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Uniform molding and demolding of structures on highly curved surfaces through conformal contact is a crucial yet often-overlooked aspect of nanoimprint lithography (NIL). This study describes the development of a NIL tool and its integration into a nanopositioning and nanomeasuring machine to achieve high-precision orthogonal molding and demolding for soft ultraviolet-assisted NIL (soft UV-NIL). The process was implemented primarily on the edges of highly curved plano-convex substrates to demonstrate structure uniformity on the edges. High-resolution nanostructures of sub-200-nm lateral dimension and microstructures in the range of tens of microns were imprinted. However, the nanostructures on the edges of the large, curved substrates were difficult to characterize precisely. Therefore, microstructures were used to measure the structure fidelity and were characterized using profilometry, white light interferometry, and confocal laser scanning microscopy. Regardless of the restricted imaging capabilities at high inclinations for high-resolution nanostructures, the scanning electron microscope (SEM) imaging of the structures on top of the lens substrate and at an inclination of 45° was performed. The micro and nanostructures were successfully imprinted on the edges of the plano-convex lens at angles of 45°, 60°,and 90° from the center of rotation of the rotating NIL tool. The method enables precise imprinting at high inclinations, thereby presenting a different approach to soft UV-NIL on curved surfaces.

When the cavity changes during spectrum acquisition process, Doppler phenomena will occur and cause conventional scanning white-light interferometry (WLI) to fail. To absolutely demodulate the cavity length of the dynamic low-finesse Fabry–Perot sensor, a novel laser frequency modulated phase-shifting WLI (PS-WLI) is proposed. Two phase-shifted spectra can be obtained by introducing a fixed phase-shift after each scanning frequency. The phase results containing modulations of frequency scanning and dynamic signals are retrieved based on quadrature demodulation. Although the full-spectrum acquisition frequency of the proposed PS-WLI is only 50 Hz, 0.5∼20 kHz vibration signals can be demodulated. It combines the advantages of frequency-switched two-step phase shifting interferometry (PSI) and scanning WLI to achieve absolute measurement with high sampling rate. Numerical simulations and experiments verify its effectiveness.

Distributed polarization measurement is a significant way to evaluate polarization-maintaining fiber. It can assess the fiber's polarization preserving ability and locate internal defects and external perturbations of a long-distance PM fiber. Distributed polarization crosstalk of a fiber-optic polarization device accurately describes its time-dependent optical performance. Therefore, distributed polarization measurement technology can be used to predict and prevent the performance degradation and failure. However, the remaining shortcomings of existing measurement methods are low dynamic range, short measurement length, inadequate spatial resolution, and low diagnostic ability. This paper reviews recent advances in solving the above issues and presents ways to obtain high performances: a dynamic range > 90 dB, a measurement length > 10 km, a full range spatial resolution < 10 cm, and developments in time domain, frequency domain, and time-frequency domain diagnosis methods. All these high-performance techniques have led to more effective diagnosis of fiber optic sensing coils. This can be demonstrated by a series of comparative measurements and analysis of three PM fiber optic sensing coils in various configurations such as a randomly-wound spool of fiber and a free-standing coil quadrupole-pattern-wound from it, a second coil with and without a flange at various temperatures, and a third coil spliced to a Y waveguide. Each is one of the key configurations during the production processes or the application of the fiber sensing coil. The technical progress reviewed here will greatly promote the development, production, and application of fiber sensing coils.

The improvement of ultra-precision machining technology has significantly boosted the demand for the surface quality and surface accuracy of the workpieces to be machined. However, the geometric shapes of workpiece surfaces cannot be adequately manufactured with simple plane, cylindrical, or spherical surfaces because of their different applications in various fields. In this research, a method was proposed to generate tool paths for the machining of complex spherical surfaces based on an ultra-precise five-axis turning and milling machine with a C-Y-Z-X-B structure. Through the proposed tool path generation method, ultra-precise complex spherical surface machining was achieved. First, the complex spherical surface model was modeled and calculated, and then it was combined with the designed model to generate the tool path. Then the tool paths were generated with a numerically controlled (NC) program. Based on an ultra-precision three-coordinate measuring instrument and a white light interferometer, the machining accuracy of a workpiece surface was characterized, and the effectiveness of the tool path generation method was verified. The surface roughness of the machined workpiece was less than 90 nm. Furthermore, the surface roughness within the spherical region appeared to be less than 30 nm. The presented tool path generation method in this research produced ultra-precision spherical complex surfaces. The method could be applied to complex spherical surfaces with other characteristics.

A white light, i.e., Fabry-Perot, interferometry was unprecedently applied to determine the rate change of the current density (J) of aluminum samples during the anodization processes of the samples in aqueous solutions. The current density(J) values were obtained by Fabry-Perot interferometry rather than the direct current (DC) or alternating current (AC), methods. Therefore, the abrupt rate change of the J was called electrochemical-emission spectroscopy. The anodization of the aluminum samples was conducted by an external DC source in 0.0,2,4,6,8,10% sulfuric acid (H2SO4) solutions at room temperature. In the meantime, the Fabry-Perot interferometry was used to determine the difference between the J of two subsequent values, dJ, as a function of the elapsed time of the DC experiment for the aluminum samples in 0.0,2,4,6,8,10% H2SO4 solutions. The Fabry-Perot interferometry was based on a fiber-optic sensor in order to make real time-white light interferometry possible at the aluminum surfaces in the sulfuric acid solutions. As a result, a new spectrometer was developed based on the combination of the Fabry-Perot, i.e., white light, interferometry and DC method for studying in situ the electrochemical behavior of metals in aqueous solutions.

