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We explore the principles, implementation details, and performance characteristics of a lensless multi-spectral digital holographic sensor and demonstrate its potential for quality assurance in semiconductor manufacturing. The method is based on capturing multi-spectral digital holograms, which are subsequently utilized to evaluate the shape of a reflective test object. It allows for a compact setup satisfying high demands regarding robustness against mechanical vibrations and thus overcomes limitations associated with conventional optical inspection setups associated with lens-based white light interferometry. Additionally, the tunable laser source enhances the versatility of the system and enables adaptation to various sample characteristics. Experimental results based on a wafer test specimen demonstrate the effectiveness of the method. The axial resolution of the sensor is ± 2.5 nm, corresponding to 1σ. [ABSTRACT FROM AUTHOR]

We explore the principles, implementation details, and performance characteristics of a lensless multi-spectral digital holographic sensor and demonstrate its potential for quality assurance in semiconductor manufacturing. The method is based on capturing multi-spectral digital holograms, which are subsequently utilized to evaluate the shape of a reflective test object. It allows for a compact setup satisfying high demands regarding robustness against mechanical vibrations and thus overcomes limitations associated with conventional optical inspection setups associated with lens-based white light interferometry. Additionally, the tunable laser source enhances the versatility of the system and enables adaptation to various sample characteristics. Experimental results based on a wafer test specimen demonstrate the effectiveness of the method. The axial resolution of the sensor is ±2.5 nm, corresponding to 1σ.

Future electric transportation systems are expected to employ electrical power trains with higher operating voltage and power density. Therefore, compact and reliable insulation systems are important, since they influence the system integration, thermal resistance, and parasitic inductance. In this paper, experiments and analysis show behavior which are not observed with mechanically produced holes before. A boundary element analysis of the electric field distribution around the voids reveals why these new observations are identified in voids with relatively sharp corners. The electric field computation shows conditions under which there is electric field enhancement at the void periphery. This drives the partial discharge (PD) activity and the erosion growth away from the center of the voids.

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Inspecting large areas with a white light interferometer is time-consuming. To shorten inspection times, additionally, a coarser sensor can be used in a preceding step to identify possible defects. These are afterwards accurately measured with the white light interferometer. Often, several points of interest can be grouped and scanned with a single white light interferometer measurement. Grouping approaches found in the literature show potential for further improvement. In this paper, a novel algorithm for view planning concerning a two-step inspection is presented. Respective literature is reviewed and discussed. Afterwards, the functionality of the algorithm is demonstrated through an example and its performance is evaluated based on comparison to other solutions. The approach generates results that are promising for reducing inspection times further than other approaches. [ABSTRACT FROM AUTHOR]

Purpose: To quantitatively analyze human corneal stromal dehydration and estimate proper corneal stromal exposure time during corneal refractive surgery. Methods: The central thickness changes over time in 34 pieces of human corneal tissue were measured using a white light interferometer. The corneal stromal tissue was obtained by femtosecond laser small incision lenticule extraction. The thickness-time dehydration fitting curves were drawn, and the determination coefficient R2 was calculated. The differences in the fitting curve equation coefficients were compared between the thin and thick lenticule groups. The optimal stromal exposure time was calculated under various conditions, including different optical zones and allowable refractive errors. Results: A water loss variation model was successfully established. Linear and quadratic fitting curves were drawn, and the determination coefficient R2 values were significantly close to 1. The average values of R2 for quadratic curves and linear phases 1, 2, and 3 were 0.998 ± 0.002, 0.995 ± 0.007, 0.996 ± 0.003, and 0.984 ± 0.035, respectively. The optimal stromal exposure time varied under different optical zones and allowable diopter error conditions. Taking the allowable error of 0.50 D and the optical zone size of 6.5 mm as an example, the optimal time was approximately 24 s. Conclusions: The dehydration rate of the human corneal stroma is nonlinear, and the quadratic stromal thickness–time dehydration fitting curve is more in line with the actual water loss trend. The length of the stroma exposure time may affect the postoperative refractive accuracy after corneal refractive surgery. [ABSTRACT FROM AUTHOR]

