Interferometric Method For Measurement Research Articles

A novel laser interferometric method for thin film thickness measurement in gas–liquid intermittent flow

Abstract In horizontal intermittent flow, the long bubbles move toward the center of the pipe due to inertia, forming the thin liquid film above the long bubbles. Accurate measurement of the liquid film thickness is crucial for heat and mass transfer. In this paper, laser interferometric technology is innovatively introduced to measure the film thickness of the intermittent flow, and the thin liquid film is detected with a resolution of 100 nm. Considering the curvature of the circular pipe wall, which leads to divergent reflected light, the effect of the pipe wall on the interference pattern is explored by the ray tracing technique. A two-dimensional interpolation phase retrieval algorithm based on light intensity is proposed to reconstruct the thickness of the liquid film, and the average error is less than 1.86%. Benefiting from the exceptionally high resolution, research is conducted on the thin liquid film at the top of the horizontal intermittent flow, revealing its dependence on the sub-regimes and gas–liquid velocities.

Incident angle optimization with multiple conflicting objectives based on BP-MOPSO in oblique laser interferometry

The oblique incident phase-shifting interferometric measurement method is an effective technique for assessing gear tooth form deviation. In the measurement process, the tooth flank incident angle is a crucial factor determining the quality of interferograms. Addressing the challenge in traditional optical path design, where the selection of the tooth flank incident angle encounters a trade-off among quality features such as measurable tooth area (MTA), interference fringe density (IFD) and interferogram compression ratio (ICR), this paper proposes an optimized method for the tooth flank incident angle. Firstly, a comprehensive evaluation model is established to calculate and analyze the MTA, IFD and ICR of the helical gear. Secondly, by integrating BP neural network and Multi-Objective Particle Swarm Optimization (MOPSO) algorithm, a tooth flank incident angle optimization method is devised to simultaneously optimize the measurement light incident angle γ and the rotation angle of the gear axis β. Finally, simulation analyses and physical experiments are employed to demonstrate the feasibility of the proposed method, compared to before optimization, the pseudocorrelation (PSD) value has increased by an average of 34%, and the residual points have decreased by an average of 80%, confirming its capability to improve quality interferogram and measurement accuracy.

Oblique-Incidence Interferometric Measurement of Optical Surface Based on a Liquid-Crystal-on-Silicon Spatial Light Modulator

An oblique-incidence interferometric measurement method is proposed to measure and adjust optical surfaces with a liquid-crystal-on-silicon spatial light modulator (LCoS-SLM). The optical system only consists of an interferometer and an LCoS-SLM with precision mounts. It could reduce the measuring cost and time consumption due to the programmable function of the LCoS-SLM and offer the ability to align the optical system. The oblique-incidence measurement theory and optical system adjustment method are established based on an off-axis paraboloid model. The ray-tracing program to calculate the compensation phase map in the measurement is proposed with math models. In the optical alignment step, the off-axis paraboloid model is used to apply the LCoS-SLM as a phase compensator to generate a focusing spot or light spot array to adjust the measured optical surface. And in the interferometric measurement step, the calculated compensation phase map from the ray-tracing calculation is loaded on the LCoS-SLM using the same optical setup as the optical alignment step without any mechanical adjustment. Two interference measurement experiments of typical optical surfaces were carried out to verify the accuracy of the measuring system.

Aspheric surface measurement by absolute wavelength scanning interferometry with model-based retrace error correction.

This paper presents a non-nulling absolute interferometric method for fast and full-area measurement of aspheric surfaces without the necessity of any mechanical movement. Several single frequency laser diodes with some degree of laser tunability are used to achieve an absolute interferometric measurement. The virtual interconnection of three different wavelengths makes it possible to accurately measure the geometrical path difference between the measured aspheric surface and the reference Fizeau surface independently for each pixel of the camera sensor. It is thus possible to measure even in undersampled areas of the high fringe density interferogram. After measuring the geometrical path difference, the retrace error associated with the non-nulling mode of the interferometer is compensated for using a calibrated numerical model (numerical twin) of the interferometer. A height map representing the normal deviation of the aspheric surface from its nominal shape is obtained. The principle of absolute interferometric measurement and numerical error compensation are described in this paper. The method was experimentally verified by measuring an aspheric surface with a measurement uncertainty of λ/20, and the results were in good agreement with the results of a single-point scanning interferometer.

