Interferometry Measurements Research Articles

Repeatability of tear film lipid layer interferometry measurements: A randomized, crossover study.

This study aimed to assess intrasession repeatability, diurnal intravisit and day-to-day intervisit reproducibility of qualitative tear film lipid layer interferometry grading obtained from the Keratograph 5M (Oculus Optikgeräte GmbH, Wetzlar, Germany), and automated quantitative layer thickness measurements obtained from the TearScience LipiView II Ocular Surface Interferometer (Johnson & Johnson Vision, Milpitas, CA), in community residents, not stratified by dry eye or blepharitis status. Forty community residents (24 women, 16 men; age mean ± standard deviation, 36 ± 14 years) were recruited in an investigator-masked, randomized, crossover study. Participants attended two sessions 6 hours apart on the same day and a third session on a separate day. During each session, tear film lipid layer grading and thickness measurements were performed in triplicate, in a masked manner, with 10-minute intervals between each measurement. There were no significant differences in lipid layer grading and thickness measurements in all pairwise intrasession, diurnal intravisit, and day-to-day intervisit comparisons (all p≥0.19), and positive correlations were observed in all cases (all p<0.001). The weighted Cohen κ coefficients for intrasession repeatability and diurnal intravisit and day-to-day intervisit reproducibility of qualitative lipid layer grading ranged from 0.670 to 0.867. The test-retest repeatability of quantitative lipid layer thickness measurements ranged from 4.5 to 11.7 nm, and the Bland-Altman biases were within the order of 3 nm in all pairwise comparisons. The intraclass correlation coefficients for lipid layer thickness measurements exceeded 0.80 for all intrasession comparisons and were between 0.60 and 0.80 for all diurnal intravisit and day-to-day intervisit comparisons. Both qualitative grading and automated quantitative thickness measurements of tear film lipid layer interferometry demonstrated relatively favorable levels of intrasession repeatability and diurnal intravisit and day-to-day intervisit reproducibility. The study findings would support the use of either qualitative or quantitative measurement in clinical and research settings, as a reliable tool for assessing lipid layer interferometry.

Finding and minimizing systematic errors in dual-comb spectroscopy

Abstract With sufficiently high signal-to-noise, several systematic errors become prominent in dual-comb interferometry measurements. This paper reviews several error sources including electrical, photo-detection, amplification and acquisition chain non-linearity. Sources of optical non-linearity such as self-phase modulation, cross-phase modulation and Raman soliton shifting are also covered, as are spectral fringing due to parasitic reflections and back-scattering. The non- linear response of the target sample itself can also be a source of errors. Methods to identify and minimize errors in experimental data are discussed. Good practices, instrument design strategies and tools, such as the dynamic range diagram, are suggested.

Simultaneous two colour intensity interferometry with H.E.S.S.

Abstract In recent years, intensity interferometry has been successfully applied to the Imaging Atmospheric Cherenkov Telescopes H.E.S.S. , MAGIC, and VERITAS. All three telescope systems have proven the feasibility and capability of this method. After our first campaign in 2022, when two of the H.E.S.S. telescopes in Namibia were equipped with our external setup and the angular diameter of two stars was measured, our setup was upgraded for a second campaign in 2023, where the goal is to perform simultaneous two colour measurements. The second campaign not only involves a third equipped telescope, but also each mechanical setup now includes two interference filters at two different wavelengths (375 nm and 470 nm) with a broader bandwidth of 10 nm. This enables having simultaneous two-colour measurements, which yields information about the star’s physical size at different wavelengths. This is the first time that simultaneous dual-waveband intensity interferometry measurements are performed. The angular diameter results of the 4 stars, Mimosa (β Cru), Eta Centauri (η Cen), Nunki (σ Sgr) and Dschubba (δ Sco), are reported, where the effects of limb darkening are also taken into account.

Transition of the thermal boundary layer and plume over an isothermal section-triangular roof: an experimental study

The development of thermal boundary layers and plume near a section-triangular roof under different isothermal heating conditions has been the focus of numerous numerical studies. However, flow transition in this type of flow has never been observed experimentally. Here, phase-shifting interferometry and thermistor measurements are employed to experimentally observe and quantify the flow transitions in a buoyancy-driven flow over an isothermal section-triangular roof. Visualisation of temperature contours is conducted across a wide range of Rayleigh numbers from laminar at 103 to chaotic state at 4 × 106. Power spectral density of the temperature measurements reveals the type of bifurcations developing as the Rayleigh number is increased. This flow transition is characterised as a complex bifurcation route with the presence of two fundamental frequencies, a low and a high frequency. We found that the thermal stratification in the environment plays a significant role in the flow transition. The spatial development of flow is also quantitatively and qualitatively described. In addition to clarifying flow transition in experiments, the work demonstrates the implementation of phase-shifting interferometry and punctual temperature measurements for characterisation of near-field flow over a heated surface.

