Interferometric Technique Research Articles

Noise assessment of cold atom interferometry gradiometry observations

Over the past few decades, the development of interferometric techniques utilizing cold atoms has significantly advanced, particularly in the realm of gravimetry. This paper explores the characterization of noise within atomic gradiometry systems, which is essential for enhancing measurement accuracy as new methodologies and tools are introduced. Specifically, we examine the noise components using advanced techniques such as least squares component estimation and Allan variance analysis. Applying these sophisticated methods to two distinct datasets, our results robustly indicate that white noise is the predominant and most resilient type of noise in gravity gradiometry measurements based on atomic interferometry, with variances of σP12=2.97×10−8 for dataset 1 and σP22=5.66×10−7 for dataset 2. The predominance of white noise simplifies the system dynamics and enhances the reliability of the estimation methods. Furthermore, our calculations yield an uncertainty in the gravity gradient resolution of σ Γ1 = 0.13 E (where 1 E = 10−9 s−2) and σ Γ2 = 3.55 E over time, underscoring the high precision achievable with current interferometric techniques.

Effect of Titanium Oxide (TiO2) Nanoparticles on the Opto-Mechanical Properties of Polyethylene Terephthalate (PET) Fibers

Polyethylene terephthalate (PET) is widely used in various applications due to its excellent mechanical properties and chemical resistance. However, PET fibers still lack specific features and functionalities that can be improved via nano-additives, particularly metal oxides. In this study, we investigate the effect of adding TiO2 nanoparticles to PET to form PET/TiO2 fibers and examine their opto-mechanical properties. This study utilizes optical interferometric techniques to assess how mechanical stretching influences the optical and mechanical properties of PET fibers treated with TiO2 nanoparticles. A Mach–Zehnder interferometric setup, integrated with a versatile device capable of mechanically stretching samples, is used to achieve this task. Variations in refractive index and birefringence along the longitudinal axis of undrawn and drawn PET/TiO2 fibers are examined. The research meticulously explores the fluctuations and spatial variations in the refractive index and birefringence properties, exhibiting anisotropy in optical behavior, along the longitudinal axis of unstretched and stretched PET/TiO2 fibers. The findings and outcomes derived from this comprehensive study provide substantive information that can facilitate the enhancement and optimization of the coupled optical and mechanical properties of materials explicitly engineered for advanced applications.

Temporal gravimetry, campaign and permanent GNSS, and interferometric radar techniques: A comparative approach to quantifying land deformation rates in coastal Texas

Land subsidence and local sea-level rise are well-known on-going hazards that negatively impacting coastal regions, exacerbating coastal flooding, threatening infrastructure stability, accelerating erosion, and amplifying the risks of inundation and property damage. This study used four techniques to quantify land deformation rates in the Texas Coastal Bend region and to investigate the controlling factors on two different spatiotemporal scales: (1) local scale, where biweekly temporal gravity and campaign Global Navigation Satellite System (GNSS) measurements were acquired at six locations over 2 years (October 2020–September 2022); and (2) regional scale, where vertical displacement time series were extracted from the Interferometric Synthetic Aperture Radar (InSAR) and 15 permanent GNSS stations over 5 years (January 2017–November 2021). The observed inconsistency between land deformation rates derived from gravity (range: −33.32 ± 149.30 to +338.68 ± 107.93 mm/yr) and campaign GNSS (range: −17.91 ± 14.90 to +5.69 ± 9.93 mm/yr) surveys could be attributed to the short campaign period and the infrequency of data acquisition. The InSAR-derived deformation rates (range: −12.16 ± 0.12 to +11.70 ± 0.00 mm/yr) were consistent with the permanent GNSS-derived rates (range: −14.0 ± 0.6 to +9.0 ± 3.0 mm/yr); both indicated spatiotemporal variability in land deformation rates across the Texas Coastal Bend. A total of 4 coastal towns (−2.3 ± 3.3 mm/yr), 3 cities (−1.4 ± 2.6 mm/yr), 3 inland towns (−3.6 ± 4.2 mm/yr), and 7 industrial plants (−3.8 ± 5.8 mm/yr) were found to have significant land subsidence rates due to sediment compaction, growth faulting, oil/gas extraction, and groundwater extraction. Results of this study emphasize the advantages and limitations of four different techniques in quantifying land deformation rates; can enhance estimates of local sea-level rise; and offer valuable insights to support coastal communities in mitigating the impacts of land subsidence and improving their resilience.

