Optical Interference Method Research Articles

Study on electric erosion in grease lubrication using optical interference method

Protecting bearings from electrical environments is crucial as modern industry evolves. With increasing exposure to electrical conditions, the risk of bearing failure due to electric erosion becomes a significant concern. To better understand how lubrication interacts with electric discharge in rolling bearings, an optical ball-on-disc tribometer was modified to measure film thickness under elastohydrodynamic lubrication (EHL) with electric discharge. The results of the study revealed that an electrical potential difference between the surfaces separated by the lubrication film leads to a reduction in film thickness, which can be attributed to the generation of Joule heating. As the electrical potential difference increases, the film thickness decreases even further, ultimately resulting in destructive electric discharge. Interestingly, sporadic discharge was observed in the region of minimum film thickness as the entrainment velocities increased prior to the occurrence of destructive discharge. In addition, the study also investigated the use of grease with a conductive additive, a double trifluoro-sulfonate ionic liquid. It was found that incorporating this ionic liquid into the grease can decrease the energy during discharge, thereby mitigating bearing electric erosion.

Optical-thermally actuated graphene mechanical resonator for humidity sensing

This paper demonstrates an optical-thermally actuated multi-layer graphene resonator for humidity sensing. A ∼10-layered graphene resonator with a diameter of 125 µm peripherally clamped on the fiber ferrule end face was actuated to vibrate using the intensity-modulated laser, and the vibration was detected based on the optical fiber Fabry-Perot interference method. The humidity sensing experiment exhibited an up to 350 Hz/%RH humidity sensitivity in the range of 0–100 % RH at 25 °C, which was 10 times higher than those of the previously reported Quartz Crystal Microbalance (QCM)-based humidity sensors. Also, a good repeatability of the frequency-humidity response was observed for the presented graphene resonator. Moreover, in view of the coupling effect of temperature on the graphene resonator, the temperature drift of 0.942 kHz/°C was measured in the range of 25–50 °C, thereby inducing an absolute humidity error of about 0.6 g/(m3·°C).

Experimental investigation of the film behavior in a model rolling bearing

Film thickness is a direct indicator of bearing lubrication; nevertheless, measuring it in a bearing is tricky. The optical relative interference method was used to measure the central film thickness in a model rolling bearing at speeds ranging from zero to 3500 rpm in this article. The film thickness for a ball-outer-ring contact in a model rolling bearing is discovered to be different when compared to the results from the conventional ball-on-disc model. Thermal effects and starvation are investigated. The key influencing factors for replenishment in a rolling bearing are discussed.

Tuning the nonlinearity of graphene mechanical resonators by Joule heating

As an inherent property of the device itself, nonlinearity in micro-/nano- electromechanical resonators is difficult to eliminate, and it has shown a wide range of applications in basic research, sensing and other fields. While many application scenarios require tunability of the nonlinearity, inherent nonlinearity of a mechanical resonator is difficult to be changed. Here, we report the experimental observation of a Joule heating induced tuning effect on the nonlinearity of graphene mechanical resonators. We fabricated multiple graphene mechanical resonators and detected their resonant properties by an optical interference method. The mechanical vibration of the resonators will enter from the linear to the nonlinear intervals if we enhance the external driving power to a certain value. We found that at a fixed drive power, the nonlinearity of a mechanical resonator can be tuned by applying a dc bias current on the resonator itself. The tuning mechanism could be explained by the nonlinear amplitude-frequency dependence theory. Our results may provide a research platform for the study of mechanical nonlinearity by using atomic-thin layer materials.

Liquid Film Condensation behind Shock Waves on the Cold Wall of a Diaphragmless Vertical Shock Tube: An Experimental Study

The aim of this study was to investigate the condensation of HFC-134a vapor on a shock tube wall behind shock waves. The time-dependent thickness of the condensed liquid film was measured using an optical interference method based on multiple reflections of a laser beam. The condensation on the wall was accompanied by an instantaneous increase in the pressure behind the incident shock wave, and when the reflected shock wave reached the observation window, condensation occurred again. In this experimental study, the characteristics of the diaphragmless vertical shock tube were verified. Reliable experimental data could be obtained using the shock tube. The shock waves could be visualized to study their behaviors in different time periods. The experimental results confirmed the formation of a liquid film on the cold wall of the shock tube after the passing of incident and reflected shock waves, with the liquid film behind the incident shock wave exhibiting a faster formation.