It is nontrivial to design an optical interferometric scheme with the advantages of high precision and nondestructive testing. Since a tested phase may be ambiguous and the system is expensive and complicated, it is challenging to realize the precision displacement and absolute distance measurement for laser interferometry. Moreover, the micro-structure measurement and manufacture are difficult goals for white light interferometry, attributing to insufficient accuracy in the positioning of zero-optical-path difference. To solve the above issues, a dark-end locking approach has thus been proposed to improve the sensitivity of traditional interferometer but the shot noise limit has not been reached though. In this work, an optical recycling method is employed to tap a local oscillator (LO) beam, for homodyne balanced detection, from the probing light beam inside the laser interferometer. The balanced detection is used for the laser interferometer to reduce classical noise, leading to the shot-noise-limited sensitivity that is otherwise hard to achieve. The present study will serve as a theoretical guide or experimental support for the forthcoming precision displacement, absolute distance measurement, and sub-shot-noise audio-frequency laser interferometry experiments. [ABSTRACT FROM AUTHOR]

The cylinder engine surface texture has a major influence on the functional performances of the ring‐pack tribo‐system. The cylinder engine surface microtexture manufactured by plateau honing (PH) and helical slide honing (HSH) processes have been analyzed using white light interferometry (WLI), and stereometric analysis. The approaches in three‐dimensional (3‐D) white light interferometer measurements and surface stereometric analysis are important for the correct interpretation of 3‐D local surface texture features and can be applied in mathematical models for calculating the friction. The samples were divided into two groups: plateau honing (PH) samples and helical slide honing (HSH) samples to discuss the obtained results, according to the honing techniques obtained after several stages: the rough and finish honing and final stage. The obtained results demonstrated that the surface of group PH has the higher values of root mean square height (Sq = 1.83 μm) and fractal dimension (Df = 2.74 ± 0.01), while the lowest values of root mean square height (Sq = 0.63 μm) and fractal dimension (Df = 2.60 ± 0.01) were found for HSH samples. These values highlight that the PH samples are more irregular (both as surface and topography) in comparison with HSH samples. Highlights: We characterized the micromorphology of surface microtexture in plateau and helical slide honing.The nanostructure morphology was investigated using the white light interferometry, fractal and stereometric analyses.The surface topography during the HSH process has different characteristics than the PH process and can be used to obtain better friction and lubrication performances. [ABSTRACT FROM AUTHOR]

Distributed polarization characteristic of Sagnac optical closed loop that composed of two polarizing devices– polarization maintaining fiber coil and Y-waveguide, can directly affect the performance of fiber optic sensors. Several existing methods are applicable for only one device testing at a time, the efficiency is therefore relatively low and the connection quality between devices is unavailable. In this paper, the Sagnac optical closed loop is split into semi-closed loop (SCL) and full-closed loop (FCL) structures. The transmission behavior of polarized optical signal is fully analyzed, and the information of polarization mode crosstalk is positioned and extracted accurately. By conducting one test of SCL and FCL respectively utilizing white light interferometry, the distributed polarization characteristic of both optical devices and connection points can be entirely obtained. The testing results of optical closed loop are highly consistent with single device test and the difference is less than 0.2dB. A good testing stability is demonstrated through ten repeat measurements and the fluctuation is almost around 0.1dB. We believe that the proposed testing method is capable of promoting the assembly of high-performance Sagnac interferometer and the development of fiber optic sensors. [ABSTRACT FROM AUTHOR]

