JEOS:RP - Journal of the European Optical Society Rapid publications
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The Forel-Ule scale revisited spectrally: preparation protocol, transmission measurements and chromaticity
Get PDFThe Forel-Ule colour comparator scale has been applied globally and intensively by oceanographers and limnologists since the 19th century,providing one of the oldest oceanographic data sets. Present and future Forel-Ule classifications of global oceanic, coastal and continentalwaters can facilitate the interpretation of these long-term ocean colour data series and provide a connection between the present and thepast that will be valuable for climate-related studies.Within the EC-funded project CITLOPS (Citizens’ Observatory for Coast and Ocean Optical Monitoring), with its main goal to empower endusers,willing to employ community-based environmental monitoring, our aim is to digitalize the colours of the Forel-Ule scale to establishthe colour of natural waters through smartphone imaging. The objective of this study was to reproduce the Forel-Ule scale following theoriginal recipes, measure the transmission of the solutions and calculate the chromaticity coordinates of the scale as Wernand and Vander Woerd did in 2010, for the future development of a smartphone application. Some difficulties were encountered when producing thescale, so a protocol for its consistent reproduction was developed and is described in this study. Recalculated chromaticity coordinates arepresented and compared to measurements conducted by former scientists. An error analysis of the spectral and colourimetric informationshows negligible experimental errors
Thickness conditions for characterizing the periodic nanostructures with the retrieved electromagnetic parameters
Get PDFBy analyzing the convergence of the retrieved effective electromagnetic parameters, we presented that one wavelength of the propagating wave in the nanostructure is the minimum thickness requirement for effectively characterizing a finite thickness nanostructure. This thickness condition has been separately validated in a photonic crystal with negative refraction and in a typical fishnet metamaterial which has been investigated theoretically and experimentally before
Synthesis of sources with Markovian features
Get PDFWe realize the design and synthesis of partially coherent secondary sources illuminating an ensemble of mobile transmittances in a tandem array. The motion states of the transmittances are random variables which are synchronized by means of the conditional probability density function whose control allows generating sources whose light emission corresponds with a Markov chain. The experimental results are shown
Wide-field common-path incoherent correlation microscopy with a perfect overlapping of interfering beams
Get PDFIncoherent correlation microscopy is recently discovered technique for digital imaging of three-dimensional objects in a quasimonochromatic spatially incoherent light. Its operation is based on wavefront division carried out by a spatial light modulator and capturing correlation recordings of the observed scene. To achieve image reconstruction, at least a partial overlapping of the signal and reference waves created by the spatial light modulator is necessary. In the known experimental configurations, the overlapping of interfering beams is strongly reduced in off-axis areas of the object and the image can be reconstructed only in a very small portion of the field of view provided by the used microscope objective lens. Here, we propose and successfully demonstrate modified experimental system working with two-component relay optics inserted between the microscope objective and the spatial light modulator and providing full overlapping of correlated beams in all areas of the field of view of the objective lens. The benefits and applicability of the proposed system design are clearly demonstrated on the imaging of the USAF resolution targets
The phase shift induced by a single atom in free space
Get PDFIn this article we theoretically study the phase shift a single atom imprints onto a coherent state light beam in free space. The calculations are performed in a semiclassical framework. The key parameters governing the interaction and thus the measurable phase shift are the solid angle from which the light is focused onto the atom and the overlap of the incident radiation with the atomic dipole radiation pattern. The analysis includes saturation effects and discusses the associated Kerr-type non-linearity of a single atom
Measurement of the optical transfer function using a white-dot pattern presented on a liquid-crystal display
