Interferometric Technique Research Articles

Implementation of coherence imaging spectroscopy for ion flow measurements in the Compact Toroidal Hybrid experiment

A new coherence imaging spectroscopy (CIS) system has been characterized and validated for measurements of impurity ion velocity in the Compact Toroidal Hybrid (CTH) experiment. CIS is an interferometric technique providing very high spatial resolution of line-integrated ion flows; however, these measurements are highly sensitive to environmental factors such as temperature fluctuations. A compact interferometer design housed in a thermally regulated environment yields CIS measurement variations due to thermal fluctuations of 0.25 km/s. CIS measurements of He+ flows in the outer regions of CTH are benchmarked using two optical grating spectrometers. The deviation between the measurements is typically less than 2 km/s for multiple lines of sight which is well within the uncertainties of the diagnostics. Additional experiments demonstrate a moderate robustness of ion flows in the outer region of CTH to changing the vacuum transform, direction of the magnetic field, and plasma current. In contrast, regions of complete flow reversal are observed when a bias probe is inserted into the plasma edge.

Subarcminute Localization of 13 Repeating Fast Radio Bursts Detected by CHIME/FRB

We report on improved sky localizations of 13 repeating fast radio bursts (FRBs) discovered by CHIME/FRB via the use of interferometric techniques on channelized voltages from the telescope. These so-called “baseband localizations” improve the localization uncertainty area presented in past studies by more than three orders of magnitude. The improved localization regions are provided for the full sample of FRBs to enable follow-up studies. The localization uncertainties, together with the limits on the source distances from their dispersion measures, allow us to identify likely host galaxies for two of the FRB sources. FRB 20180814A lives in a massive passive red spiral at z ∼ 0.068 with very little indication of star formation, while FRB 20190303A resides in a merging pair of spiral galaxies at z ∼ 0.064 undergoing significant star formation. These galaxies show very different characteristics, further confirming the presence of FRB progenitors in a variety of environments even among the repeating subclass.

Label-free optical interferometric microscopy to characterize morphodynamics in living plants.

During the last century, fluorescence microscopy has played a pivotal role in a range of scientific discoveries. The success of fluorescence microscopy has prevailed despite several shortcomings like measurement time, photobleaching, temporal resolution, and specific sample preparation. To bypass these obstacles, label-free interferometric methods have been developed. Interferometry exploits the full wavefront information of laser light after interaction with biological material to yield interference patterns that contain information about structure and activity. Here, we review recent studies in interferometric imaging of plant cells and tissues, using techniques such as biospeckle imaging, optical coherence tomography, and digital holography. These methods enable quantification of cell morphology and dynamic intracellular measurements over extended periods of time. Recent investigations have showcased the potential of interferometric techniques for precise identification of seed viability and germination, plant diseases, plant growth and cell texture, intracellular activity and cytoplasmic transport. We envision that further developments of these label-free approaches, will allow for high-resolution, dynamic imaging of plants and their organelles, ranging in scales from sub-cellular to tissue and from milliseconds to hours.

The Detection Scheme and Applications of Gravitational Waves

In recent years, gravitational waves have already attracted attention as the gateway to a new era in physics since they were first directly detected and observed. This paper summarizes the development of gravitational waves from the first proposed to the present and the main observation methods, as well as the main uses and significance of the detection of them. To be specific, in this paper, the most popular laser interferometer technique for the detection based on Michelson interferometer is discussed, and several purposes of the detection of gravitational waves are given. The detection signatures are available to adopt to the analysis of the collision of binary star systems. Gravitational radiation or primordial gravitational radiation can carry more information about black holes or the Big Bang than electromagnetic waves. The gravitational wave astronomy created by gravitational waves has opened a new horizon for astronomers to explore the universe, and the detection of them is an integral part of the future development of physics and astronomy. To sum up, these results shed light on guiding further exploration of gravitational waves detection as well as applications of them.