We experimentally investigate the near-wall heat transfer at single bubble growth in nucleate saturated pool boiling of water at atmospheric pressure. Our focus is on the evaporation of the micro-metric thin film of liquid (microlayer) that is formed between the heating wall and the bubble. High speed and high resolution optical techniques are employed. Synchronous and simultaneous measurements of the microlayer thickness, wall temperature and bubble macroscopic shape are performed by white light interferometry, infrared thermography and side-wise shadowgraphy, respectively. We measure the wall temperature of an ITO heating film through a transparent to the infrared waves porthole. The heating is provided by an infrared laser. The wall heat flux is numerically reconstructed by using the experimental wall temperature data. We reveal a temporal rise of the thermal resistance of the liquid–vapor interface during the microlayer evaporation, which corresponds to a decrease of the accommodation coefficient. We attribute it to the progressive accumulation of impurities at the interface during evaporation. The contribution of microlayer evaporation to the overall bubble growth is about 18%. • Advanced optical techniques are used to investigate the microlayer evaporation. • Microlayer thickness and wall temperature distribution are measured synchronously. • Wall heat flux is reconstructed from wall temperature distribution. • Interfacial thermal resistance increases over time during microlayer evaporation. [ABSTRACT FROM AUTHOR]

Austenite and ferrite phases share equal fractions in the steel and thus coins the name austenitic-ferritic steels, widely known as duplex steels, among researchers. The current study focuses on revealing the sliding wear behavior of the steels, which is of great industrial importance in oil & gas and chemical processing industries, where it is used as valves in pipelines. Austenitic-ferritic steel and its niobium (Nb) added castings were produced through the induction melting route. Thermodynamic analyses of the systems were performed using Thermo-calc software. Isopleths generated through thermodynamic simulation predicted niobium carbide (NbC) formation in the system, and the same was asserted through x-ray diffraction peaks. Scanning electron microscope (SEM) with energy-dispersive spectroscopy (EDS) study also confirmed the presence. The dry sliding wear performance of these castings was investigated. Experiments have been performed where cast austenitic-ferritic steel pins, slid against non-shrinking, oil-hardened steel disk, with sliding speeds 1, 1.5, and 2 m/s, under loads of 20, 30, and 40 N, without lubrication at room temperature. Variations in wear rate, friction coefficient, and volume loss were studied with respect to sliding distance, load, and sliding velocity. SEM was used to understand the wear phenomena and mechanisms involved, and white light interferometry analysis over the worn-out surfaces gives insight to the understanding. NbC formed in the system imparts stability to the steel against sliding wear. The results show that Nb addition can be beneficial in applications like valves, elbows, and other fittings in the pipelines, where degradation of a material due to wear is high and thus improves the productivity of the industry. [ABSTRACT FROM AUTHOR]

Solid lubricants such as polytetrafluoroethylene (PTFE) are used in rolling-element bearings (REBs) when conventional lubrication (i.e. by fluids or greases) cannot be applied owing to extreme operating conditions (e.g. high temperatures or vacuum). Often a double transfer film mechanism is used with a cage acting as a lubricant reservoir resupplying the REB with solid lubricant by cage wear. An increase in service life of such bearings requires a better understanding of the transfer processes in the sliding and rolling contacts. Here, we investigate the effect of PTFE resupply on friction and lubricant film formation in a steel/steel and steel/glass rolling contact by tribometry and classical molecular dynamics (MD). A ball-on-disk tribometer is enhanced by a pin-on-disk sliding contact that transfers PTFE to the disk. The experiment allows simultaneous in situ measurement of friction and film thickness by white light interferometry in the rolling point contact. Increasing the pin load results in an increased PTFE film thickness in the rolling contact accompanied by a significant decrease in friction. To elucidate the observed film transfer and friction mechanism, sliding MD simulations with a newly developed density-functional-based, non-reactive force field for PTFE-lubricated iron oxide surfaces are performed. A strong adhesion of PTFE chains to iron oxide drives transfer film formation, whilst shear-induced chain alignment within PTFE results in reduced friction. The simulations reveal an anti-correlation between PTFE film thickness and friction coefficient—in agreement with the experiments. These investigations are a first step towards methods to control PTFE transfer film formation in REBs. [ABSTRACT FROM AUTHOR]