A method for continuously monitoring the quality of Masson pine seedlings.

Root growth potential (RGP) is a popular physiological indicator used to evaluate seedling vigor. However, the time scale used in the RGP test is the order of days, which leads to poor performance of the RGP method. We propose an optical interference method, called statistical interferometry, to measure minute root elongation at a sub-nanometer scale, which can decrease the time used in measuring RGP. The time scale of this method is also 104 times less than that of the RGP method. Because we can measure the length of root elongation continuously, we can compute the root elongation rate (RER), which is the variety of the length of root elongation per second. Continuous monitoring can help determine the quality of Masson pine seedling as soon as possible. To show the effectiveness of our proposed method, we designed an experiment, in which we applied different water stresses to our collected Masson pine seedlings and acquired two groups of pines, representing two different qualities: one stressed by water and one not. After measuring the RER of the groups in our experiments, we found that RER is interrelated with the quality of seedlings.

Flower‐Shaped Optical Vortex Array

AbstractHerein, the generation of an optical vortex array dubbed the flower‐shaped optical vortex array (FOVA) is proposed and experimentally demonstrated using a single optical path interference method. FOVA is generated by the superposition of even and odd Ince–Gaussian (IG) beams, which have the same degree m and different order p. The number of optical vortices (OVs) in the FOVA is determined based on the values of order p and degree m of the even and odd IG beams. Furthermore, the positive sign of the OVs in the array can be transformed to negative by adding a specific initial phase difference. The OVs vanish and then recover as the initial phase difference increases from 0 to 2π. Moreover, the gradient force and energy flow distribution of the FOVA are studied. The OVA with flower‐shaped structure generated herein has potential significance in applications, such as microparticle manipulation and optical measurements.

Long-range ordered silver nanoflower array structure for surface enhanced Raman scattering detecting

Surface enhanced Raman spectroscopy (SERS) is a key nondestructive detecting technology with a broad application demands. However, relative low stability and homogeneity of the SERS substrate hinder its practical applications. Here, a simple and flexible approach is proposed to achieve the arrayed SERS substrates with the periodicity and local randomness by directly growing silver nanoflowers on the patterned wafer fabricated by the optical interference method. By utilizing the hotspot effect of nanogaps within/between the Ag nanoflowers, the SERS substrates demonstrate the low detecting limit of 5 × 10−10 M and 5 × 10−9 M in one-dimensional (1D) and two-dimensional (2D) pattern structures for Rhodamine 6G (R6G) probe molecule, respectively. The periodicity assures the fabricated substrate a promising reproducibility and stability. After the 1D array structure is left for 21 days, the intensity of Raman signal of R6G maintains at 80%. Moreover, the proposed method has the advantages of simple preparation, low cost, flexible tunability, and easy-fabrication large scale substrate. The results indicate that the long-range ordered silver nanoflower array structures are promising candidates for the high performance SERS substrate in chemical analysis, medicine and environment monitoring.

Drainage of lubrication film around stuck bubbles in vertical capillaries

A bubble in a vertical cylindrical capillary can get stuck due to the drainage of its lubrication film, according to the prediction originally made by Bretherton. When stuck, the profile of the lubrication film around the bubble is measured using an optical interference method. Our experimental results verified the theoretical prediction of the time-dependent minimum thickness hmin ∼ t−4/5 [C. Lamstaes and J. Eggers, “Arrested bubble ‘rise’ in a narrow tube,” J. Stat. Phys. 167, 656–682 (2017)]. The bubble is stuck in a cylindrical capillary if the critical radius is proportional to the capillary length. We show that this result can be extended to square capillaries, where bubbles will get stuck in square capillaries below a critical width. For the same capillary length, the critical width of the square capillaries is much smaller than the critical radius of the cylindrical ones, due to the fluid leakage at the corners. As the square channels are also commonly used in microfluidic devices, our results provide helpful insights into the different features of the motion of bubbles resulting from the shape of channels.