Tunnel-induced land subsidence assessment in a densely populated residential area using Sentinel-1 PS-InSAR

Land subsidence detection in residential areas based on advanced remotely sensed data is an effective technique to mitigate catastrophic disasters in time. Synthetic aperture radar (SAR) in spaceborne platforms is a highly sophisticated technique to estimate ground surface subsidence with millimeter accuracy for wide-area observation. SAR is beneficial for large-scale social infrastructure project planning and monitoring in densely populated residential areas. In this study, we applied a permanent scatterer (PS) interferometric SAR (PS-InSAR)-based technique for monitoring land subsidence in a tunnel construction site in the Greater Tokyo Area to investigate tunnel-induced ground surface subsidence. Sentinel-1 repeat-pass SAR data in ascending and descending orbital directions were used for continuous observation. Consecutively estimated interferograms based on repeat-pass SAR data were generated to monitor and detect tunnel-induced land subsidence as well as confirm long-term stability along the tunnel excavation path. A bidirectional displacement of the ground area parallel to the earth’s surface in the east–west direction and perpendicular to the earth’s surface in the up–down direction was estimated at a high-phase consistency location using a PS interferometric stacking technique. The resultant data were then analyzed to detect anomalies in the ground area in the spatiotemporal domains by performing displacement time-series analysis. An area near Higashi-Tsutsujigaoka’s local administrative region in the metropolitan center of Tokyo was observed to have 15-mm subsidence and 30-mm displacement in the east–west direction during August–October 2020. The conventional level survey results in the same ground area showed 15–20-mm subsidence above the tunnel excavation path. The findings of this study offer insights into understanding land subsidence in residential environments.

A Review: Non-Contact and Full-Field Strain Mapping Methods for Experimental Mechanics and Structural Health Monitoring.

Non-contact and full-field strain mapping captures strain across an entire surface, providing a complete two-dimensional (2D) strain distribution without attachment to sensors. It is an essential technique with wide-ranging applications across various industries, significantly contributing to experimental mechanics and structural health monitoring. Although there have been reviews that focus on specific methods, such as interferometric techniques or carbon nanotube-based strain sensors, a comprehensive comparison that evaluates these diverse methods together is lacking. This paper addresses this gap by focusing on strain mapping techniques specifically used in experimental mechanics and structural health monitoring. The fundamental principles of each method are illustrated with specific applications. Their performance characteristics are compared and analyzed to highlight strengths and limitations. The review concludes by discussing future challenges in strain mapping, providing insights into potential advancements and developments in this critical field.

LArRI — A new setup for Liquid Argon Refractive index measurement

Liquid argon (LAr), widely used as the active target in neutrino and dark matter experiments, is a scintillator with a light yield of approximately 40 photons/keV. The scintillation spectrum is centered at 128 nm, and the attenuation length is of the order of meters, depending on the purity. The addition of small amounts of dopants allows for shifting the scintillation peak simplifying the light detection and opening the possibility to the development of imaging systems. There is no precise knowledge of the optical properties of LAr in the VUV range, but it could be exploited to improve the performances of liquid argon-based experiments, especially when the involved mass is in the ton scale. LArRI (Liquid Argon Refractive Index) aims to directly measure the refractive index of LAr in the VUV spectrum, using an interferometric technique. The refractive index is obtained by comparing two interference patterns, created in vacuum and liquid, acquired with cryogenic silicon photomultipliers. This work primarily presents the methodology, the preliminary tests, and the analysis strategy, which are intended to be applied to real data shortly.