Landslide Measurement in Glendroud Region (From the Central Part of Noor City) in Mazandaran Province Iran by Using Remote Sensing and Radar Interferometry Techniques

Studying and monitoring the amount of displacement caused by changes in the shape of the earth's surface is one of the important and practical studies in various topics of geology and geophysics, which plays a significant role in the prevention and behavior of natural disasters such as earthquakes, subsidence, and landslides. Among them, there are various methods for geodetic measurements and monitoring of these deformations, among them the radar interferometric technique with the capabilities of producing wide, frequent and continuous ground covers, as well as high temporal and spatial resolution, is one of the techniques has become importantand significant. Landslides in the Yilagh area of GlenrodRoyan, Noor city, caused a lot of damage to some residential areas, gardens and roads of several villages in the region. Due to the movement of the earth, water and electricity have been cut off in some areas. About one kilometer of the north-south road has been destroyed and the most damage has been done to the houses of Foulad welfare complex. After passing through a long period (more than 60 years) of drought, the country of Iran has faced various risks in recent years, especially in 2018 and 2019, including floods and landslides. The aim of this thesis is to obtain the amount of displacements caused by the landslide in Glenrod region in 2019 using sentinel-1 satellite images by using the differential radar interferometry method using snap software. In this regard, from 4 satellite images It has been used during the years 2019-2020, and according to the results obtained, the largest landslide during the second period was 15 cm, which is based on the information obtained from the mapping organization and the opinion of geologists and experts in the region who stated that the largest displacement in area under report was March 2019 and it matches with the findings carried out by the present authors.

A theoretical investigation of magnetic susceptibility measurement of diamagnetic liquids using a Mach–Zehnder interferometer

In this study, we present a novel method for measuring the magnetic susceptibility of liquids using a Mach–Zehnder interferometer. The proposed technique employs a ring magnet to deform the liquid, while a laser beam passes through the liquid to measure the resulting interference pattern. The deformation of the liquid, caused by the known magnetic field of the ring magnet, is used to calculate the magnetic susceptibility. We provide a comprehensive theoretical framework, including the relevant equations and models, for analyzing the data obtained using this method. We compare the Mach–Zehnder interferometer method with other established techniques, highlighting its advantages and disadvantages. Our findings indicate that the Mach–Zehnder interferometer technique offers high accuracy, sensitivity, and potential applications in characterizing the magnetic properties of various liquid systems.

Deep learning-based image enhancement in optical coherence tomography by exploiting interference fringe

Optical coherence tomography (OCT), an interferometric imaging technique, provides non-invasive, high-speed, high-sensitive volumetric biological imaging in vivo. However, systemic features inherent in the basic operating principle of OCT limit its imaging performance such as spatial resolution and signal-to-noise ratio. Here, we propose a deep learning-based OCT image enhancement framework that exploits raw interference fringes to achieve further enhancement from currently obtainable optimized images. The proposed framework for enhancing spatial resolution and reducing speckle noise in OCT images consists of two separate models: an A-scan-based network (NetA) and a B-scan-based network (NetB). NetA utilizes spectrograms obtained via short-time Fourier transform of raw interference fringes to enhance axial resolution of A-scans. NetB was introduced to enhance lateral resolution and reduce speckle noise in B-scan images. The individually trained networks were applied sequentially. We demonstrate the versatility and capability of the proposed framework by visually and quantitatively validating its robust performance. Comparative studies suggest that deep learning utilizing interference fringes can outperform the existing methods. Furthermore, we demonstrate the advantages of the proposed method by comparing our outcomes with multi-B-scan averaged images and contrast-adjusted images. We expect that the proposed framework will be a versatile technology that can improve functionality of OCT.

Land Subsidence Susceptibility Mapping Using Interferometric Synthetic Aperture Radar (InSAR) and Machine Learning Models in a Semiarid Region of Iran

Most published studies identify groundwater extraction as the leading cause of land subsidence (LS). However, the causes of LS are not only attributable to groundwater extraction. Other land-use practices can also affect the occurrence of LS. In this study, radar interferometric techniques and machine learning (ML) models were used for the prediction, susceptibility zoning, and prioritization of influential variables in the occurrence of LS in the Bakhtegan basin. The LS rate was characterized by applying an interferometric synthetic aperture radar (InSAR). The recursive feature elimination (RFE) method was used to detect and select the dominant combination of indicators to prepare an LS susceptibility map. Three ML models, including random forest (RF), k-nearest neighbors (KNN), and classification and regression trees (CART), were used to develop predictive models. All three models had acceptable performance. Among the ML models, the RF model performed the best (i.e., Nash–Sutcliffe efficiency, Kling–Gupta efficiency, correlation coefficient, and percent bias metrics of 0.76, 0.78, 0.88, and 0.70 for validating phase, respectively). The analysis conducted on all three ML model outputs showed that high and very high LS susceptibility classes were located on or near irrigated agricultural land. The results indicate that the leading cause of land LS in the study region is not due to groundwater withdrawals. Instead, the distance from dams and the proximity to anticlines, faults, and mines are the most important identifiers of LS susceptibility. Additionally, the highest probability of LS susceptibility was found at distances less than 18 km from synclines, 6 to 13 km from anticlines, 23 km from dams, and distances less than 20 to more than 144 km from mines. The validated methods presented in this study are reproducible, transferrable, and recommended for mapping LS susceptibility in semiarid and arid climate zones with similar environmental conditions.