Interferometric Method for Direct Measurement of the Effective Mass in Two-Dimensional Systems

We have developed a method of determining the effective mass of charge carriers in a two-dimensional electron system (2DES) based on the phase analysis of the radiation transmitted through the 2DES. This measurement technique is demonstrated in the experiments with a high-quality 2DES in $\mathrm{In}\mathrm{As}$/$\mathrm{Al}\mathrm{Sb}$ and $\mathrm{Ga}\mathrm{As}$/$(\mathrm{Al},\mathrm{Ga})\mathrm{As}$ heterostructures. Furthermore, we find that the proposed approach gives compatible results with the cyclotron resonance spectroscopy method.

Features for image processing of OCT images for seam tracking applications in laser welding

The coaxial integration of optical coherence tomography (OCT) enables the determination of surface topography and measurement of object features along the optical path within laser machining. The measurement of surface information from the processed workpiece allows for the identification of features from the joint configuration and the subsequent control of the welding process by seam tracking. State-of-the-art seam tracking approaches are based on monochromatic cameras or laser triangulation. Typically, these approaches apply line segmentations for the identification of the joint position. The interferometric measurement method of OCT gives rise to the identification of new features for image processing in seam tracking. In this work, we identify specific noise components and features based on the theoretical background of OCT for image processing in seam tracking applications. Two different features are derived for the detection of arbitrary joint configurations with corresponding systematic image processing approaches. In the first step, we show the applicability of line detection methods for feature detection of arbitrary joint configurations. The necessary evaluation algorithm for case sensitivity and limitations (e.g., chamfer) in detecting different joint geometries are discussed. In the second step, we show an approach in feature extraction with feature detectors (e.g., ORB, SURF) for a new image feature. Here, significant image space from (multiple) reflections at the joint position is used for joint detection. The detectability is discussed depending on the joint configuration. The results show good suitability of both features for seam tracking applications.

A novel interferometric method for simultaneous measurement of film thickness and film interface temperature for a horizontal tube falling film evaporator for MED systems

Horizontal tube falling film evaporation spans a lot of applications, especially in multi-effect desalination application. Hence, the improvement of its gain output ratio is of prime importance, and for that, the studies on the characteristics associated with the flow, mainly falling film thickness and falling film interface temperature, are inevitable. As the falling film flow is a delicate fluid structure, non-intrusive measurement techniques have to be preferred for the experiment. In this work, we introduce a novel interferometric method to calculate film interface temperature and a shadowgraph approach to estimate film thickness simultaneously. A Mach-Zehnder interferometer with infinite fringe setting was used to capture the thermal fluctuations around the horizontal tube falling film evaporator. Interferometric method implemented in this work also serves as an image visualization technique and does the purpose of qualitative as well as quantitative analysis. An in house designed experimental setup was fabricated for producing a thin and uniform falling film with a fully wetted flow over the horizontal copper tube. A heater controller setup was incorporated into it for accurate temperature control. This method holds the advantage of scanning falling film thickness over circumferential angle for the range 5∘≤θ≤175∘, which is an improvement to state of the art. Furthermore, dynamic film thickness and instantaneous film interface temperature studies were also incorporated to prove the efficacy of the technique and to test the robustness of the algorithms implemented. CFD analysis was also carried out for the entire process by means of VOF scheme and was found to be in good agreement with the experimental results, which proves our technique to be a good one. A standard error of mean analysis was performed on every data set, which validates the reproducibility and the dynamic measurement capability of the technique used.

Interferometric measurement of high-order aspheric surface parameter errors based on a virtual-real combination iterative algorithm.

Aspheric surface parameters, including vertex radius of curvature, conic constant, and high-order aspheric coefficients, decide the optical properties of aspheric surfaces. The measurement of aspheric surface parameter errors (SPEs) is a substantial issue for the fabrication of aspheric surfaces. Interferometry is a mature high-accuracy method in aspheric surface figure error measurement, but challenges still exist in the measurement of SPEs for high-order aspheric surfaces or convex aspheric surfaces. We propose an interferometric measurement method for high-order aspheric SPEs based on a virtual-real combination iterative algorithm (VRCIA). We also propose a recommended measurement system including a partial compensation interferometer to obtain the partial compensated wavefront and a laser differential confocal system to obtain the best compensation distance for calculating SPEs through the VRCIA. A high-order convex aspheric surface is measured to demonstrate the feasibility of the method. The relative accuracy of vertex radius of curvature error, conic constant error and fourth-order aspheric coefficient error can reach 0.025%, 0.095% and 3.02%, respectively.

