Coherence Interferometry Research Articles

All fiber single frequency pulsed Yb doped laser source scaling up to 600 uJ at 1 kHz

An all-fiber based high energy single frequency pulsed laser at 1030 nm with fixed repetition rate of 1 kHz was demonstrated. The system adopts a master oscillator power amplifier configuration. In the main amplification stage, we employed a highly doped, very large core diameter of 50 μm YDF fiber as the laser gain media. 670 μJ, 500 ns pulse train was obtained, corresponding to a peak power of 1.34 kW. Such a high-peak-power and high-repetition-rate SF source is well suited for long range coherent imaging, optical remote sensing, and coherent interferometry, etc.

Feature Enhancement Using Multi-Baseline SAR Interferometry-Correlated Synthesis Images for Power Transmission Tower Detection in Mountain Layover Area

The detection performance of power transmission towers in mountainous areas using SAR amplitude images is obviously influenced by the strong layover background (mainly including vegetation and soil) clutter interference around the towers. In this paper, power transmission tower detection in a mountainous layover area, using single-baseline SAR interferometry coherence images, which show better feature enhancement effectiveness compared to SAR amplitude images, is presented. Moreover, a novel feature enhancement method, that of generating multi-baseline SAR interferometry-correlated synthesis images for power transmission tower detection in a mountain layover area, is proposed. It demonstrates better feature enhancement (layover background cluster suppression) than that using single-baseline SAR interferometry coherence images. Theoretical analysis illustrates that the mountainous layover background clutter interference can be suppressed in the proposed single-baseline/multi-baseline SAR interferometry-correlated synthesis image. Experiments including over 12 repeat-pass TerraSAR-X staring spotlight mode acquisitions were conducted, and the results demonstrate that the detection performance with the use of multi-baseline SAR interferometry-correlated synthesis images showed an improvement of more than 43.6%, compared with the traditional method of using SAR amplitude images when benchmark deep learning-based detectors are used, i.e., Faster RCNN and YOLOv7.

A New Strategy for Forest Height Estimation Using Airborne X-Band PolInSAR Data

Because the penetration depth of electromagnetic waves in forests is large in the longer wavelength band, most traditional forest height estimation methods are carried out using polarimetric interferometry synthetic aperture radar (PolInSAR) data of the L or P band, and the estimation method is a three-stage method based on the random volume over ground (RVoG) model. For X-band electromagnetic waves, the penetration depth of radar waves in forests is limited, so the traditional forest height estimation method is no longer applicable. In view of the above problems, in this paper we propose a new forest height estimation strategy for airborne X-band PolInSAR data. Firstly, the sub-view interferometric SAR pairs obtained via frequency segmentation (FS) in the Doppler domain are used to extend the polarimetric interferometry coherence coefficient (PolInCC) range of the original SAR image under different polarization states, so as to obtain the accurate ground phase. For the determination of the effective volume coherence coefficient (VCC), part of the fitting line of the extended-range PolInCC distribution that is intercepted by the fixed extinction coherence coefficient curve (FECCC) of the fixed range is averaged to obtain the accurate effective VCC. Finally, the high-precision forest canopy height in the X-band is estimated using the effective VCC with the ground phase removed in the look-up table (LUT). The effectiveness of the proposed method was verified using airborne-measured data obtained in Shaanxi Province, China. The comparison was carried out using different strategies, in which we substituted one step of the process with the conventional method. The results indicated that our new strategy could reduce the root mean square error (RMSE) of the predicted canopy height vastly to 1.02 m, with a lower estimation height error of 12.86%.

Characterization of recycled Inconel 718 metal powder for assessing its reusability in the laser powder bed fusion process

