Showing papers by "Michael Mazilu published in 2014"

Random super-prism wavelength meter

Abstract: 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. The method is based on the application of principal component analysis, which is used for pattern recognition and is applied here to the case of speckle pattern categorization.

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

Abstract: 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. Our results represent a critical step toward the creation of SERS-based biosensor for rapid, label-free, and reproducible detection of specific molecules, overcoming limits of current experimental methods.

Biologically enabled sub-diffractive focusing.

Abstract: 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. Their evolution was probably guided by the necessity to survive in harsh conditions of sunlight deprivation. Here, we exploit such diatom valves, in conjunction with structured illumination, to realize a biological super-resolving lens to achieve sub-diffractive focusing in the far field. More precisely, we consider a single diatom valve of Arachnoidiscus genus which shows symmetries and fine features. By characterizing and using the transmission properties of this valve using the optical eigenmode technique, we are able to confine light to a tiny spot with unprecedented precision in terms of resolution limit ratio, corresponding in this case to 0.21λ/NA.

Dynamics of Microparticles Trapped in a Perfect Vortex Beam

Abstract: We trap and rotate particles using a perfect vortex beam with integer or fractional topological charges. A linear relationship is observed between the rotation speed and orbital angular momentum content of the beam.

Generation of attenuation-compensating Airy beams

Abstract: 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.

Nonredundant Raman imaging using optical eigenmodes

Abstract: Various forms of imaging schemes have emerged over the last decade that are based on correlating variations in incident illuminating light fields to the outputs of single “bucket” detectors. However, to date, the role of the orthogonality of the illumination fields has largely been overlooked, and, furthermore, the field has not progressed beyond bright field imaging. By exploiting the concept of orthogonal illuminating fields, we demonstrate the application of optical eigenmodes (OEis) to wide-field, scan-free spontaneous Raman imaging, which is notoriously slow in wide-field mode. The OEi approach enables a form of indirect imaging that exploits both phase and amplitude in image reconstruction. The use of orthogonality enables us to nonredundantly illuminate the sample and, in particular, use a subset of illuminating modes to obtain the majority of information from the sample, thus minimizing any photobleaching or damage of the sample. The crucial incorporation of phase, in addition to amplitude, in the imaging process significantly reduces background noise and results in an improved signal-to-noise ratio for the image while reducing the number of illuminations. As an example we can reconstruct images of a surface-enhanced Raman spectroscopy sample with approximately an order of magnitude fewer acquisitions. This generic approach may readily be applied to other imaging modalities such as fluorescence microscopy or nonlinear vibrational microscopy.

Optical trapping with a perfect vortex beam

Abstract: Vortex beams with dierent topological charge usually have dierent proles and radii of peak intensity. This introduces a degree of complexity the fair study of the nature of optical OAM (orbital angular momentum). To avoid this, we introduced a new approach by creating a perfect vortex beam using an annular illuminating beam with a xed intensity prole on an SLM that imposes a chosen topological charge. The radial intensity prole of such an experimentally created perfect vortex beam is independent to any given integer value of its topological charge. The well-dened OAM density in such a perfect vortex beam is probed by trapping microscope particles. The rotation rate of a trapped necklace of particles is measured for both integer and non-integer topological charge. Experimental results agree with the theoretical prediction. With the exibility of our approach, local OAM density can be corrected in situ to overcome the problem of trapping the particle in the intensity hotspots. The correction of local OAM density in the perfect vortex beam therefore enables a single trapped particle to move along the vortex ring at a constant angular velocity that is independent of the azimuthal position. Due to its particular nature, the perfect vortex beam may be applied to other studies in optical trapping of particles, atoms or quantum gases.

