Optical trapping: optical interferometric metrology and nanophotonics

The two main themes in this thesis are the implementation of interference methods with optically trapped particles for measurements of position and optical phase (optical interferometric metrology) and the optical manipulation of nanoparticles for studies in the assembly of nanostructures, nanoscale heating and nonlinear optics (nanophotonics). The first part of the thesis (chapter 1, 2) provides an introductory overview to optical trapping and describes the basic experimental instrument used in the thesis respectively. The second part of the thesis (chapters 3 to 5) investigates the use of optical interferometric patterns of the diffracting light fields from optically trapped microparticles for three types of measurements: calibrating particle positions in an optical trap, determining the stiffness of an optical trap and measuring the change in phase or coherence of a given light field. The third part of the thesis (chapters 6 to 8) studies the interactions between optical traps and nanoparticles in three separate experiments: the optical manipulation of dielectric enhanced semiconductor nanoparticles, heating of optically trapped gold nanoparticles and collective optical response from an ensemble of optically trapped dielectric nanoparticles

In situ retrieval and correction of aberrations in moldless lenses using Fourier ptychography

Liquid droplets cured at low temperatures or using ultraviolet light are primary approaches for fabricating refractive lenses without molds. Until now the performance of moldless lens fabrication process relied heavily on this step to precisely control the shape of each liquid droplet. Hence, a major hurdle in lenses fabricated from liquid droplets is the large variability of droplet shapes because they are sensitive to small amounts of interfacial forces. The shape of the final droplet critically affects the imaging performance of the lenses and cannot be reversed easily. Here, we aim to overcome this hurdle by performing in situ aberration correction using Fourier ptychography techniques. We demonstrate, for the first time, that computational optics can reverse high amounts of optical aberrations in moldless lenses and achieve high resolution imaging. In terms of imaging resolution, we successfully increased the resolving power of low powered moldless elastomer lenses by almost three-fold, from a numerical aperture of 0.035 to 0.099. The computational approach directly elucidates the spatially varying wavefront aberrations from each lens using the same imaging system. This provides direct feedback of droplet lens fabrication techniques without the need for advanced wavefront correction methods. The application of computational imaging onto moldless lenses, using consumer digital imaging systems, lends itself to the global efforts in decentralising high resolution image intensive scientific tools to the wider community.FERL program; Australian Research Council Early Career Researcher Award (DE160100843

Intravital microscopic interrogation of peripheral taste sensation

Intravital microscopy is a powerful tool in neuroscience but has not been adapted to the taste sensory organ due to anatomical constraint. Here we developed an imaging window to facilitate microscopic access to the murine tongue in vivo. Real-time two-photon microscopy allowed the visualization of three-dimensional microanatomy of the intact tongue mucosa and functional activity of taste cells in response to topically administered tastants in live mice. Video microscopy also showed the calcium activity of taste cells elicited by small-sized tastants in the blood circulation. Molecular kinetic analysis suggested that intravascular taste sensation takes place at the microvilli on the apical side of taste cells after diffusion of the molecules through the pericellular capillaries and tight junctions in the taste bud. Our results demonstrate the capabilities and utilities of the new tool for taste research in vivo

Mobile microscopy on the move

In this paper, we demonstrate the application of low cost light weight imaging device that amplifies the imaging resolution of a smartphone camera by three orders of magnitude from millimeters to sub-micrometers. We attached the lens onto a commercial smartphone camera and imaged micrometer graticules, pathological biological tissue slides and skin which validate the imaging quality of lenses

Optical trapping using ultrashort 12.9fs pulses

We demonstrate stable three-dimensional optical trapping of 780nm silica particles using a dispersion-compensated 12.9fs infrared pulsed laser and a trapping microscope system with 1.40NA objective. To achieve these pulse durations we use the Multiphoto

Resolving inter-particle position and optical forces along the axial direction using optical coherence gating

We demonstrate the use of coherence gating to resolve particle positions and forces in the axial direction. High depth resolvability (axial) and weak optical force (10-15 N) measurements in an optical trapping system is achieved

Spatially optimized gene transfection by laser-induced breakdown of optically trapped nanoparticles

We demonstrate laser-induced breakdown of an optically trapped nanoparticle with a nanosecond laser pulse. Controllable cavitation within a microscope sample was achieved, generating shear stress to monolayers of live cells. This efficiently permeabilize their plasma membranes. We show that this technique is an excellent tool for plasmid-DNA transfection of cells with both reduced energy requirements and reduced cell lysis compared to previously reported approaches. Simultaneous multisite targeted nanosurgery of cells is also demonstrated using a spatial light modulator for parallelizing the technique.Publisher PDFPeer reviewe

Shaping self-imaging bottle beams with modified quasi-Bessel beams

Coherent generated self-imaging bottle beams, typically formed by interfering two coherent quasi-Bessel beams, possess a periodic array of intensity maxima and minima along their axial direction. In practice, the overall quality of the self-repeating intensity patterns is prone to unresolved large intensity variations. In this Letter, we increased consistency of intensity of self-imaging bottle beams through a spatial frequency optimization routine. By doing so, we increased the effective length of self-imaging bottle beams by 74%. Further, we showed that this approach is applicable to higher-order self-imaging beams that display complex intensity structures. The enhancement in these modified self-imaging beams could play a significant role in optical trapping, imaging, and lithography.This work is financially supported by the State Key Program for Basic Research of China (Grant No. 2012CB921904), the National Natural Science Foundation of China (Grant No. 61205018), the Fundamental Research Funds for the Central Universities, and Australian Research Council’s/Discovery Projects/ funding scheme (Project No. DP110100975)

Dynamic axial control over optically levitating particles in air with an electrically-tunable variable-focus lens

Efficient delivery of viruses, proteins and biological macromelecules into a micrometer-sized focal spot of an XFEL beam for coherent diffraction imaging inspired new development in touch-free particle injection methods in gaseous and vacuum environments. This paper lays out our ongoing effort in constructing an all-optical particle delivery approach that uses piconewton photophoretic and femtonewton light-pressure forces to control particle delivery into the XFEL beam. We combine a spatial light modulator (SLM) and an electrically tunable lens (ETL) to construct a variable-divergence vortex beam providing dynamic and stable positioning of levitated micrometer-size particles, under normal atmospheric pressure. A sensorless wavefront correction approach is used to reduce optical aberrations to generate a high quality vortex beam for particle manipulation. As a proof of concept, stable manipulation of optically-controlled axial motion of trapped particles is demonstrated with a response time of 100ms. In addition, modulation of trapping intensity provides a measure of the mass of a single, isolated particle. The driving signal of this oscillatory motion can potentially be phase-locked to an external timing signal enabling synchronization of particle delivery into the x-ray focus with XFEL pulse train.This work has been supported by the Australian Research Council under DP110100975. W. M. Lee acknowledges the support of Australian Research Council Early Career Researcher Award, DE160100843