Purpose This study aims to introduce a novel approach in form of a comprehensive software suite to help understanding and optimizing the build orientation toward maximizing the fatigue lifetime of complex geometries. The objective is to find an optimized build orientation under a given in-service loading state, which brings on smoother surfaces in stressed regions, mitigated roughness-induced stress concentration and deferred crack initiation stage. The solution addresses scenarios that no post-build surface treatment can be applied. Design/methodology/approach To account for the surface topography, the staircase induced surface roughness is registered as a function of build angle using the white light interferometry characterization, based on which the stress concentration factor (kt) is calculated. Thereafter, the developed module in “Fatlab toolbox” is used to find the optimum build angle, considering the integrated surface orientations and stress analysis under a given loading condition. Findings Surface topography creates local stress concentrations upon loading, directly influencing the fatigue lifetime. It is a well-established fact that the conditions of the staircase geometry and surface roughness affect the magnitude of the stress concentration upon loading, which is influenced by the build orientation of the component. The proposed solution suggests the best build orientation that mitigates staircase-related surface roughness. Originality/value The suggested numerical approach assists the designers with positioning of the part on the build plate to minimize the build orientation-induced surface roughness and improve the as-built fatigue lifetime of the component.

The surface morphology of parts made by the laser powder bed fusion (L-PBF) process is governed by the flow of the melt pool. The nature of the molten metal flow depends on the material properties, process parameters, and powder-bed particles, etc., and may result in potentially significant variations along a laser scanning path. This study investigates the formation of transient and steady-state zones through a single-track l -PBF experiment using Inconel 625 powder. Single tracks with lengths of 1 mm and 2 mm were fabricated using 195 W laser power and scan speeds of 400 mm/s or 800 mm/s. The surface morphology of the track was analyzed using a white light interferometer (WLI), and an individual single track can be divided into three distinct zones based on the track width and height. The initial transient region has a wider and taller solidified track geometry, the region near the end of a scan has a tapered profile with a decreasing track width and height, while the steady-state region in the middle has a smaller variation in the width and height. A mesoscale numerical model was further developed using FLOW-3D to examine the formation of the transient and steady-state zones. At the start of a scan, strong flow occurs outward and backward, leading to the formation of a wider track with a bump. As the scan continues, the thermal gradient stabilizes, leading to a steady state, which resulted in a very small fluctuation in the width. Furthermore, the tapered end of the scan track is due to the half-lemniscate shape of the melt pool during laser scanning.

Optical quality of glass components are determined by its surface finish either at lapping stage or at final polished stage. The criticality of optical components is defined by its application. For commercial application its surface finish can be of the order of few microns, whereas for special purpose applications such as aerospace, navigation and laser based sensors its surface finish requires super smooth polish ranging from angstrom to sub angstrom level. In order to achieve such high surface figure, the optical components has to be pre-processed from lapping stage. Two parameters play a major role for obtaining better quality of optical components; they are Surface Roughness (Ra) and Sub Surface Damage (SSD). These parameters have to be monitored from the initial stage of lapping. In this work, Fused Silica glass substrate has been considered and lapped with different deterministic grinding methods, such as Diamond Pellet, Diamond Trizact Tile and Diamond Cup Tools. The abrasives used are pre determined diamond particles embedded in different matrix, such as metal bound, resin bound, ceramic bound and electroplated. The processed samples were characterized for its Average Roughness (Ra) through White Light Interferometry technique and its corresponding depth of SSD was calculated. Images of processed samples were captured through Field Emission Scanning Electron Microscope (FESEM). Process optimization and comparative study between various deterministic lapping processes has been established. Average Surface Roughness (Ra) has been reduced from 274 nm to 3.3 nm and its corresponding depth of SSD values were also reduced from 14.5 µm to 0.151 µm. Earlier, studies determine that SSD depends on grit size of diamond whose relation was given by 0.5d, irrespective of processing parameter or methodology adopted. In this study results have been obtained with one order down with respect to earlier achieved results.

In this paper, the different methods of processing of surface topography image (STI) were proposed for the characterization of selected features from the surface texture. The proposed analysis was performed to improve the functionality of the image assessment in the characterization of material contact properties (e.g. wear-resistant, lubricant retention, sealing or friction) according to the results of surface topography measurement. Various type of surfaces from manufactured details was considered, e.g. turned, ground, honed, laser-textured or isotropic. They were measured by the white light interferometer. Results were analyzed with areal surface topography maps (image) characterization. It was found that wavelet filtering approaches might be valuable in assessments of the selected surface texture features, such as dimple (size or distributions) or treatment trace distances, received by an application of STI processing methods. Additionally, proposed in the paper, the image digital extension method might be crucial in the definition of feature size (depth, width), especially when they are located on the edge of analyzed (measured) detail. Moreover, STI might be advantageous in the reduction of some surface texture measurement errors (a selected type of noise).

Soil grains when treated with dimethyldichlorosilane (DMDCS) create a thin soft coating layer. The presence of such a layer changes the grain surface wettability giving desirable hydraulic properties which has great potential in engineering practice. The thickness of such a layer has been identified to be an influencing parameter for the mechanical properties. But its estimation is not straightforward as the soil grain contains a relatively rough surface which is non-negligible compared to the thin soft coating. In this paper, we proposed a method that is based on the surface topography to estimate the soft coating thickness. A high-resolution microscope equipped with a white light interferometer was employed to examine the soil grain surface. It was found that the coating thickness is largely dependent on the surface topography of soil grains. The present method, applicable for particles with a very thin coating layer that is comparable to the surface roughness, such as for natural sands, could be used to further study the effect of coatings, of synthetic or natural origin, on the hydro-mechanical behaviour of coated soil samples.

Multi-pole arrangements in magnetorheological plane finishing technology have been investigated in this study. A method of combining the material removal mechanism of micro-points using the empirical Preston equation is proposed to establish a prediction model for surface flatness, and the new Semiconductor Equipment and Materials International (SEMI) standard has been used to evaluate workpiece surface flatness. Based on the model, the effects of process parameters (polishing time, speed ratio, translational amplitude, polishing gap, etc.) on the flatness of workpieces with different shapes are predicted through simulation, and the effects of multi-pole arrangements are explored. The results of the analysis indicate that with changes in process parameters, the extent of change in surface flatness differs based on the shape of the workpiece. After polishing, concave workpieces show the highest levels of surface flatness. From simulations of magnetic pole arrangements, it is also found that magnetic field generators with different magnetic pole arrangements can be used for workpieces with different shapes to improve their surface flatness. Experiments with a workpiece with its shape measured using a white light interferometer showed that the surface flatness improved from being 33.561 μm initially to 21.822 μm after polishing, thereby demonstrating the effectiveness of the proposed method.

