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

The concept of the transmission cross-coefficient (TCC) is used to describe three-dimensional (3D) imaging in transmission and reflection confocal scanning microscopes with a finite-sized detector. The effects of the detector size are studied in detail in terms of the 3D weak-object transfer functions (WOTFs) for weakly scattering objects. As is already known, 3D transmission imaging for an infinitely large detector and for a point detector are identical, whereas it is shown that between two limiting cases the behaviour is different, suggesting that axial phase information can be imaged. It is found that 3D reflection imaging for an infinitely large detector can be equivalent to 3D true confocal imaging using one annular and one circular pupil. The 3D WOTF in reflection reveals negative values which may reverse the contrast of an image at some spatial frequencies.

Three-dimensional Partially-coherent Image Formation in Confocal Microscopes with a Finite-sized Detector

Perovskite solar cells hold great promise as prospective alternatives of renewable power sources. Recently hole blocking layer-free perovskite solar cells, getting rid of complex and high-temperatu...

Hole Blocking Layer-Free Perovskite Solar Cells with High Efficiencies and Stabilities by Integrating Subwavelength-Sized Plasmonic Alloy Nanoparticles

The surface stress on the real shape (biconcave disklike) of an erythrocyte under laser irradiation is theoretically studied according to the finite-difference time-domain (FDTD) method. The distribution of the surface stresses depends on the orientation of erythrocytes in the laser beam. Typically when the erythrocyte was irradiated from the side direction (the laser beam was perpendicular to the normal of the erythrocyte plane), the surface stresses were so asymmetrical and nonuniform that the magnitude of the surface stress on the back surface was three times higher than that on the front surface, and the highest-to-lowest ratio of the stress reached 16 times. For comparison, the surface stress was also calculated according to the ray optics (RO) method. The tendency of the stress distribution from the RO calculation was roughly similar to that of the FDTD method. However the RO calculation produced some unphysical results, such as the infinite stress on some surface region and the zero stress on the most parts of the erythrocyte surface, which is due to the neglecting of light diffraction. The results obtained from the FDTD calculation are believed quantitatively reliable, because the FDTD method automatically takes into account of the diffraction and interference effects of the light wave. Thus, the FDTD method is more suitable than the RO method for the stress study of erythrocytes.

https://researchbank.swinburne.edu.au/file/e866a141-9f54-4d6e-bd5e-2eeeae204d55/1/PDF (Published version).pdf

Surface stress on the erythrocyte under laser irradiation with finite-difference time-domain calculation.

In this paper, we report on the enhanced photorefractivity induced by the exciton-plasmon coupling in type-II CdSe/CdTe quantum-dot (QD) and gold-nanoparticle (NP)-doped polymeric nanocomposites (NCs). The new NCs exhibit a nearly 110% increase in the refractive-index grating construction speed and a 100% enhancement in the two-beam coupling gain coefficient compared with those of QD-sensitized samples at moderate biases. These features are achieved by the exciton-plasmon coupling between QDs and Au NPs, which leads to not only an enhanced charge separation process but also a reduced recombination probability of free carriers during the charge transport.

https://researchbank.swinburne.edu.au/file/198c85aa-7781-4f79-ac03-64a4438453b5/1/PDF (Published version).pdf

Exciton-plasmon coupling mediated photorefractivity in gold-nanoparticle- and quantum-dot-dispersed polymers

We demonstrate the direct detection of photon spin angular momentum in the mid-infrared region by a single surface-plasmon-enhanced graphene photodetector. We utilize chiral surface plasmon nanostructures as photodetector electrodes to generate photocurrents of equal and opposite sign according to incident photon spin. Our detector possesses a current circular dichroism of 60% and a responsivity of 0.80 μA/W at a resonant wavelength of 3.8 μm. The photocurrent dichroism is attributed to the presence of opposite handedness circularly polarized surface plasmon resonances on adjacent electrodes, of which each enhances graphene absorption by a factor of 17. The direct detection of spin angular momentum will be useful in the next wave of multiplexed sensing and communications systems utilizing the optical angular momentum states of light to enhance bandwidth and information collection.

Min Gu

Papers

Three-dimensional Partially-coherent Image Formation in Confocal Microscopes with a Finite-sized Detector

Hole Blocking Layer-Free Perovskite Solar Cells with High Efficiencies and Stabilities by Integrating Subwavelength-Sized Plasmonic Alloy Nanoparticles

Surface stress on the erythrocyte under laser irradiation with finite-difference time-domain calculation.

Exciton-plasmon coupling mediated photorefractivity in gold-nanoparticle- and quantum-dot-dispersed polymers

Direct detection of photon spin angular momentum by a chiral graphene mid-infrared photodetector