Black Metals: Optical Absorbers.

We demonstrate a concept and fabrication of lithography-free layered metal-SiO2 thin-film structures which have reduced reflectivity (black appearance), to as low as 0.9%, with 4.9% broadband reflectance (8.

Breaking the Symmetry of Momentum Conservation Using Evanescent Acoustic Fields.

Although the conservation of momentum is a fundamental law in physics, its constraints are not fulfilled for wave propagation at material boundaries, where incident waves give rise to evanescent field distributions. While nonlinear susceptibility tensor terms can provide solutions in the optical regime, this framework cannot be applied directly to acoustic waves. Now, by considering a complete representation of wave interactions and scattering at boundaries, we are able to show a generic formalism of sum-frequency mixing for the whole scattering field including all evanescent waves.

Wide-field multiphoton imaging through scattering media without correction.

Optical approaches to fluorescent, spectroscopic, and morphological imaging have made exceptional advances in the last decade. Super-resolution imaging and wide-field multiphoton imaging are now underpinning major advances across the biomedical sciences. While the advances have been startling, the key unmet challenge to date in all forms of optical imaging is to penetrate deeper.

Ultrasonic waves in uniaxially stressed multilayered and one-dimensional phononic structures: Guided and Floquet wave analysis.

This paper shows that acoustoelasticity in one-dimensional (1D) multilayered isotropic hyperelastic materials can be understood through the analysis of elastic wave velocities as a function of applied stress. This theoretical framework is used for eigenvalue analyses in stressed elastic structures through a reformulation of the stiffness matrix method, obtaining modal solutions, as well as reflection and transmission coefficients for different multilayered configurations. Floquet wave analysis for the stressed 1D structures is supported using numerical results.

Hyperelastic Tuning of One-Dimensional Phononic Band Gaps Using Directional Stress.

In this paper, we show that acoustoelasticity in hyperelastic materials can be understood using the framework of nonlinear wave mixing, which, when coupled with an induced static stress, leads to a change in the phase velocity of the propagating wave with no change in frequency. By performing Floquet wave eigenvalue analysis, we also show that band gaps for periodic composites, acting as 1-D phononic crystals, can be tuned using this static stress. In the presence of second-order elastic nonlinearities, the phase velocity of propagating waves in the phononic structure changes, leading to observable shifts in the band gaps.

Light-sheet microscopy with attenuation-compensated propagation-invariant beams.

Scattering and absorption limit the penetration of optical fields into tissue. We demonstrate a new approach for increased depth penetration in light-sheet microscopy: attenuation-compensation of the light field. This tailors an exponential intensity increase along the illuminating propagation-invariant field, enabling the redistribution of intensity strategically within a sample to maximize signal and minimize irradiation.

Harnessing speckle for a sub-femtometre resolved broadband wavemeter and laser stabilization.

The accurate determination and control of the wavelength of light is fundamental to many fields of science. Speckle patterns resulting from the interference of multiple reflections in disordered media are well-known to scramble the information content of light by complex but linear processes. However, these patterns are, in fact, exceptionally rich in information about the illuminating source.

Rotational Dynamics and Heating of Trapped Nanovaterite Particles.

We synthesize, optically trap, and rotate individual nanovaterite crystals with a mean particle radius of 423 nm. Rotation rates of up to 4.9 kHz in heavy water are recorded.

Encoding complex valued fields using intensity.

We present an approach enabling the representation of complex values using intensity only fields. The method can be used for imaging with structured illumination and allows the study of new propagating physical quantities with the classical coherent or incoherent light field playing the role of hidden variable. This approach can further be generalized to encode higher order N-dimensional vectors and ensembles of N orthogonal fields.

Is there an optimal basis to maximise optical information transfer?

We establish the concept of the density of the optical degrees of freedom that may be applied to any photonics based system. As a key example of this versatile approach we explore information transfer using optical communication. We demonstrate both experimentally, theoretically and numerically that the use of a basis set with fields containing optical vortices does not increase the telecommunication capacity of an optical system.

Rotation of two trapped microparticles in vacuum: observation of optically mediated parametric resonances.

We demonstrate trapping and rotation of two mesoscopic particles in vacuum using a spatial-light-modulator-based approach to trap more than one particle, induce controlled rotation of individual particles, and mediate interparticle separation. By trapping and rotating two vaterite particles, we observe intensity modulation of the scattered light at the sum and difference frequencies with respect to the individual rotation rates. This first demonstration of optical interference between two microparticles in vacuum leads to a platform to potentially explore optical binding and quantum friction effects.

Modulated Raman Spectroscopy for Enhanced Cancer Diagnosis at the Cellular Level.

Raman spectroscopy is emerging as a promising and novel biophotonics tool for non-invasive, real-time diagnosis of tissue and cell abnormalities. However, the presence of a strong fluorescence background is a key issue that can detract from the use of Raman spectroscopy in routine clinical care. The review summarizes the state-of-the-art methods to remove the fluorescence background and explores recent achievements to address this issue obtained with modulated Raman spectroscopy.