Reinforcement of glass fibers at the weld joint interface of polyamide 66 (PA66) was investigated aiming to improve the weld strength but rather found to improve the tribological properties. The weld strength of glass fiber reinforced polyamide 66 was found to be in the range of 46 %–52 % of that of the parent material. The dry sliding wear behavior of the friction stir welded polyamide 66 with and without glass fiber strengthening was investigated in this experimental study, using a pin-on-disk wear tester. The worn surface topography and morphology were analyzed via white light interferometry and scanning electron microscope, respectively. The wear study confirmed that PA66 reinforced with high fiber content of 20 % by weight of polymer (GF/PA66) yielded a minimum specific wear rate and coefficient of friction.

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.

Dry wear experiments provide an insight detail on how severely contacting surfaces change under unlubricated sliding condition. The theory of dry sliding wear is used for understanding mixed-lubrication regime in which asperity interactions play a significant role in controlling of the friction coefficient (f). The purpose of this work is to study the tribological behavior of AISI 304 steel in contact with AISI 52100 steel during wear. Both materials are used in rolling element bearings commanly. Experiments are carried out using a pin-on-disc tribometer under dry friction condition. The areal (three dimensional, 3D) topography parameters are measured using a 3D white light interferometer (WLI) with a 10× objective. After wear tests, wear mechanisms are analyzed utilizing scanning electron microscope (SEM). Factorial design with custom response surface design (C-RSD) is used to study the mutual effect of load and speed on response variables such as f and topography parameters. It is observed that the root mean square roughness (Sq) decreases with an increase in sliding time. Within the range of sliding time, Sq decreases with an increase in the normal load. Within the range of sliding speed and normal load, it is found that Sq, mean summit curvature (Ssc), and root mean square slope (Sdq) are positively correlated with f. Whereas, negative correlation is found between f and correlation length (Sal), mean summit radius (R), and core roughness depth (Sk).

Fluid jet polishing (FJP) is a versatile polishing process that has many advantages compared to other polishing processes. Stand-off distance (SOD) is one of the key parameters in fluid jet polishing. However, relatively little research work has been carried out to investigate its effect of SOD on material removal characteristics and surface generation in FJP. In this paper, a systematic investigation of the effect of SOD on the tool influence function and surface topography in FJP was conducted. Experiments were designed for FJP two kinds of materials corresponding to ductile and brittle materials. They are nickel copper (NiCu) alloy and BK7 optical glass, respectively. In this study, the SOD was varied from 2 to 35 mm. Analysis and discussions were made on its effect on the shape of TIF, material removal rate, and surface topography. It is interesting to note that the TIF shape becomes a Gaussian-like shape with large SOD both on NiCu and BK7, which provides a novel way to optimize the TIF in FJP. The variation of the material removal rate and surface roughness versus SOD on NiCu and BK7 were also determined from the experimental results. Moreover, the surface topography of NiCu and BK7 were characterized from the results measured from the white light interferometer and scan electron microscope. The outcome of the study provides a better understanding of the material removal characteristics and surface generation mechanism in FJP.

In order to obtain a better surface micro-morphology on the difficult-to-machine materials such as titanium alloys, the influence of ultrasonic parameters and cutting parameters on the tool path was analyzed theoretically under the ultrasonic longitudinal-torsional vibration. Ultrasonic longitudinal-torsional assisted milling (ULTAM) of titanium alloy was performed, based on a 20° slope. The effects of the ultrasonic parameters and cucuttintting parameters were studied on the surface morphology and surface roughness. The machined surface was examined using scanning electron microscopy (SEM) and white light interferometry. The characterization parameters of the three-dimensional surface micro-morphology including the arithmetic mean height (Sa), the surface skewness (Ssk), and the density of summits (Sds), were obtained under the corresponding cutting parameters. It was found that the ultrasonic amplitude exhibited a significant influence on the surface micro-morphology, followed by the spindle speed n, while the effect of the depth of cut (ap), and the feed amount per tooth (fz) was relatively less. Under the same cutting parameters for the surface, a comparative analysis for the friction and wear testing was performed between the ultrasonic milling and conventional milling (CM). The results showed that the ULTAM transformed the original ravines and anisotropic surface imperfections into an uniform and orderly scaly micro-texture, thus forming an isotropic surface texture in all directions. Furthermore, ULTAM transformed the surface into a fish-scale micro-texture, and thereby improved the surface quality. The fine and smooth surface morphology was conducive by shortening the running-in time, allowing the stable state of friction to be reached quickly, and thereby offering a higher stability in the friction process. `Compared to CM, the tool wear was reduced by 30%, due to the unique tool-work separation characteristics of the ultrasonic longitudinal-torsional assisted milling. Moreover, the unique intermittent cutting characteristics of the ultrasonic longitudinal and torsional milling not only reduced the cutting force and tool wear, but also inhibited the generation of the burr, thus improving the surface quality.

Experimental data collection methods and a corresponding numerical model are presented to investigate the quality of waveguide fabrication in nonlinear optics. The method utilises white light interferometry and standard image recognition techniques to calculate a waveguide propagation constant function. This enables comparison of a numerical second harmonic spectrum in quasi-phasematched materials, such as periodically poled lithium niobate, with the waveguide’s experimental phase-matching spectrum. Using the presented method, a 3rd order polynomial fit to waveguide ridge width is demonstrated to be in good agreement with experimental phasematching spectra. The presented technique provides a nondestructive route to discriminate between issues in fabrication steps in nonlinear waveguide design.

A fiber optic dual-cavity Fabry-Perot interferometer(DFPI) for simultaneous high- temperature and high-gas-pressure measurements is proposed and experimentally demonstrated. The proposed sensing structure consists of an extrinsic Fabry-Perot interferometer (EFPI) with a short piece of hollow core fiber (HCF) for gas pressure sensing, and an intrinsic Fabry-Perot interferometer (IFPI) made of photonic crystal fiber (PCF) for temperature sensing. The composite interference signal is filtered in the frequency domain to obtain two independent interference spectra, and then is demodulated by using white light interferometry (WLI). The experimental results show that the sensor exhibits good linearity over a temperature range from 40 to 1000°C with a cavity-length temperature sensitivity of 25.3 nm/°C, and a pressure range from 0 to 10 MPa with a cavity-length pressure sensitivity of 1460 nm/MPa at 40°C. This proposed sensor are light-weight and small, and it has a compact structure and a high temperature resistance.

