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Wu, Wan Duo, Qiang Xian Huang, Chao Qun Wang, Ting Ting Wu i Hong Xie. "The Analysis and Design of a Large Stroke with High-Precision Polarized Laser Interferometer System". Key Engineering Materials 679 (luty 2016): 129–34. http://dx.doi.org/10.4028/www.scientific.net/kem.679.129.
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The technique utilizing single-frequency laser interferometry has very high measurement accuracy, but it has rigorous requirements for optical design which is affected by many factors. In order to achieve single-frequency laser interferometry with large stroke and high precision, the integral layout, the polarization phase shifting technique and the common mode rejection method are adopted to design the length interferometry system. This paper analyzes factors and design requirements which affect measurement accuracy with large stroke. Based on polarization phase shifting technique, the system employs the four-beam-signal detection technique and the common mode rejection method, to make a differential processing of four mutually orthogonal signals. Thus, the influences of zero-drift of intensity and environmental change on system are reduced. Combined with a 200 phase subdivision, the system achieves the resolution with 0.8 nm. Under the VC++ environment, the displacement measurement results are compensated and corrected according to the environmental parameters. Compared with the Renishaw XL-80 laser interferometer, the system has better stability in short term. In the measuring range of 60 mm, the effectiveness of the system is verified.
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Liu, Tiegen, Junfeng Shi, Junfeng Jiang, Kun Liu, Shuang Wang, Jinde Yin i Shengliang Zou. "Nonperpendicular Incidence Induced Spatial Frequency Drift in Polarized Low-Coherence Interferometry and Its Compensation". IEEE Photonics Journal 7, nr 6 (grudzień 2015): 1–7. http://dx.doi.org/10.1109/jphot.2015.2494505.
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Qian, Yibin, Jiakun Li, Qibo Feng, Qixin He i Fei Long. "Error Analysis of Heterodyne Interferometry Based on One Single-Mode Polarization-Maintaining Fiber". Sensors 23, nr 8 (19.04.2023): 4108. http://dx.doi.org/10.3390/s23084108.
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Using polarization-maintaining fiber (PMF) in dual-frequency heterodyne interferometry has the advantages of reducing the laser’s own drift, obtaining high-quality light spots, and improving thermal stability. Using only one single-mode PMF to achieve the transmission of dual-frequency orthogonal, linearly polarized beam requires angular alignment only once to realize the transmission of dual-frequency orthogonal, linearly polarized light, avoiding coupling inconsistency errors, so that it has the advantages of high efficiency and low cost. However, there are still many nonlinear influencing factors in this method, such as the ellipticity and non-orthogonality of the dual-frequency laser, the angular misalignment error of the PMF, and the influence of temperature on the output beam of the PMF. This paper uses the Jones matrix to innovatively construct an error analysis model for the heterodyne interferometry using one single-mode PMF, to realize the quantitative analysis of various nonlinear error influencing factors, and clarify that the main error source is the angular misalignment error of the PMF. For the first time, the simulation provides a goal for the optimization of the alignment scheme of the PMF and the improvement of the accuracy to the sub-nanometer level. In actual measurement, the angular misalignment error of the PMF needs to be smaller than 2.87° to achieve sub-nanometer interference accuracy, and smaller than 0.25° to make the influence smaller than ten picometers. It provides theoretical guidance and an effective means for improving the design of heterodyne interferometry instruments based on PMF and further reducing measurement errors.
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Kakuma, Seiichi, i Yasuhiko Katase. "Frequency scanning interferometry immune to length drift using a pair of vertical-cavity surface-emitting laser diodes". Optical Review 19, nr 6 (listopad 2012): 376–80. http://dx.doi.org/10.1007/s10043-012-0061-3.
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Zhang, Jinge, Hamish A. S. Reid, Eoin Carley, Laurent Lamy, Pietro Zucca, Peijin Zhang i Baptiste Cecconi. "Imaging a Large Coronal Loop Using Type U Solar Radio Burst Interferometry". Astrophysical Journal 965, nr 2 (1.04.2024): 107. http://dx.doi.org/10.3847/1538-4357/ad26fd.
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Abstract Solar radio U-bursts are generated by electron beams traveling along closed magnetic loops in the solar corona. Low-frequency (<100 MHz) U-bursts serve as powerful diagnostic tools for studying large-sized coronal loops that extend into the middle corona. However, the positive frequency drift component (descending leg) of U-bursts has received less attention in previous studies, as the descending radio flux is weak. In this study, we utilized LOFAR interferometric solar imaging data from a U-burst that has a significant descending leg component, observed between 10 and 90 MHz on 2020 June 5th. By analyzing the radio source centroid positions, we determined the beam velocities and physical parameters of a large coronal magnetic loop that reached just about 1.3 R ⊙ in altitude. At this altitude, we found the plasma temperature to be around 1.1 MK, the plasma pressure around 0.20 mdyn, cm−2, and the minimum magnetic field strength around 0.07 G. The similarity in physical properties determined from the image suggests a symmetric loop. The average electron beam velocity on the ascending leg was found to be 0.21c, while it was 0.14c on the descending leg. This apparent deceleration is attributed to a decrease in the range of electron energies that resonate with Langmuir waves, likely due to the positive background plasma density gradient along the downward loop leg.
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Monselesan, D. P., R. J. Morris, P. L. Dyson i M. R. Hyde. "Southern high-latitude Digisonde observations of ionosphere E-region Bragg scatter during intense lacuna conditions". Annales Geophysicae 22, nr 8 (7.09.2004): 2819–35. http://dx.doi.org/10.5194/angeo-22-2819-2004.
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Abstract. During summer months at solar cycle minimum, F-region lacuna and slant-Es conditions (SEC) are common features of daytime ionograms recorded around local magnetic noon at Casey, Antarctica. Digisonde measurements of drift velocity height profiles show that the occurrence of lacuna prevents the determination of F-region drift velocities and also affects E-region drift velocity measurements. Unique E-region spectral features revealed as intervals of Bragg scatter superimposed on typical background E-region reflection were observed in Digisonde Doppler spectra during intense lacuna conditions. Daytime E-region Doppler spectra recorded at carrier frequencies from 1.5 to 2.7MHz, below the E-region critical frequency foE, have two side-peaks corresponding to Bragg scatter at approximately ±1-2Hz symmetrically located on each side of a central-peak corresponding to near-zenith total reflections. Angle-of-arrival information and ray-tracing simulations show that echo returns are coming from oblique directions most likely resulting from direct backscatter from just below the total reflection height for each sounding frequency. The Bragg backscatter events are shown to manifest during polar lacuna conditions, and to affect the determination of E-region background drift velocities, and as such must be considered when using standard Doppler-sorted interferometry (DSI) techniques to estimate ionospheric drift velocities. Given the Doppler and spatial separation of the echoes determined from high-resolution Doppler measurements, we are able to estimate the Bragg scatter phase velocity independently from the bulk E-region motion. The phase velocity coincides with the ExB direction derived from in situ fluxgate magnetometer records. When ionospheric refraction is considered, the phase velocity amplitudes deduced from DSI are comparable to the ion-acoustic speed expected in the E-region. We briefly consider the plausibility that these previously unreported polar cap E-region Bragg scatter Doppler spectral signatures, observed at Casey in December 1996 during SEC/lacuna conditions may be linked to ionosphere irregularities. These irregularities may possibly be generated by primary plasma waves triggered by current-driven instabilities, that is to say, a hybrid of the "modified two-stream" and "gradient drift" instability mechanisms.
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Denbina, Michael, Marc Simard, Ernesto Rodriguez, Xiaoqing Wu, Albert Chen i Tamlin Pavelsky. "Mapping Water Surface Elevation and Slope in the Mississippi River Delta Using the AirSWOT Ka-Band Interferometric Synthetic Aperture Radar". Remote Sensing 11, nr 23 (21.11.2019): 2739. http://dx.doi.org/10.3390/rs11232739.
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AirSWOT is an airborne Ka-band synthetic aperture radar, capable of mapping water surface elevation (WSE) and water surface slope (WSS) using single-pass interferometry. AirSWOT was designed as a calibration and validation instrument for the forthcoming Surface Water and Ocean Topography (SWOT) mission, an international spaceborne synthetic aperture radar mission planned for launch in 2022 which will enable global mapping of WSE and WSS. As an airborne instrument, capable of quickly repeating overflights, AirSWOT enables measurement of high frequency and fine scale hydrological processes encountered in coastal regions. In this paper, we use data collected by AirSWOT in the Mississippi River Delta and surrounding wetlands of coastal Louisiana, USA, to investigate the capabilities of Ka-band interferometry for mapping WSE and WSS in coastal marsh environments. We introduce a data-driven method to estimate the time-varying interferometric phase drift resulting from radar hardware response to environmental conditions. A system of linear equations based on AirSWOT measurements is solved for elevation bias and time-varying phase calibration parameters using weighted least squares. We observed AirSWOT WSE uncertainty of 12 cm RMS compared to in situ water level measurements when averaged over an area of 0.5 km 2 at incidence angles below 15 ∘ . At higher incidence angles, the observed AirSWOT elevation bias is possibly due to residual phase calibration errors or radar backscatter from vegetation. Elevation profiles along the Wax Lake Outlet river channel indicate AirSWOT can measure WSS over a 24 km distance with uncertainty below 0.3 cm/km, 8% of the true water surface slope as measured by in situ data. The data analysis and results presented in this paper demonstrate the potential of AirSWOT to measure water surface elevation and slope within highly dynamic and spatially complex coastal environments.
