JEOS:RP - Journal of the European Optical Society Rapid publications
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Fluorescence quenching and photobleaching in Au/Rh6G nanoassemblies: impact of competition between radiative and non-radiative decay
Get PDFFluorescence quenching from nanoassemblies formed by Rhodamine 6G and gold nanoparticles (Au NPs) of 2.6 nm radius has been investigated. The presence of Au NPs also induces long-term degradation of the photostability (photobleaching) of Rhodamine 6G used as gain medium in a Fabry-Perot laser cavity. We found that the degradation gets profound when the Au NPs concentration is significantly increased. Calculation of the radiative rate and direct time-resolved measurement of the fluorescence decay indicates that both the decrease of radiative decay rate and increase of non-radiative decay rate are responsible for the fluorescence quenching and photostability degradation. An energy transfer from the dye molecules to gold nanoparticles is dominating within the small distance between them and suppresses the quantum efficiency of Rhodamine 6G drastically. In long time scale, the photobleaching rate was slowing down, and laser output intensity reached a stabilized level which depends on the gold nanoparticles concentration
Contrast transfer characteristics of the light sword optical element designed for presbyopia compensation
Get PDFThe paper discusses the abilities of the light sword optical element (LSOE) for presbyopia compensation. The imaging properties are analyzed by means of the modulation transfer functions and output images of the star resolution test. All numerical calculations are performed assuming an optical set-up simulating the presbyopic human eye and based on the Gullstrand model. In order to have a meaningful comparison we expand our study and present adequate analysis for other elements potentially useful in ophthalmology as reading glasses, bifocal lenses and axicons. According to the obtained results the LSOE can successfully realize vision with an extended depth of field. The element makes possible the compensation of an assumed defocus up to 4 dioptres. The output images formed by the LSOE are well recognizable and have acceptable qualities for near as well as far object distances
New analytic results for the Zernike circle polynomials from a basic result in the Nijboer-Zernike diffraction theory
Get PDFSeveral quantities related to the Zernike circle polynomials admit an expression, via the basic identity in the diffraction theory of Nijboer and Zernike, as an infinite integral involving the product of two or three Bessel functions. In this paper these integrals are identified and evaluated explicitly for the cases of (a)~the expansion coefficients of scaled-and-shifted circle polynomials, (b)~the expansion coefficients of the correlation of two circle polynomials, (c)~the Fourier coefficients occurring in the cosine representation of the circle polynomials
A review on methods used to record and analyze microfluctuations of the accommodation in the human eye.
Get PDFIn steady state conditions, the accommodation of the human eye presents fluctuations. These fluctuations, called microfluctuations, are described in the literature as having an amplitude of less than 1D and a frequency up to a few Hz. Since Collins’ report about microfluctuations in 1937 [Collins 1937], several methods have been used to record and analyze microfluctuations. Results reported in the literature are partially in disagreement; we show how these disagreements could be due to the different methodologies used to record and analyze the accommodation signals. We classify and discuss properties of instruments used to record the microfluctuations and methods used to elaborate the resulting signals; to conclude we suggest how to validate the instrumentation and which analysis method to adopt when investigating microfluctuations
Two-photon polymerization with optimized spatial light modulator
Get PDFThe application of diffractive optical elements can enhance the efficiency of the two-photon polymerization (TPP) process by multiplying the polymerizing beams. Spatial light modulators (SLMs) can dynamically change the light intensity pattern used for polymerization, making single shot polymerization possible. Most reflective, liquid crystal-based instruments, however, suffer from various surface aberrations. In order to enable SLMs to generate suitable polymerizing beams for TPP, these aberrations need to be corrected. Several methods were introduced earlier to compensate SLM aberrations in different applications. For the nonlinear process of TPP, we developed and specifically characterized a correction procedure. We used a simple interferometric method to determine the surface distortion of the SLM, calculated a correcting hologram and confirmed the correction with the polymerization of test structures. The corrected SLM was capable of parallel polymerization of 3D structures with a quality achievable with non-SLM beams