The surface integrity and structural characteristics of titanium alloy blades have great influence on the aerodynamic performance of aero-engines. It has been proved that shark-skin bio-inspired riblets can improve the aerodynamic performance of parts by 10%. At present, the process of this structure is mainly formed by laser, rolling, etc., and the above processing methods have low efficiency, poor surface integrity and other problems. Belt grinding is widely used in surface polishing of titanium alloy blades, which plays an important role in improving the surface integrity. However, it is difficult to guarantee the surface’s microstructure characteristics. Therefore, combining the advantages of laser processing, the U-shaped structure produced by laser assisted belt grinding processing of shark skin is proposed. Firstly, based on the characteristics of the structure, a laser assisted belt grinding processing method is proposed and the forming process of the surface structure is analyzed. Then the experiments of titanium alloy plates with different surface roughness were carried out. Finally, the U-shaped structure is analyzed by white light interferometer. The experimental results show that the ratio of depth to width is h/s=0.4~0.6, the surface structure is mainly U-shaped structure, and the machining error is less than 10%. So this method can be used for the processing of U-shaped structure.

This paper investigates the cutting performance and anti-adhesive properties of textured single-point polycrystalline diamond (PCD) cutting tools in machining Aluminium 6082 alloys. The micro/nano textures were first milled using a fibre laser (1064-nm wavelength) at different power intensities, feed speeds and pulse durations, and finally characterised using scanning electron microscopy, white light interferometry and energy dispersive X-ray spectroscopy. The effect of different textures on the cutting performance was investigated in turning tests under dry cutting conditions. The test was stopped at regular lengths of cut to allow analysis of height of adhesion through 3D white light interferometry. The data processing of the cutting forces and the microscopical characterisation of the tested cutting tools enabled the evaluation of the effects of texture design, friction coefficient and adhesive properties. The results indicated that feed force in tools with grooves perpendicular to the chip flow direction (CFD) was more stable (20–40 N) than the benchmark (6–41 N). Similarly, the thrust force for tools with grooves parallel to CFD and grooves perpendicular to CFD showed a homogeneous trend fluctuating between 60 and 75 N as compared with the benchmark (ranging between 73 and 90 N). For texture depth in the order of 260 nm and post process roughness in the order of tens of nanometers, a reduction of average friction coefficient (0.28 ± 0.14) was reported when using lasered inserts with grooves parallel to the chip flow direction compared with the benchmark tools (0.34 ± 0.26) corroborated by reduced stiction of workpiece material on the rake face. In machining via textured tools with grooves perpendicular to CFD, the cutting forces were reduced by 23%, and the surface quality of the machined workpiece was improved by 11.8%, making this geometry the preferred choice for finishing applications. Using grooves parallel to CFD reduced the cutting forces by 11.76%, adhesion by 59.36% and friction coefficient by 14.28%; however, it increased the surface roughness of the machined workpiece, making this geometry suitable for roughing operations. For the first time, laser manufacturing is proposed as a flexible technique to functionalise the geometrical and wear properties of PCD cutting tools to the specific applications (i.e. roughing, finishing) as opposed to the standard industrial approach to use microstructurally different PCDs (i.e. grain size and binder %) based on the type of operation.

The current research focuses on the characterization of the produced heat affected zone when laser heats AISI H13 steel, AISI 1045 steel and Ti6Al4V alloy workpieces via finite element simulations and experimental investigation. The surface roughness designedly varies on the surface of the samples and its influence on the absorption of laser light is investigated. Experiments are conducted at 1-4 W laser power and for two scanning speeds of 2 and 100 mm/min. A 3D transient thermo-structural finite element model for a moving Gaussian laser heat source is developed to simulate the micromachining process and predict the depth and width of the heat affected zone. The Johnson-Cook material model that takes into account the effect of plastic strain, strain rate and temperature, along with a fracture model, is adapted to the simulations. A good agreement between the experimental data and the simulation results is found. The depth and width of the heat affected zone strongly depend on the laser parameters and material properties of the irradiated samples. This study constitutes the basis to the optimization and improvement of the laser assisted micromachining process parameters and provides key insights on the roughness-absorptivity relation for the three metallic materials.

The noncontact optical probe-based surface scanning is promising for the measurement of complex-shaped optical surfaces. In this study, by combining a chromatic confocal sensor and a planar nano-positioning stage, a sub-aperture scanning and stitching method is developed for the noncontact measurement of the microstructured optical surfaces, with the measured form accuracy being irrespective of the accuracy of the global scanning stage. After the scanning, the Gaussian process-based denoising is employed to remove the measurement noises, and a hybrid registration algorithm is proposed to achieve a 6-DOF alignment of any neighbored sub-apertures. For the registration, the differential evolution-based minimization is implemented to find a coarse transformation which then serves as the initial value for the iterative closest point-based fine registration. The hybrid method is beneficial in finding an optimal registration with a greatly reduced computation burden. Finally, the effectiveness of the developed measurement system, as well as the stitching algorithm, is comprehensively demonstrated through practically measuring a sinusoidal micro-grid surface.

A novel, to the best of our knowledge, thickness measurement scheme based on a phase shifting spectrally resolved interferometry is proposed for a thin film measurement from spectral reflectance and phase in a single sequence. This purpose is realized by introducing a spectral reflectance phase surface (SRPS). The spectral phase, originally existing in the form of an imaginary term, is revealed as a real term with the spectral reflectance due to the proposition of SRPS. Therefore, the reflectance and phase are contained in a single parameter, SRPS, and are measured in a single sequence. The phase shift error compensation is presented to form the accurate SRPS and ensure the performance of the measurement. The thickness of the sample is determined as the measured SRPS, and the theoretical SRPSs are compared by the cross correlation method. The performance of the proposed system is validated by measuring several samples of the S i O 2 on a silicon substrate and comparing the results with the commercial ellipsometer.