Hexagonal vector field of polarization singularities with a gradient basis structure

The coherent superposition of vector fields can yield interesting field distributions. For example, the superposition of two right-handed polarization singularities can result in left-handed polarization singularities. Unlike the coherent superposition of scalar fields which modulate resultant intensity, the vector field superposition can modulate additional parameters such as ellipticity and azimuth in the field distribution. By making use of computational optics and programmable spatial light modulators, we demonstrate here the generation of a polarization singularity lattice structure with gradient basis, which is normally not possible by a conventional optical interference method.

A new optical interference method to measure He-Ne laser wavelength

A new optical method used in our lab to get clear fringes of interference use “He Ne laser” as a light source. These experiment construct firstly to avoid our need to sodium lamb, Secondly, a convex lens was used to obtain a large image fringes to make the parameters more accurate than using the real fringes, by using a new mathematical relationships, the wavelength was measured. The results were more accurate than the normal methods used.

Development of a New Optical Measuring Set-Up

The paper proposes a description of the developed optical measuring set-up for the contactless recording and processing of measurement results for small spatial (linear and angular) displacements of control surfaces based on the use of laser technologies and optical interference methods. The proposed set-up is designed to solve all the arising measurement tasks in the study of the physical and mechanical properties of new materials and in the process of diagnosing the state of structural materials by acoustic active methods of nondestructive testing. The structure of the set-up, its constituent parts are described, and the features of construction and functioning during measurements are discussed. New technical solutions for the implementation of the components of the set-up under consideration are obtained. The purpose and description of the original specialized software, used to perform a priori analysis of measurement results, are present, while performing measurements, for a posteriori analysis of measurement results. Moreover, the influences of internal and external disturbance effects on the measurement results and correcting measurement results directly in their implementation are determined. The technical solutions, used in the set-up, are protected by the patents of the Russian Federation for inventions, and software is protected by the certificates of state registration of computer programs. The proposed set-up is intended for use in instrumentation, mechanical engineering, shipbuilding, aviation, energy sector, etc.

A method to improve the stability of the optical interference system

The measurement system based on optical interference has obvious advantages of high precision and high sensitivity. However, the signal is easy to be disturbed by vibration from environment, so the system needs to stay away from the vibration source. To use the optical interference method for real-time measurement, it has to im-prove the system’s stability. In this paper, we proposed an integrated Michelson interference device to measure the thicknesses of multiple layers of optical plate, which could improve the stability of the optical interference system in a new way. Through smart design and high precision processing technique, the light path of the structure was integrated into a whole, which could avoid disturbing successfully. Compared with fiber based interferometer, this device could bring obviously more stable signal. The thicknesses of the multiple layers of optical plate were measured to confirm its feasibility to do the real-time precision measurement.

Перспективное устройство для измерения линейной и угловых составляющих малых перемещений поверхностей объектов контроля