Fluoride is a key dentifrice ingredient for mitigating dental erosion and promoting remineralisation in tooth enamel. A dentifrice formulation (NaF/CL ‐ where C = Copolymer, L = Lactate), optimised for fluoride delivery, containing sodium fluoride, polyvinylmethylether–maleic anhydride (PVM/MA) copolymer and lactate ion at controlled pH of 6.2 is compared with six commercial dentifrices from European and US regulatory regions. The in vitro study utilised white light interferometry (WLI) and dynamic secondary ion mass spectrometry (DSIMS) to assess dental erosion resistance and remineralisation potential of the dentifrices. For WLI, polished enamel samples were immersed in dentifrice slurry (1:3 wt./wt. in artificial saliva, 2 min), brushed, washed in deionised water, acid challenged (1% citric acid, pH 3.8, 5 min), washed and air dried. Surface roughness and bulk tissue loss were measured. DSIMS samples for fluoride uptake were acid challenged (1% citric acid, pH 3.8, 5 min), rinsed, immersed in dentifrice slurry (1:3 wt./wt. in artificial saliva, 2 min), washed and air dried. DSIMS samples for 44Ca uptake were prepared similarly but with 44Ca‐doped artificial saliva. The NaF/CL dentifrice provided highest protection against dental erosion, with highest fluoride and 44Ca uptake in all treatment groups (n = 5 per group). Dentifrices containing other fluoride salts and/or ingredients known to inhibit fluoride uptake (e.g., polyphosphates, sodium lauryl sulfate), performed significantly worse. [ABSTRACT FROM AUTHOR]

To quantitatively evaluate the cutting quality of small incision lenticule extraction (SMILE) by measuring human corneal lenticule surface roughness in different areas with white light interferometer. A white light interferometer was used to quantitatively measure the corneal lenticule surface roughness in different areas. Sixty-three myopic patients (102 eyes) who underwent SMILE surgery were recruited. The surface roughness of the central, pericentral, and peripheral parts of the corneal lenticule surface was measured in both the anterior and posterior planes. Differences in corneal lenticule surface roughness were analyzed between different myopic groups. The surface roughness of the anterior plane of the corneal lenticule was lower than the posterior plane in various areas (central, pericentral, and peripheral parts) (P <.01). Surface roughness gradually increased from the center to the periphery, in both the anterior and posterior planes (P <.01). There were no significant differences in the surface roughness of the central part in both the anterior and posterior planes between the low and high myopic groups. The surface roughness of the high myopic group was higher than that of the low myopic group in the peripheral part (P <.01). There were no significant differences among the three cylinder-specific groups. There was no significant correlation between two paired eyes. A positive correlation between posterior central surface roughness and the percentage tissue altered score (PTA) was found (r = 0.248, P =.012). The cutting surface of the corneal lenticule performed by femtosecond laser was evaluated with a white light interferometer and displayed inhomogeneity. Deeper cutting with higher myopia and some intraoperative complications, such as suction loss, may result in larger irregularities. [ABSTRACT FROM AUTHOR]

Despite the encouraging short- and medium-term clinical results and increased usage of reverse shoulder replacements, a higher revision rate is documented compared with other major joint arthroplasties. Adverse reaction to polyethylene wear debris is still an important factor which may influence the long-term survival of reverse shoulder arthroplasty. To date, only a small number of retrieval studies of reverse shoulder arthroplasty have reported the different damage modes on polyethylene components, but none have quantified the ex vivo surface roughness on both articulating surfaces. The main purpose of this study was to assess, for the first time, the surface roughness of 13 retrieved metal-on-polyethylene reverse shoulder replacements using a white light profilometre with nanometre resolution. Although no significant relationship was observed between the surface roughness values and patient variables, it was noted that half of the polyethylene components still showed their original machining marks, indicating little change in vivo and that the metallic humeral components in the reversed design configuration showed low values of surface roughness after their time in vivo. [ABSTRACT FROM AUTHOR]