Characterization of optical depth for laser produced plasma extreme ultraviolet source

This study investigates the emission mechanism of laser-produced plasma extreme ultraviolet source (LPP-EUV). In the experiment, the EUV radiation is generated by a 1064 nm laser interacting with slab Sn target. The EUV emission is characterized by EUV energy monitors and an EUV spectrometer. The dependency of CE on laser intensity and plasma relative optical depth is explored by a plasma emission-absorption layer model. The dependency is confirmed by an optical interferometry measurement of plasma electron density for the first time. Our work provides a method for characterizing and optimizing the optical depth of laser driven EUV source.

Physical mechanisms of femtosecond laser induced refractive index change in direct-written mid-infrared fiber Bragg gratings

Femtosecond laser inscription of fluoride Fiber Bragg Gratings (FBGs) has enabled the realization of all-fiber laser sources at mid-infrared wavelengths. However, many fundamental aspects of the fabrication process remain unknown, which hinders further development. In this paper, we for the first time reveal the physical mechanisms that underpin the laser-induced permanent refractive index change in the periodic grating elements that constitute an FBG. Quadriwave lateral shearing interferometry and micro-reflectivity measurements are introduced as techniques for the full characterization of the refractive index change profile of the grating structure. The fundamental processes that eventually result in a permanent index change were found to differ significantly between the chemically closely related fluoroindate and fluorozirconate glass families. In fluoroindate fibers, the index change can almost entirely be attributed to elemental migration, whereas in fluorozirconate fibers the involved processes are more intricate and include the selective migration of fluorine ions as well as the formation of F-centers, more specifically unpaired electrons trapped in anion vacancies. In addition, in fluorozirconate fibers, the formation of dynamic stress regions in-between the grating planes was observed, more specifically a build-up of higher stress in areas adjacent to positive index-change regions and of lower stress in areas adjacent to negative index-change regions, which for the first time explains the unusual annealing behavior of mid-IR FBGs.

Clock noise evaluation of space-based gravitational wave detectors based on time-delay interferometry

The heterodyne measurements are adopted in space-based gravitational wave detectors to detect gravitational wave signals in the millihertz range. Due to the difficulty in maintaining the equal distance between these spacecrafts in the detector, laser phase noise is a main noise in the detection process, so time-delay interferometry combination is adopted to eliminate this noise by synthesizing virtual equal arm interferometry. However, when conducting heterodyne laser interferometry measurements in space-based gravitational wave detection, clock noise is also introduced into the measurement, but the analytical results of clock noise have been ignored in previous studies. Based on time-delay interferometry combination, we analyze the impact of clock noise and provide analytical results of the total noise in various data combinations. Through this result, we evaluate the required clock accuracy of 10−16 for the gravitational wave detector when clock noise is not reduction, so the analytical result can more intuitively reflect how the clock noise effects the sensitivity of the detector.

Molecular Analysis of Changes in DNA Binding Affinity and Bending Extent Induced by the Mutations on the Aromatic Amino Residues in Cren7.

Proteins from Crenarchaeal organisms exhibit remarkable thermal stability. The aromatic amino acids in Cren7, a Crenarchaeal protein, regulate protein stability and further modulate DNA binding and its compaction. Specific aromatic amino acids were mutated, and using spectroscopic and theoretical approaches, we have examined the effect of the mutation on the structure, DNA binding affinity, and DNA bending ability of Cren7. The mutants were compared to the structure and function of wild-type (WT) Cren7. The reverse titration profiles were analysed by a noncooperative McGhee-von Hippel model to estimate affinity constant (Ka) and binding site size (n) associated with binding to the DNA. The biolayer interferometry (BLI) measurements showed that the binding affinity decreased at higher salt concentrations. For theoretical analysis of the extent of DNA bending, radius of gyration and bending angle were compared for WT and mutants. The time evolution of order parameters based on the translational and rotational motion of tryptophan residue (W26) was used for the qualitative detection of stacking interactions between W26 of Cren7 and DNA nucleobases. It was observed that the orientation of W26 in F41A favored the formation of a new lone pair-lone pair interaction between DNA and Cren7. Consequently, in thermostable proteins, the aromatic residues at the terminus maintain structural stability, whereas the residues at the core optimize the degree of DNA bending and compaction.