Introduction. Measuring the linear and angular components of small displacements of the monitor object surfaces is considered. A high-precision non-contact device based on the advanced laser technologies and methods of optical interferometry, namely a double-pass laser interferometer with integrated branches, is developed to perform these measurements. The calculated and experimental validation of the device is offered. Thus, the quality and condition of the materials and products can be controlled by means of the acoustic non-destructive methods. Materials and Methods. New software and mathematical models describing optical fields of the interference patterns generated by the interferometer under consideration are offered. Various types of beam splitters and cases of polarization are used under the numerical simulation of the intensity distributions in the interference patterns. Research Results. New mathematical models and software for the numerical simulation of the optical radiation intensity fields in the interference patterns considering both linear and angular components of small displacement of the surface of the test object are developed. A new interference technique of measuring small linear and angular displacements is developed and theoretically grounded. It allows combining the meter measuring capabilities for both small linear and angular displacements of the monitor object surfaces in a single tool. New optical interference methods and means for the noncontact measurements of small linear and angular movements of the monitor object surfaces that implement the method capabilities and extend the functionality of the known indicators of small displacements are offered. Discussion and Conclusions. The obtained results can be used for the high-precision measurements of small linear and angular displacements of surfaces of the objects under control. Areas of application are the following: experimental research; assessment and diagnostics of the structural materials samples; investigations of fast wave processes in the layered structures of complex shape made of the anisotropic composite materials. The methods developed in this study are applicable in such industries as mechanical engineering, shipbuilding, aircraft engineering, instrument making, power engineering, and etc.

Обработка результатов измерений интенсивности оптических полей интерференционных картин, создаваемых лазерными интерференционными средствами измерений

Introduction. Currently, the introduction of modern methods and means of laser interferometry opens up new possibilities in solving various practical problems under studying properties and processes of defect formation in new materials (laminated, polymeric, composite), and diagnosing the state of structural materials of the product power components at all stages of their life cycle. One of the ways to improve the measurement results quality can be the introduction of new software for the outcome analysis of the intensities of the optical fields of interference patterns uniquely associated with the metered small displacements of control objects surfaces. The work objective is to develop new software for processing data of measuring intensities of the optical fields of interference patterns generated by the optical instrumentation of small linear and angular displacements of the control objects surfaces. The solution is based on the two-way laser interferometer with combined branches that allows increasing the measurement results quality. Materials and Methods. To achieve this purpose, modern software is applied, and the data obtained with new measuring instruments based on new optical interference methods is used. Research Results. New software is developed for processing the measurement results of the intensities of the optical fields of interference patterns generated by the optical instrumentation of small linear and angular displacements of the control objects surfaces based on the proposed two-pass laser interferometer with combined branches. New software allows improving the measurement data quality. It is protected by certificates of the Russian Federation on the state registration of computer programs. Discussion and Conclusions. The proposed software can be used successfully for simulating measurements of small linear and angular displacements of the control objects surfaces in order to create new methods of treatment of the intensities of the optical fields of interference patterns generated by the optical instrumentation based on laser interferometers of various types. The described software and technical solutions received approval at the International scientific conferences in 2016-2017, and they were also presented at the International innovation salons “Inventions Geneva 2017” and “Euroinvent 2017”.

Study on the collinear delay double pulse laser induced air plasma expansion by optical interference

In this paper, the air plasma expansion dynamics induced by collinear delayed double nanosecond laser pulses are studied by optical interference method, and comparative analyzed the difference of the air plasma expansion generated by single pulse laser and collinear delayed double pulse laser. The experimental results show that the air plasma expansion distance, expansion velocity and shock wave pressure produced by collinear delay double pulse laser are all larger than that of single pulse because of existing the second laser pulse interaction with the air plasma formed by the first one, and the plasma action time is effectively delay. Finally the mechanisms of the inter-pulse delay time effect on air plasma expansion process are analyzed.

Lubrication film thickness calculation from contact resistance measurement in point contact

Purpose– The purpose of this study is to solve this problem. Different lubrication states play a huge role in friction, wear and service life of parts. To ensure the reliability and power of the internal combustion engine, it is necessary to ensure that the friction pair has been in the best lubrication state. One of the key problems of lubrication state and transformation characteristics is to achieve real-time measurement of lubrication state.Design/methodology/approach– Previous studies show that the contact resistance method is very effective in the qualitative analysis of lubrication state test. The circuit is simple and does not require expensive test equipment. But this method could not accurately reflect the film thickness ratio. Through a combination of experimental and theoretical analysis methods, the limitation of the contact resistance method could be overcome.Findings– The relationship between the point contact film-thickness ratio and contact resistance was established, then the film-thickness ratio could be obtained through the contact resistance, thus providing the basis for determining the point contact lubrication state.Research limitations/implications– According to existing research, the lubrication state of the friction pair mainly was determined through two methods, the friction coefficient and film-thickness ratio. But there are limitations on either using Stribeck curves or optical interference methods. The method used in this paper not only provides a verified way of design theory and model, but is also beneficial to the formation of a new design theory.Originality/value– A new real-time measurement method of lubrication state based on contact resistance is established and its practicability and veracity are verified by series experiments.