We present a novel, to the best of our knowledge, remote gas detection and identification technique based on correlation spectroscopy with a piezoelectric tunable fiber-optic Fabry–Perot filter. We show that the spectral correlation amplitude between the filter transmission window and gas absorption features is related to the gas absorption optical depth, and that different gases can be distinguished from one another using their correlation signal phase. Using a previously captured telluric-corrected high-resolution near-infrared spectrum of Venus, we show that the radial velocity of Venus can be extracted from the phase of higher order harmonic lock-in signals. This correlation spectroscopy technique has applications in the detection and radial velocity determination of weak spectral features in astronomy and remote sensing. We experimentally demonstrate a remote C O 2 detection system using a lock-in amplifier, fiber-optic Fabry–Perot filter, and single channel avalanche photodiode.

We outline the basic theory behind white light interferometry and the workings of a typical light interferometer microscope. We study WLI images obtained for rough and smooth chrome steel spheres to illustrate the principle that curved rough surfaces can be imaged with such a device as long as the surface roughness is kept within certain limits.

This paper describes the dependence of the precision of digital holographic methods on measurement parameters. The predominantly discussed parameters are illumination intensity and its homogeneity, surface microroughness, the influence of measurement geometry, as well as object shape, since most of them can be optimized by experimental arrangement. Frequency sweeping digital holography as well as dual-wavelength digital holography in the Fourier arrangement are tested and the results are discussed. It transpires that the methods are not very sensitive to object microroughness or overall reflectivity. Instead, it is the similarity of signal and reference waves that has the highest impact on measurement. After parameter optimization, the holographic methods can be advantageously used for ground surface measurements in optical workshops.

Our limited understanding of the nervous system forms a bottleneck which impedes the effective treatment of neurological disorders. In order to improve patient outcomes it is highly desirable to interact with the nervous tissue at the resolution of individual cells. As neurons number in the billions and transmit signals electrically, high-density, cellular-resolution microelectrode arrays will be a useful tool for both treatment and research.This paper investigates the advantages and versatility of laser-patterning technologies for the development of such high-density microelectrode arrays in flexible polymer substrates. In particular, it aims to elucidate the mechanisms involved in laser patterning of thin polymers on top of thin metal layers. For this comparative study, a pulsed picosecond laser (Schmoll Picodrill) with two separate wavelengths (1064 nm (infrared (IR)) and 355 nm (ultraviolet (UV))) was used. A 5 $\mu$ m thick electroplated layer of gold (Au) was used to form the microelectrodes. Laser-patterning was investigated to expose the Au electrodes when encapsulated by two different thermoplastic polymers: thermoplastic polyurethane (TPU), and Parylene-C, with thicknesses of maximum 25 $\mu$ m. The electrode diameter and the distance between electrodes were reduced down to 35 $\mu$ m and 30 $\mu$ m, respectively. The structures were evaluated using optical microscopy and white light interferometry and the results indicated that both laser wavelengths can be successfully used to create high-density microelectrode arrays in polymer substrates. However, due to the lower absorption coefficient of metals in the IR spectrum, a higher uniformity of the exposed Au layer was observed when IR-based lasers were used. This paper provides more insight into the mechanisms involved in laser-patterning of thin film polymers and demonstrates that it can be a reliable and cost-effective method for the rapid prototyping of thin-film neural interfaces.

Inflatable membrane primary optics for space telescopes are a smart approach in the context of saving flight payload weight and volume. The Orbiting Astronomical Satellite for Investigating Stellar systems (OASIS) adopted the membrane architecture for primary optics (primary antenna, A1) to have 20 meter diameter collection area with operation bands at the terahertz frequency. The membrane is made of Kapton or Mylar film with an aluminized surface, and the balloon (transparent surface + aluminized surface) is inflated to work as the convex mirror. In order to leverage the carrying volume advantage of inflatable optics, it must be folded during launch and deployed in orbit. The thin membrane film can crumple easily when it is folded, and it should be ironed out when the telescope is deployed for observation. We studied the microroughness and mid-to-high spatial frequency characteristics of the membrane via optical metrology to evaluate the surface properties. Because it is not of traditional shape and material, it is impossible to test with an offthe- shelf interferometer and profilometer. Moreover, the defect spatial frequency of interest is a few hundred microns to millimeters range, so the measurable field and dynamic range need to be in range of a few centimeters with microns resolution. To meet those requirements for metrology, we developed a flexible optics testbed utilizing deflectometry. The microroughness and mid-to-high frequency properties are measured with a white light interferometer and proposed methodology. The test results show that the candidate membrane is suitable for OASIS and this reliable test will guide the further design study of A1 assembly and optical system error budget.

In this paper, a cost-effective and high-precision optical fiber sensing system based on VT-DBR laser for white light interferometry is proposed. A low-noise, low power, high modulation-bandwidth laser driver with excellent long-term stability is described. A stable and high laser drive current has been obtained using a high-precision ADN8810 chip. Self-designed data acquisition module based on the Analog-to-Digital acquisition chip AD9226 was developed to collect data from Fabry-Perot (FP) sensor interference spectrum, and then the acquired spectral data were transferred to the PC by USB serial port. Laser scanning monitoring, data acquisition and data transmission are carried out using a field-programmable gate array (FPGA). An integral temperature chip ADN8831 was used to drive the thermoelectric cooler controller of the Vernier Tuned Distributed Bragg Reflector (VT-DBR) tunable laser. This system has a broad sweep range (1527-1567nm)with a wavelength interval of 8 pm, and a full-spectrum scanning rate of 100 Hz. Contrast observation of spectrum experiment with commercial optical sensing interrogator sm125 and temperature sensing experiments of FP sensor cavity length demodulation using cross-correlation algorithm was carried out to investigate the performance of the system. Experimental results show that the system is reliable and has superior performance. Benefiting from the self-developed and integrated essential electrical circuits, the whole system has small size, cost-effective and potential application value.

Subsurface microstructures influence the friction and wear behavior of metallic tribological systems, among other factors. To gain a basic understanding of the microstructural changes occurring during sliding processes, face-centered cubic model systems, for example a copper system with a sapphire sphere sliding against it, were previously characterized. Such systems showed the evolution of the dislocation self-organization phenomenon called the dislocation trace line. To test the occurrence of this dislocation arrangement in bcc metals, in this study a ruby ball was slid against electropolished bcc iron under an increasing normal load. The wear track topography and subsurface microstructure were characterized using white light interferometry and scanning transmission electron microscopy. The analysis suggested that at least for bcc iron, the evolution of a dislocation trace line is connected with the onset of pronounced plastic deformation.