Evaluating subsurface damage in optical glasses
Get PDFHard brittle materials (e.g. glasses and ceramics) increasingly appeal to general interests because of their excellent physical, mechanical and chemical properties such as super hardness and strength at extreme temperature and chemical stability. The precision manufacturing of these materials is primarily achieved by grinding and polishing, which generally employs abrasives to wear the materials. With this manufacturing technology, the materials are removed due principally to the fracture of brittle materials, which will leave a cracked layer on the surface of manufactured components, namely subsurface damage (SSD). The subsurface damage affects the strength, performance and lifetime of components. As a result, investigation into the subsurface damage is needed. A host of characterizing techniques have been developed during the past several decades. These techniques based on different mechanisms provide researchers with invaluable information on the subsurface damage in various materials. In this article the typical SSD evaluation techniques are reviewed, which are regularly used in optical workshops or laboratories
Mould fabrication for polymer optics
Get PDFThis work focuses on the process chain for mould fabrication for the injection moulding of optical components. The goal is to achieve a good form and surface quality on steel moulds; the new process chain should consist of just 3 steps instead of 5; nickel plating and diamond turning are superseded. Manual polishing is replaced by robot polishing
Scalar Readout Model for Super-Rens Focused Spot
No full textA scalar readout model is presented to investigate the readout characteristics of the super resolution near field (SRens) disc. The super resolution effect is described by means of a threshold model, where the super resolution material imparts a phase change on the focused spot if the laser density energy is high enough to trigger the SRens effect. This approach results in a very fast way of computing the basic characteristics of the SRens readout signal, being suitable for large investigations. Moreover, many simulation results have been experimentally confirmed by other groups, which further validates the model. Thus, this simplified model is an useful tool for a better comprehension of the readout signal of the super resolution effect in optical data storage and other super resolution applications
Computation of Hopkins’ 3-circle integrals using Zernike expansions
Get PDFThe integrals occurring in optical diffraction theory under conditions of partial coherence have the form of an incomplete autocorrelation integral of the pupil function of the optical system. The incompleteness is embodied by a spatial coherence function of limited extent. In the case of circular optical systems and coherence functions supported by a disk, this gives rise to Hopkins’ 3-circle integrals. In this paper, a computation scheme for these integrals (initially with coherence functions that are constant on their disks) is proposed where the required integral is expressed semi-analytically in the Zernike expansion coefficients of the pupil function. To this end, the Zernike expansion coefficients of a shifted pupil function restricted to the coherence disk are expressed in terms of the pupil function’s Zernike expansion coefficients. Next, the required integral is expressed as an infinite series involving two sets of restricted Zernike coefficients using Parseval’s theorem for orthogonal series. The computation method is extended to the case of coherence functions that are not necessarily constant on their supporting disks by using a result on linearization of the product of two Zernike circle polynomials involving Wigner coefficients
Tridimensional multiphysics model for the study of photo-induced thermal effects in arbitrary nano-structures
Get PDFIn the present paper, we detail the implementation of a numerical scheme based on the Finite Element Method (FEM) dedicated to a tri-dimensional investigation of photo-induced thermal effects in arbitrary nano-structures. The distribution of Joule losses resulting from the scattering of an incident wave by an arbitrary object embedded in a multilayered media is used as source of a conductive thermal transient problem. It is shown that an appropriate and rigorous formulation of the FEM consists in reducing the electromagnetic scattering problem to a radiative one whose sources are localized inside the scatterer. This approach makes the calculation very tractable. Its advantage compared to other existing methods lies in its complete independence towards the geometric, optical and thermal properties of both the scatterer and the medium in which it lies. Among the wide range of domain of application of this numerical scheme, we illustrate its relevance when applied to two typical cases of laser damage of optical components in high power applications