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Liu, Sixun, Zhuo Wang i Yueyang Zhai. "In-Situ Detection for Atomic Density in the K-Rb-21Ne Co-Magnetometer via an Optical Heterodyne Interferometry". Photonics 10, nr 10 (28.09.2023): 1091. http://dx.doi.org/10.3390/photonics10101091.
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The low-frequency fluctuations of the atomic density within the cell can induce the longterm drift of the K-Rb-21Ne spin-exchange relaxation-free (SERF) co-magnetometer output, such that the accurate measurement of in situ atomic density is of great significance for improving the performance of co-magnetometer. In this paper, the complex refractive index model of the spin ensembles under the hybrid optical pumping condition is established first, according to which the relation between atomic density and its complex refractive index is revealed and an optical heterodyne-based scheme for atomic density detection is proposed. The dependence of the atomic density on the demodulated phase signal from the optical heterodyne-based scheme is provided by numerical simulations. After that, a dual acousto-optics frequency shifter (AOFS)-based optical heterodyne interferometry is constructed with a noise level below 1 mrad/Hz for frequencies > 1 Hz, and a compact SERF co-magnetometer is implemented as the testing medium, by which the atomic density detection with resolution of 0.40 K @ 473 K is reached and the experimental results agree well with theoretical simulations. Moreover, the detection scheme proposed in this paper has the properties of high detection sensitivity and immunity to laser power fluctuation, which are also proved experimentally.
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Saito, S., M. Yamamoto, S. Fukao, M. Marumoto i R. T. Tsunoda. "Radar observations of field-aligned plasma irregularities in the SEEK-2 campaign". Annales Geophysicae 23, nr 7 (13.10.2005): 2307–18. http://dx.doi.org/10.5194/angeo-23-2307-2005.
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Abstract. During the Sporadic E Experiment over Kyushu 2 (SEEK-2) campaign, field-aligned irregularities (FAIs) associated with midlatitude sporadic-E (Es) layers were observed with two backscatter radars, the Lower Thermosphere Profiler Radar (LTPR) and the Frequency Agile Radar (FAR), which were located 40 km apart in Tanegashima, Japan. We conducted observations of FAI echoes from 31 July to 24 August 2002, and the radar data were used to determine launch timing of two sounding rockets on 3 August 2002. Our comparison of echoes obtained by the LTPR and the FAR revealed that echoes often appeared at the FAR about 10min earlier than they did at the LTPR and were well correlated. This indicates that echoing regions drift with a southward velocity component that maintains the spatial shape. Interferometry observations that were conducted with the LTPR from 3 to 8 August 2002, revealed that the quasi-periodic (QP) striations in the Range-Time-Intensity (RTI) plots were due to the apparent motion of echoing regions across the radar beam including both main and side lobes. In most cases, the echo moved to the east-southeast at an almost constant altitude of 100–110 km, which was along the locus of perpendicularity of the radar line-of-sight to the geomagnetic field line. We found that the QP pattern on the RTI plot reflects the horizontal structure and motion of the (Es layer, and that echoing regions seemed to be in one-dimensionally elongated shapes or in chains of patches. Neutral wind velocities from 75 to 105 km altitude were simultaneously derived with meteor echoes from the LTPR. This is the first time-continuous simultaneous observation FAIs and neutral wind with interferometry measurements. Assuming that the echoing regions were drifting with an ambient neutral wind, we found that the echoing region was aligned east-northeast-west-southwest in eight out of ten QP echo events during the SEEK-2 campaign. A range rate was negative (positive), when a frontal structure of echoing regions elongated east-northeast-west-southwest drifts with southward (northward) neutral wind. Keywords. Ionosphere-atmosphere interactions; Ionospheric irregularities; Plasma waves and instabilities
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Ma, Maoli, Guifré Molera Calvés, Giuseppe Cimò, Ming Xiong, Peijia Li, Jing Kong, Peijin Zhang i in. "Detecting the Oscillation and Propagation of the Nascent Dynamic Solar Wind Structure at 2.6 Solar Radii Using Very Long Baseline Interferometry Radio Telescopes". Astrophysical Journal Letters 940, nr 2 (25.11.2022): L32. http://dx.doi.org/10.3847/2041-8213/ac96e7.
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Abstract Probing the solar corona is crucial to study the coronal heating and solar wind acceleration. However, the transient and inhomogeneous solar wind flows carry large-amplitude inherent Alfvén waves and turbulence, which make detection more difficult. We report the oscillation and propagation of the solar wind at 2.6 solar radii (Rs) by observation of China’s Tianwen and ESA’s Mars Express with radio telescopes. The observations were carried out on 2021 October 9, when one coronal mass ejection (CME) passed across the ray paths of the telescope beams. We obtain the frequency fluctuations (FFs) of the spacecraft signals from each individual telescope. First, we visually identify the drift of the frequency spikes at a high spatial resolution of thousands of kilometers along the projected baselines. They are used as traces to estimate the solar wind velocity. Then we perform the cross-correlation analysis on the time series of FF from different telescopes. The velocity variations of solar wind structure along radial and tangential directions during the CME passage are obtained. The oscillation of tangential velocity confirms the detection of a streamer wave. Moreover, at the tail of the CME, we detect the propagation of an accelerating fast field-aligned density structure indicating the presence of magnetohydrodynamic waves. This study confirms that the ground-station pairs are able to form particular spatial projection baselines with high resolution and sensitivity to study the detailed propagation of the nascent dynamic solar wind structure.
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Amiri, Mandana, Kevin Bandura, Anja Boskovic, Tianyue Chen, Jean-François Cliche, Meiling Deng, Nolan Denman i in. "An Overview of CHIME, the Canadian Hydrogen Intensity Mapping Experiment". Astrophysical Journal Supplement Series 261, nr 2 (27.07.2022): 29. http://dx.doi.org/10.3847/1538-4365/ac6fd9.
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Abstract The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a drift scan radio telescope operating across the 400–800 MHz band. CHIME is located at the Dominion Radio Astrophysical Observatory near Penticton, BC, Canada. The instrument is designed to map neutral hydrogen over the redshift range 0.8–2.5 to constrain the expansion history of the universe. This goal drives the design features of the instrument. CHIME consists of four parallel cylindrical reflectors, oriented north–south, each 100 m × 20 m and outfitted with a 256-element dual-polarization linear feed array. CHIME observes a two-degree-wide stripe covering the entire meridian at any given moment, observing three-quarters of the sky every day owing to Earth’s rotation. An FX correlator utilizes field-programmable gate arrays and graphics processing units to digitize and correlate the signals, with different correlation products generated for cosmological, fast radio burst, pulsar, very long baseline interferometry, and 21 cm absorber back ends. For the cosmology back end, the N feed 2 correlation matrix is formed for 1024 frequency channels across the band every 31 ms. A data receiver system applies calibration and flagging and, for our primary cosmological data product, stacks redundant baselines and integrates for 10 s. We present an overview of the instrument, its performance metrics based on the first 3 yr of science data, and we describe the current progress in characterizing CHIME’s primary beam response. We also present maps of the sky derived from CHIME data; we are using versions of these maps for a cosmological stacking analysis, as well as for investigation of Galactic foregrounds.
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Eastwood, Michael W., i Gregg Hallinan. "Full-Sky Maps of the VHF Radio Sky with the Owens Valley Radio Observatory Long Wavelength Array". Proceedings of the International Astronomical Union 12, S333 (październik 2017): 110–13. http://dx.doi.org/10.1017/s1743921317011231.
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Abstract21-cm cosmology is a powerful new probe of the intergalactic medium at redshifts 20 ≳ z ≳ 6 corresponding to the Cosmic Dawn and Epoch of Reionization. Current observations of the highly-redshifted 21-cm transition are limited by the dynamic range they can achieve against foreground sources of low-frequency (<200 MHz) of radio emission. We used the Owens Valley Radio Observatory Long Wavelength Array (OVRO-LWA) to generate a series of new modern high-fidelity sky maps that capture emission on angular scales ranging from tens of degrees to ∼15 arcmin, and frequencies between 36 and 73 MHz. These sky maps were generated from the application of Tikhonov-regularized m-mode analysis imaging, which is a new interferometric imaging technique that is uniquely suited for low-frequency, wide-field, drift-scanning interferometers.
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Witschas, Benjamin, Christian Lemmerz, Oliver Lux, Uwe Marksteiner, Oliver Reitebuch, Fabian Weiler, Frederic Fabre i in. "Spectral performance analysis of the Aeolus Fabry–Pérot and Fizeau interferometers during the first years of operation". Atmospheric Measurement Techniques 15, nr 5 (16.03.2022): 1465–89. http://dx.doi.org/10.5194/amt-15-1465-2022.
