JEOS:RP - Journal of the European Optical Society Rapid publications
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Digital in-line holography assessment for general phase and opaque particle
Full text linkWe propose using the circle polynomials to describe a particle’s transmission function in a digital holography setup. This allows both opaque and phase particles to be determined. By means of this description, we demonstrate that it is possible to estimate the digital in-line hologram produced by a spherical particle. The experimental intensity distribution due to an opaque micro-inclusion is compared to the theoretical one obtained by our new model. Moreover, the simulated hologram and reconstructed image of the particle by an optimal fractional Fourier transformation under the opaque disk, quadratic phase, and quasi-spherical phase approximation are compared with the results obtained by simulating holograms by the Lorenz–Mie Theory (LMT). The Zernike coefficients corresponding to the considered particles are evaluated using the double exponential (DE) method which is optimal in various respects
Quality control of injection molded eyewear by non-contact deflectometry
Full text linkOccupational eye wear such as safety spectacles are manufactured by injection molding techniques. Testing of the assembled safety spectacle lenses in transmission is state of the art, but there is a lack of surface measurement systems for occupational safety lenses. The purpose of this work was to validate a deflectometric setup for topography measurement, detection of defects and visualization of the polishing quality, e.g. casting indentations or impressions, for the production process of safety spectacles. The setup is based on a customized stereo phase measuring deflectometer (PMD), equipped with 3 cameras with f’1,2 = 16 mm and f’3 = 8.5 mm and a specified measurement uncertainty of ± 3 μm. Sixteen plastic lenses and 8 corresponding injection molds from 4 parallel cavities were used for validation of the deflectometer. For comparison an interferometric method and a reference standard (< λ/10 super polished) was used. The accuracy and bias with a spherical safety spectacle sample was below 1 μm, according to DIN ISO 5725-2.2002-12. The repeatability was 2.1 μm and 35.7 μm for a blind radius fit. In conclusion, the PMD technique is an appropriate tool for characterizing occupational safety spectacle and injections mold surfaces. With the presented setup we were able to quantify the surface quality. This can be useful and may optimize the quality of the end product, in addition to standardized measuring systems in transmission
Nonlinear optical properties of Au-nanoparticles conjugated with lipoic acid in water
Full text linkGold nanoparticles were chemically conjugated with lipoic acid to control their optical properties. Z-scan and other optical techniques were used to characterize the non-linear behavior of the resulting nanostructured materials. The results show that the nonlinearity is of thermal origin, which can be controlled by the use of lipoic acid as well as other organic molecules conjugated onto metal nanoparticles. In particular, the presence of lipoic acid increases n2 and dn/dT
Reflection-based fibre-optic refractive index sensor using surface plasmon resonance
Full text linkA reflection-based fibre-optic refractive index sensor using surface plasmon resonance (SPR) in a thin metal film sputtered on a bare core of a multimode optical fibre is presented. The sensing element of the SPR fibre-optic sensor is the core of a step-index optical fibre made of fused silica with a gold film double-sided sputtered on the whole core surface, including the core end face. Consequently, a terminated reflection-based sensing scheme to measure the refractive indices of liquids is realized. The sensing scheme uses a wavelength interrogation method and the refractive index of a liquid is sensed by measuring the position of the dip in the reflected spectral intensity distribution. As an example, the aqueous solutions of ethanol with refractive indices in a range from 1.333 to 1.363 are measured. In addition, the increase in the sensitivity of the SPR fibre-optic refractive index sensor with the decrease of the fibre sensing length is demonstrated
Waveguide structures for efficient evanescent field coupling to zero mode waveguides
Full text linkThe use of waveguide structures is examined to improve the efficiency of evanescent field coupling into zero-mode waveguides. Model calculations show that waveguide excitation using diffractive structures, increases the magnitude of the evanescent electric field by an order of magnitude compared to far field excitation of the evanescent field. A more efficient excitation of fluorescent markers used in e.g. sequencing instrumentation ultimately enables real-time single molecule detection using laser systems with moderate output power
Low-cost resonant cavity Raman gas probe for multi-gas detection
Full text linkRaman based gas sensing can be attractive in several industrial applications, due to its multi-gas sensing capabilities and its ability to detect O_2 and N_2. In this article, we have built a Raman gas probe, based on low-cost components, which has shown an estimated detection limit of 0.5 % for 30 second measurements of N_2 and O_2. While this detection limit is higher than that of commercially available equipment, our estimated component cost is approximately one tenth of the price of commercially available equipment. The use of a resonant Fabry-Pérot cavity increases the scattered signal, and hence the sensitivity, by a factor of 50. The cavity is kept in resonance using a piezo-actuated mirror and a photodiode in a feedback loop.The system described in this article was made with minimum-cost components to demonstrate the low-cost principle. However, it is possible to decrease the detection limit using a higher-powered (but still low-cost) laser and improving the collection optics. By applying these improvements, the detection limit and estimated measurement precision will be sufficient for e.g. the monitoring of input gases in combustion processes, such as e.g. (bio-)gas power plants. In these processes, knowledge about gas compositions with 0.1 % (absolute) precision can help regulate and optimize process conditions.The system has the potential to provide a low-cost, industrial Raman sensor that is optimized for specific gas-detection applications