The accurate determination of wear volumes is a prerequisite for the study of numerous tribological phenomena. Wear volumes can be measured with different techniques (profilometry, confocal microscopy, white light interferometry, atomic force microscopy) or else be calculated starting from some quantities (usually the width and the planimetric wear) measured from the wear scar. Advantages and drawbacks of the mentioned measuring techniques are shown by means of wear scars and calottes resulting from ball-on-plane tests with 100Cr6 specimens. When measuring wear volumes, white light interferometry results to be one of the most suitable techniques, since it offers high accuracy and is not as time consuming as atomic force microscopy. When wear volumes are calculated, errors result mainly from two sources: (1) the arbitrary choice of one or few line profiles for the determination of the width and of the planimetric wear, and (2) approximations in the calculation, which are even necessary when values of the wear volumes of the single tribological partners, i.e., ball and plane, and not only the total volume, are of interest. The effect of both the statistical distribution of values of the width and of the planimetric wear and the propagation of errors due to approximations on the accuracy in the determination of wear volumes is characterized and elucidated by examples. It is found that errors due to approximations are negligible when compared to errors due to the arbitrary choice of one line profile.

Up to now, the distributed polarization coupling (DPC) measurement system based on white light interferometry (WLI) has been mainly studied for static and quasi-static measurement. In this paper, we developed the DPC system to measure the instantaneous frequency of dynamic stress. First, we set up a model of transversal stress on the panda polarization maintaining fiber (PMF) and simulated the interferograms of dynamic coupling points when the PMF is subjected to stress of cosine wave, sawtooth wave and square wave. Then, we did groups of experiments to measure the interferograms of dynamic coupling points, including cosinoidal coupling point, sawtooth wave coupling point, square wave coupling point, and two cosinoidal coupling points. By applying wavelet transform to the envelops of interferograms, we can obtain the time-frequency distribution images and demodulate the instantaneous frequency of external stress. The absolute error of experiments is less than 1.84 Hz. Finally, we deduced the upper and lower limits for frequency measurement and discussed the methods of enlarging the frequency range in detail. The method introduced in this paper has potential application in fiber sensing of dynamic stress.

Distributed polarization coupling measurement can be used to detect coupling points (CPs) in polarization-maintaining fibers (PMFs). Owing to the imperfection of the PMF structure and external weak disturbance, weak CPs are produced. However, weak CPs are easily submerged in background noise, so they are difficult to detect. In this article, we propose a method based on variational mode decomposition (VMD) to detect weak CPs. Using VMD and empirical mode decomposition (EMD), a comparison is made to evaluate the performance of extracting weak CPs in interferograms. As the VMD approach is embedded with the Wiener filter, it exhibits robustness to noise, which outperforms EMD in extracting weak CPs for both simulated and experimental interferograms. The noise level and mechanical scanning vibration frequency reduce the reconstruction accuracy of CPs. Moreover, the effects of mode number and bandwidth on decomposed results in the VMD method are discussed in detail. Additionally, the VMD-based method can be used to process other optical signals. [ABSTRACT FROM AUTHOR]

In ultra-precision diamond turning of freeform optics, it is necessary to obtain submicron-level form accuracy with high efficiency. In this study, we proposed a new method for the quick measurement and compensation of tool contour errors to improve the form accuracy of the workpiece. In this method, the nanometer-scale contour error of a diamond tool is quickly and precisely measured using a white light interferometer and then compensated for, before machining. Results showed that the contour of a diamond tool was measured with an error less than 0.05 μm peak-to-valley (P-V) and the feasibility of error compensation was verified through cutting experiments to create a paraboloid mirror and a microlens array. The form error decreased to 0.2 μm P-V regardless of the contour error of the diamond tools when cutting the paraboloid mirror, and that of the microlens array was reduced to 0.15 μm P-V during a single machining step. [ABSTRACT FROM AUTHOR]