Random wavelength meter

Abstract: An optical system comprising a randomizer that has a plurality of randomly positioned scatterers for scattering and thereby randomizing light to generate a speckle pattern and a detector for detecting the speckle pattern to determine at least one property of the light and/or change in at least one property of the light

Combining focusing properties of a single diatom valve with optical eigenmodes in ultra-shrinking of light

Abstract: It is known that a properly arranged distribution of nanoholes on a metallic slab is able to produce, in far field conditions, light confinement at sub-diffraction and even sub-wavelength scale. The same effect can also be implemented by the use of Optical Eigenmode (OEi) technique. In this case, a spatial light modulator (SLM) encodes phase and amplitudes of N probe beams whose interference is able to lead to sub-wavelength confinement of light focused by an objective. The OEi technique has been already used in a wide range of applications, such as photoporation, confocal imaging, and coherent control of plasmonic nanoantennas. Here, we describe the application of OEi technique to a single valve of a marine diatom. Diatoms are ubiquitous monocellular algae provided with an external cell wall, the frustule, made of hydrated porous silica which play an active role in efficient light collection and confinement for photosynthesis. Every frustule is made of two valves interconnected by a lateral girdle band. We show that, applying OEi illumination to a single diatom valve, we can achieve unprecedented sub-diffractive focusing for the transmitted light.

Density of optical degrees of freedom : intensity, linear and angular momentum

Abstract: For any optical system, optical eigenmodes describe solutions of Maxwells equations that are orthogonal to each other. In their simplest free space form, these modes correspond, for example, to Bessel, Laguerre-Gaussian or Hermite-Gaussian beams. However, the orthogonality property is not limited to the intensity of the optical eld but more generally the optical eigenmode decomposition can be applied to the linear and angular momentum arising from complex coherent beams. These modes can be seen as describing the independent degrees of freedom of the optical system and are characterized by the mode, their density and coupling eciency. It is interesting to study the eect of dierent optical systems on the density of the optical degrees of freedom propagating through them. Here, we look at systems containing dierent elements such as: dielectric, meta-material and random lenses. Using the optical eigenmode decomposition, we determine their density in these dierent cases and discuss the origin of the variations observed. Further, we study the overall number of optical degrees of freedom accessible including linear and angular momentum of optical

Real-time optical eigenmode characterisation

Abstract: An optical system is characterised by its transmission eigenmodes. Here, we are using a digital micromirror device to detect these optical eigenmodes experimentally and to achieve applications in aberration correction and imaging.

SERS sensing of cancer biomarkers

Abstract: In this work, we establish the use a SERS biosensor based on gold fishnet as a label-free analytical technique for direct detection of glycerophosphoinositol (GroPIns). Here we demonstrate that with our approach we can quantitatively determine low concentration of GroPIns (200 nM) in multicomponent mixtures, with a high accuracy (up to 6%).

Biomolecular sensing for cancer diagnostics using highly reproducible SERS substrates

Abstract: We developed a SERS biosensor based on gold fishnets fabricated by using e-beam lithography. This device is used for glycerophosphoinositol (GroPIns) molecule sensing. GroPIns is an abundant component of cell cytosol and high GroPIns levels have been reported in several tumour cells. We demonstrate that our SERS sensor is able to accurately and quantitatively determine the concentration of GroPIns. These results indicate that SERS may provide a novel platform technology to identify GroPIns profiles in disease pathogenesis.

Sub-diffractive light confinement: A biological-based approach

Abstract: We report the generation of subdiffractive laser light focal spots in far-field regime, by means of the so-called Optical Eigenmodes (OEi) technique applied to the focusing properties of a single valve of Arachnoidiscus genus diatom. Diatoms are ubiquitous microalgae whose external walls are able to confine light in several hot-spots. We demonstrated that the presence of the valve brings a significant contribution to the OEi-induced light squeezing, improving its performance.

Multi-mode fibre correction for applications in optomechanics using a digital micromirror device

Abstract: We discuss the development of a digital micromirror based adaptive optical system that corrects for the propagation of coherent light through multimode fibres with the aim to achieve optical trapping in vacuum.

Attenuation compensating Airy beams generated by using a digital micro-mirror device

Abstract: We present a novel form of the attenuation-compensated propagation-invariant Airy beam. We generate finite-energy versions of these beams using a digital micro-mirror device, with similar properties over a finite distance of propagation.

Rotation induced cooling of an optically trapped microgyroscope in vacuum

Abstract: We demonstrate optical trapping of a microgyroscope rotating at MHz rates in vacuum. The particle is cooled to 40K. This is a major step towards measuring the Casimir force resulting in rotational quantum friction.