The modern Forel-Ule scale: a ‘do-it-yourself’ colour comparator for water monitoring
Full text linkThe colour comparator Forel-Ule scale has been used to estimate the colour of natural waters since the 19th century, resulting in one of the longest oceanographic data series. This colour index has been proven by previous research to be related to water quality indicators such as chlorophyll and coloured dissolved organic material. The aim of this study was to develop an affordable, ‘Do-it-Yourself’ colour scale that matched the colours of the original Forel-Ule scale, to be used in water quality monitoring programs by citizens. This scale can be manufactured with high-quality lighting filters and a white frame, an improvement with respect to the materials employed to manufacture the original scale from the 19th century, which required the mixing of noxious chemicals. The colours of the new scale were matched to the original colours using instrumental and visual measurements carried out under controlled lighting conditions, following the standard measurement protocols for colour. Moreover, the colours of the scale are expressed in Munsell notations, a standard colour system already successfully used in water quality monitoring. With the creation of this Modern Forel-Ule scale, as a ‘Do-it-yourself’ kit, the authors foresee a possible use of the Forel-Ule number as a water quality index that could be estimated by means of participatory science and used by environmental agencies in monitoring programs
Optical-fiber thermal-wave-cavity technique to study thermal properties of silver/clay nanofluids
Full text linkThermal properties enhancement of nanofluids have varied strongly with synthesis technique, particle size and type, concentration and agglomeration with time. This study explores the possibility of changing the thermal wave signal of Ag/clay nanofluids into a thermal diffusivity measurement at well dispersion or aggregation of nanoparticles in the base fluid. Optical-Fiber Thermal-Wave-Cavity (OF-TWC) technique was achieved by using a small amount of nanofluid (only 0.2 mL) between fiber optic tip and the Pyroelectric detector and the cavity-length scan was performed. We established the accuracy and precision of this technique by comparing the thermal diffusivity of distilled water to values reported in the literature. Assuming a linear Pyroelectric signal response, the results show that adding clay reduced the thermal diffusivity of water, while increasing the Ag concentration from 1 to 5 wt.% increased the thermal diffusivity of the Ag nanofluid from 1.524×10−3 to 1.789×10−3 cm2/s. However, in particular, nanoparticles show the tendency to form aggregates over time that correlated with the performance change of thermal properties of nanofluid. Our results confirm the high sensitivity of OF-TWC technique raises the potential to be applied to measuring the optical and thermal properties of nanofluids. Furthermore, this technique allows the extraction of information not obtained using other traditional techniques
Comparison of aberrations after standard and customized refractive surgery
Full text linkTo detect possible differences in residual wavefront aberrations between standard and customized laser refractive surgery based onmathematical modeling, the residual optical aberrations after conventional and customized laser refractive surgery were compared accordingto the ablation profile with transition zone. The results indicated that ablation profile has a significant impact on the residual aberrations.The amount of residual aberrations for conventional correction is higher than that for customized correction. Additionally, the residualaberrations for high myopia eyes are markedly larger than those for moderate myopia eyes. For a 5 mm pupil, the main residual aberrationterm is coma and yet it is spherical aberration for a 7 mm pupil. When the pupil diameter is the same as optical zone or greater, themagnitudes of residual aberrations is obviously larger than that for a smaller pupil. In addition, the magnitudes of the residual fifth orsixth order aberrations are relatively large, especially secondary coma in a 6 mm pupil and secondary spherical aberration in a 7 mm pupil.Therefore, the customized ablation profile may be superior to the conventional correction even though the transition zone and treatmentdecentration are taken into account. However, the customized ablation profile will still induce significant amount of residual aberrations
Fabrication of single-mode channel polymer waveguides using vacuum assisted microfluidic soft lithography
Full text linkWe report on the fabrication of single-mode channel waveguide structures produced by the vacuum assisted microfluidic soft lithography technique. The soft lithographic technique in conjunction with a specially designed photomask pattern and a synthesized UV curable epoxy resin can result in a high yield, cost-effective method for fabrication of channel waveguides. In particular, the use of the microfluidic technique allows for the production of freestanding high quality single-mode channel waveguides on various substrates. Notably, the introduction of sectional flow tapers allows for proper uniform filling of long length small cross-sectional waveguide structures that would ordinarily succumb to clogging at shorter distances during channel filling. The fabricated polymer waveguide was 30 mm in length with a cross section dimension of 7x7 μm. The single-mode waveguide propagation was confirmed with beam profiler measurement, and the measured propagation loss for this polymer waveguide was about 0.55 dB/cm