Get PDFThe optical transfer function (OTF) and its modulus, the modulation transfer function (MTF), are widely accepted measurements of the quality of optical systems. There are different ways of estimating both OTF and MTF. Random-dot-pattern methods have some advantages when computing MTFs, especially those which present the pattern on a liquid crystal-display (LCD) screen because no additional light source is needed. Nevertheless spatial information is not usually available in the image plane because MTFs are computed for the whole image in a finite number of directions only. We propose a way of providing spatial information by measuring a number of point-spread functions (PSFs). Created by a white-dot pattern on a LCD screen, white pixels operate as point sources and PSFs are calculated to eventually result in the OTF of the system. MTFs in the main directions are computed to compare with reference values obtained by the random-dot method. Sensor and LCD resolutions define the achievable MTF range. Our proposed method is used to characterize a liquid-crystal tunable filter (LCTF) attached to a monochrome camera at different wavelengths. This method, which is both easy to install and to use, achieves results with errors of less than 3%, and has advantages over classical OTF estimation methods: spatial information provided in the image plane, all frequencies and directions covered in a single capture, no additional light source needed and derivative-dependent noise avoided
Tunable, low frequency microwave generation from AWG based closely-spaced dual-wavelength single-longitudinal-mode fibre laser
Get PDFStable, closely-spaced Dual-Wavelength Fibre Lasers (DWFLs) have high potential for applications such as Radio-over-Fibre and optical sensing. In this work, a DWFL using two Arrayed Waveguide Gratings (AWGs) to generate a closely-spaced dual-wavelength output is proposed and demonstrated. A 1 m long highly doped Leikki Er80-8/125 Erbium Doped Fibre (EDF) is used as the linear gain medium, while two AWGs are used to generate the closely-spaced lasing wavelengths. A Mach-Zehnder modulator, driven at 180 kHz, splits the closely spaced wavelengths into two clearly defined wavelengths, while a 7 cm long un-pumped Leikki Er80-8/125 EDF and sub-ring cavity is used to suppress unwanted side-modes. Close spacing of between 0.01 to 0.03 nm are obtained, with beating frequencies of between 1.4 to 3.2 GHz. The output is highly stable, with almost no fluctuations over the test period
Multipole polarizability of a nanodimer in optical waves
Get PDFIn this work we study the interaction of visible light with plasmonic nanodimers that, under particular illumination conditions, do not exhibit any electric dipole excitations. It has previously been found out that the dipole suppression phenomenon disappears when the illumination direction is reversed. As a consequence, a homogeneous nanomaterial consisting of such nanodimers can be expected to be spatially dispersive, such that the conventional electric polarization vanishes for certain directions of light propagation. In order to reveal the complete picture of the light-nanodimer interaction, we analyze the multipole excitations in a dimer at various illumination angles. In particular, we introduce an analytical model for the multipole polarizability tensors of the dimer that, in contrast to conventional polarizability tensors, depend on the light propagation direction. The model is verified by rigorous numerical calculations. It can be used to gain insight into the properties of optical nanomaterials, such as metamaterials, in which higher-order multipoles can be efficiently excited
Reduction of the nonlinear phase shift induced by stimulated Brillouin scattering for bi-directional pumping configuration system using particle swarm optimization algorithm
Get PDFWe present a theoretical analysis of an additional nonlinear phase shift of backward Stokes wave based on stimulated Brillouin scattering in the system with a bi-directional pumping scheme. We optimize three parameters of the system: the numerical aperture, the optical loss and the pumping wavelength to minimize an additional nonlinear phase shift of backward Stokes waves due to stimulated Brillouin scattering. The optimization is performed with various Brillouin pump powers and the optical reflectivity values are based on the modern, global evolutionary computation algorithm, particle swarm optimization. It is shown that the additional nonlinear phase shift of backward Stokes wave varies with different optical fiber lengths, and can be minimized to less than 0.07 rad according to the particle swarm optimization algorithm for 5 km. The bi-directional pumping configuration system is shown to be efficient when it is possible to transmit the power output to advanced when frequency detuning is negative and delayed when it is positive, with the optimum values of the three parameters to achieve the reduction of an additional nonlinear phase shift
Temporal coherence shaping based on spectral-domain destructive interference of pulses with different self-phase modulations
Get PDFWe show via a numerical simulation that the temporal coherence function (TCF) can be shaped by the destructive interference of pulses characterized by different amounts of self-phase modulation (SPM) in the spectral domain. We find that pulse spectra destructively interfering with one another can yield a TCF with distinct peaks. Numerical investigation demonstrates that the shape of the TCF is changeable not only by broadening the spectrum but also by overlapping spectra of the pulses that have experienced different amounts of SPM