The use of wavelength modulated Raman spectroscopy in label-free identification of T lymphocyte subsets, natural killer cells and dendritic cells.

Determining the identity of cells of the immune system usually involves destructive fixation and chemical staining, or labeling with fluorescently labeled antibodies recognising specific cell surface markers. Completely label-free identification would be a significant advantage in conditions where untouched cells are a priority. We demonstrate here the use of Wavelength Modulated Raman Spectroscopy, to achieve label-free identification of purified, unfixed and untouched populations of major immune cell subsets isolated from healthy human donors.

Quantitative detection of pharmaceuticals using a combination of paper microfluidics and wavelength modulated Raman spectroscopy.

Raman spectroscopy has proven to be an indispensable technique for the identification of various types of analytes due to the fingerprint vibration spectrum obtained. Paper microfluidics has also emerged as a low cost, easy to fabricate and portable approach for point of care testing. However, due to inherent background fluorescence, combining Raman spectroscopy with paper microfluidics is to date an unmet challenge in the absence of using surface enhanced mechanisms.

Development of a graded index microlens based fiber optical trap and its characterization using principal component analysis.

We demonstrate a miniaturized single beam fiber optical trapping probe based on a high numerical aperture graded index (GRIN) micro-objective lens. This enables optical trapping at a distance of 200μm from the probe tip. The fiber trapping probe is characterized experimentally using power spectral density analysis and an original approach based on principal component analysis for accurate particle tracking.

Prospects for versatile phase manipulation in the TEM: beyond aberration correction.

In this paper we explore the desirability of a transmission electron microscope in which the phase of the electron wave can be freely controlled. We discuss different existing methods to manipulate the phase of the electron wave and their limitations. We show how with the help of current techniques the electron wave can already be crafted into specific classes of waves each having their own peculiar properties.

Biologically enabled sub-diffractive focusing.

Evolution shows that photonic structures are a constituent part of many animals and flora. These elements produce structural color and are useful in predator-prey interactions between animals and in the exploitation of light for photosynthetic organisms. In particular, diatoms have evolved patterned hydrated silica external valves able to confine light with extraordinary efficiency.

Generation of attenuation-compensating Airy beams.

We present an attenuation-corrected "nondiffracting" Airy beam. The correction factor can be adjusted to deliver a beam that exhibits an adjustable exponential intensity increase or decrease over a finite distance. A digital micromirror device that shapes both amplitude and phase is used to experimentally verify the propagation of these beams through air and partially absorbing media.

Reproducible surface-enhanced Raman quantification of biomarkers in multicomponent mixtures.

Direct and quantitative detection of unlabeled glycerophosphoinositol (GroPIns), an abundant cytosolic phosphoinositide derivative, would allow rapid evaluation of several malignant cell transformations. Here we report label-free analysis of GroPIns via surface-enhanced Raman spectroscopy (SERS) with a sensitivity of 200 nM, well below its apparent concentration in cells. Crucially, our SERS substrates, based on lithographically defined gold nanofeatures, can be used to predict accurately the GroPIns concentration even in multicomponent mixtures, avoiding the preliminary separation of individual compounds.

Random super-prism wavelength meter.

The speckle pattern arising from a thin random, disordered scatterer may be used to detect the transversal mode of an incident beam. On the other hand, speckle patterns originating from meter-long multimode fibers can be used to detect different wavelengths. Combining these approaches, we develop a method that uses a thin random scattering medium to measure the wavelength of a near-infrared laser beam with picometer resolution.

Dynamics of microparticles trapped in a perfect vortex beam.

We analyze microparticle dynamics within a "perfect" vortex beam. In contrast to other vortex fields, for any given integer value of the topological charge, a "perfect" vortex beam has the same annular intensity profile with fixed radius of peak intensity. For a given topological charge, the field possesses a well-defined orbital angular momentum density at each point in space, invariant with respect to azimuthal position.

Laser-induced rotation and cooling of a trapped microgyroscope in vacuum.

Quantum state preparation of mesoscopic objects is a powerful playground for the elucidation of many physical principles. The field of cavity optomechanics aims to create these states through laser cooling and by minimizing state decoherence. Here we demonstrate simultaneous optical trapping and rotation of a birefringent microparticle in vacuum using a circularly polarized trapping laser beam--a microgyroscope.

Exploiting lens aberrations to create electron-vortex beams.

A model for a new electron-vortex beam production method is proposed and experimentally demonstrated. The technique calls on the controlled manipulation of the degrees of freedom of the lens aberrations to achieve a helical phase front. These degrees of freedom are accessible by using the corrector lenses of a transmission electron microscope.

Optimisation of wavelength modulated Raman spectroscopy: towards high throughput cell screening.

In the field of biomedicine, Raman spectroscopy is a powerful technique to discriminate between normal and cancerous cells. However the strong background signal from the sample and the instrumentation affects the efficiency of this discrimination technique. Wavelength Modulated Raman spectroscopy (WMRS) may suppress the background from the Raman spectra.