Heterodyne background-oriented schlieren for the measurement of thermoacoustic oscillations in flames

In aircraft engines, thermoacoustic oscillations in the combustion chamber contribute significantly to noise emissions, which, like all other emissions, must be drastically reduced. Thermoacoustic oscillations are not only a concern, they can also be beneficial in hydrogen combustion. This work demonstrates that thermoacoustic density oscillations with amplitudes at least an order of magnitude smaller than those resulting from density gradients in a turbulent flame can be detected using laser interferometric vibrometry. This improvement was made possible by heterodyning a carrier fringe system in background-oriented schlieren (BOS) recordings, which were subsequently analyzed using techniques commonly used for holographic interferometry. In comparison with other BOS evaluation techniques, the filtering of the individual frames in the Fourier domain offers a more efficient computational approach, as it allows for phase averaging of a high number of single recordings to reduce noise from turbulence. To address fringe pattern distortions and cross talk in the Fourier domain, which both have been observed by other authors, we propose background subtraction methods and an optimized background pattern. Additionally, the procedure provides a visualization tool for marking the high turbulence regions of heat release by the variations in fringe amplitude. Finally, the line-of-sight data are reconstructed using the inverse Abel transform, with the data calibrated by laser interferometric techniques, resulting in local values for density oscillations.Graphical abstract

Thermal Expansion of Hexagonal Boron Nitride

A heuristic model is proposed for the dependence with temperature of the linear coefficients of thermal expansion (TEC) of hexagonal boron nitride (hBN) parallel to the crystallographic a and c axes, namely and . The model proposed for the linear TECs of hBN is consistent with physical constraints at the low‐ and high‐temperature limits. The model's free parameters are determined by a multi‐objective fitting to literature data on lattice parameters and linear TECs versus temperature, as determined experimentally by X‐ray diffraction and interferometric techniques. For hBN, is negative up to 1290(170) K (more than twice the corresponding temperature for graphite), with a minimum of around 230 K. According to the calculations and literature data, the linear TEC should remain negative at least up to 9 GPa. Furthermore, the linear coefficient of thermal expansion should decrease with pressure as = .

Interaction of second-mode instability and distributed roughness elements in the hypersonic boundary layer over a sharp cone

The ablation of the thermal protection system (TPS) on the aircraft surface generates distributed roughness elements (DRE), which is expected to affect the hypersonic boundary-layer instability seriously. This work presents the experimental investigation of hypersonic boundary-layer instability waves on a 7° half-angle sharp cone with DRE allocated downstream of synchronization point at 0° angle of attack using surface flush-mounted pressure sensors, focused laser differential interferometer (FLDI), infrared thermography and schlieren technique. The experimental results showed that when the DRE (lower than the local boundary-layer height) was located downstream of the synchronization point, the Mack second mode still dominate the boundary-layer instability, and the transition onset was not significantly affected by DRE at various Reynolds numbers. Based on further analysis in the region downstream of roughness, the DRE didn't influence the nonlinear interaction among instability waves materially, although it promoted the growth of instability waves compared with the smooth case. However, the nonlinear interactions were decaying adjacent to the DRE, as the Mack second-mode instability waves cannot penetrate into the separation bubble because of the flow separation induced by the DRE. The FLDI measurement along the wall-normal direction revealed the second-mode instability waves were suppressed close to the wall by the complex roughness surface at the DRE region, and also confirmed the existence of second-mode instability waves at these streamwise locations. The evolution of instability waves followed the linear stability theory (LST), despite the existence of complex wall surfaces. This work enriches the understanding of the effect of DRE on hypersonic boundary-layer transition and demonstrates the spatial characteristics of instability waves above the complex surface.