Kinematic Response of Subaerial Salt Diapirs to Geomorphic, Tectonic and Climatic Regimes: Insights From Space‐Based Observations in the Western Kuqa Fold‐Thrust Belt, NW China

AbstractEphemeral subaerial salt diapirs are gravitationally unstable and vulnerable to climate and tectonic activity due to the rheology and incompressibility of rock salt. Quantifying the kinematics of subaerial salt and clarifying the role of tectonics, surface processes, and climate in reshaping the surface salt morphology provides an invaluable opportunity to explore the interactions between Earth’s spheres on a much shorter timescale. With diverse exposed salt diapirs and potential motions, the Kuqa fold‐thrust belt (KFTB), NW China, represents an optimum natural laboratory to understand subaerial salt kinematics. Here, we integrated ascending and descending geometries of Sentinel‐1 synthetic aperture radar images with optical remote sensing data, seismic profiles, digital elevation models, and meteorological records to explore the potential correlation between subaerial salt motions and geomorphic, tectonic, and climatic factors. Using the interferometric synthetic aperture radar technique, we observed a maximum of 25 mm/yr in vertical and 40 mm/yr in horizontal surface salt deformation in the KFTB from 2014 to 2020. Our findings demonstrate a gravity spreading dominant system, where topography exerts a primary control on the surface displacement patterns of salt structures, while weather variables influence deformation mainly by softening salt and facilitating gravity‐driven salt flow.

Accurate Dynamic Electromechanical Solution for Rectangular Piezoelectric Plate Based on Modified FSDT

In this study, the modified first-order shear deformable theory (FSDT) is applied to analyze the resonant characteristics of piezoelectric (PZT) moderately thick plate vibrators with different thicknesses. A simple and straightforward simplification method between mechanical and electrical functions is also proposed based on the modified FSDT. The natural frequencies and associated mode shapes of piezoelectric plates with completely free boundary are analyzed. The displacement fields of the flexural modes are presented based on the superposition method. This analytical method provides a strong-form novel solution for the flexural-dominated motion’s out-of-plane and in-plane coupling displacement fields. The solutions of displacement functions, which are obtained from the superposition method, show excellent convergence for numerical calculation. To verify the validity of the theoretical solution, the resonant frequencies and the corresponding mode shapes are compared with that obtained by the finite element method (FEM) and experimental measurements using the amplitude-fluctuation electronic speckle pattern interferometer (AF-ESPI) technique. According to the electromechanical formula and the derived theoretical solution, four types of electrode are designed to excite the moderately thick PZT specimen for examining the application feasibility of the proposed method. It is shown in this study that the theoretical analysis, numerical calculation, and experimental measurement are fully compared, and excellent agreements of the piezoelectric moderately thick plate are also obtained.

Real‐Time Superresolution Interferometric Measurement Enabled by Structured Nonlinear Optics

AbstractOptical interferometers are pillars of modern precision metrology, but their resolution is limited by the wavelength of the light source, which cannot be infinitely reduced. Magically, this limitation can be circumvented by using an entangled multiphoton source because interference produced by an N‐photon amplitude features a reduced de Broglie wavelength . However, the extremely low efficiency in multiphoton state generation and coincidence counts actually negates the potential of using multiphoton states in practical measurements. Here, a novel interferometric technique based on structured nonlinear optics is demonstrated, i.e., parametric upconversion of a structured beam, capable of superresolution measurement in real time. The main principle relies in that the orbital angular momentum (OAM) state and associated intramodal phase within the structured beam are both continuously multiplied in cascading upconversion to mimic the superresolved phase evolution of a multiphoton amplitude. Owing to the use of bright sensing beams and OAM mode projection, up to a 12‐photon de Broglie wavelength with almost perfect visibility is observed in real time and, importantly, by using only a low‐cost detector. The results open the door to real‐time superresolution interferometric metrology and provide a promising way toward multiphoton superiority in practical applications.