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Abstract. In August 2018, the European Space Agency (ESA) launched the first Doppler wind lidar into space, which has since then been providing continuous profiles of the horizontal line-of-sight wind component at a global scale. Aeolus data have been successfully assimilated into several numerical weather prediction (NWP) models and demonstrated a positive impact on the quality of the weather forecasts. To provide valuable input data for NWP models, a detailed characterization of the Aeolus instrumental performance as well as the realization and minimization of systematic error sources is crucial. In this paper, Aeolus interferometer spectral drifts and their potential as systematic error sources for the aerosol and wind products are investigated by means of instrument spectral registration (ISR) measurements that are performed on a weekly basis. During these measurements, the laser frequency is scanned over a range of 11 GHz in steps of 25 MHz and thus spectrally resolves the transmission curves of the Fizeau interferometer and the Fabry–Pérot interferometers (FPIs) used in Aeolus. Mathematical model functions are derived to analyze the measured transmission curves by means of non-linear fit procedures. The obtained fit parameters are used to draw conclusions about the Aeolus instrumental alignment and potentially ongoing drifts. The introduced instrumental functions and analysis tools may also be applied for upcoming missions using similar spectrometers as for instance EarthCARE (ESA), which is based on the Aeolus FPI design.
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Zhang, Ya-Fei, Yu-Tao Feng, Di Fu, Chen-Guang Chang, Juan Li, Qing-Lan Bai i Bing-Liang Hu. "Thermal imaging drift monitoring of Doppler asymmetric spatial heterodyne spectroscopy for wind measurement based on segmented edge fitting". Acta Physica Sinica 71, nr 8 (2022): 084201. http://dx.doi.org/10.7498/aps.71.20212086.
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Doppler asymmetric spatial heterodyne spectroscopy is recently developed for spaceborne measurement of middle and upper atmospheric wind field, which relies on the accurate inverse of interferogram phase to calculate the Doppler shift of airglow emission lines. The change of temperature leads the optical and mechanical components to thermally deformed, causing the imaging plane to thermally drift relative to the detector, changing the distribution of interferogram phase on pixels, and directly introducing phase errors to affect the wind speed inversion. In order to reduce the influence of imaging thermal drift on phase inversion, the segmented fitting method is used in this paper to detect the sub-pixel edges of notch patterns and monitor imaging thermal drift accordingly. In the thermal stability test of a near-infrared Doppler asymmetric spatial heterodyne interferometer prototype, the thermal imaging drifts and ambient temperature show a high consistency in the trend of high-frequency oscillation, and the correlation coefficient can reach 0.86 after removing the baseline. After phase correct by using the thermal imaging shift, the high-frequency oscillation of interferogram phase shift is also greatly suppressed. In order to further verify the accuracy of the algorithm, the influence of the data signal-to-noise ratio and the data distribution characteristic parameter errors used in the fitting on the edge detection are simulated. The results show that the edge detection accuracy is restricted mainly by the data signal-to-noise ratio and the accuracy of the fringe frequency parameters. When the error of the fringe frequency parameter used for fitting is less than 0.5%, the error of other data distribution characteristic parameters is less than 5%, and the data signal-to-noise ratio is enhanced more than 35 times, the algorithm in this paper can achieve a detection accuracy higher than 0.05 pixels.
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Yang, Hongxing, Ziqi Yin, Ruitao Yang, Pengcheng Hu, Jing Li i Jiubin Tan. "Design for a Highly Stable Laser Source Based on the Error Model of High-Speed High-Resolution Heterodyne Interferometers". Sensors 20, nr 4 (17.02.2020): 1083. http://dx.doi.org/10.3390/s20041083.
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Heterodyne interferometers with two opposite Doppler shift interference signals have been proposed for high-resolution measurement with high measurement speed, which can be used in the background of high-speed high-resolution measurement. However, a measurement error model for high-speed high-resolution heterodyne interferometers (HSHR-HIs) has not yet been proposed. We established a HSHR-HI measurement error model, analyzed the influence of beat frequency stability with a simplified optical structure, and then designed an offset-locked dual-frequency laser source with a digital control system to reduce the impact of beat frequency drift. Experiments were used to verify the correction of the measurement error model and the validity of the laser source. The results show that the new laser source has a maximum beat frequency range of 45 MHz, which shows the improvements in the measuring speed and resolution.
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Tao Long, 陶龙, 刘志刚 Liu Zhigang, 吕涛 Lü Tao, 邓忠文 Deng Zhongwen i 龚海 Gong Hai. "Drift Error Compensation Method of Frequency Sweeping Interferometer by Consecutive Forward and Reverse Optical Frequency Scanning". Acta Optica Sinica 34, nr 2 (2014): 0212002. http://dx.doi.org/10.3788/aos201434.0212002.
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Zhang, Shiwen, Liyan Li, Yuliang Liu i Yan Zhou. "Drift Error Compensation Algorithm for Heterodyne Optical Seawater Refractive Index Monitoring of Unstable Signals". Sensors 23, nr 20 (14.10.2023): 8460. http://dx.doi.org/10.3390/s23208460.
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The refractive index measurement of seawater has proven significance in oceanography, while an optical heterodyne interferometer is an important, highly accurate, tool used for seawater refractive index measurement. However, for practical seawater refractive index measurement, the refractive index of seawater needs to be monitored for long periods of time, and the influence of drift error on the measurement results for these cases cannot be ignored. This paper proposes a drift error compensation algorithm based on wavelet decomposition, which can adaptively separate the background from the signal, and then calculate the frequency difference to compensate for the drift error. It is suitable for unstable signals, especially signals with large differences between the beginning and the end, which is common in actual seawater refractive index monitoring. The authors identify that the primary cause of drift error is the frequency instability of the acousto-optic frequency shifter (AOFS), and the actual frequency difference was measured through experimentation. The frequency difference was around 0.1 Hz. Simulation experiments were designed to verify the effectiveness of the algorithm, and the standard deviation of the optical length of the results was on the scale of 10−8 m. Liquid refractive index measurement experiments were carried out in a laboratory, and the measurement error was reduced from 36.942% to 0.592% after algorithm processing. Field experiments were carried out regarding seawater refractive index monitoring, and the algorithm-processing results are able to match the motion of the target vehicle. The experimental data were processed with different algorithms, and, according to the comparison of the results, the proposed algorithm performs better than other existing drift error elimination algorithms.
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Tao, Long, Zhigang Liu, Weibo Zhang, Zhe Liu i Jun Hong. "Real-time drift error compensation in a self-reference frequency-scanning fiber interferometer". Optics Communications 382 (styczeń 2017): 99–104. http://dx.doi.org/10.1016/j.optcom.2016.07.036.
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Brotzer, Andreas, Felix Bernauer, Karl Ulrich Schreiber, Joachim Wassermann i Heiner Igel. "Automated Quality Assessment of Interferometric Ring Laser Data". Sensors 21, nr 10 (14.05.2021): 3425. http://dx.doi.org/10.3390/s21103425.
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In seismology, an increased effort to observe all 12 degrees of freedom of seismic ground motion by complementing translational ground motion observations with measurements of strain and rotational motions could be witnessed in recent decades, aiming at an enhanced probing and understanding of Earth and other planetary bodies. The evolution of optical instrumentation, in particular large-scale ring laser installations, such as G-ring and ROMY (ROtational Motion in seismologY), and their geoscientific application have contributed significantly to the emergence of this scientific field. The currently most advanced, large-scale ring laser array is ROMY, which is unprecedented in scale and design. As a heterolithic structure, ROMY’s ring laser components are subject to optical frequency drifts. Such Sagnac interferometers require new considerations and approaches concerning data acquisition, processing and quality assessment, compared to conventional, mechanical instrumentation. We present an automated approach to assess the data quality and the performance of a ring laser, based on characteristics of the interferometric Sagnac signal. The developed scheme is applied to ROMY data to detect compromised operation states and assign quality flags. When ROMY’s database becomes publicly accessible, this assessment will be employed to provide a quality control feature for data requests.
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Волков, П. В., Д. А. Семиков, О. С. Вязанкин, А. В. Горюнов, А. Ю. Лукьянов i А. Д. Тертышник. "Метод детектирования малых колебаний на основе гомодинной демодуляции с тандемным низкокогерентным интерферометром". Журнал технической физики 93, nr 7 (2023): 959. http://dx.doi.org/10.21883/jtf.2023.07.55753.78-23.
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The paper proposes a method for detecting small oscillations in the length of interference fiber-optic sensors, which makes it possible to compensate for the problem of slow drift of the working point with a remote sensor. The result is achieved by combining homodyne demodulation methods with a tandem low-coherence interferometer. Theoretically and experimentally, the possibility of detecting acoustic effects in the operating frequency band of 4 kHz with a sensitivity of up to 0.3 nm has been shown.
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Wang, Jingying, Mario G. Santos, Philip Bull, Keith Grainge, Steven Cunnington, José Fonseca, Melis O. Irfan i in. "H i intensity mapping with MeerKAT: calibration pipeline for multidish autocorrelation observations". Monthly Notices of the Royal Astronomical Society 505, nr 3 (17.05.2021): 3698–721. http://dx.doi.org/10.1093/mnras/stab1365.