<abstract> <p>Additive manufacturing technologies such as laser powder bed fusion (LPBF) provide unprecedented abilities to manufacture complex 3-D parts and structures; however, the process produces leftover metal powder that is often unused, resulting in significant cost and disposal overhead. Towards this end, to ensure the ability to recycle the unused powder that is typically found within the build volume and in the overflow compartments of LPBF systems, a thorough chemical and structural analysis is required. Such an analysis will help in determining the extent of recyclability and reusability of the unused powder. For these purposes, characterization of recycled powder for Inconel 718 was performed in this work as a function of build-cycle to compare and contrast the evolution in physical and chemical properties such as particle size distribution, morphology, and composition. We note that the analysis was carried out for 21 build-cycles. Characterization of the particle size distribution and circularity was performed using traditional scanning electron microscopy methods and that information was later compared to measurements of surface profile using coherent scanning interferometry. Reusability was assessed using these results in conjunction with chemical analysis of the powder that was carried out using energy dispersive X-ray spectroscopy. For the extent of build-cycles considered in this work, it was seen that the physical and chemical changes in the recycled powder were will within accepted limits for powder usage and that with appropriate measures, recycled powder can be re-incorporated for subsequent builds without compromise in the powder quality. This study provides a pathway for greatly reducing powder consumption and thus cost during the LPBF process.</p> </abstract>

Coherent interferometric imaging in a random flow

This paper is concerned with the development of imaging methods to localize sources or reflectors in inhomogeneous moving media with acoustic waves that have travelled through them. A typical example is the localization of broadband acoustic sources in a turbulent jet flow for aeroacoustic applications. The proposed algorithms are extensions of Kirchhoff migration (KM) and coherent interferometry (CINT) which have been considered for smooth and randomly inhomogeneous quiescent media so far. They are constructed starting from the linearized Euler equations for the acoustic perturbations about a stationary ambient flow. A model problem for the propagation of acoustic waves generated by a fixed point source in an ambient flow with constant velocity is addressed. Based on this result imaging functions are proposed to modify the existing KM and CINT functions to account for the ambient flow velocity. They are subsequently tested and compared by numerical simulations in various configurations, including a synthetic turbulent jet representative of the main features encountered in actual jet flows.

A Review on Guided Optical Feedback in Super-Luminescence Diodes for Metrological Purposes

Low-coherence interferometry (LCI) is a widely used measurement technique. Typical applications of LCI range from optical low-coherence reflectometry (OLCR) to optical coherence tomography (OCT). The main advantages offered by LCI over coherent-interferometry (CI) are its usual greater capacity to spatially locating the region of the sample from where the interferometric signal came from (the volume under test - VUT), and the greater robustness to straylight. When the LCI technique is combined with the self-mixing (SM, or optical-feedback, OF) technique, it is possible to obtain additional benefits in terms of compactness, and signal to noise ratio (SNR) of the interferometric signal. Optical layouts based on guided lightwaves generally allow to further improve the robustness and performances of the system. In this review, we focus on metrological applications of guided LCI-SM and, in particular, on the use of LCI-SM to measure positions and absolute distances, flow rates, fluid velocity profiles, and thicknesses.

Translational studies of electrophoretic mobility and phase picture of erythrocytes with consideration of development of stress response during a pathological process

Rationale:Modern cell diagnostic methods are in high demand during the development of new approaches in personalized medicine. Coherent phase interferometry and cell microelectrophoresis are among such methods that are being actively introduced into the diagnostic process in medical institutions.Aim:To substantiate the potential use of biophysical and morphodensitometrical erythrocytes parameters as criteria of treatment efcacy and course of adaptation process in patients with gastrointestinal tract disorders.Materials and methods:The study included 25 patients aged from 40 to 54 years (11 males and 14 females), among them 9 (36%) with gastric peptic ulcer, 3 (12%) with duodenal ulcer, 8 (32%) with acute gastritis, and 5 (20%) with acute pancreatitis. Biophysical and morphological particulars of peripheral blood erythrocytes were assessed before and after treatment using cell diagnostic techniques, such as microelectrophoresis and laser modulation interference microscopy. Also, we evaluated changes over time in routine clinical laboratory tests, such as red and white blood cell counts, hemoglobin levels, and erythrocyte sedimentation rate (ESR), and differential leukocyte counts. The control group included 10 healthy donors aged from 36 to 52 years.In vitroexperiments were performed to assess the erythrocyte electrophoretic mobility (EEPM) and morphology of erythrocytes treated with epinephrine or cortisol.Results:After the treatment, the patients demonstrated a decrease in their leukocyte counts (by 27%), a 2-fold increase in monocyte counts and an ESR decrease (by 10%), compared to the corresponding baseline values before treatment (p < 0.05 for all comparisons). EEPM increased by 12% (1.37 vs. 1.22 mcm × cm/V × s, p < 0.05). The erythrocyte pool of the patients before treatment, had a decreased proportion of discocytes, compared to that in the control group (85.2 vs. 95.4%, р < 0.05), increased proportions of echinocytes, stomatocytes and degenerative forms (11, 2.8 and 1%, respectively, р < 0.05). After the treatment, the discocytes counts increased virtually up to their physiological normal range (91.3%). However, the surface of the discoid cells remained heterogeneous with multiple microspicules; this resulted in changes of electrokinetic and morphological properties of erythrocyte response to stress reaction occurring in the body. The impact of the stress effectors was confrmed inin vitroexperiments assessing the effects of epinephrine (1 × 10-9 g/mL) and cortisol (5 × 10-7 g/mL) on erythrocytes. At 120 minutes of the experiment, epinephrine decreased EEPM (1.14 vs. 1.24 mcm × cm/V × s at baseline, р < 0.05) and increased cell sphericity. On the contrary, cortisol increased EEPM (1.72 vs. 1.36 mcm × cm/V × s, р < 0.05), with non-signifcant echinocytic transformation.Conclusion:Biophysical and morphodensitometric parameters of red blood cells obtained with the use of current express methods of cell microelectrophoresis and coherent interference microscopy help to objectivize the intensity of stress response during a pathological process and activation of adaptation mechanisms during the treatment.