The performance of Tiangong-2 InIRA in gravity anomaly recovery from fused conventional nadir-observing altimeter data

Satellite altimetry has emerged as the primary data source for deriving marine gravity, owing to advancements in satellite altimetry technologies. The Tiangong-2 interferometric imaging radar altimeter (TG2 InIRA) is a new generation wide-swath altimeter (WSA) launched by China on 15 September 2016. TG2 InIRA employs a short-baseline interferometry measurement method at a small incidence angle, thereby enabling the precise measurement of wide-swath sea surface heights (SSHs). The present study demonstrates the efficacy of utilizing data from the TG2 InIRA in conjunction with data from the CryoSat-2 (CS2) satellite to recover marine gravity anomalies. In the Northwest Pacific region (15°N ∼ 25°N, 140°E ∼ 150°E), the TG2 InIRA data were filtered to a 2 km × 2 km grid and any anomalous values were excluded using a mean sea surface model. Deflections of the vertical (DOVs) were calculated using the remove-restore technique, and the inverse Vening-Meinesz formula was applied to invert the gravity anomaly. A power spectral density analysis was conducted to assess variations in gravity anomalies at ship locations in the frequency domain. The results, based on the SIO V31.1 (DOV) model, indicate that the gridded vertical deflections derived from CS2 and TG2 InIRA data achieve more balanced accuracy in the east–west and north–south directions. The integration of TG2 InIRA and CS2 data yielded gravity results exhibiting a root mean square (RMS) of 0.519 mGal lower than those derived from TG2 InIRA data alone, and 0.034 mGal lower than those derived from CS2 data. These findings were derived from shipborne gravity data. Furthermore, the inversion of gravity anomalies from TG2 InIRA demonstrated an enhanced capability in the reduction of high-frequency gravity noise.

Ground-based radar interferometry measures strain in sea ice

Ground-based radar interferometry measures strain in sea ice

Improved Res-UNet Network for Phase Unwrapping of Interferometric Gear Tooth Flank Measurements

This article introduces an improved deep learning network, GRU-Net, designed to facilitate direct and precise phase unwrapping of wrapped phase measurements in gear tooth surface interferometry. GRU-Net incorporates a Gram matrix within each down-sampling process to compute style loss, thereby capturing essential stripe structure information features. This network exhibits enhanced capability in handling larger and more intricate gear tooth interferograms, particularly in scenarios involving pronounced noise and aliasing, while still yielding favorable outcomes. A comparative evaluation was conducted, contrasting GRU-Net with the Res-UNet network and other conventional methods. The results demonstrate that GRU-Net surpasses the alternative approaches in terms of unwrapping accuracy, noise resilience, and anti-aliasing capabilities, with accuracy improved by at least 24%, exhibiting significantly superior performance. Additionally, in contrast to the Res-UNet network, GRU-Net demonstrates accelerated learning speed and generates more compact models.

The Suppression Effect of an Imaging System on the Geometric Tilt-to-Length Coupling in a Test Mass Interferometer

Tilt-to-length (TTL) coupling noise arises from angular misalignments of interfering beams in optical path length (OPL) measurements and significantly impacts the accuracy of interferometry measurement systems. This paper focuses on geometric TTL coupling in a test mass (TM) interferometer and examines how an imaging system influences TTL noise suppression. First, the analytical expression of the geometric TTL coupling in a TM interferometer with alignment errors is derived and confirmed through numerical simulation. Subsequently, an imaging system is incorporated into the geometric model and the corresponding analytical expressions are obtained under two common conjugate relationships. Nevertheless, the TTL coupling remains beyond the requirement of TM interferometer, as the residual TTL coupled with alignment errors persists even with the imaging system. Therefore, an optimal position of the imaging system capable of eliminating the second-order term of the TTL coupling is determined. Meanwhile, the first-order term can be mitigated through in-orbit calibrations. These findings offer valuable guidance for the design and adjustment of imaging systems in space-borne gravitational wave detection missions, which require high-precision laser interferometry.

Axial confinement of wire array Z-pinch precursor plasmas by a pulsed magnetic mirror field

A novel wire-array Z-pinch platform has been developed to study the effect of a pulsed magnetic mirror field on a collisional high energy density plasma. The mirror is driven in series with the Z-pinch target and, therefore, scales with driver current. Axial confinement is observed based on visible imaging and axial flow velocity measurements. The presence of axial compressing J ×B force is determined indirectly based on Thomson scattering and interferometry measurements and corroborated by three-dimensional extended-MHD simulations. Compared to non-magnetized wire array Z-pinch, a modified pulsed mirror configuration is observed to increase precursor plasma thermal energy density by about 30%. If optimized, such a configuration could potentially improve magnetized liner inertial fusion performance by reducing axial plasma end loss.