In this article, we present a self-calibrated absolute thickness measurement method for opaque specimens based on fiber-optic white light interferometry. A new type of self-reference probe, which is composed of a fiber ferrule, an integrated beam splitter, and a gradient index lens, is presented. In our setup, two probes of this kind are fixed facing each other, and the distance between them can be measured. Then we insert a specimen between the probes and measure the distance between the specimen surfaces and probes on both sides. This way, a self-calibrated measurement of specimen thickness can be realized without the traditional calibration process using a standard thickness sample. Thus, the uncertainty component introduced by the standard thickness sample can be eliminated. The performance of the proposed method is evaluated by measuring standard thickness samples calibrated by the National Institute of Metrology of China, and the results show a good agreement with the nominal values. Also, we analyzed several key uncertainty components, as well as the reliability of our method. The calculated extended measurement uncertainty ($\bf {k} = 2$) is $0.06~\mu \text{m}$ for Cr specimen with a nominal thickness of 10.56, and $0.08~\mu \text{m}$ for Ni specimen with a nominal thickness of $31.46~\mu \text{m}$. [ABSTRACT FROM AUTHOR]

We have developed a Fabry–Perot extensometer that is able to operate at high temperature (up to 400 °C), for in pile experiments in material testing reactor, under high neutron and gamma flux. For that purpose, we have revised the basic scheme of an extrinsic Fabry–Perot interferometer (EFPI) to limit the effects of radiation and especially of the fast neutron fluence and to adapt the sensor to high temperature. After a description of the sensor and its operation, we present, in this article, two types of tests that were carried out to check the accuracy of the sensor at high temperature. First, four sensors are fixed either on stainless steel plates or on tantalum plates and the temperature is raised from room temperature to 400 °C. Knowing the thermal expansion of both the supports and the sensor parts, it is possible to predict the expected variation of the sensor output. The comparison between the predicted and experimental outputs provides the information about the accuracy of the sensor. Second, we performed high-temperature tensile testing at 300 °C and 350 °C. The Fabry–Perot measurements are compared, in the elastic domain, with the expected strain given by Hooke’s law, and on a larger strain domain, with the measurements of a high-temperature axial extensometer. The experiments and the results are presented. The error appears to be limited to about 1~μm when the strain is low (0.1%) and can be of few micrometers on a larger range (up to 2%). Strain measurements up to more than 5% are also reported. [ABSTRACT FROM AUTHOR]

• The novel surface recovery algorithm for white light interferometry based on carrier phase extraction and scan step noise correction which can perform precise surface profiling. • The surface profiles can be recovered simultaneously according to the corrected scan step and regenerated carrier after phase correction. • The scan step noise correction method can achieve effective measurement even when random and harmonic disturbances are combined. As a type of interference microscopy, white light interferometry (WLI) is well-established measuring technique in advanced manufacturing industry and scientific research for contactless inspection of surface topographies in micro- and nanometer range. In this paper, a scan step noise correction based surface recovery algorithm is proposed for WLI precision measurement, which provides an effective solution to the inevitable scan step noise. The carrier is firstly obtained by removing the envelope in the interference signal, then the carrier phase is extracted. Based on the theoretical linearity of the phase distribution, a corrected relationship is designed in terms of scan position and phase distribution. Afterwards, the surface profiles can be precisely recovered according to the regenerated carrier after phase correction simultaneously. Simulations show that the reconstruction error is less than 5 nm when WLI is disturbed by harmonic error and random noise. In order to test the effectiveness and reliability of the proposed, a step height with nominal value 45.5 ± 1.2 nm is used to calibrate the proposed system and the new algorithm, where within 10 rounds of scanning the mean height of 44.99 nm with the repeatability of 1.39% is achieved. In the experiment, a laser marking sample is measured and the 3D shape of the marking area is successfully recovered. The repeat measurements and the comparison with the commercial profiler are also provided, which exhibits good consistence and further proves the potential of the new method in the perspective of industry applications. [ABSTRACT FROM AUTHOR]

