this technique has considerable scope for promoting the role of near-field optical manipulation at the nanometer scale.
The concept of photonic crystal (PC) was raised by E.Yablonovitch and S.John respectively in 1989. Since then on, photonic crystal made tremendous progress in the research and application. Photonic crystal is not some kind of new materials but periodic dielectric materials. We have designed, fabricated photonic crystal slab (PCS) based on porous silicon. These alternating dielectric porous silicon layers show a band gap in one direction. Incident light is reflected for colors of light in the band gap, so porous silicon photonic crystal slabs have high reflection in the range of band gap. By mean of electrochemical lift-off, the PCS could be removed from silicon substrate, and PC band gap could be observed clearly in the reflectivity spectra.
We describe a new method for doping high-quality porous silicon microcavities with erbium using ion implantation, where the erbium is confined to the spacer layer of the structure. This method involves fabricating porous silicon microcavities from a crystalline silicon wafer that has been implanted with erbium to a depth that coincides with a spacer layer of the microcavity. Using this technique erbium doped microcavities with Q-factors in excess of 1500 have been demonstrated. From low temperature photoluminescence measurements we observe a strong modification of the spontaneous emission spectrum of the erbium doped PSi, where the emission is enhanced 25 times at the resonance and suppressed elsewhere. Temperature dependent photoluminescence exhibited strong thermal quenching and excitation power dependent photoluminescence measurement showed saturation at high excitation powers. Both of these trends are characteristically similar to luminescent erbium centres in crystalline silicon. In addition we discuss the merits of localising the erbium in the crystalline part of the PSi and its potential for reducing the effects of Auger recombination and energy back-transfer, which limit the performance of the structures at room high temperatures.
We review a number of optical devices made from microporous silicon. Particular emphasis is placed on the fabrication method of porous silicon laser-mirrors, optical microcavities and one-dimensional photonic crystals with true photonic bandgap.