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ABSTRACT While most purpose-built 21-cm intensity mapping experiments are close-packed interferometer arrays, general-purpose dish arrays should also be capable of measuring the cosmological 21-cm signal. This can be achieved most efficiently if the array is used as a collection of scanning autocorrelation dishes rather than as an interferometer. As a first step towards demonstrating the feasibility of this observing strategy, we show that we are able to successfully calibrate dual-polarization autocorrelation data from 64 MeerKAT dishes in the L band (856–1712 MHz, 4096 channels), with 10.5 h of data retained from six nights of observing. We describe our calibration pipeline, which is based on multilevel radio frequency interference flagging, periodic noise diode injection to stabilize gain drifts, and an absolute calibration based on a multicomponent sky model. We show that it is sufficiently accurate to recover maps of diffuse celestial emission and point sources over a 10° × 30° patch of the sky overlapping with the WiggleZ 11-h field. The reconstructed maps have a good level of consistency between per-dish maps and external data sets, with the estimated thermal noise limited to 1.4 × the theoretical noise level (∼2 mK). The residual maps have rms amplitudes below 0.1 K, corresponding to $\lt 1{{\ \rm per\ cent}}$ of the model temperature. The reconstructed Galactic H i intensity map shows excellent agreement with the Effelsberg–Bonn H i Survey, and the flux of the radio galaxy 4C + 03.18 is recovered to within 3.6 per cent, which demonstrates that the autocorrelation can be successfully calibrated to give the zero-spacing flux and potentially help in the imaging of MeerKAT interferometric data. Our results provide a positive indication towards the feasibility of using MeerKAT and the future Square Kilometre Array to measure the H i intensity mapping signal and probe cosmology on degree scales and above.
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Zhao, Yang, Shaokai Wang, Wei Zhuang i Tianchu Li. "Raman-Laser System for Absolute Gravimeter Based On 87Rb Atom Interferometer". Photonics 7, nr 2 (15.05.2020): 32. http://dx.doi.org/10.3390/photonics7020032.
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The paper describes a Raman-laser system with high performance for an absolute gravimeter that was based on 87Rb atom interferometer. As our gravimeter is a part of the standard acceleration of gravity of China, the Raman lasers’ characteristics should be considered. This laser system includes two diode lasers. The master laser is frequency locked through the frequency-modulation (FM) spectroscopy technology. Its maximum frequency drift is better than 50 kHz in 11 h, which is measured by home-made optical frequency comb. The slave laser is phase locked to the master laser with a frequency difference of 6.8346 GHz while using an optical phase lock loop (OPLL). The phase noise is lower than −105 dBc/Hz at the Fourier frequency from 200 Hz to 42 kHz. It is limited by the measurement sensitivity of the signal source analyzer in low Fourier frequency. Furthermore, the power fluctuation of Raman lasers’ pulses is also suppressed by a fast power servo system. While using this servo system, Raman lasers’ pulses could be fast re-locked while its fast turning on again in the pulse sequence. The peak value fluctuation of the laser power pulses is decreased from 25% to 0.7%, which is improved over 35 times. This Raman-laser system can stably operate over 500 h, which is suited for long-term highly precise and accurate gravity measurements.
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Malykin, G. B. "Effect of higher harmonics of phase-modulation frequency on zero drift in a fiber ring interferometer". Radiophysics and Quantum Electronics 39, nr 5 (maj 1996): 416–19. http://dx.doi.org/10.1007/bf02124699.
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Melnik, V. N., A. A. Konovalenko, V. V. Dorovskyy, A. Lecacheux, H. O. Rucker i M. V. Shevchuk. "EXPLORATION OF THE SOLAR DECAMETER RADIO EMISSION WITH THE UTR-2 RADIO TELESCOPE". Radio physics and radio astronomy 26, nr 1 (3.03.2021): 74–89. http://dx.doi.org/10.15407/rpra26.01.074.
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Purpose: The overview of the scientifi c papers devoted to the study of the solar decameter radio emission with the world’s largest UTR-2 radio telescope (Ukraine) published for the last 50 years. Design/methodology/approach: The study and analysis of the scientifi c papers on both sporadic and quiet (thermal) radiation of the Sun recorded with the UTR-2 radio telescope at the decameter wavelength range. Findings: The most signifi cant observational and theoretical results of the solar radio emission studies obtained at the Institute of Radio Astronomy of the National Academy of Sciences of Ukraine for the last 50 years are given. Conclusions: For the fi rst time, at frequencies below 30 MHz, the Type II bursts, Type IV bursts, S-bursts, drift pairs and spikes have been recorded. The dependences of these bursts parameters on frequency within the frequency band of 9 to 30 MHz were obtained. The models of their generation and propagation were suggested. Moreover, for the fi rst time the fi ne time-frequency structures of the Type III bursts, Type II bursts, Type IV bursts, U- and J-bursts, S-bursts, and drift pairs have been observed due to the high sensitivity and high time-frequency resolutions of the UTR-2 radio telescope. The super-fi ne structure of Type II bursts with a “herringbone” structure was identifi ed, which has never been observed before. New types of bursts were discovered: “caterpillar” bursts, “dog-leg” bursts, Type III bursts with decay, Type III bursts with changing drift rate sign, Type III-like bursts, Jb- and Ub-bursts, etc. An interpretation of the unusually high drift rates and drift rates with alternating signs of the Type III-like bursts was suggested. Based on the dependence of spike durations on frequency, the coronal plasma temperature profi le at the heliocentric heights of 1.5–3RS was determined. Usage of the heliographic and interferometric methods gave the possibility to start studies of the spatial characteristics – sizes and locations of the bursts emission sources. Thus, it was shown that at the decameter band, the Type III burst durations were defi ned by the emission source linear sizes, whereas the spike durations were governed by the collision times in the source plasma. It was experimentally proved that the effective brightness temperatures of the sources of solar sporadic radio emission at the decameter band may reach values of 1014–1015 K. In addition, it was found that the radii of the quiet Sun at frequencies 20 and 25 MHz are close to the distances from the Sun at which the local plasma frequency is equal to the corresponding observed frequency of radio emission in the Baumbach–Allen model. Key words: UTR-2; Sun; decameter radio emission; radio bursts; corona
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Yuan, Quan, Feng Wang, Tao Liu, Yixin Zhang i Xuping Zhang. "Using an Auxiliary Mach–Zehnder Interferometer to Compensate for the Influence of Laser-Frequency-Drift in Φ-OTDR". IEEE Photonics Journal 11, nr 1 (luty 2019): 1–9. http://dx.doi.org/10.1109/jphot.2018.2884659.
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Zhao, Na, Qijing Lin, Zhuangde Jiang, Kun Yao, Bian Tian, Xudong Fang, Peng Shi i Zhongkai Zhang. "High Temperature High Sensitivity Multipoint Sensing System Based on Three Cascade Mach–Zehnder Interferometers". Sensors 18, nr 8 (16.08.2018): 2688. http://dx.doi.org/10.3390/s18082688.
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A temperature multipoint sensing system based on three cascade Mach–Zehnder interferometers (MZIs) is introduced. The MZIs with different lengths are fabricated based on waist-enlarged fiber bitapers. The fast Fourier transformation is applied to the overlapping transmission spectrum and the corresponding interference spectra can be obtained via the cascaded frequency spectrum based on the inverse Fourier transformation. By analyzing the drift of interference spectra, the temperature response sensitivities of 0.063 nm/°C, 0.071 nm/°C, and 0.059 nm/°C in different furnaces can be detected from room temperature up to 1000 °C, and the temperature response at different regions can be measured through the sensitivity matrix equation. These results demonstrate feasibility of multipoint measurement, which also support that the temperature sensing system provides new solution to the MZI cascade problem.
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Volkov, Petr, Andrey Lukyanov, Alexander Goryunov, Daniil Semikov, Evgeniy Vopilkin i Stanislav Kraev. "Fiber Optic Impact Location System Based on a Tracking Tandem Low-Coherence Interferometer". Sensors 23, nr 2 (10.01.2023): 772. http://dx.doi.org/10.3390/s23020772.
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This study proposes a method for detecting small-length fluctuations for fiber-optic sensors (FOS). The method is based on a tracking tandem low-coherence interferometer and enables the ability to compensate for temperature and deformation drifts in FOS. As a result, the constant high sensitivity of FOS over a wide frequency range is guaranteed. Sensitivity to the level of 2 nm in the frequency range of 200 kHz has been demonstrated. The operation of the circuit is demonstrated on the example of the 2D location of acoustic signals using a correlation algorithm for signal processing, known as the time reversal method. It is shown that this system enables us to determine the place of the impact on the sample under the test with an accuracy of about 2 cm using a single sensor.
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Bourgoin, A., C. Le Poncin-Lafitte, S. Mathis i M. C. Angonin. "Magnetic fields in galactic binaries and gravitational waves". Proceedings of the International Astronomical Union 16, S363 (czerwiec 2020): 361–62. http://dx.doi.org/10.1017/s1743921322000813.
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AbstractThe Laser Interferometer Space Antenna (LISA) mission will observe from space gravitational waves emitted by neutron stars and white dwarfs within galactic binaries. These compact stars can have intense magnetic fields. Therefore, the impact of the magnetic fields on the orbital and the spins evolution of binary systems can potentially be detected by LISA through the GW’s strain. Within the magnetic dipole-dipole approximation, we found that magnetism generates a secular drift of the mean longitude which, in turn, shifts all the frequencies contained in the GW signal. For a quasi-circular orbit, the signal is mainly monochromatic and the magnetic shift is proportional to the product of the magnetic moments and is inversely proportional to the 7/2 power of the semi-major axis. Hence, for a highly magnetic binary system in compact orbit, a non-negligible amount of the frequency measured by LISA might have a magnetic origin.