Virtual simulations are a relevant element in product engineering processes and facilitate engineers to test different concepts during early phases of the development. However, in tribological product engineering, simulations are hardly used because input data such as material behavior are often missing. Besides the material behavior, the surface roughness of the contacting elements is relevant for tribological systems. To expand the capabilities of the virtual engineering of tribological components such as bearings or brakes, the hereby presented approach allows for the depiction of real rough surfaces in finite element simulations. Rough surfaces are scanned by a white-light interferometer (WLI) and further processed by removing the outliers and replacing non-measured samples. Next, a spline generation creates a solid body, which is imported to CAD software and afterwards meshed with triangle and quadrilateral elements in different sizes. The results comprise the evaluation of six differently manufactured (turned, coated, and pressed) real surfaces. The surfaces are compared by the deviations of the roughness values after measuring with the WLI and after meshing them. Furthermore, the elements’ aspect ratios and skewness describe the mesh quality. The results show that the transfer is dependent upon deep cliffs and large Sz values in comparison to the lateral expansion.

Lateral scanning white light interferometry (LSWLI) is a promising technique for high-resolution topography measurements on moving surfaces. To achieve resolutions typically associated with white light interferometry, accurate information on the lateral displacement of the measured surface is essential. Since the uncertainty requirement for a respective displacement measurement is currently not known, Monte Carlo simulations of LSWLI measurements are carried out at first to assess the impact of the displacement uncertainty on the topography measurement. The simulation shows that the uncertainty of the displacement measurement has a larger influence on the total height uncertainty than the uncertainty of the displacing motion itself. Secondly, a sufficiently precise displacement measurement by means of digital speckle correlation (DSC) is proposed that is fully integrated into the field of view of the interferometer. In contrast to externally applied displacement measurement systems, the integrated combination of DSC with LSWLI needs no synchronization and calibration, and it is applicable for translatory as well as rotatory scans. To demonstrate the findings, an LSWLI setup with integrated DSC measurements is realized and tested on a rotating cylindrical object with a surface made of a linear encoder strip.

The increasing rate of antimicrobial resistance (AMR) in pathogenic bacteria is a global threat to human and veterinary medicine. Beyond antibiotics, antimicrobial peptides (AMPs) might be an alternative to inhibit the growth of bacteria, including AMR pathogens, on different surfaces. Biofilm formation, which starts out as bacterial adhesion, poses additional challenges for antibiotics targeting bacterial cells. The objective of this study was to establish a real-time method for the monitoring of the inhibition of (a) bacterial adhesion to a defined substrate and (b) biofilm formation by AMPs using an innovative thermal sensor. We provide evidence that the thermal sensor enables continuous monitoring of the effect of two potent AMPs, protamine and OH-CATH-30, on surface colonization of bovine mastitis-associated Escherichia (E.) coli and Staphylococcus (S.) aureus. The bacteria were grown under static conditions on the surface of the sensor membrane, on which temperature oscillations generated by a heater structure were detected by an amorphous germanium thermistor. Bacterial adhesion, which was confirmed by white light interferometry, caused a detectable amplitude change and phase shift. To our knowledge, the thermal measurement system has never been used to assess the effect of AMPs on bacterial adhesion in real time before. The system could be used to screen and evaluate bacterial adhesion inhibition of both known and novel AMPs.