Thin lubrication film around moving bubbles measured in square microchannels

The thin lubrication film around bubbles moving in square microchannels was measured using an optical interference method down to the scale of 0.1–10 μm in thickness, and the three-dimensional profile of the lubrication film around the bubble was obtained experimentally. The lubrication film of the elongated bubble translating along the microchannels presented a three-dimensional saddle shape, and the thinnest locations were located at the sides where the rupture of the lubrication film was found to occur. The minimum film thickness of the axial section in the downstream direction was found to obey the relationship of hmin ∼ Ca2/3 as predicted by the Bretherton equation, where Ca is the capillary number. Also, the minimum film thickness in the across-stream direction gradually deviated from this relationship and eventually obeyed hmin ∼ Ca1 as the film thickness was decreasing, which matches well with the existing theoretical results. Therefore, the optical interference method is effective to reveal the dynamics of the thin lubrication film in droplet microfluidics three-dimensionally.

28pm1-F-5 光干渉法を用いた薄膜計測に関する研究 : 表面の反射率分布に起因する油膜厚さの測定誤差

This study presented a measurement error for determining the thickness of thin film lubrication based on optical interference methods. The measurement error is caused by the reflective index distribution on the sliding surface, which is characterized by the profile of the surface. In order to demonstrate the measurement error, two types of model specimens with different surface roughness were prepared. Using these specimens, the optical interference measurements of film thickness were performed. As a result, it was found that the reflective index distribution sometimes acts to underestimate the measurement values of the film thickness. The finding of this study provided a new insight for improving the measurement accuracy of thin film measurement using optical interference methods.

Dependence on pressure of the refractive indices of wurtzite ZnO, GaN, and AlN

We have measured both the ordinary and extraordinary refractive index of $m$-plane cuts of wurtzite ZnO, GaN, and AlN single crystals at room temperature and as a function of hydrostatic pressure up to 8 GPa. For that purpose we have developed an alternative optical interference method, called bisected-beam method, which leads, in general, to high contrast interference fringes. Its main feature, however, is to be particularly suitable for high pressure experiments with the diamond anvil cell, when the refractive index of the sample is low and similar to that of diamond and/or the pressure transmitting medium, as is the case here. For all three wide-gap materials we observe a monotonous decrease of the ordinary and extraordinary refractive indices with increasing pressure, being most pronounced for GaN, less marked for ZnO, and the smallest for AlN. The frequency dependence of the refractive indices was extrapolated to zero energy using a critical-point-plus-Lorentz-oscillator model of the ordinary and extraordinary dielectric function. In this way, we determined the variation with pressure of the electronic part (no-phonon contribution) of the static dielectric constant ${\ensuremath{\varepsilon}}_{\ensuremath{\infty}}$. Its volume derivative, $r=d\phantom{\rule{0.16em}{0ex}}ln{\ensuremath{\varepsilon}}_{\ensuremath{\infty}}/d\phantom{\rule{0.16em}{0ex}}lnV$, serves as single scaling coefficient for comparison with experimental and/or theoretical results for other semiconductors, regarding the pressure effects on the dielectric properties. We have obtained an ordinary/extraordinary average value $\overline{r}$ of 0.49(15) for ZnO, 1.22(9) for GaN, and 0.32(4) for AlN. With the values for the ordinary and extraordinary case being within experimental uncertainty, there is thus no apparent change in dielectric anisotropy under pressure for these wurtzite semiconductors. Results are discussed in terms of the pressure-dependent electronic band structure of the materials.