Vulnerability assessment of power transmission towers affected by land subsidence via interferometric synthetic aperture radar technique and finite element method analysis: a case study of Zanjan and Qazvin provinces

Vulnerability assessment of power transmission towers affected by land subsidence via interferometric synthetic aperture radar technique and finite element method analysis: a case study of Zanjan and Qazvin provinces

Smart Gateway for Healthcare Networks Based on Beam Steering Technology

To ensure high-reliability communication in healthcare networks, this paper presents a smart gateway system that includes an angle-of-arrival (AOA) estimation and a beam steering function for a small circular antenna array. To form a beam toward healthcare sensors, the proposed antenna estimates the direction of the sensors utilizing the radio-frequency-based interferometric monopulse technique. The fabricated antenna was assessed based on the measurements of complex directivity and the over-the-air (OTA) testing in Rice propagation environments using a two-dimensional fading emulator. The measurement results reveal that the accuracy of the AOA estimation agrees well with that of the analytical data obtained through the Monte Carlo simulation. This antenna is embedded with a beam steering function employing phased array technology, which can form a beam spaced at 45° intervals. The ability of full-azimuth beam steering with regard to the proposed antenna was evaluated by beam propagation experiments using a human phantom in an indoor environment. The received signal of the proposed antenna with beam steering increases more than that of a conventional dipole antenna, confirming that the developed antenna has great potential of achieving high-reliability communication in a healthcare network.

On the use of two emerging laser-based flaw-detection techniques – Considerations and practicalities

The pursuit of non-contact techniques for detecting ultrasonic waves propagating on the surface of solids is stimulated by the possibility of gaining some advantages over conventional contact methods. Non-contact methods are becoming a milestone in performing non-destructive evaluation in several industrial fields, where hazardous environments, narrow spaces, high temperatures, and complex geometries are encountered. Such methods exploit photo-acoustic interactions between light and sound waves. This work compares two non-contact laser-based methods for detecting artificial flaws of different sizes in metallic specimens. It uses multi-signal homodyne interferometry and single beam deflectometry to record the ultrasonic waves produced by a piezoelectric probe capable of generating surface Rayleigh waves. The results were analysed in both time and frequency domains. Moreover, the signal-to-noise ratio was evaluated for both measurement systems by changing the distance between the defect and the point where the signals were collected. The results show the main differences between the two techniques and the practicalities associated with their usage. The employed refractometric method has a lower sensitivity to surface roughness than the interferometric method. On the other hand, the interferometric technique allows for higher spatial resolution, wider frequency bandwidth and a higher detectable frequency (i.e., detecting low-sized defects).

Kelvin‐Helmholtz Billows in the Troposphere and Lower Stratosphere Detected by the PANSY Radar at Syowa Station in the Antarctic

AbstractWe conducted two 10‐day observational campaigns in 2019 targeting turbulence in the troposphere and lower stratosphere by adopting a frequency domain radar interferometric imaging technique using Program of the Antarctic Syowa radar (PANSY radar) and radiosonde observations obtained at Syowa Station in the Antarctic. Seventy three Kelvin‐Helmholtz (K‐H) billows were detected, and two characteristic cases likely excited by the same cyclone were examined in detail. In the first case with the longest observational duration of ∼6.5 hr, the K‐H billows had a thickness of ∼800 m and a horizontal wavelength of ∼2,500 m. According to a numerical simulation, continuously existing gravity waves associated with the cyclone maintained strong vertical wind shear sufficient to cause the K‐H instability. In the second case with the deepest thickness of ∼1,600 m, the K‐H billows had a horizontal wavelength of ∼4,320 m. Numerical simulation suggested that an enhanced upper‐tropospheric jet associated with a well‐developed synoptic‐scale cyclone caused the K‐H instability. Such background conditions, frequently observed in the Antarctic coastal region, are typical mechanisms for K‐H excitation. Linear stability analysis also indicated that the characteristics of the observed K‐H billows were consistent with the most unstable modes. Furthermore, statistical analysis was performed using data of all 73 observed cases. The characteristics of K‐H billows observed at Syowa Station are similar to those observed over Japan. However, the K‐H billows tend to have longer wave periods over Syowa Station than over Japan, likely due to the weaker tropospheric jet in the Antarctic.