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Weemstra, Cornelis, Janneke I. de Laat, Arie Verdel i Pieter Smets. "Systematic recovery of instrumental timing and phase errors using interferometric surface-waves retrieved from large-N seismic arrays". Geophysical Journal International 224, nr 2 (20.10.2020): 1028–55. http://dx.doi.org/10.1093/gji/ggaa504.
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SUMMARY Instrumental timing and phase errors are a notorious problem in seismic data acquisition and processing. These can be frequency independent, for example due to clock drift, but may also be frequency dependent, for example due to imperfectly known instrument responses. A technique is presented that allows both types of errors to be recovered in a systematic fashion. The methodology relies on the time-symmetry usually inherent in time-averaged cross-correlations of ambient seismic noise: the difference between the arrival time of the direct surface-wave at positive time and the arrival time of the direct surface-wave at negative time is quantified. Doing this for all eligible receiver–receiver pairs of a large-N seismic array, including one or more receivers devoid of instrumental timing errors, the instrumental timing errors of all incorrectly timed receivers can be determined uniquely. Most notably, this is accomplished by means of a weighted least-squares inversion. The weights are based on the receiver–receiver distances and decrease the adverse effect of inhomogeneities in the noise illumination pattern on the recovered instrumental timing errors. Inversion results are furthermore optimized by limiting the inversion to receiver couples that (i) exceed a specific receiver–receiver distance threshold and (ii) whose time-averaged cross-correlations exceed a specific signal-to-noise ratio threshold. Potential frequency dependence of the timing errors is incorporated by means of an iterative, frequency-dependent approach. The proposed methodology is validated using synthetic recordings of ambient seismic surface-wave noise due to an arbitrary non-uniform illumination pattern. The methodology is successfully applied to time-averaged cross-correlations of field recordings of ambient seismic noise on and around the Reykjanes peninsula, SW Iceland.
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Sovers, O. J., C. D. Edwards, C. S. Jacobs, G. E. Lanyi i R. N. Treuhaft. "The JPL 1986–3 Extragalactic Reference Frame". Symposium - International Astronomical Union 133 (1988): 461–64. http://dx.doi.org/10.1017/s0074180900140021.
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Intercontinental dual-frequency radio interferometric measurements were carried out during 1978 to 1985 between NASA's Deep Space Network stations in California, Spain, and Australia. Analysis of 6800 pairs of delay and delay rate observations made during 51 sessions produced a catalog of positions of 106 extragalactic radio sources, fairly uniformly distributed over the celestial sphere between −45° and +85° declination. Almost all of the resulting source positions have formal uncertainties between 0.5 and 3 milliarcseconds, with their distributions peaking somewhat below 1 mas. Root-mean-square uncertainties are 2.1 and 2.0 mas for RA and declination, respectively. Evidence is found for a long-term drift of the Earth's rotation axis in inertial space, relative to the 1984 IAU precession and nutation models. Tests for time variability of positions of 32 frequently observed sources place limits at the 1 mas/yr level. Comparisons with independently determined source catalogs of comparable quality show differences of positions of common sources that amount to a few mas, and may indicate the level of systematic errors in VLBI source position measurements.
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Ansari, R., J. E. Campagne, D. Charlet, M. Moniez, C. Pailler, O. Perdereau, M. Taurigna i in. "Design, operation and performance of the PAON4 prototype transit interferometer". Monthly Notices of the Royal Astronomical Society 493, nr 2 (7.03.2020): 2965–80. http://dx.doi.org/10.1093/mnras/staa345.
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ABSTRACT PAON4 is an L-band (1250–1500 MHz) small interferometer operating in transit mode deployed at the Nançay observatory in France, designed as a prototype instrument for intensity mapping. It features four 5 m diameter dishes in a compact triangular configuration, with a total geometric collecting area of ${\sim} 75\, \mathrm{m^2}$, and is equipped with dual polarization receivers. A total of 36 visibilities are computed from the eight independent RF signals by the software correlator over the full 250 MHz RF band. The array operates in transit mode, with the dishes pointed toward a fixed declination, while the sky drifts across the instrument. Sky maps for each frequency channel are then reconstructed by combining the time-dependent visibilities from the different baselines observed at different declinations. This paper presents an overview of the PAON4 instrument design and goals, as a prototype for dish arrays to map the large-scale structure in radio, using intensity mapping of the atomic hydrogen 21 cm line. We operated PAON4 over several years and use data from observations at different periods to assess the array performance. We present a preliminary analysis of a large fraction of these data and discuss crucial issues for this type of instrument, such as the calibration strategy, instrument response stability and noise behaviour.
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Sesana, Alberto, Astrid Lamberts i Antoine Petiteau. "Finding binary black holes in the Milky Way with LISA". Monthly Notices of the Royal Astronomical Society: Letters 494, nr 1 (9.03.2020): L75—L80. http://dx.doi.org/10.1093/mnrasl/slaa039.
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ABSTRACT We determine the main properties of the Galactic binary black hole (BBH) population detectable by Laser Interferometer Space Antenna (LISA) and strategies to distinguish them from the much more numerous white dwarf binaries. We simulate BBH populations based on cosmological simulations of Milky Way-like galaxies and binary evolution models. We then determine their gravitational wave emission as observed by LISA and build mock catalogues. According to our model, LISA will detect ≈4 (6) BBHs assuming 4 (10) yr of operations. Those figures grow to ≈6 (9) when models are re-normalized to the inferred LIGO/Virgo merger rates. Largely independent on mass and distance, sources emitting at f > 0.5 mHz – 40 per cent (70 per cent) of the detections – have a measurable frequency drift, which allows a good enough chirp mass measurement to separate them from the much lighter white dwarf and neutron star binaries. Most of the remaining, lower frequency, sources should be identifiable by their lack of electromagnetic (EM) counterpart within ≈100 pc. These results are robust with respect to the current uncertainties of the BBH merger rate as measured by LIGO/Virgo as well as the global mass spectrum of the binaries. Based on the LIGO/Virgo merger rate, we determine that there is a 94 per cent chance that LISA finds at least one of these systems within 4 yr, which will allow us to pinpoint the conditions where they were formed and possibly find unique EM signatures.
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Hussey, G. C., C. Haldoupis, A. Bourdillon, J. Delloue i J. T. Wiensz. "Mid-latitude <i>E</i>-region bulk motions inferred from digital ionosonde and HF radar measurements". Annales Geophysicae 22, nr 11 (29.11.2004): 3789–98. http://dx.doi.org/10.5194/angeo-22-3789-2004.
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Abstract. In the mid-latitude E-region there is now evidence suggesting that neutral winds play a significant role in driving the local plasma instabilities and electrodynamics inside sporadicE layers. Neutral winds can be inferred from coherent radar backscatter measurements of the range-/azimuth-time-intensity (RTI/ATI) striations of quasi-periodic (QP) echoes, or from radar interferometer/imaging observations. In addition, neutral winds in the E-region can be estimated from angle-of-arrival ionosonde measurements of sporadic-E layers. In the present paper we analyse concurrent ionosonde and HF coherent backscatter observations obtained when a Canadian Advanced Digital Ionosonde (CADI) was operated under a portion of the field-of-view of the Valensole high frequency (HF) radar. The Valensole radar, a mid-latitude radar located in the south of France with a large azimuthal scanning capability of 82° (24° E to 58° W), was used to deduce zonal bulk motions of QP echoing regions using ATI analysis. The CADI was used to measure angle-of-arrival information in two orthogonal horizontal directions and thus derive the motion of sporadic-E patches drifting with the neutral wind. This paper compares the neutral wind drifts of the unstable sporadic-E patches as determined by the two instruments. The CADI measurements show a predominantly westward aligned motion, but the measured zonal drifts are underestimated relative to those observed with the Valensole radar.
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de Gasperin, F., T. J. Dijkema, A. Drabent, M. Mevius, D. Rafferty, R. van Weeren, M. Brüggen i in. "Systematic effects in LOFAR data: A unified calibration strategy". Astronomy & Astrophysics 622 (luty 2019): A5. http://dx.doi.org/10.1051/0004-6361/201833867.
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Context. New generation low-frequency telescopes are exploring a new parameter space in terms of depth and resolution. The data taken with these interferometers, for example with the LOw Frequency ARray (LOFAR), are often calibrated in a low signal-to-noise ratio regime and the removal of critical systematic effects is challenging. The process requires an understanding of their origin and properties. Aim. In this paper we describe the major systematic effects inherent to next generation low-frequency telescopes, such as LOFAR. With this knowledge, we introduce a data processing pipeline that is able to isolate and correct these systematic effects. The pipeline will be used to calibrate calibrator observations as the first step of a full data reduction process. Methods. We processed two LOFAR observations of the calibrator 3C 196: the first using the Low Band Antenna (LBA) system at 42–66 MHz and the second using the High Band Antenna (HBA) system at 115–189 MHz. Results. We were able to isolate and correct for the effects of clock drift, polarisation misalignment, ionospheric delay, Faraday rotation, ionospheric scintillation, beam shape, and bandpass. The designed calibration strategy produced the deepest image to date at 54 MHz. The image has been used to confirm that the spectral energy distribution of the average radio source population tends to flatten at low frequencies. Conclusions. We prove that LOFAR systematic effects can be described by a relatively small number of parameters. Furthermore, the identification of these parameters is fundamental to reducing the degrees of freedom when the calibration is carried out on fields that are not dominated by a strong calibrator.