Surface topography is a tool to endow biomaterials with bioactive properties. However, the large number of possible designs makes it challenging to find the optimal surface structure to induce a specific cell response. The TopoChip platform is currently the largest collection of topographies with 2176 in silico designed microtopographies. Still, it is exploring only a small part of the design space due to design algorithm limitations and the surface engineering strategy. Inspired by the diversity of natural surfaces, it is assessed as to what extent the topographical design space and consequently the resulting cellular responses can be expanded using natural surfaces. To this end, 26 plant and insect surfaces are replicated in polystyrene and their surface properties are quantified using white light interferometry. Through machine-learning algorithms, it is demonstrated that natural surfaces extend the design space of the TopoChip, which coincides with distinct morphological and focal adhesion profiles in mesenchymal stem cells (MSCs) and Pseudomonas aeruginosa colonization. Furthermore, differentiation experiments reveal the strong potential of the holy lotus to improve osteogenesis in MSCs. In the future, the design algorithms will be trained with the results obtained by natural surface imprint experiments to explore the bioactive properties of novel surface topographies.

Degradation of paper and the consequent loss of its chemical and mechanical properties has been studied for many decades. For conservators an understanding of the loss of mechanical properties of paper during degradation is highly relevant from a practical point of view. Considering the fibrous microstructure of paper, the mechanical properties of single cellulose fibers and their change in time has been of interest in paper degradation studies. With current advances in experimental micromechanics, the characterization of cellulose fibers is achievable at small scales and with very high accuracy. Such detailed analyses on naturally aged paper in combination with accelerated aging experiments lead to valuable insight in the degradation of paper. The current study represents a novel methodology for the accurate mechanical characterization of micro-scale fibers, such as cellulose fibers. To this end, in-situ mechanical tests are performed using high resolution optical profilometry (white light interferometry) in combination with Digital Image Correlation (DIC) to attain detailed strain measurements. Given the curly geometry of cellulose fibers, there is considerable out-of-plane deformation during a micro-tensile test, making is necessary to use profilometric images. An in-house built setup is used for application of micro-scale speckle pattern needed for DIC. Reliable evaluation of the cross-sectional area of fibers is attained by acquiring profilometric images of both the front and back sides of each fiber, using a mirror in a novel self-calibrating setup. Detailed analyses of the results from different samples show the accuracy and reliability of the measurements and the methodology. By these means, an accurate evaluation of the stiffness and strength of cellulose fibers is attained. Performing such measurements on cellulose fibers from aged papers is expected to result in better understanding of the effect of cellulose degradation on the mechanical properties of paper.

Real-time measurement of plastic film thickness during production is extremely important to guarantee planarity of the final film. Standard techniques are based on capacitive measurements, in close contact with the film. These techniques require continuous calibration and temperature compensation, while their contact can damage the film. Different optical contactless techniques are described in literature, but none has found application to real production, due to the strong vibration of the films. We propose a new structure of low-coherence fiber interferometer able to measure blown film thickness during productions. The novel fiber-optic setup is a cross between an autocorrelator and a white light interferometer, taking the advantages of both approaches.

Rise in demand for wearable consumer electronics products has given an impetus to the development of flexible electronics technology encompassing flexible substrates and compatible circuitry. Also, additive manufacturing of flexible electronics is emerging rapidly via several techniques such as Inkjet and Aerosol Jet Printing (AJP). The basic component of all flexible circuits to be printed by these technologies is conductible ink, which is generally silver ink. Few studies exist on the printing of copper conductible ink and not many copper ink formulations are available in the market as that of silver inks. This study aims to develop a process development study for deposition of copper conductible lines on flexible substrates using the aerosol jet printing technology. The process development study includes investigation of photosintering parameters for obtaining desirable electrical resistance and shear load to failure values for the printed line. Different pre-drying techniques such as oven pre-drying and platen pre-drying have been used for improving the electrical and mechanical properties of the conductive traces. Techniques such as optical microscopy and white light interferometry have been used for the characterization of print quality of the conductible lines.

In this paper, we propose and utilize a deep convolutional neural network (CNN) model to study the contribution of multiple morphologies and their corresponding mechanisms in through-silicon via (TSV) extrusion. Extrusion surface profiles were obtained from TSV samples with two different pitch distances using white light interferometry (WLI). Visual analysis of a large number of vias revealed three classes of morphologies, i.e. granular, ring, and bulge, that could appear on a single via, individually or simultaneously. In addition, pitch distance was perceived to effectively alter the extrusion morphologies. Leveraging deep learning (DL) approaches, 2408 vias were labeled according to the contribution of each morphology and a CNN-based regression model was developed to efficiently recognize the contribution of these morphologies in TSVs. Achieving a RMSE value of 0.1724, a R2 score of 0.6859, and a top-1 accuracy rating of 82.37%, the proposed model detailed herein demonstrates promising results in recognizing the extrusion morphologies.

Ultrashort Fiber Bragg Gratings (FBGs) may be very useful whenever highly localized pressure measurements are desired. Obviously, very short FBGs will exhibit lower, as well as spectrally broader, reflections; however, these deficiencies may be outweighed by the advantage of the potential for highly localized measurement. In addition, with such short gratings, their accurate localization along the fiber is of great importance. In this paper, commercial 100 μ m FBGs are characterized, and their location along the fiber is accurately determined by two methods: Spectral and white-light interferometry. We also demonstrate the advantage of ultrashort gratings in a shock-wave experiment; when a solid target is hit by a projectile, the resultant pressure waves may change rapidly in both location and time. In this paper, the suitability of a 100 μ m grating to this scenario is demonstrated, revealing features in good agreement with theory—in particular, an approximately 0.7 mm long constant pressure region. Although these pressure waves may be monitored by ordinary (∼6–8 mm long) FBGs, due to the high-pressure gradients involved, the FBG response will be very complicated and data retrieval may be ambiguous. Thus the advantage of ultrashort FBGs is demonstrated.