Joint Probability Integral Method and TCPInSAR for Monitoring Mining Time-Series Deformation

Because of the high vegetation coverage, fast deformation in certain mine areas, some SAR interferograms are seriously incoherent. When using time-series synthetic aperture radar interferometry (InSAR) to monitor the surface movement basin of the mining area, there may be a certain period of missing deformation information, making the obtained surface time-series deformation incomplete. To this end, this paper proposes a way of using the results predicted by probability integral method (PIM) to replacing the monitoring results that cannot be obtained because of the seriously incoherent SAR interferograms; then, the monitoring results of the high-coherence SAR interferograms and the results predicted by PIM are used by the improved temporarily coherent point SAR interferometry (TCPInSAR) to invert the deformation, thereby obtaining a complete mining time-series deformation. The TCPInSAR using a linear model does not reflect the complex deformation characteristics of the mining area. So this paper focus on the characteristics of deformation of study area, the original linear model is changed to a polynomial model, which improves the applicability of TCPInSAR to monitoring mine deformation. Comparison between the experimental results and levelling shows that the root mean square error (RMSE) and the maximum deviation (MD) of the results obtained by combining the PIM with the improved TCPInSAR are 14.2 mm and 43.0 mm, respectively. Compared with the results obtained by combining the PIM with the TCPInSAR (RMSE = 16.2 mm, MD = 57.5 mm) and the results of using only the TCPInSAR (RMSE = 26.5 mm, MD = 88.4 mm), the monitoring accuracy is increased by 12.3% and 46.4%, respectively.

An imaging system integrating optical coherence tomography and interferometry for in vivo measurement of the thickness and dynamics of the tear film

BackgroundThe outermost layer of the tear film consists of a thin lipid layer (LL). The lipid layer serves as a barrier against evaporation of the aqueous component of the tear film. The ability to simultaneously image both the lipid layer thickness and overall tear film thickness is novel, and will help further understandings of mechanisms of how the lipid layer assembles and interacts with the full tear film thickness.MethodsWe developed a system that combines simultaneous optical coherence tomography (OCT) and thickness dependent fringes (TDF) interferometry for in vivo imaging of the tear film. The OCT possesses an axial resolution of 1.38 µm in tear film, providing an accurate measurement of the thickness of the overall tear film. The TDF can detect a minimal change of approximately 15 nm in LL thickness. In addition, the spatial resolution of TDF images in x–y plane is 5 µm.ResultsThe effect of instilling artificial tears on the PCTF and PLTF was examined. In both contact lens and non-contact lens wear, it could be observed from the OCT results that instillation of artificial tears increased the thickness of the overall tear film immediately, followed by a gradual reduction thereafter. These findings were consistent with other studies. However, unlike those previous reports, the thickness of the LL in this study was quantified simultaneously with the TDF subsystem. The results showed that bulking agents such as these artificial tears were not necessarily intended to increase the LL thickness. Immediately after instillation of artificial tears, the PCTF increased from 4.4 ± 0.97 to 20.3 ± 3.6 µm. The PCTF then decreased to 8.8 ± 2.1 µm at 4 min post-instillation. The thicknesses of the LL were 62.4 ± 14.5 nm, 48.7 ± 5.3 nm, and 55.2 ± 9.8 nm at pre-drop instillation, post-drop instillation, and 4-min post-drop instillation, respectively.ConclusionsIn this work, we have described a novel imaging system that integrated OCT and TDF imaging techniques, which may facilitate the study of many physiological and clinical aspects of the tear film.