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Haider Ali Muse, Al-Sudani. "Principles of constructing gyroscopes based on photonic crystal (band-gap) fibers". Radiotekhnika, nr 205 (2.07.2021): 100–107. http://dx.doi.org/10.30837/rt.2021.2.205.10.
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The gyroscope is a device that makes it possible to measure the change in the orientation angles associated rotation of the body relative to an inertial coordinate system. Photonic crystal fiber gyroscopes are a kind of optical gyroscopes that offer many new features beyond that conventional fiber optic gyroscopes can offer. In any case, the properties of the optical fiber can play a large role in determining the characteristics of the gyroscope. The principle of operation of most optical gyroscopes is based on the Sagnac effect or the Sagnac interferometer, the essence of which is as follows. If two light waves propagate in a closed optical circuit in opposite directions, then in the case of an immovable circuit, the phase incursions of both waves that have passed the entire circuit in opposite directions will be the same. When the contour rotates around an axis normal to the contour plane, the phase incursions of the waves become unequal, and their difference in the general case will be proportional to the angular velocity of the contour rotation, the area covered by the contour, and the frequency of the electromagnetic wave (EMW). Since the area and frequency of the EMW remain unchanged during the operation of the gyroscope, the phase shift will be proportional only to the angular velocity. The use of photonic crystal fiber to increase the sensitivity is very promising; it significantly reduces the drift through thermal polarization, resistance, and the Kerr effect. This article suggests the use of photonic-crystal (hollow-core) fiber in optical gyroscope instead of conventional fibers.
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Lemoine, Anne, Pierre Briole, Didier Bertil, Agathe Roullé, Michael Foumelis, Isabelle Thinon, Daniel Raucoules, Marcello de Michele, Pierre Valty i Roser Hoste Colomer. "The 2018–2019 seismo-volcanic crisis east of Mayotte, Comoros islands: seismicity and ground deformation markers of an exceptional submarine eruption". Geophysical Journal International 223, nr 1 (3.06.2020): 22–44. http://dx.doi.org/10.1093/gji/ggaa273.
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SUMMARY On 10 May 2018, an unprecedented long and intense seismic crisis started offshore, east of Mayotte, the easternmost of the Comoros volcanic islands. The population felt hundreds of events. Over the course of 1 yr, 32 earthquakes with magnitude greater than 5 occurred, including the largest event ever recorded in the Comoros (Mw = 5.9 on 15 May 2018). Earthquakes are clustered in space and time. Unusual intense long lasting monochromatic very long period events were also registered. From early July 2018, Global Navigation Satellite System (GNSS) stations and Interferometric Synthetic Aperture Radar (InSAR) registered a large drift, testimony of a large offshore deflation. We describe the onset and the evolution of a large magmatic event thanks to the analysis of the seismicity from the initiation of the crisis through its first year, compared to the ground deformation observation (GNSS and InSAR) and modelling. We discriminate and characterize the initial fracturing phase, the phase of magma intrusion and dyke propagation from depth to the subsurface, and the eruptive phase that starts on 3 July 2018, around 50 d after the first seismic events. The eruption is not terminated 2 yr after its initiation, with the persistence of an unusual seismicity, whose pattern has been similar since summer 2018, including episodic very low frequency events presenting a harmonic oscillation with a period of ∼16 s. From July 2018, the whole Mayotte Island drifted eastward and downward at a slightly increasing rate until reaching a peak in late 2018. At the apex, the mean deformation rate was 224 mm yr−1 eastward and 186 mm yr−1 downward. During 2019, the deformation smoothly decreased and in January 2020, it was less than 20 per cent of its peak value. A deflation model of a magma reservoir buried in a homogenous half space fits well the data. The modelled reservoir is located 45 ± 5 km east of Mayotte, at a depth of 28 ± 3 km and the inferred magma extraction at the apex was ∼94 m3 s−1. The introduction of a small secondary source located beneath Mayotte Island at the same depth as the main one improves the fit by 20 per cent. While the rate of the main source drops by a factor of 5 during 2019, the rate of the secondary source remains stable. This might be a clue of the occurrence of relaxation at depth that may continue for some time after the end of the eruption. According to our model, the total volume extracted from the deep reservoir was ∼2.65 km3 in January 2020. This is the largest offshore volcanic event ever quantitatively documented. This seismo-volcanic crisis is consistent with the trans-tensional regime along Comoros archipelago.
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Kiefer, Michael, Thomas von Clarmann, Bernd Funke, Maya García-Comas, Norbert Glatthor, Udo Grabowski, Sylvia Kellmann i in. "IMK/IAA MIPAS temperature retrieval version 8: nominal measurements". Atmospheric Measurement Techniques 14, nr 6 (7.06.2021): 4111–38. http://dx.doi.org/10.5194/amt-14-4111-2021.
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Abstract. A new global set of atmospheric temperature profiles is retrieved from recalibrated radiance spectra recorded with the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS). Changes with respect to previous data versions include a new radiometric calibration considering the time dependency of the detector nonlinearity and a more robust frequency calibration scheme. Temperature is retrieved using a smoothing constraint, while tangent altitude pointing information is constrained using optimal estimation. ECMWF ERA-Interim is used as a priori temperature below 43 km. Above, a priori data are based on data from the Whole Atmosphere Community Climate Model Version 4 (WACCM4). Bias-corrected fields from specified dynamics runs, sampled at the MIPAS times and locations, are used, blended with ERA-Interim between 43 and 53 km. Horizontal variability of temperature is considered by scaling an a priori 3D temperature field in the orbit plane in a way that the horizontal structure is provided by the a priori while the vertical structure comes from the measurements. Additional microwindows with better sensitivity at higher altitudes are used. The background continuum is jointly fitted with the target parameters up to 58 km altitude. The radiance offset correction is strongly regularized towards an empirically determined vertical offset profile. In order to avoid the propagation of uncertainties of O3 and H2O a priori assumptions, the abundances of these species are retrieved jointly with temperature. The retrieval is based on HITRAN 2016 spectroscopic data, with a few amendments. Temperature-adjusted climatologies of vibrational populations of CO2 states emitting in the 15 µm region are used in the radiative transfer modeling in order to account for non-local thermodynamic equilibrium. Numerical integration in the radiative transfer model is now performed at higher accuracy. The random component of the temperature uncertainty typically varies between 0.4 and 1 K, with occasional excursions up to 1.3 K above 60 km altitude. The leading sources of the random component of the temperature error are measurement noise, gain calibration uncertainty, spectral shift, and uncertain CO2 mixing ratios. The systematic error is caused by uncertainties in spectroscopic data and line shape uncertainties. It ranges from 0.2 K at 20 km altitude for northern midlatitude summer conditions to 2.3 K at 12 km for tropical conditions. The estimated total uncertainty amounts to values between 0.6 K at 20 km for midlatitude summer conditions to 2.5 K at 12–15 km for tropical conditions. The vertical resolution varies around 3 km for altitudes below 50 km. The long-term drift encountered in the previous temperature product has been largely reduced. The consistency between high spectral resolution results from 2002 to 2004 and the reduced spectral resolution results from 2005 to 2012 has been largely improved. As expected, most pronounced temperature differences between version 8 and previous data versions are found in elevated stratopause situations. The fact that the phase of temperature waves seen by MIPAS is not locked to the wave phase found in ECMWF analyses demonstrates that our retrieval provides independent information and does not merely reproduce the prior information.
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Zhang, Shihua, Hao Jin, Lingqi Zhang i Liping Yan. "Absolute distance measurement using frequency sweeping interferometry with large swept range and target drift compensation". Measurement Science and Technology, 10.05.2023. http://dx.doi.org/10.1088/1361-6501/acd40e.
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Abstract Frequency sweeping interferometry (FSI) is an attractive absolute distance measurement (ADM) method because of the advantages of large unambiguity range, simple structure and excellent flexibility. By using reference interferometer, the calibration of the frequency sweeping range in FSI can be avoided, and the complexity and cost of the system can be further reduced. Then, the measurement accuracy is associated with the accuracy of phase demodulation, the width of frequency sweeping range and the compensation of target drift. In this paper, ADM using FSI with large swept range and target drift compensation is presented. An incremental interferometer which has a complete common path with the swept source laser was employed to monitor the target drifts of the measurement and reference interferometer. Interference phases of the corresponding interferometers were extracted simultaneously using phase generated carrier (PGC) demodulation technique, and an accuracy better than 1° was verified by nanometer displacement measurement. Comparative experiments of ADM at a distance of ~ 4.5 m with different swept ranges and before and after target drift compensation were carried out, and the results demonstrated that larger swept range and target drift compensation could greatly improve the stability and accuracy of measurement.
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Wei, Wei, Langfeng Zhou, Weilin Xie i Yi Dong. "High-resolution measurement of laser frequency drift utilizing ultra-stable delayed self-heterodyne interferometry". Optics Letters, 2.08.2023. http://dx.doi.org/10.1364/ol.497956.
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Chen, Wenjia, Yiwen Ou, Chunfu Cheng, Yuanchang Zhu, Wen Xiao i Hui Lv. "Optical sensor using space-domain active fiber cavity ringdown technique". Scientific Reports 12, nr 1 (4.08.2022). http://dx.doi.org/10.1038/s41598-022-17565-6.