In this paper, we discuss the design, fabrication, and testing of an external Fabry–Perot interferometer (EFPI)-based absolute type fiber optic pressure sensor of range 0–50 mbar. The FPI has sapphire as the first reflecting surface and stainless steel (SS) sheet (SS316L of thickness 0.18 mm) as the second one. In order to achieve high specular reflectivity, the reflecting surface of sapphire is coated with a broad band thin film coating, while the SS316L sheet is surface finished with the Chemo Mechanical Magneto Rheological finishing process. The parallelism between two reflecting surfaces of FPI and their individual flatness is around $\lambda $ /15, which was achieved by precision machining and assembly with stretched diaphragm. The SS sheet also works as the deflecting diaphragm of the pressure sensor and causes change in the FPI gap with applied pressure. FPI gap is calculated from the reflected spectrum by an improvised yet simple scheme. In this paper, FPI is an enclosed cell with vacuum inside, which acts as the reference pressure of the sensor. Applied pressure of 0–50 mbar changed the FPI gap by around $17~\mu \text{m}$. This sensor was tested with white light interferometric technique, and the best finesse obtained was 5.5. The proposed device is an optical analogous of a capacitance-based pressure sensor. To the best of our knowledge, FPI-based absolute pressure sensors of sub-atmospheric range with a metal diaphragm have not been reported anywhere. [ABSTRACT FROM AUTHOR]

The paper presents a new method of surface topology reconstruction from a white light interferogram. The method is based on interferogram modelling by complex exponents (Prony method). The compatibility of white light interferogram and Prony models has already been proven. Effectiveness of the method was tested by modelling and examining reconstruction of tilted and spherical surfaces, and by estimating the reconstruction accuracy.

In order to have a better understanding of the real contact area of granular materials, the white light interference method is applied to explore the real surface morphology of clay soils under high stress. Analysis of the surface profile indicates that there exists a support point height z0 with the highest distribution frequency. A concept of a real contact region (from z0 to z0 + d90; d90 represents the particle size corresponding to 90% of the volume fraction) is proposed by combining a surface profile with the particle size distribution of clay soil. It was found that under the compressive stress of 106 MPa–529 MPa, the actual contact area ratio of clay soil varies between 0.375 and 0.431. This demonstrates an increasing trend with the rise of stress. On the contrary, the apparent porosity decreases with an increasing stress, varying between 0.554 and 0.525. In addition, as the compressive stress increases, the cumulative frequency of apparent profile height (from z0 − d90 to z0 + d90) has a concentrated tendency with a limited value of 0.9.

Fabry-Perot (FP) sensors like other Fiber Optic (FO) sensors may be of particular interest for in pile experiments in MTR with little room available thanks to their compact size. Light weight also reduces gamma heating hence limiting the thermal effect. Different physical parameters such as temperature, strain, displacement, vibration, pressure, or refractive index may be sensed through the measurement of the optical path length difference in the cavity. We have developed a Fabry-Perot extensometer able to operate at high temperature (up to 400°C), under a high level of radiation (neutron and gamma flux). The measurement based on interferometry is largely insensitive to radiation induced attenuation (RIA) thanks to the wavelength encoding of the useful signal, but for such high fluence as encountered in a reactor core, a special rad-hard fiber is needed. Operating in the wavelength domain around 1ím remains preferable to minimize the impact of irradiation. Moreover, fast neutron radiation is expected to change the structure of the fiber and possibly others materials in the transducer. Then, we revised the basic scheme of Extrinsic Fabry-Perot Interferometer (EFPI) so that the effects of compaction remain limited. Tests under mixed neutron and gamma irradiation permitted to verify the general behavior and particularly the low drift with radiation induced compaction (RIC). Also, two types of tests have been conducted to verify the accuracy at high temperature. The first ones are “measurements” of thermal dilatation of materials: the sensor is fixed on a sample and knowing its thermal expansion, it is possible to predict the measurement expected from the optical sensor when the temperature is increased from low to high temperature. The comparison between the predicted and experimental outputs informs on how the sensor is accurate. The second types are tests on a tensile test bench operating at high temperature. The Fabry-Perot measurements are compared, in the elastic domain, with the expected strain given by the Young modulus of the material, and also on a larger strain domain, with the measurements of a high temperature axial extensometer. Both types of tests are presented and commented.