Optical tweezers use the forces exerted by a strongly focused beam of light to trap and move objects ranging in size from tens of nanometres to tens of micrometres. Since their introduction in 1986, the optical tweezer has become an important tool for research in the fields of biology, physical chemistry and soft condensed matter physics. Recent advances promise to take optical tweezers out of the laboratory and into the mainstream of manufacturing and diagnostics; they may even become consumer products. The next generation of single-beam optical traps offers revolutionary new opportunities for fundamental and applied research.

http://physics.nyu.edu/grierlab/nreview2c/nreview2c.pdf

A revolution in optical manipulation

On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory simultaneously observed a transient gravitational-wave signal. The signal sweeps upwards in frequency from 35 to 250 Hz with a peak gravitational-wave strain of 1.0×10(-21). It matches the waveform predicted by general relativity for the inspiral and merger of a pair of black holes and the ringdown of the resulting single black hole. The signal was observed with a matched-filter signal-to-noise ratio of 24 and a false alarm rate estimated to be less than 1 event per 203,000 years, equivalent to a significance greater than 5.1σ. The source lies at a luminosity distance of 410(-180)(+160)  Mpc corresponding to a redshift z=0.09(-0.04)(+0.03). In the source frame, the initial black hole masses are 36(-4)(+5)M⊙ and 29(-4)(+4)M⊙, and the final black hole mass is 62(-4)(+4)M⊙, with 3.0(-0.5)(+0.5)M⊙c(2) radiated in gravitational waves. All uncertainties define 90% credible intervals. These observations demonstrate the existence of binary stellar-mass black hole systems. This is the first direct detection of gravitational waves and the first observation of a binary black hole merger.

/pdf/the-observation-of-gravitational-waves-from-a-binary-black-58srpupgg9.pdf

The Observation of Gravitational Waves from a Binary Black Hole Merger

With few exceptions biological tissues strongly scatter light, making high-resolution deep imaging impossible for traditional⎯including confocal⎯fluorescence microscopy. Nonlinear optical microscopy, in particular two photon–excited fluorescence microscopy, has overcome this limitation, providing large depth penetration mainly because even multiply scattered signal photons can be assigned to their origin as the result of localized nonlinear signal generation. Two-photon microscopy thus allows cellular imaging several hundred microns deep in various organs of living animals. Here we review fundamental concepts of nonlinear microscopy and discuss conditions relevant for achieving large imaging depths in intact tissue.

/pdf/deep-tissue-two-photon-microscopy-2aqu6d6n65.pdf

Deep tissue two-photon microscopy

Multiphoton microscopy (MPM) has found a niche in the world of biological imaging as the best noninvasive means of fluorescence microscopy in tissue explants and living animals. Coupled with transgenic mouse models of disease and 'smart' genetically encoded fluorescent indicators, its use is now increasing exponentially. Properly applied, it is capable of measuring calcium transients 500 microm deep in a mouse brain, or quantifying blood flow by imaging shadows of blood cells as they race through capillaries. With the multitude of possibilities afforded by variations of nonlinear optics and localized photochemistry, it is possible to image collagen fibrils directly within tissue through nonlinear scattering, or release caged compounds in sub-femtoliter volumes.

/pdf/nonlinear-magic-multiphoton-microscopy-in-the-biosciences-3fszv5aq8z.pdf

Nonlinear magic: multiphoton microscopy in the biosciences

Diarylethenes for Memories and Switches

We demonstrate that the use of a radially polarized beam is more efficient for both imaging and therapy for cancer cells labelled with gold nanorods, compared with that of a linearly polarized beam.

https://researchbank.swinburne.edu.au/file/4566e347-bee7-47dd-b041-9476a6699151/1/PDF (Published version).pdf

Use of a Radially Polarized Beam for Ultra-low Energy Threshold for Cancer Photothermal Therapy with Gold Nanorods