Computational vibration mitigation using phase interpolation in digital holographic microscopy for overlay metrology

Digital holographic microscopy retrieves amplitude and phase information of an image which allows us to computationally correct for imperfections in the imaging optics. However, digital holographic microscopy is an interferometric technique that is inherently sensitive to undesired phase variations between object and reference beam. These phase variations lower the fringe contrast if they are integrated over a finite exposure time which leads to a reduced amplitude of the retrieved image. This results in significant errors in applications that rely on a stable and accurate amplitude measurement, such as optical overlay metrology in the semiconductor industry. We present experimental results on a computational vibration mitigation method for the application of overlay metrology using phase interpolation between a sequence of measured holograms and demonstrate its capability to improve metrology precision in an overlay metrology application that uses digital holographic microscopy.

Single-shot picosecond interferometry for the characterization of laser-driven shock waves

In conventional laser-driven shock experiments, an out-of-plane shock wave is launched and is typically detected interferometrically after it propagates through the sample. In such experiments, the target materials are unavoidably optically damaged at each laser shot. This necessitates changing targets after laser exposure, lowering the shot-to-shot reproducibility and data quality. Here we present a Sagnac interferometer combined with an echelon that can split a single femtosecond probe into many beams, very well adapted for single-shot interferometric characterization of laser-induced shock waves. The echelon provides a 10 ps time resolution and a full time window of about 150 ps. The simplicity, stability, and sensitivity of the single-shot Sagnac interferometer technique ease the thorough characterization of picosecond to nanosecond shock waves, specifically for samples available in limited quantities or for samples that are not uniform from one region to the next.

Study of the $$\boldsymbol{\mu}$$ Cet Binary with Speckle Interferometric, Photometric, and Spectroscopic Techniques

Study of the $$\boldsymbol{\mu}$$ Cet Binary with Speckle Interferometric, Photometric, and Spectroscopic Techniques

Facile dual-shot measurement of Schmidt number in type-0 and type-2 downconversion

High-dimensional entangled states have now been identified as excellent candidates towards the enhancement of the bandwidth of quantum systems. A variety of methods exist that aim to certify and set the bounds to entanglement. However, rapid and accurate approaches for precise quantification of the dimensions remain a challenge. Here, we report a facile, rapid and robust approach that quantifies a wide range of the spatial dimensions of high-dimensional entangled states using an interferometric technique using only two images. Our process works for a class of pure two-photon states, regardless of its separability and provides a fast and easy way to accurately measure the spatial Schmidt number which is a quantitative measure of dimensionality of entanglement. We apply our method to two-photon states generated by spontaneous parametric down-conversion (SPDC) and show that our results are in excellent agreement with numerical estimates. Since such estimates only exist for collinear phase matching in SPDC crystals, we also derive a noncollinear phase-matching condition applicable for type-2 crystals. In these nonlinear crystals, the commonly applied assumption of degenerate daughter photons no longer holds, leading to deviations from earlier theoretical predictions. Our interferometric technique provides excellent results for both type-0 and type-2 collinear phase-matching conditions, endorsing its wide applicability in quantum photonics. Published by the American Physical Society 2024

Wimpled thin films via multiple motions of a bubble decorated with surface-active molecules

HypothesisThin liquid films play a crucial role in various systems and applications. Understanding the mechanisms that regulate their morphology is a scientific challenge with obvious implications for application optimization. Thin liquid films trapped between bubbles and air-liquid interface can show various configurations influenced by their deformation history and system characteristics. ExperimentsThe morphology of thin liquid films formed in the presence of surface-active molecules is here studied with interferometric techniques. Three different systems with varying interfacial properties are investigated to understand their influence on film morphology. Specific deformation histories are applied to the films to generate complex film structures. FindingsWe achieve the creation of a rather stable wimple by implementing controlled bubble motions against the air-liquid interface. We provide a criterion for wimple formation based on lubrication theory. The long-term stability of the wimple is also investigated, and more complex multi-wimple structures are experimentally produced building upon the achieved wimple stability.