Three tailorable optical vortices generated by a modified fractal spiral forked plate

A modified fractal spiral forked plate (MFSFP) is proposed to generate three tailorable coplanar optical vortices at multiple focal planes, which consist of two off-axis vortices and one axial vortex. The axial vortex and one low-intensity off-axis vortex can have equal intensity by designing an appropriate spiral-like filter. In addition, the MFSFP has self-similar axial and off-axis optical vortices. Moreover, the tailorable topological charges of two off-axis vortices are related to those of the fractal spiral zone plate (FSZP) and forked grating and the topological charge of the axial vortex is equal to that of the FSZP. In the experiments, based on the interferometric measurement method, the differences between fingers of forked fingers are used to prove the above topological charge transformation rule. The method of constructing the MFSFP is illustrated. The MFSFP is applicable to rotate particles at multiple positions of the different planes simultaneously, increase optical communication capacities and produce multiple images simultaneously.

Physical-model-based reconstruction of axisymmetric three-dimensional sound field from optical interferometric measurement

Optical interferometric measurement methods for sound fields have garnered considerable attention owing to their contactless nature. The capabilities of non-invasive measurement and reconstruction of three-dimensional sound fields are significant for characterizing acoustic transducers. However, three-dimensional reconstructions are typically time consuming because of the two-dimensional scanning and rotation of the measurement system. This paper presents a scan and rotation-free reconstruction of an axisymmetric sound field in the human hearing range. A physical-model-based algorithm is proposed to reconstruct an axisymmetric sound field from optical interferograms recorded using parallel phase-shifting interferometry and a high-speed polarization camera. We demonstrate that audible sound fields can be reconstructed from data measured in 10 ms. The proposed method is effective for the rapid evaluation of axially symmetric acoustic transducers.

STUDY OF MEASUREMENT SYSTEM ACCURACY OF OPEN PIT SIDES DISPLACEMENT ON THE EXAMPLE OF 3DRADARGROUNDPROBESSR-XT

The article considers the modern technology of interferometric measurementsfor the purposes of open pit sides geotechnical monitoring, based on the use of 3D radar Ground Probe SSR-XT. Experimental research of measurement accuracy of the given equipment was performed. The results of the mentioned research state the actual accuracy of interferometric measurement method.The optimal application of this method for studying the sides of quarries is described. With the interferometric measurement method for geotechnical monitoring of the sides of quarries under development, there is no need to install deformation marks, which simplifies the work process. With traditional methods, it is necessary to install such marks, which increases security risks for the performers of geotechnical monitoring.

Laser beam angular stabilization system based on a compact interferometer and a precise double-wedge deflector.

To increase the laser beam pointing stability required for precise interferometric measurements, we designed an active laser beam angular stabilization system. We used two recently proposed techniques: an interferometric measurement method of laser beam angular deflection which allows compact sensor design and a double wedge-prism beam deflector for precise laser beam steering. Our system provides long-term angular stabilization independently in the horizontal and the vertical planes, providing a hundredfold reduction of the output beam deviations. First, we describe the compact sensor setup with a new measurement algorithm prepared specifically for our stabilization system. Then, the system is introduced, and experimental evaluation is described. The test results show a good performance for the proposed design. We reached a reduction in beam angular deviations amplitude down to 100 nrad/h (in terms of double standard deviation of beam fluctuations).

Contrast computation methods for interferometric measurement of sensor modulation transfer function

Accurate measurement of image-sensor frequency response over a wide range of spatial frequencies is very important for analyzing pixel array characteristics, such as modulation transfer function (MTF), crosstalk, and active pixel shape. Such analysis is especially significant in computational photography for the purposes of deconvolution, multi-image superresolution, and improved light-field capture. We use a lensless interferometric setup that produces high-quality fringes for measuring MTF over a wide range of frequencies (here, 37 to 434 line pairs per mm). We discuss the theoretical framework, involving Michelson and Fourier contrast measurement of the MTF, addressing phase alignment problems using a moiré pattern. We solidify the definition of Fourier contrast mathematically and compare it to Michelson contrast. Our interferometric measurement method shows high detail in the MTF, especially at high frequencies (above Nyquist frequency). We are able to estimate active pixel size and pixel pitch from measurements. We compare both simulation and experimental MTF results to a lens-free slanted-edge implementation using commercial software.