Passive Array Imaging in Random Media

We present a novel algorithm for a high-resolution coherent imaging of sound sources in random scattering media using time-resolved measurements of the acoustic pressure at an array of receivers. The sound waves travel a long distance between the sources and receivers so that they are significantly affected by scattering in the random medium. We model the scattering effects by large random wavefront distortions, but the results extend to stronger effects, as long as the waves retain some coherence, i.e., before the onset of wave diffusion. It is known that scattering in random media can be mitigated in imaging using coherent interferometry (CINT). This method introduces a statistical stabilization in the image formation, at the cost of image blur. We show how to modify the CINT method in order to image wave sources that are too close to each other to be distinguished by CINT alone. We introduce the algorithm from first principles and demonstrate its performance with numerical simulations.

Mapping Three-Dimensional Co-Seismic Deformations Fields by Combining Multiple-Aperture Interferometry and Differential Interferometric Synthetic Aperture Radar Techniques

DInSAR technique based displacement measurement is sensitive to only radar line-of-sight, which renders it hard to determine 3D co-seismic deformations. To infer these deformations, a method based on the robust least squares method by combining the multiple-aperture interferometry (MAI) and DInSAR is applied to one ascending and one descending interferometric pair for the 2003 Bam, Iran, earthquake. The results reveal that co-seismic deformations not has the level strike-slip in north-south direction, but also has a large vertical component and a horizontal component in east-west direction. In areas with high interferometry coherence (>0.6), the standard deviation of MAI results is less than 0.075 m, and the 3D deformations are consistent with results of combining DInSAR and Offset Tracking technology in up-down and east-west directions with the maximum difference of 0.031 m. But the differences in south-north direction are relatively large on decimeter level. Therefore, the proposed method can be used to model reliable and accurate 3D surface displacement fields and benefit for analyzing the causes and effects of the earthquake.

Full-field parallel interferometry coherence probe microscope for high-speed optical metrology.

Parallel detection of several achromatic phase-shifted images is used to obtain a high-speed, high-resolution, full-field, optical coherence probe tomography system based on polarization interferometry. The high enface imaging speed, short coherence gate, and high lateral resolution provided by the system are exploited to determine microbump height uniformity in an integrated semiconductor chip at 50 frames per second. The technique is demonstrated using the Linnik microscope, although it can be implemented on any polarization-based interference microscopy system.

Ultrasound Imaging in Nuclear Reactors Cooled by Liquid Metals

In nuclear reactors cooled by liquid metals, ultrasound is the only type of field that allows obtaining images of the reactor cores and diagnostics of the integrity of the fuel assemblies. The article discusses the features of the practical realization of ultrasonic imaging systems based on phased arrays and offers an alternative solution of imaging on the basis of the acoustic lenses of refractive and diffraction types. Using lenses eliminates many of the technical and technological problems associated with the development of multi-element phased arrays. It is shown that lens systems allow using traditional methods of transformation of acoustic fields into the visible images by 2D piezo matrix and a more promising way of acoustooptical transformation based on coherent optical interferometry.

Comparative Analysis of Forest Height Retrieval Methods by Polarimetric SAR Interferometry

The objective of this paper is to compare and analyze the forest height retrieval methods from Polarimetric SAR Interferometry(POLINSAR).Both of the methods based on DEM difference and that on interferometry coherence amplitude are generalized, analyzed, and compared.Also in this paper combined methods of DEM difference and interferometry coherence amplitude are proposed and validated.The ESA fullpolarimetric interferometry L-band data are used for forest height analysis.The results show that the height is severely underestimated using DEM difference method,In constast,interferometry coherence amplitude method has a overest imation of height.The combined method of DEM difference and interferometry coherence amplitude has a much better estimate,closer to the true height than these two methods.