Distance Estimate Method for Asymptotic Giant Branch Stars Using Infrared Spectral Energy Distributions

We present a method to estimate distances to asymptotic giant branch (AGB) stars in the Galaxy, using spectral energy distributions (SEDs) in the near- and mid-infrared. By assuming that a given set of source properties (initial mass, stellar temperature, composition, and evolutionary stage) will provide a typical SED shape and brightness, sources are color matched to a distance-calibrated template and thereafter scaled to extract the distance. The method is tested by comparing the distances obtained to those estimated from very long baseline interferometry or Gaia parallax measurements, yielding a strong correlation in both cases. Additional templates are formed by constructing a source sample likely to be close to the Galactic center, and thus with a common, typical distance for calibration of the templates. These first results provide statistical distance estimates to a set of almost 15,000 Milky Way AGB stars belonging to the Bulge Asymmetries and Dynamical Evolution (BAaDE) survey, with typical distance errors of ±35%. With these statistical distances, a map of the intermediate-age population of stars traced by AGBs is formed, and a clear bar structure can be discerned, consistent with the previously reported inclination angle of 30° to the GC–Sun direction vector. These results motivate deeper studies of the AGB population to tease out the intermediate-age stellar distribution throughout the Galaxy, as well as determining statistical properties of the AGB population luminosity and mass-loss-rate distributions.

Detecting white interference fringes in noisy conditions via supervised learning neural networks

White interferograms are signals recorded using the interference of light with positional information obtained using a white interferometer, which is a laser technology that uses light interference for the non-contact measurement of the surface topography of a sample. In long-range measurements, the reflected light weakens with increasing distance. When the peak-to-peak value of interference fringe signals is less than the noise level interference fringes cannot be visually confirmed. We propose a neural network-based supervised learning method to detect white interference fringes in noisy conditions. The interference fringes obtained were transformed into time series signals and stored as images. Some of the data was used to train the neural network. Some data was used to validate the trained neural network. The trained model could distinguish between the presence and absence of white interference fringes in noise-contaminated conditions with a certain probability. Numerical calculations and optical experiments validated the proposed method. This technique can be applied to detect weak reflections and extend the interferometry measurement range.

Design and Analysis of Orthogonal Polarization Point Diffraction Pinhole Plate

The pinhole plate is a key component of the point diffraction interferometer (PDI). The reasonable improvement and simulation of this device would enhance the application of point diffraction interferometry technology during the measurement of wavefronts. The traditional point diffraction interferometry measurement method is easily disturbed by environmental noise, making it difficult to obtain high-precision dynamic measurements. This paper introduces a four-step phase-shift PDI that can be employed in a common optical path. By using the principle of the finite-difference time-domain method (FDTD), a simulation model of the orthogonal polarization point diffraction pinhole plate (OP-PDPP) structure is established. The results show that when Cr is used as the film material in the pinhole plate, the parameters include a film thickness of 150 nm, a pinhole diameter of 2 μm, a wire grid period of 150 nm, and a wire grid width of 100 nm; in addition, the comprehensive extinction ratio of the pinhole plate is the greatest and the diffraction wavefront error is the smallest. Finally, the constructed experimental system is used to test the wavefront of a flat sample with a 25.4 mm aperture, and the test results are compared with those of the ZYGO interferometer. The difference in the peak-to-valley (PV) value between the OP-PDI and the ZYGO interferometer measurement is 0.0028λ, with an RMS value difference of 0.0011λ; this verifies the feasibility of the scheme proposed in this paper. The experimental results show that the proposed OP-PDPP is an effective tool for high-precision dynamic measurement.

Sound velocities in lunar mantle aggregates at simultaneous high pressures and temperatures: Implications for the presence of garnet in the deep lunar interior

Recent experimental and theoretical studies on lunar magma ocean crystallisation have suggested the presence of significant proportions of garnet in the deep lunar interior. While phase relation studies indicate a deep lunar mantle consisting of olivine, pyroxene, and garnet, the compatibility of such an assemblage with seismic models of the lunar interior is yet untested. In this study we report compressional and shear wave velocities in an iron-rich assemblage consisting of olivine, orthopyroxene, clinopyroxene, and garnet up to ∼8 GPa and 1300 K, by means of ultrasonic interferometry measurements combined with synchrotron techniques using the multi-anvil press apparatus. Sound velocity and density models of lunar mantle rocks along a selenotherm based on our experimental results find good agreement with the seismic and density profiles at lunar interior depths of 740–1260 km. Further models are constructed, allowing for the variation of chemical composition, phase proportion, and temperature; these suggest that a garnet-rich deep lunar mantle is compatible with present-day lower lunar mantle temperatures of between 1400–1800 K. Our results show that lunar mantle rocks with up to 33 wt.% garnet may provide an explanation for the observed high velocities of the lower lunar mantle. The presence of garnet in the lowermost part of the Moon's mantle has significant implications for the depth and temperature of the Moon's magma ocean as well as the composition, structure and internal dynamics of the solid Moon.