The Detectability of Post-Seismic Ground Displacement Using DInSAR and SBAS in Longwall Coal Mining: A Case Study in the Upper Silesian Coal Basin, Poland

The Upper Silesian coal basin (USCB) in Poland faces significant ground deformation issues resulting from mining activities conducted without backfill, which can persist for years. These activities can cause damage to surface structures and phenomena such as induced seismicity. Ground deformations can be monitored using differential synthetic aperture radar interferometry (DInSAR). However, various DInSAR approaches have their own advantages and limitations, particularly regarding accuracy and atmospheric filtering. This is especially important for high-frequency displacement signals associated with seismic activity, which can be filtered out. Therefore, this study aims to assess the detectability of mining-induced seismic events using interferometric techniques, focusing on the USCB area. In this experiment, we tested two InSAR approaches: conventional DInSAR without atmospheric filtering and the small baseline subset (SBAS) approach, where the atmospheric phase screen was estimated and removed using high-pass and low-pass filtering. The results indicate that, in most cases, post-seismic ground displacement is not detectable using both methods. This suggests that mining-related seismic events typically do not cause significant post-seismic ground displacement. Out of the 17 selected seismic events, only two were clearly visible in the DInSAR estimated deformation, while for four other events, some displacement signals could neither be definitively confirmed nor negated. Conversely, only one seismic event was clearly detectable in the SBAS displacement time series, with no evidence of induced tremors found for the other events. DInSAR proved to be more effective in capturing displacement signals compared to SBAS. This could be attributed to the small magnitude of the tremors and, consequently, the small size of the seismic sources. Throughout the investigated period, all registered events had magnitudes less than 4.0. This highlights the challenge of identifying any significant influence of low-magnitude tremors on ground deformation, necessitating further investigations. Moreover, SBAS techniques tend to underestimate mining displacement rates, leading to smoothed deformation estimates, which may render post-seismic effects invisible for events with low magnitudes. However, after an in-depth analysis of the 17 seismic events in the USCB, DInSAR was found to be more effective in capturing displacement signals compared to SBAS. This indicates the need for significant caution when applying atmospheric filtering to high-frequency displacement signals.

Multi‐Frequency SuperDARN Interferometer Calibration

AbstractThe ground‐based, high‐frequency radars of the Super Dual Auroral Radar Network (SuperDARN) observe backscatter from ionospheric field‐aligned plasma irregularities and features on the Earth's surface out to ranges of several thousand kilometers via over‐the‐horizon propagation of transmitted radio waves. Interferometric techniques can be applied to the received signals at the primary and secondary antenna arrays to measure the vertical angle of arrival, or elevation angle, for more accurate geolocation of SuperDARN observations. However, the calibration of SuperDARN interferometer measurements remains challenging for several reasons, including a 2π phase ambiguity when solving for the time delay correction factor needed to account for differences in the electrical path lengths between signals received at the two antenna arrays. We present a new technique using multi‐frequency ionospheric and ground backscatter observations for the calibration of SuperDARN interferometer data, and demonstrate its application to both historical and recent data.

Dispersion mismatch correction for evident chromatic anomaly in low coherence interferometry.

The applications of ultrafast optics to biomedical microscopy have expanded rapidly in recent years, including interferometric techniques like optical coherence tomography and microscopy (OCT/OCM). The advances of ultra-high resolution OCT and the inclusion of OCT/OCM in multimodal systems combined with multiphoton microscopy have marked a transition from using pseudo-continuous broadband sources, such as superluminescent diodes, to ultrafast supercontinuum optical sources. We report anomalies in the dispersion profiles of low-coherence ultrafast pulses through long and non-identical arms of a Michelson interferometer that are well beyond group delay or third-order dispersions. This chromatic anomaly worsens the observed axial resolution and causes fringe artifacts in the reconstructed tomograms in OCT/OCM using traditional algorithms. We present DISpersion COmpensation Techniques for Evident Chromatic Anomalies (DISCOTECA) as a universal solution to address the problem of chromatic dispersion mismatch in interferometry, especially with ultrafast sources. First, we demonstrate the origin of these artifacts through the self-phase modulation of ultrafast pulses due to focusing elements in the beam path. Next, we present three solution paradigms for DISCOTECA: optical, optoelectronic, and computational, along with quantitative comparisons to traditional methods to highlight the improvements to the dynamic range and axial profile. We explain the piecewise reconstruction of the phase mismatch between the arms of the spectral-domain interferometer using a modified short-term Fourier transform algorithm inspired by spectroscopic OCT. Finally, we present a decision-making guide for evaluating the utility of DISCOTECA in interferometry and for the artifact-free reconstruction of OCT images using an ultrafast supercontinuum source for biomedical applications.