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AbstractA novel active fiber cavity ringdown (FCRD) technique using frequency-shifted interferometry (FSI) is proposed for the first time. Using this scheme, external parameters can be monitored in the space domain by measuring the ringdown distance instead of ringdown time. A bidirectional erbium-doped fiber amplifier (Bi-EDFA) is employed to compensate the inherent cavity loss for achieving higher sensitivity. And two band-pass filters are used to reduce the amplified spontaneous emission (ASE) noise of the Bi-EDFA. Compared with the well-known time-domain active FCRD scheme, our proposed method enables us to avoid using pulsed laser needed in time-domain active FCRD, it uses continuous-wave laser to inject into the fiber cavity and stabilize the optical power in the fiber cavity, which can suppress the baseline drift of ringdown signal caused by the gain fluctuations of the EDFA and thus improve the detecting precision. Moreover, this novel method enables us to use differential detection method for further reducing the ASE noise, and thus eliminating the baseline drift of ringdown signal. A magnetic field sensor was developed as a proof-of-concept demonstration. The experimental results demonstrate that the proposed sensor with a sensitivity of 0.01537 (1/km·Gs) was achieved. This is the highest magnetic field sensitivity compared to the time-domain active FLRD method. Due to the reduced ASE noise, the stability of the proposed sensing system was also greatly improved.
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Hull, Arthur J., Laurent Muschietti, Oleksiy V. Agapitov, Christopher C. Chaston, Olivier Le Contel i Per‐Arne Lindqvist. "Energy Transport and Conversion Within Earth's Supercritical Bow Shock: The Role of Intense Lower‐Hybrid Whistler Waves". Journal of Geophysical Research: Space Physics 129, nr 5 (29.04.2024). http://dx.doi.org/10.1029/2023ja031630.
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AbstractDetailed analysis of a high Mach number quasiperpendicular Earth bow shock crossing by the Magnetospheric Multiscale (MMS) spacecraft fleet reveal that lower‐hybrid (LH) whistler waves generated in the shock foot region transport energy predominately along the shock surface and slightly toward the shock ramp in the shock normal incidence frame, where wave energy accumulates and is dissipated into the plasma. This suggests the LH whistlers play an integral role in energy reconfiguration at high Mach number collisionless shocks with ramifications to plasma heating. The multipoint observations are used to quantify the wave characteristic parameters (via interferometry), Poynting fluxes, and energy conversion rates D, and to assess their scale dependencies and spatial and temporal properties. The whistler associated energy transport and conversion are found to depend on scale and location within the layer. High‐frequency electrostatic waves yield largest values of D. However, the dominant net energy exchange contribution is from the LH whistlers. In the foot spatially temporally coherent net energy exchange from the plasma to whistlers is observed, whereas deeper in the ramp net wave energy dissipation to the plasma is observed exhibiting significant space‐time variability. These results are consistent with the modified two stream instability driven by the relative drift between reflected ions and electrons as the mechanism for wave growth in the foot. Owing to strong electron heating, whistler energy dissipation in the ramp is attributed to Landau damping, which out‐competes the destabilizing effect of the reflected ion and electron drift.
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Chen, Hong-Hui, Zhan-Wei Yao, Ze-Xi Lu, Si-Bin Lu, Min Jiang, Shao-Kang Li, Xiao-Li Chen i in. "Self-calibrated atom-interferometer gyroscope by modulating atomic velocities". Review of Scientific Instruments 95, nr 5 (1.05.2024). http://dx.doi.org/10.1063/5.0198240.
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Atom-interferometer gyroscopes have attracted much attention for their long-term stability and extremely low drift. For such high-precision instruments, self-calibration to achieve an absolute rotation measurement is critical. In this work, we propose and demonstrate the self-calibration of an atom-interferometer gyroscope. This calibration is realized by using the detuning of the laser frequency to control the atomic velocity, thus modulating the scale factor of the gyroscope. The modulation determines the order and the initial phase of the interference stripe, thus eliminating the ambiguity caused by the periodicity of the interferometric signal. This self-calibration method is validated through a measurement of the Earth’s rotation rate, and a relative uncertainty of 162 ppm is achieved. Long-term stable and self-calibrated atom-interferometer gyroscopes have important applications in the fields of fundamental physics, geophysics, and long-time navigation.
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Trott, Cathryn M. "Comparison of Observing Modes for Statistical Estimation of the 21 cm Signal from the Epoch of Reionisation". Publications of the Astronomical Society of Australia 31 (2014). http://dx.doi.org/10.1017/pasa.2014.23.
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AbstractNoise considerations for experiments that aim to statistically estimate the 21 cm signal from high redshift neutral hydrogen during the Epoch of Reionisation (EoR) using interferometric data are typically computed assuming a tracked observation, where the telescope pointing centre and instrument phase centre are the same over the observation. Current low frequency interferometers use aperture arrays of fixed dipoles, which are steered electronically on the sky, and have different properties to mechanically-steered single apertures, such as reduced sensitivity away from zenith, and discrete pointing positions on the sky. These properties encourage the use of two additional observing modes: (1) zenith drift, where the pointing centre remains fixed at the zenith, and the phase centre tracks the sky, and (2) drift + shift, a hybrid mode where the telescope uses discrete pointing centres, and the sky drifts during each fixed pointing. These three observing modes view the sky differently, and therefore yield different uncertainties in the power spectrum according to the balance of radiometric noise and cosmic variance. The coherence of measurements made by the instrument in these modes dictates the optimal reduction in thermal noise by combination of coherent modes, and the reduction in cosmic variance by combination of incoherent modes (views of different patches of the sky). Along with calibration and instrument stability considerations, the balance between these noise components provides one measure for the utility of these three modes for measuring a statistical signature of the EoR signal. We provide a general framework for estimating the uncertainty in the power spectrum for a given observing mode, telescope beam shape, and interferometer antenna distribution. We then apply this framework to the Murchison Widefield Array (MWA) using an analysis of the two-dimensional (2D) and one-dimensional (1D) power spectra for 900 hours of observing. We demonstrate that zenith drift scans can yield marginally lower uncertainty in the signal power compared with tracked scans for the MWA EoR experiment, and that moderately higher signal-to-noise ratio (S/N) estimates of the amplitude (3%) and slope (1%) of the 1D power spectrum are accessible, translating directly into a reduction in the required observing time to reach the same estimation precision. We find that the additional sensitivity of pointing at zenith, and the reduction in cosmic variance available with a zenith drift scan, makes this an attractive observing mode for current and future arrays.
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LIANG Yue, XIE Yong-hui, SHUAI Tao, CHEN Peng-fei, PEI Yu-xian, XU Hao-tian, ZHAO Yang i in. "Simulation analysis of a hydrogen atomic clock double state-selection beam optical system". Acta Physica Sinica, 2023, 0. http://dx.doi.org/10.7498/aps.72.20221363.
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Hydrogen maser utilises transition frequency of hydrogen atom in hyperfine energy level of ground state for precise timing. It has excellent frequency stability, especially in medium and short-term, and low frequency drift. It has been used as high-precision frequency standard in engineering fields such as time keeping, navigation, and very long baseline interferometry. Clock transition of hydrogen maser is transition between states of |F=1, m<sub>F</sub>=0> and |F=0, m<sub>F</sub>=0>. State selection is realized by state selection magnet, through which high energy atoms are converged and low energy atoms are dispersed. In conventional magnet state-selecting system, both atoms of |F=1, m<sub>F</sub>=0> states, which is required for the maser transition, and useless atoms of |F=1, m<sub>F</sub>=1> states are focused into storage bulb, which places restrictions on the medium and long-term frequency stability performance of hydrogen maser. In order to further improve quality of atomic transition spectral lines and the performance of hydrogen maser, double state-selection beam optical system which based on the Majorana transition mode was constructed through calculations and simulations. In this paper, we used Majorana method to invert atomic states. The magnetic field required for Majorana transition is established using two coils with reverse current, which are spaced 71 mm apart with and the coil axes aligned with the direction of atomic beam. Two additional pairs of transverse Helmholtz coils are spaced 22 mm apart set in the center of the state reversal to adjust the magnetic field zero point, which should coincide with the atomic beam to ensure a complete reversal of atomic polarity. The state reversal region is surrounded by four magnetic shields to reduce the influence of stray magnetic fields. Relationship between selected-state magnetic field gradient and distance of magnetic poles is analysed by simulation, and trajectories of the atoms in the high and low energy under different selected-state magnetic fields are calculated. The utilization and purity of high energy states atoms entering bulb atoms are obtained. The purity of the selected |F=1, m<sub>F</sub>=0> state atoms reaches 99% and the utilization rate is 58%. This is ideal for engineering applications. It effectively enhances the proportion of |F=1, m<sub>F</sub>=0> state atoms entering the atomic storage bulb and ensures utilization of atoms. We have verified the state-selection beam optical system through experiments. By turning on double state-selection system enhancement of the maser signal can be observed; By adjusting coils current of the double state-selection system, variation of maser signal with coils current can be observed, which verifies the effectiveness of double state-selection system.
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Zhao, Na, Qijing Lin, zhang fuzheng, Zhongkai(zn) Zhang, Kun Yao, Libo Zhao, Bian Tian, Ping Yang i Zhuangde Jiang. "High-precision and long-range optical fiber Fabry-Perot interferometer for high temperature measurement". Measurement Science and Technology, 21.06.2022. http://dx.doi.org/10.1088/1361-6501/ac7b10.