Interaction Studies of Hexameric and Pentameric IgMs with Serum-Derived C1q and Recombinant C1q Mimetics.

The interaction between IgM and C1q represents the first step of the classical pathway of the complement system in higher vertebrates. To identify the significance of particular IgM/C1q interactions, recombinant IgMs were used in both hexameric and pentameric configurations and with two different specificities, along with C1q derived from human serum (sC1q) and two recombinant single-chain variants of the trimeric globular region of C1q. Interaction and complement activation assays were performed using the ELISA format, and bio-layer interferometry measurements to study kinetic behavior. The differences between hexameric and pentameric IgM conformations were only slightly visible in the interaction assay, but significant in the complement activation assay. Hexameric IgM requires a lower concentration of sC1q to activate the complement compared to pentameric IgM, leading to an increased release of C4 compared to pentameric IgM. The recombinant C1q mimetics competed with sC1q in interaction assays and were able to inhibit complement activation. The bio-layer interferometry measurements revealed KD values in the nanomolar range for the IgM/C1q interaction, while the C1q mimetics exhibited rapid on and off binding rates with the IgMs. Our results make C1q mimetics valuable tools for developing recombinant C1q, specifically its variants, for further scientific studies and clinical applications.

Liquefaction ground deformations and cascading coastal flood hazard in the 2023 Kahramanmaraş earthquake sequence

The 2023 Kahramanmaraş earthquake sequence produced extensive liquefaction-induced ground deformations and ongoing flooding along the shoreline of the Mediterranean port city of İskenderun, Türkiye. This study compiles field observations and analyses from cross-disciplinary perspectives to investigate whether earthquake-induced liquefaction was a significant factor for increasing the flood hazard in İskenderun. Geotechnical reconnaissance observations following the earthquakes included seaward lateral spreading, settlement beneath buildings, and failures of coastal infrastructure. Three presented lateral spreading case histories indicate consistent ground deformation patterns with areas of reclaimed land. Persistent scatterer interferometry (PSI) measurements from synthetic aperture radar (SAR) imagery identify a noticeably greater rate of pre- and post-earthquake subsidence within the İskenderun coastal and urban areas relative to the surrounding regions. The PSI measurements also indicate subsidence rates accelerated following the earthquakes and were typically highest near the observed liquefaction manifestations. These evaluations suggest that while the liquefaction of coastal reclaimed fill caused significant ground deformations in the shoreline area, ongoing subsidence of İskenderun and other factors likely also exacerbated the flood hazard. Insights from this work suggest the importance of evaluating multi-hazard liquefaction and flood consequences for enhancing the resilience of coastal cities.

Frequency-modulated continuous-wave laser interferometry measurement method based on cross-correlation

Frequency-modulated continuous-wave (FMCW) laser interferometry technology holds significant potential for applications in the fields of ultraprecision manufacturing and high-precision sensing. This paper proposes a novel approach among current phase demodulation methods is based on cross-correlation to address the challenge of this technology. On the basis of nonlinear correction of a distributed feedback laser, the intercepted beat frequency signal was first preprocessed with Z-score signal normalization and a smoothing filter. Subsequently, the interference beat signal was subjected to processing using a correlation method to derive the correlation function. Finally, the phase difference between adjacent beat signals was determined by pinpointing the maximum value of the cross-correlation function, enabling accurate displacement demodulation. Experimental validation was performed by constructing an FMCW laser interferometric displacement measurement system. The results indicated that the standard deviation of the displacement error for the cross-correlation method was 2.41 nm during static measurements. Compared to conventional maximum-point method, the static measurement error of the cross-correlation method has been reduced by 1.43 times. In dynamic measurements in the 500 μm range, The measurement error of the cross-correlation method has been reduced by 6.04 times, avoiding the dynamic measurement positioning problem of conventional feature point demodulation methods and making the measurement results more accurate. This advancement holds substantial practical value in the realm of phase demodulation in laser interferometry.