Multistatic MIMO Sparse Imaging Based on FFT and Low-Rank Matrix Recovery Techniques

This article proposes a simple sparse imaging scheme using a linear sparse aperiodic array and a new fast Fourier transform matched filtering (FFTMF) algorithm for a THz multistatic multiple-input and multiple-output (MIMO) imaging system. The simple linear sparse aperiodic array and multipass interferometric synthetic aperture focusing technique are used to achieve fast sampling, low system cost, and high imaging performance. Unlike a traditional generalized synthetic aperture focusing technique (GSAFT) for multistatic MIMO imaging, which is time-consuming and exhibits increased reconstruction time with increased data volume, the proposed FFTMF image reconstruction algorithm is capable of providing comparable image quality but significantly reducing the reconstruction time. For example, we show that for an image of 300 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times320$ </tex-math></inline-formula> mm with a pixel size of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.75\times0.83$ </tex-math></inline-formula> mm, the reconstruction time is reduced from about 1.50 min to 0.25 s in the 220-GHz five-pass synthetic imaging experiments. The proposed imaging algorithm uses internal zero padding, a multipass interferometric synthetic aperture focusing technique, and a wideband imaging technique to improve the imaging performance under a low-cost, sparse sampling scheme. It shows a strong antinoise ability and a high tolerance to target focusing distance. In addition, integrated with an algorithm of principal component pursuit by alternating directions method (PCPADM), sparse imaging is available to further save system cost and sampling data without a loss of image quality while the novel use of an error matrix provides an additional detection capability for imaging systems.

A method for resolving the phase difference ambiguity in interferometric monopulse angle of arrival estimation

This paper presents a method to eliminate the phase difference ambiguity in angle of arrival (AOA) estimation using the radio-frequency-based interferometric monopulse technique. In order to uniquely determine the AOA, we utilize four directivities which are formed by using selected elements with the same weight function as the AOA estimation. We investigate the AOA estimation accuracy for the direction of the incoming wave from a high elevation angle and in multi-path propagation environments using a three-dimensional fading emulator. The results show that the proposed method is valid for complex propagation environments.

Shape resonances in photoionization cross sections and time delay

Shape resonances in photoionization of atoms and molecules arise from a particular geometry of the ionic potential which traps the receding photoelectron in a quasi-bound state in a particular partial wave. This mechanism allows us to connect the photoionization cross section in the resonant region with the photoelectron scattering phase in this partial wave by a simple formula $\sigma \propto \sin^2\delta_\ell$. Due to this relation, the phase $\delta_\ell$ can be extracted from an experimentally known cross section and then converted to the photoelectron group delay (Wigner time delay) $\tau_{\rm W} = \partial \delta_\ell/\partial E$ which is measurable by recently developed laser interferometric techniques. Such a direct connection of the photoionization cross section and the time delay is a fundamental property of shape resonances which provides a comprehensive test of novel measurements against a large body of older synchrotron data.

Mapping the geometry dependent relative stress in stretched polymer membranes by polarization and interferometric techniques

This paper reports experimental results on contactless geometry dependent stress characterisation and mapping in elastic polymer membranes using polarization and interferometric techniques. Three different geometries of polydimethylsiloxane (PDMS) namely, rectangular, wedge and bowtie shaped membranes are studied. The membranes were initially stretched and then relaxed from one edge during the characterisation. In the rectangular membrane the stress was observed to be concentrated at the static edge of the membrane. Whereas, in the wedge and bowtie shaped membranes, the stress is found to be concentrated at the locations wherein the membrane has a narrower width. The proposed facile methods for characterisation are helpful in designing stress induced tuneable optics and to analyze stress in polymer membranes during their industrial production.

Realisation of an optical pressure standard by a multi-reflection interferometric technique

A novel realization of an optical pressure standard, alternative to Fabry-Perot cavity-based techniques, is presented. It is based on the measurement of the refractive index of a gas through an unbalanced homodyne interferometer, designed to have one of its two arms formed by a multi reflection double mirror assembly to establish an unbalance length larger than 6 m in a compact setup.The paper illustrates the most important steps concerning its realization: the estimate of the pressure-induced deformation of the interferometer, the temperature control at millikelvin level and the measurement in vacuum of the unbalance of the interferometer.The evaluation of the uncertainty of the realized optical pressure standard currently demonstrated to fulfill the main goal of having the ability to measure pressure with a relative uncertainty of 10 ppm at 100 kPa.