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Abstract In order to solve the problem of near-field measurement of aero-engine, a novel large-range, high-precision Fabry-Perot interferometer (FPI) is developed in this paper, which is verified by high temperature experiment. Based on the principle of FPI wavelength drift and frequency spectrum drift, a double-beam interference FPI is designed. Through the analysis of the optical path difference between the two beams, the conclusion that the spectrum drifts to the long-wave direction with the increase of temperature is obtained. Moreover, through frequency spectrum analysis, the measurement error caused by the distortion of the spectrum is avoided, and it is found that the increase in temperature will cause the change in frequency spectrum. Due to the glass-type FPI temperature sensitivity is only 0.0011nm/℃, in order to improve the sensitivity, a ceramic material with higher thermal expansion coefficient was selected as the collimating tube, so that the sensitivity of the temperature sensor was as high as 0.691nm/℃ from normal temperature to 100℃. In order to meet the needs of a wide range of measurement from room temperature to 1000℃, the frequency drift method is utilized. Field experiments were carried out on the ceramic FPI at the tail spray of the aero-engine simulation platform, and the temperature response test from normal temperature to 1000℃ was completed, and the accuracy of the sensor reached 0.098%. In this paper, the principle, design, production and testing of optical fiber sensors are carried out. The developed optical fiber sensor has significance for the high temperature monitoring.
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Neradovskaia, Elizaveta A., Benjamin Maingot, Gilles Cheriaux, Cyrille Claudet, Nicolas Forget i Aurelie Jullien. "Nonlinear chirped interferometry for frequency-shift measurement and χ(3) spectroscopy". APL Photonics, 19.10.2022. http://dx.doi.org/10.1063/5.0109265.
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Four-wave mixing processes are ubiquitous in ultrafast optics and the determination of the coefficients of the χ(3) tensor is thus essential. We introduce a novel time-resolved ultrafast spectroscopic method to characterize the third-order nonlinearity on the femtosecond time-scale. This approach, coined as "nonlinear chirped interferometry", makes use of the variation of the optical group delay of a transmitted probe under the effect of an intense pump pulse in the nonlinearmedium of interest. The observable is the spectral interference between the probe and a reference pulse sampledupstream and the metric is the transient swing of the probe group delay. We show that the detected signal is enhancedwhen the pulses are weakly chirped, and that, although interferometric, the method is immune to environmental phasefluctuations and drifts. By chirping adequately the reference pulse, the transient frequency shift of the probe pulsesis also detected in the time domain and the detected nonlinear signal is enhanced. Nonlinear phase shifts as lowas 10 mrad, corresponding to a frequency shift of 30 GHz, i.e. 0.01% of the carrier frequency, are detected withoutheterodyne detection or active phase-stabilization. The diagonal and/or non-diagonal terms of reference glasses (SiO2)and crystals (Al2O3, BaF2, CaF2) are characterized. The method is finally applied to measure the soft vibration modeof KTiOAsO4 (KTA)
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Sahu, B., P. Pavanchaitanya, A. K. Patra i K. Niranjan. "On the Linkage Between Daytime E Region Field‐Aligned Irregularities and Sporadic E Layer at Low Latitude". Journal of Geophysical Research: Space Physics 129, nr 2 (luty 2024). http://dx.doi.org/10.1029/2023ja031877.
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AbstractWe investigate the generation of low latitude daytime E region field‐aligned irregularities (FAIs) and focus on whether the FAIs are exclusively linked with sporadic E (Es) and whether the FAIs are driven by wind‐driven gradient‐drift instability (GDI). For this investigation, we use observations of FAIs made by the 30 MHz Gadanki Ionospheric Radar Interferometer (GIRI) and Es made by the DPS‐4D digital ionosonde, both collocated at Gadanki. We have also examined simultaneous GIRI and Ionospheric Connection Explorer wind observations to substantiate our results. Results show that daytime E region FAIs are closely linked with Es activity and FAIs are not formed when Es is absent. FAIs are formed when blanketing frequency of Es (fbEs) exceeds frequency of the E layer. Both signal‐to‐noise ratio (SNR) and spectral width of the FAIs echoes display close relationship with top frequency of Es (ftEs). Further, SNR and spectral width of the FAIs echoes display a near‐linear relationship with minimum deviation when Es activity is moderate and show dispersion from near‐linear relationship when Es activity is strong. Zonal drift of the FAIs are predominantly eastward displaying both positive and negative vertical shear. Results also show that Es activity in terms of fbEs and ftEs is found to be closely related to the vertical shear in the zonal drift of the FAIs. Considering the height region of FAIs being highly collisional, we argue that zonal drifts are dominated by zonal wind and vertical shear in the zonal neutral wind is responsible for the formation/maintenance of Es layer and the eastward neutral wind is primarily responsible for the generation of the FAIs through the GDI.
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Zhang, Peijin, Diana Morosan, Anshu Kumari i Emilia Kilpua. "Spatially resolved radio signatures of electron beams in a coronal shock". Astronomy & Astrophysics, 8.01.2024. http://dx.doi.org/10.1051/0004-6361/202347799.
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Type II radio bursts are a type of solar radio bursts associated with coronal shocks. Type II bursts usually exhibit fine structures in dynamic spectra that represent signatures of accelerated electron beams. So far, the sources of individual fine structures in type II bursts have not been spatially resolved in high-resolution low-frequency radio imaging. The objective of this study is to resolve the radio sources of the herringbone bursts found in type II solar radio bursts and investigate the properties of the acceleration regions in coronal shocks. We used low-frequency interferometric imaging observations from the Low Frequency Array to provide a spatially resolved analysis for three herringbone groups (A, B, and C) in a type II radio burst that occurred on 16 October 2015. The herringbones in groups A and C have a typical frequency drift direction and a propagation direction along the frequency. Their frequency drift rates correspond to those of type III bursts and previously studied herringbones. Group B has a more complex spatial distribution, with two distinct sources separated by 50 arcsec and no clear spatial propagation with frequency. One of the herringbones in group B was found to have an exceptionally large frequency drift rate. The characteristics derived from imaging spectroscopy suggest that the studied herringbones originate from different processes. Herringbone groups A and C most likely originate from single-direction beam electrons, while group B may be explained by counterstreaming beam electrons.
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Luchinin, A. S., i I. V. Malygin. "MEASUREMENT OF PHASE AND AMPLITUDE NOISE OF SEMICONDUCTOR LASERS. MEASUREMENT TECHNIQUE. CALIBRATION. RESULTS". Journal of Radio Electronics 2023, nr 8 (sierpień 2023). http://dx.doi.org/10.30898/1684-1719.2023.8.2.
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The application of the frequency detector method for measuring the phase noise spectrum of semiconductor lasers has been experimentally demonstrated. The frequency detector is based on an unbalanced Mach-Zehnder interferometer and a photodetector. Analytical relations are obtained that allow one to choose the parameters of the Mach-Zehnder interferometer and perform experimental calibration of the measuring system. A technique is proposed for measuring the spectral components of the phase noise of lasers in the presence of a slow drift of the delay in fiber-optic lines and the frequency of the laser under study. The results of measuring the phase noise of a low-noise DX-1 laser module and high-noise laser diodes LSDLD155 (DFB) and LSFLD155 (FP) are presented. A strong correlation between the amplitude and phase noise levels of these lasers is found. The decisive influence of the noise of LSDLD155 and LSFLD155 lasers on the level of phase noise of optoelectronic (OE) microwave generators built using them is shown. It has been suggested that the low-noise laser module DX-1, which has a phase noise level 20–60 dB lower (in different parts of the spectrum), is not decisive in the level of phase and amplitude noise of an optoelectronic microwave generator. The investigated OE generator was built during the research in this work. The generator has low phase noise: −120 dBc/Hz at a frequency detuning of 10 kHz. Oscillation frequency 6.8 GHz; fiber optic delay line length 200 m.
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Yan, Jingtao, Lijun Miao, Heliang Shen, Xiaowu Shu, Tengchao Huang i Shuangliang Che. "Low-Drift Closed-Loop Fiber Optic Gyroscope of High Scale Factor Stability Driven by Laser With External Phase Modulation". Photonic Sensors 12, nr 3 (18.01.2022). http://dx.doi.org/10.1007/s13320-022-0648-7.
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AbstractIn view of the poor scale factor stability of the interferometric fiber optic gyroscope (IFOG), it is a creative method to use laser to drive the IFOG for its better frequency stabilization characteristics instead of the broadband light source. As the linewidth of laser is narrow, the errors of coherent backscattering, polarization coupling, and Kerr effect are reintroduced which cause more noise and drift. This paper studies laser spectrum broadening based on external phase modulation of Gaussian white noise (GWN). The theoretical analysis and test results indicate that this method has a good effect on spectrum broadening and can be used to improve the performance of the laser-driven IFOG. In the established closed-loop IFOG, a four-state modulation (FSM) is adopted to avoid temperature instability of the multifunction integrated-optic chip (MIOC) and drift caused by the electronic circuit in demodulation. The experimental results show that the IFOG driven by broadened laser has the angular random walk noise of 0.003 8 °/√h and the drift of 0.017 °/h, which are 62% and 66% better than those without modulation respectively, of which the drift has reached the level of the broadband light source. Although the noise still needs further reduction, its scale factor stability is 0.38 ppm, which has an overwhelming advantage compared with the traditional IFOG.