Zero-index medium (ZIM) enables light propagating without spatial phase distortions, resulting in perfectly stationary phase profiles [1] . Due to this extraordinary electromagnetic property, ZIM has extensive applications in the manipulation of electromagnetic waves, novel antenna and waveguide devices, electro-optical modulation, etc [2] . It is recently found that Dirac-like conical dispersions at k=0 in certain two-dimensional (2D) photonic crystals (PC) can facilitate the realization of ZIM [3] . Compared with ZIM using metallic or topological insulating materials [4] , PCs can eliminate ohmic losses via their pure dielectric structures. However, the 2D nature of these PCs still entails inevitable out-of-plane radiation loss and incompatibility for three-dimensional (3D) applications [5] . To realize ZIM in PCs, a Dirac-like cone at k=0 is necessary, and it could to be mapped to an e eff =0 and μ eff =0 system only if an effective medium theory can be satisfactorily applied [3] . In this sense, design a 3D PC with a linear Dirac-like cone at k=0 that can function as ZIM would be of great significance for 3D applications where ultra-low loss is required, but also could unveil the subtle link between Dirac-like cones and effective medium theory.

Design and Realization of a Three-dimensional Dielectric Zero-Index Metamaterial based on Steiner Tree Networks


 Nonlinear materials have gained wide interest as saturable absorbers and pulse compression for pulsed laser applications due to their unique optical properties. This work investigates the third-order nonlinear phenomenon of tungsten trioxide (WO3) thin films. The giant nonlinear absorption and nonlinear refractive index of WO3 thin films are characterized by Z-scan method at 800 nm. We experimentally observed the giant saturable absorption (SA) and nonlinear refractive index of WO3 thin films prepared by the seedless layer hydrothermal method, with SA coefficient being as high as -2.59×105 cm GW-1. The SA coefficient is at least one order of magnitude larger than those of the conventional semiconductors. The nonlinear refractive index n2 of WO3 film has been observed for the first time in recent studies and the corresponding coefficient can be up to 1.793 cm2 GW-1. The large third-order nonlinear optical (NLO) response enables WO3 thin films to be promising candidates for optoelectronic and photonic applications in the near-infrared domain.

Giant saturation absorption of tungsten trioxide film prepared based on the seedless layer hydrothermal method

Far-field super-resolution optical technologies offer methods to high-capacity nanoscale optical memory. Typical approaches need high beam power and energy consumption. Because they can convert near-infrared excitation to ultraviolet and visible emission, upconversion nanoparticles show potential for photo-activation. Upconversion nanoparticles have metastable excited energy levels, enabling low-power stimulated emission depletion microscopy. We show the use of upconversion nanoparticles for low-power nanoscale photo-activation for high-capacity low-energy consumption optical memory. Upconversion nanoparticles were combined with photo-active compounds. Super-resolution irradiation excited upconversion nanoparticles for photo-activation in the nanocomposite. Written features showed nanoscale size under low-intensity irradiation and enabled multiple optical readouts. 

Low-power nanoscale optical memory by upconversion-based photo-activation

We present the results of using polymer-dispersed liquid crystal for three-dimensional bit optical data storage based on its two-photon induced polarisation sensitivity. A bit density of 23.5 Gbits/cm/sup 3/ and complete erasure of the data via ultra-violet illumination were achieved.

https://researchbank.swinburne.edu.au/file/3558c28b-3f10-4f29-9fdb-0be9a1427e20/1/PDF (Published version).pdf

Min Gu

Papers

Use of a Radially Polarized Beam for Ultra-low Energy Threshold for Cancer Photothermal Therapy with Gold Nanorods

Design and Realization of a Three-dimensional Dielectric Zero-Index Metamaterial based on Steiner Tree Networks

Giant saturation absorption of tungsten trioxide film prepared based on the seedless layer hydrothermal method

Low-power nanoscale optical memory by upconversion-based photo-activation

Multi-layered optical data storage in a polymer-dispersed liquid crystal material under two-photon excitation