Remote sensing and characterization of oil on water using coherent fringe projection and holographic in-line interferometry

We suggest combining several optical methods for remote sensing and characterization of crude oil films and emulsions. These are coherent fringe projection illumination (CFP), holographic in-line interferometry (HILI), and laser-induced fluorescence. The combined methods of CFP and HILI are described in the frame of coherent superposition of partial interference patterns. It is shown that in addition to detection and identification of oil, laser illumination in the green-blue region can also degrade oil. This finding indicates that properly structured laser clean-up can be an alternative method of decontamination.

Coherent Interferometry Algorithms for Photoacoustic Imaging

The aim of this paper is to develop new coherent interferometry (CINT) algorithms to correct the effect of an unknown cluttered sound speed (random fluctuations around a known constant) on photoacoustic images. By back-propagating the correlations between the preprocessed pressure measurements, we show that we are able to provide statistically stable photoacoustic images. The preprocessing is exactly in the same way as when we use the circular or the line Radon inversion to obtain photoacoustic images. Moreover, we provide a detailed stability and resolution analysis of the new CINT--Radon algorithms. We also present numerical results to illustrate their performance and to compare them with Kirchhoff--Radon migration functions.

Optical monitoring of substrate temperature and etching speed of multilayered structures during plasmochemical etching

Using weakly coherent tandem interferometry, the possibility of simultaneous temperature and film thickness measurements in plasmochemical etching processes of silicon on insulator structure is demonstrated. It is shown that changes of the structure’s total optical thickness related to temperature variation can be separated from a change of the physical film thickness. For that purpose we have to take in account changes of zeros interference peak amplitude caused by changes of the interferentional conditions inside the film when its thickness is changing. Temperature measurement precision is ±1°C. Thickness measurement precision is ±10 nm. The results of process monitoring closely correlate with the results of a stair’s profile obtained with a profilometer.

Enhanced statistical stability in coherent interferometric imaging

We analyze the resolution and statistical fluctuations of images when the ambient medium is random and scattering can be modeled primarily by wavefront distortion. We compare the coherent interferometric imaging method to the widely used Kirchhoff migration and show how the latter loses statistical stability at an exponential rate with the distance of propagation. In Kirchhoff migration we form images by superposing the array data back-propagated to the image domain. In coherent interferometry, we back-propagate local cross-correlations of the array data. This is a denoising process that enhances the signal-to-noise ratio of images but also reduces the resolution. We quantify analytically the trade-off between enhanced stability and reduced resolution in coherent interferometric imaging.

Optical coherence tomography in otolaryngology

Optical coherence tomography is an imaging technique based on coherence interferometry. It is used in many medical fields due to its non-invasive imaging capabilities with micrometer resolution. The aim of the authors was to review the applicability of the optical coherence tomography in otolaryngology. Literature data and their own studies show that optical coherence tomography is a reliable method for identifying and targeted biopsy of inflammated, pre-malignant or cancer tissue in human laryngeal and pharyngeal mucosa. Another emerging field for optical coherence tomography is diagnosis of middle ear diseases, especially stapes ankylosis and cholesteatoma.

Coherent interferometric imaging, time gating and beamforming

Coherent interferometric imaging is based on the backpropagation of local spacetime cross-correlations of array data and was introduced in order to improve images when the medium between the array and the object to be imaged is inhomogeneous and unknown (Borcea et al 2005 Inverse Problems 21 1419). Although this method has been shown to be effective and is well founded theoretically, the coherent interferometric imaging function is computationally expensive and therefore difficult to use. In this paper, we show that this function is equivalent to a windowed beamformer energy function, that is, a quadratic function that involves only time gating and time delaying signals in emission and in reception. In this form the coherent interferometric imaging can be implemented efficiently both in hardware and software, that is, at a computational cost that is comparable to the usual beamforming and migration imaging methods. We also revisit the trade-off between enhanced image stability and loss of resolution in coherent interferometry from the point of view of its equivalence to a windowed beamformer energy imaging function.