Stability, robustness, sensitivity, and reproducibility are important parameters in the interferometry. We propose a wavefront splitting fiber Mach–Zehnder interferometer (MZI) to achieve such performances. A polyethylene terephthalate (PET) film splits the wavefront of a Gaussian beam emitted from the first fiber collimator. Then, the Gaussian beam is focused into a single mode fiber by another collimator, constituting a stable and robust fiber MZI. The effective spectral width is larger than 390 nm, which is wide enough for constructing a sensitive fiber MZI. The COMSOL multiphysics simulation and the experimental results demonstrate that this MZI is based on the multi-beam interference. Thanks to the low insertion loss of the fiber MZI, two types of stable and repeatable interference fringes are obtained when the sampling accuracy of the optical spectrum analyzer is as high as 0.1 nm. It ensures that the fiber sensor based on this MZI has a high resolution. For the first type of interference fringe, the two adjacent resonant wavelengths, respectively, shift –0.78 and –0.81 nm when salinity increases one part per thousand, showing high sensitivities. The low order interference fringe has a larger sensitivity. However, its visibility may be small due to the modulation of the second type of interference fringe that has small sensitivity to the refractive index of the sample. Since the PET film has uniform thickness, the fiber MZI can ensure good reproducibility. It can be widely utilized in detecting physical, chemical, or biological quantities.

Recycled concrete aggregate (RCA) is an excellent substitute of natural aggregates and its use in civil engineering projects has received great attention in recent years. One of the important factors that control the behavior of RCA when used as granular construction material or ballast in geotechnical and infrastructure engineering projects is the mechanical behavior at the contacts of the grains. In the present study, an experimental work is presented investigating the micromechanical behavior of RCA with a focus on the normal and shearing contact response of pairs of grains. Based on these tests, normal and tangential contact stiffness as well as the interface friction coefficient are quantified and thoroughly compared with studies presented in the literature on a broad range of geological and engineered materials. Microscopic image and white light interferometry were applied to inspect changes of grain surface characteristics before and after shearing, while, the basic characterization of the grains was conducted performing SEM analysis, roughness and micro-hardness measurements. The results from the study provide some basic understanding of the contact behavior of RCA interfaces and can be useful in DEM simulations of aggregate assemblies.

Accurate characterization of thin films and geometric features including the cavities during and after the fabrication process is crucial for proper CMUT operation, reliability, consistent array operation, and improved yield. Three different optical profilometry techniques: white light interferometry, laser confocal microscopy, and structural grid illumination microscopy have been reviewed in this paper with a focus on characterization of various thin films and geometric features during different CMUT fabrication stages and post processing. The relative merits of each technique have been investigated experimentally in the context of CMUT fabrication for better characterization and process development. The surface roughness and diaphragm deformation results have also been compared with AFM data. From the review, it appears that characterization needs of CMUTs are unique and a combination of complex diversified characterization tools is necessary to generate sufficient data for design verification and functional optimization.

In this study, the tribochemical polishing of a bulk GaN substrate, prepared by hydride vapor phase epitaxy, was investigated. Two different types of silica plates, a quartz glass plate and a soda-lime glass plate, were used as a polishing plate to polish the GaN substrate under atmospheric conditions at room temperature. Before and after polishing, the surface morphology was measured and evaluated by scanning white light interferometry and atomic force microscopy. The wear debris and wear track produced by polishing were analyzed in detail. The obtained results showed that an oxide layer was formed on the GaN surface because of the chemical reaction between the surfaces of the glass plate and the GaN substrate. This generated oxide layer was efficiently removed by polishing with the soda-lime glass plate, resulting in an atomic step and terrace structures on the GaN surface. Moreover, the obtained experimental results indicate that the soda-lime glass plate's alkali material components and the temperature increase induced by the frictional heat play important roles in the removal of the tribochemically generated layer on the GaN surface.

Hypothesis: Under axisymmetric conditions, changes in the thickness of the thin film between a fluid drop and a solid revealed by white light interferometry can provide information about the interaction of the bodies. Thus, in principle one can quantify the force between the surfaces using interferometric information of film thickness profile. This is needed to quantify and analyze drop-solid interactions across complex fluids such as an ionic liquid to independently characterize new surface forces. Experiments: Interferometric fringes were obtained in experiments on the interaction between a mercury drop and mica across a film of room temperature ionic liquid. The data is analyzed using a novel formula giving the total force acting on the drop. The calculations are compared with two other approaches to estimating forces. Qualitative and quantitative differences are discussed. Findings: This is the first report of forces measured between mercury and mica across an ionic liquid. The system is subjected to different applied electric potentials. In each case a long ranged, exponentially decaying repulsive force is found. At small separations, the system becomes unstable and the surfaces jump into contact. The comparison of force calculation methods demonstrates the superiority of the force approach proposed here. Refereed/Peer-reviewed

Tribo-fatigue behaviors of carbon structural steel wires under coupled tension-torsion in the tests with different tribo-fatigue parameters in different environmental media were investigated in the present study. The coefficient of friction was recorded by the self-made test rig. The wear depth profile was measured using three-dimensional white light interferometer. Morphologies of the wear scar and fracture of steel wire were observed employing the scanning electron microscope. The electrochemical analyzer was used to investigate electrochemical corrosion characteristics of steel wire. The crack propagation of steel wire was explored employing the X-ray computed tomography. The results show that coefficients of friction in different environmental media decreases by the order: air, alkaline and neutral electrolyte solutions, deionized water and acid electrolyte solution. The decrease order of maximum wear depth and increase order of fatigue life are as follows: air, acid, neutral and alkaline electrolyte solutions, and deionized water. Wear mechanisms include abrasive wear, adhesive wear, corrosion wear, fatigue wear in cases of different environmental media. The degree of electrochemical corrosion and maximum crack depth of fatigue wire are the largest in the acid electrolyte solution. The fracture is divided into zones of crack initiation, crack propagation and final fracture. Increases of tribo-fatigue parameters cause overall decreases in the coefficient of friction, degree of electrochemical corrosion and fatigue life, and increases in the maximum wear depth, crack propagation rate and surface damage.