Probing recombinant AAV capsid integrity and genome release after thermal stress by mass photometry

Adeno-associated viruses (AAVs) are gaining traction as delivery vehicles for gene therapy although the molecular understanding of AAV-transgene release is still limited. Typically, the process of viral uncoating is investigated (in vitro) through thermal stress, revealing capsid disintegration at elevated temperatures. To assess the (in)stability of different empty and filled AAV preparations, we used the light-scattering-based interferometric microscopy technique of mass photometry (MP) that, on a single-particle basis, determines the molecular weight of AAVs. By introducing a heat-stable DNA plasmid as an internal standard, we quantitatively probed the impact of heat on AAVs. Generally, empty AAVs exhibited greater heat resistance than genome-filled particles. Our data also indicate that upon DNA release, the capsids do not transform into empty AAVs, but seem to aggregate or disintegrate. Strikingly, some AAVs exhibited an intermediate state with disrupted capsids but preserved bound genome, a feature that experimentally only emerged following incubation with a nuclease. Our data demonstrate that the thermal uncoating process is highly AAV specific (i.e., can be influenced by serotype, genome, host system). We argue that nuclease treatment in combination with MP can be used as an additional analytical tool for assessing structural integrity of recombinant and/or clinical AAV vectors.

Multicolor phase-correlation interferometer for shock wave refractive index measurements.

Refractive index measurements are critical for characterizing the properties of hypersonic flows, but moderate- to high-pressure experiments require alternative methods to traditional interferometric fringe counting. In this work, we introduce a novel, to the best of our knowledge, multi-wavelength phase-correlation interferometric technique to estimate the refractive index changes across nearly discrete shock wave boundaries and also simultaneously capture optical dispersion and vibrational relaxation times. By comparing the interference pattern of three or more wavelengths against each other, the refractive index can be accurately determined. To demonstrate this technique, laser diodes in two wavelength combinations are tested producing refractive index resolutions on the order of 2.65 × 10-7. Results in air across a range of initial pressure conditions (P1 = 2.66 to 5.33 kPa) and incident wave speeds (Mach 2 to 5) show density changes that agree with theoretical estimates within 2%. Single-shot dispersion and vibrational relaxation measurements with this method also illustrate good agreement with other techniques.

Linewidth measurement of external cavity lasers

Narrowband laser sources are used in applications that require high-precision or stable optical frequency. Such applications include high-resolution spectroscopy, long-distance measurement, and coherent optical communication. The linewidth of a laser is a direct measure of the laser's stability; therefore, characterization of laser linewidth is essential. In practice, however, determining a laser's linewidth is not a trivial task and typically requires expensive equipment or a complex experimental arrangement. This paper presents a straightforward, low-cost method based on unbalanced interferometry, which allows us to determine the visibility of fringe patterns as a function of the optical path difference and, consequently, the linewidth of the laser. As a test laser, we use a tunable external cavity laser source at around 780 nm, where an interference filter is employed for wavelength selection. Data obtained by applying the interferometric technique to this laser and the analysis of these data, along with the resulting linewidth value, are presented. Given that the described measurement setup is inexpensive, straightforward, and pedagogically accessible, it is well-suited for an instructional physics laboratory experiment and will also be of interest to laboratory researchers.