APMP supplementary comparison (APMP.L-S8) measurement of flatness of optical flat by interferometry

A reginal supplementary comparison, APMP.L-S8, was started in 2015 to demonstrate the equivalence of routine calibration services offered by NMIs to clients. Participants in this APMP.L-S8 comparison agreed to apply interferometric method for flatness measurement of the optical flats. There are two configurations of flatness interferometer used in this comparison, vertical type and horizontal type. There are seven laboratories from NMIs participated this supplementary comparison which included NIMT, NMIJ, NIM, NMC/A*STAR, MSL, NPLI and NMISA.This report describes the measurement results of two optical flats, diameter of 70 mm and 160 mm. The calibrations of this comparison were carried out by participants during the period from July 2015 to September 2016. The results show that there is a degree of equivalence below 1 for all measurands. Hence, there is a close agreement between the measurements from all participants.Main textTo reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCL, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Absolute Distance Measurement Using Optical Sampling by Cavity Tuning

We propose here an interferometric method for absolute distance measurement using optical sampling by cavity tuning. The cross correlation patterns can be obtained by constantly changing the repetition frequency of a femtosecond pulse laser, and the distances can be determined by the instantaneous repetition rate of the peak of the interferogram. Our experimental results show agreement within $10~\mu \text{m}$ , corresponding to a relative precision of $2\times 10^{-7}$ in a range up to 47 m, compared with an incremental distance meter.

Measurement of Temperature Distribution around a Vertical Fin by Mach-zehnder Interferometry

Interferometry is an optical non-intrusive technique becoming increasingly popular in the flow and heat transfer visualisation and measurement. In the present study, experimental investigation on heat transfer around an isothermal vertical fin using Mach-Zehnder Interferometry is carried out. The temperature of surrounding air, at a reference point, is recorded by a thermocouple placed at a distance from the heat source. Interference patterns are captured by a camera and analyzed using an image processing tool in MATLAB software. From the observations, it is pellucid that the change of air temperature in one path of the coherent laser beam results in the deformation of the interference pattern. By comparing the initial and deformed fringe patterns using the digital image processing technique, the temperature distribution around the heat source is obtained. The experimental values compared with the analytical results of vertical heated plate, show very good agreement. This indicates the reliability of interferometric measurement method.

Self-referenced interferometer for cylindrical surfaces.

We present a new interferometric method for shape measurement of hollow cylindrical tubes. We propose a simple and robust self-referenced interferometer where the reference and object waves are represented by the central and peripheral parts, respectively, of the conical wave generated by a single axicon lens. The interferogram detected by a digital camera is characterized by a closed-fringe pattern with a circular carrier. The interference phase is demodulated using spatial synchronous detection. The capabilities of the interferometer are experimentally tested for various hollow cylindrical tubes with lengths up to 600mm.

Interference method for ultra-precision measurement and compensation of laser beam angular deflection

A new interferometric method for ultra-precise measurement of laser-beam angular deflection is proposed. The angular tilt of a measuring device in relation to the beam axis also can be measured. The method is based on interference fringe period analysis in the selected plane of measurement. The theoretical basis and experimental verification of the method are presented. It is shown that by using the proposed technique, it is possible to measure the laser beam angular deflection or instability with ultrahigh resolution reaching single nanoradians. The proposed method allows the measurement and further compensation of laser beam deflections in a very compact design.

Optical sensing techniques for temperature measurement

Temperature is an important parameter that needs accurate measurement. Theoretical descriptions of the fluorescence ratio method, fluorescence lifetime sensing, and interferometric methods for temperature measurement are given. Fluorescence lifetime sensing calibration plots have been developed for temperature measurement from 20°C to 600°C using Er(3+)-doped glass, and from 20°C to 90°C using Sm(3+)-doped CaF(2). Lifetime sensing results of Pr(3+)-doped YAG and Ho(3+)-doped fluoride crystals for temperature measurement are also summarized. Mach-Zehnder interferometer measurements revealed that the passage of a 300 mW laser beam of 915 nm changed the temperature of the Yb(3+)-doped YAG crystal by 7.1°C. The interferometer technique is useful for measuring absolute temperature changes in laser cooling studies.

Digital Holographic setup for Measurement of Asymmetric Temperature Field and Tomographic Reconstruction

This paper presents a digital holographic multidirectional interferometric method for measurement of periodic asymmetric temperature fields. This method uses a modified Twymann-Green setup having double sensitivity. The setup employs one precisely synchronized and triggered CCD camera with a measured coherent phenomenon. That allows a large number of the phenomenon’s different projections capturing which are used for 3D tomographic reconstruction..