We present a novel method for determining chromatic dispersion profile from a broadband spectral interferogram obtained by using a white-light interferometry technique. The proposed method is based on direct calculations of a second derivative of the registered spectral intensity at extremal points, which in result gives a spectral phase difference derivative further used for dispersion determining. Although the method is best suited for processing interferograms with modulation around a zero level (zero-mean value interferograms) and slowly changing envelope, the conducted numerical tests show that it is highly tolerable to different types of perturbations of the input interference signal. The proposed method can be applied both to spectral interferograms with monotonically changing phase difference as well as containing stationary phase difference points. We demonstrate the effectiveness and accuracy of the proposed method in measurements of chromatic dispersion of commercially available samples like the BK7 glass plate and the Corning SMF-28 optical fiber.

This paper investigates the effects of femtosecond laser surface texturing on the interfacial bond strength of steel and a thermoplastic polymer PA 6 film. Ultimately the textures will be used for hybrids that are manufactured using a near-infrared (NIR) laser-assisted automated tape placement (ATP) process and carbon fibre / PA 6 composites, therefore the NIR absorptance of the textured metal substrate is also of interest. To identify the influence of different surface structures on the bonding strength, lap shear samples were manufactured with laser textures varying in pulse length, hatch distance and ablated depth and tested by ASTM D 3165. The surface structures were analysed with white light interferometry (WLI) and scanning electron microscopy (SEM). Additional optical measurements in the infrared radiation range of 900 nm to 1100 nm were executed with a spectrophotometer to evaluate the laser absorptance for the NIR automated tape placement process. The lap shear strength increased to the highest value of 31.9 MPa with a tooth shaped laser texture using a 275 fs laser pulse width, a hatch distance of 600 μm an ablated depth of 40 μm. Also the absorptance for this sample increased by approximately 13% to 73% compared to the unprocessed pickled steel.

This paper investigates the manufacture of selectively reinforced metal/composite hybrids in a laser-assisted automated tape placement process. Unidirectional carbon fibre/PA 6 composite tapes were applied to 1.9 mm hot rolled steel substrates. The bonding of the first ply to the substrate is critical to the success of the metal-composite hybrid. This work investigates the effect of increasing the first-ply placement rate for speeds of 25 mm/s, 50 mm/s and 100 mm/s. The steel substrates were pre-treated by garnet blasting and then coating with a 60 μm layer of PA 6. The garnet blasted surface texture was quantified using white light interferometry. The thermal history for bonding of the first ply was measured with fine wire thermocouples. The interfacial bond strength of the hybrid laminates was assessed by ASTM D 3165 lap shear tests. The lap shear strength increased to the highest value of 22.4 MPa at 50 mm/s. Analysis of the fracture surfaces and thermal history suggest that the lower strengths at 25 mm/s and 100 mm/s are due to lower adhesion of the PA 6 coating to the metal substrate, most probably due to lower levels of crystallization.

The current study presents methods to predict the governing crack initiation site and fatigue crack initiation life of components with surface roughness. The surface topography is measured with white light interferometry and explicitly accounted for in detailed finite element models. The micro-notch stress fields are used in multiaxial and uniaxial crack initiation criteria where the relative stress gradient is included. The numerical predictions are compared with test results for cylindrical aluminum specimens with axi-symmetric surface roughness. Damage parameters based on the average stress fields over a certain distance were found to be highest in the micro-notches where cracks grew to failure. Lifetime predictions using a multiaxial damage criterion with a gradient correction and elastic-plastic stress fields showed good correlation with the experiments. Uniaxial criteria, criteria without gradient correction, and criteria based on linear elastic stress fields were found to be overly conservative. In some specimens, the failure location could not be identified by the proposed damage criterion. This is likely due to the presence of microstructural weaknesses near the micro-notches, leading to shorter initiation lives that cannot be described by geometry alone. It is concluded that resolving the detailed surface topography and accounting for this geometry in a detailed finite element model provide a predictive approach when multiaxial stresses are accounted for, but the importance of microstructure needs further attention. This is a submitted manuscript of an article published by Elsevier Ltd in International Journal of Fatigue, 20 August 2018.

Transparent materials do not absorb light but have profound influence on the phase evolution of transmitted radiation. One consequence is chromatic dispersion, i.e., light of different frequencies travels at different velocities, causing ultrashort laser pulses to elongate in time while propagating. Here we experimentally demonstrate ultrathin nanostructured coatings that resolve this challenge: we tailor the dispersion of silicon nanopillar arrays such that they temporally reshape pulses upon transmission using slow light effects and act as ultrashort laser pulse compressors. The coatings induce anomalous group delay dispersion in the visible to near-infrared spectral region around 800 nm wavelength over an 80 nm bandwidth. We characterize the arrays’ performance in the spectral domain via white light interferometry and directly demonstrate the temporal compression of femtosecond laser pulses. Applying these coatings to conventional optics renders them ultrashort pulse compatible and suitable for a wide range of applications., Controlling the dispersion of femtosecond light pulses remains a key challenge for their application. Here, the authors report dispersion-engineered transmissive nanocoatings for ultrashort laser pulse compression in the vis-NIR spectral region.

We report a white-light interferometric method for broad-band measurements of chromatic dispersion of higher-order-modes (HOMs) selectively excited in an optical fiber using a spatial light modulator (SLM). To excite a specific mode we appropriately modulated a phase distribution across a supercontinuum input beam with the SLM used in reflective configuration. For this purpose, the SLM surface was divided into azimuthally and radially distributed sectors which introduce the phase shifts equal alternately to 0 or π radians, similarly as in the targeted mode. The voltage applied to respective sectors of the SLM was corrected versus wavelength to ensure broad-band dispersion measurements for the required mode. For a given voltage setting, the dispersion measurements were possible without any correction over 250 nm in the visible and over even greater range in the infrared. We demonstrate feasibility of the proposed approach in the measurements of chromatic dispersion for all modes supported by Corning SMF-28e, i.e., LP01, LP11, LP21, LP02, and LP31. The measurements were conducted in the spectral range from 450 nm up to the cut-off wavelengths of respective higher order modes and up to 1600 nm for the fundamental mode.