Optical Calibration Research Articles

Method and portable bench for tests of the laser optical calibration system components for the Baikal-GVD underwater neutrino Cherenkov telescope

The Large-scale deep underwater Cherenkov neutrino telescopes like Baikal-GVD, ANTARES or KM3NeT, require calibration and testing methods of their optical modules. These methods usually include laser-based systems which allow us to check the telescope responses to the light and for real-time monitoring of the optical parameters of water such as absorption and scattering lengths, which show seasonal changes in natural reservoirs of water. We will present a testing method of a laser calibration system and a set of dedicated tools developed for Baikal-GVD, which includes a specially designed and built, compact, portable, and reconfigurable scanning station. This station is adapted to perform fast quality tests of the underwater laser sets just before their deployment in the telescope structure, even on ice, without a darkroom. The testing procedure includes the energy stability test of the laser device, 3D scan of the light emission from the diffuser and attenuation test of the optical elements of the laser calibration system. The test bench consists primarily of an automatic mechanical scanner with a movable Si detector, beam splitter with a reference Si detector and, optionally, Q-switched diode-pumped solid-state laser used for laboratory scans of the diffusers. The presented test bench enables a 3D scan of the light emission from diffusers, which are designed to obtain the isotropic distribution of photons around the point of emission. The results of the measurement can be easily shown on a 3D plot immediately after the test and may be also implemented to a dedicated program simulating photons propagation in water, which allows us to check the quality of the diffuser in the scale of the Baikal-GVD telescope geometry.

Optical and Topological Characterization of Hexagonal DNA Origami Nanotags.

DNA origami can be applied as a "ruler" for nanoscale calibration or super-resolution fluorescence microscopy with an ideal structure for defining fluorophore arrangement, allowing the distance between fluorophores to be precisely controlled at the nanometer scale. DNA origami can also be used as a nanotag with arbitrary programmable shapes for topological identification. In this study, we formed a hexagonal origami structure embedded with three different fluorescent dyes on the surface. The distance between each fluorescent block was ~120 nm, which is below the diffraction limit of light, allowing for its application as a nano-ruler for super-resolution fluorescence microscopy. The outside edge of the hexagonal structure was redesigned to form three different substructures as topological labels. Atomic and scanning force microscopy demonstrated the consistent nanoscale distance between morphological and fluorescent labels. Therefore, this fluorophore-embedded hexagonal origami platform can be used as a dual nanoruler for optical and topological calibration.

Optical calibration of the SNO+ detector in the water phase with deployed sources

SNO+ is a large-scale liquid scintillator experiment with the primary goal of searching for neutrinoless double beta decay, and is located approximately 2 km underground in SNOLAB, Sudbury, Canada. The detector acquired data for two years as a pure water Cherenkov detector, starting in May 2017. During this period, the optical properties of the detector were measured in situ using a deployed light diffusing sphere, with the goal of improving the detector model and the energy response systematic uncertainties. The measured parameters included the water attenuation coefficients, effective attenuation coefficients for the acrylic vessel, and the angular response of the photomultiplier tubes and their surrounding light concentrators, all across different wavelengths. The calibrated detector model was validated using a deployed tagged gamma source, which showed a 0.6% variation in energy scale across the primary target volume.

Multi-frequency passive and active microrheology with optical tweezers

Optical tweezers have attracted significant attention for microrheological applications, due to the possibility of investigating viscoelastic properties in vivo which are strongly related to the health status and development of biological specimens. In order to use optical tweezers as a microrheological tool, an exact force calibration in the complex system under investigation is required. One of the most promising techniques for optical tweezers calibration in a viscoelastic medium is the so-called active–passive calibration, which allows determining both the trap stiffness and microrheological properties of the medium with the least a-priori knowledge in comparison to the other methods. In this manuscript, we develop an optimization of the active–passive calibration technique performed with a sample stage driving, whose implementation is more straightforward with respect to standard laser driving where two different laser beams are required. We performed microrheological measurements over a broad frequency range in a few seconds implementing an accurate multi-frequency driving of the sample stage. The optical tweezers-based microrheometer was first validated by measuring water, and then exemplarily applied to more viscous medium and subsequently to a viscoelastic solution of methylcellulose in water. The described method paves the way to microrheological precision metrology in biological samples with high temporal- and spatial-resolution allowing for investigation of even short time-scale phenomena.

Optical calibration and first light for the deformable mirror demonstration mission CubeSat (DeMi)

Microelectromechanical systems (MEMS) deformable mirrors (DMs) can provide high-precision wavefront control with a small form-factor, low power device. This makes them a key technology option for future space telescopes requiring adaptive optics for high-contrast imaging of exoplanets with a coronagraph instrument. The Deformable Mirror Demonstration Mission (DeMi) CubeSat payload is a miniature space telescope designed to demonstrate MEMS DM technology in space for the first time. The DeMi payload contains a 50-mm primary mirror, an internal calibration laser source, a 140-actuator MEMS DM from Boston Micromachines Corporation, an image plane wavefront sensor, and a Shack–Hartmann wavefront sensor (SHWFS). The key DeMi payload requirements are to measure individual actuator wavefront displacement contributions to a precision of 12 nm and correct both static and dynamic wavefront errors in space to less than 100-nm RMS error. The DeMi mission will raise the technology readiness level of MEMS DM technology from a five to at least a seven for future space telescope applications. We summarize the DeMi optical payload design, calibration, optical diffraction model, alignment, integration, environmental testing, and preliminary data from in-space operations. Ground testing data show that the DeMi SHWFS can measure individual actuator deflections on the MEMS DM to within 10 nm of interferometric calibration measurements and can meet the 12-nm precision mission requirement for actuator deflection voltages between 0 and 120 V. Payload data from throughout environmental testing show that the MEMS DM and DeMi payload survived environmental testing and provides a valuable baseline to compare with space data. Initial data from space operations show the MEMS DM actuating in space with a median agreement between individual actuator measurements from space and equivalent ground testing data of 12 nm.

Optical Aberration Calibration and Correction of Photographic System Based on Wavefront Coding.

The image deconvolution technique can recover potential sharp images from blurred images affected by aberrations. Obtaining the point spread function (PSF) of the imaging system accurately is a prerequisite for robust deconvolution. In this paper, a computational imaging method based on wavefront coding is proposed to reconstruct the wavefront aberration of a photographic system. Firstly, a group of images affected by local aberration is obtained by applying wavefront coding on the optical system’s spectral plane. Then, the PSF is recovered accurately by pupil function synthesis, and finally, the aberration-affected images are recovered by image deconvolution. After aberration correction, the image’s coefficient of variation and mean relative deviation are improved by 60% and 30%, respectively, and the image can reach the limit of resolution of the sensor, as proved by the resolution test board. Meanwhile, the method’s robust anti-noise capability is confirmed through simulation experiments. Through the conversion of the complexity of optical design to a post-processing algorithm, this method offers an economical and efficient strategy for obtaining high-resolution and high-quality images using a simple large-field lens.

Optical calibration system for the LUX-ZEPLIN (LZ) outer detector

The LUX-ZEPLIN experiment will search for dark matter particle interactions with a detector containing a total of 10 tonnes of liquid xenon. Surrounding the liquid xenon cryostat is an outer detector veto system with the primary aim of vetoing neutron single-scatter events in the liquid xenon that could mimic a weakly interacting massive particle (WIMP) dark matter signal. The outer detector consists of approximately 17 tonnes of gadolinium-loaded liquid scintillator confined to acrylic tanks surrounding the cryostat and 228,000 litres of water as the outermost layer. It will be monitored by 120 inward-facing 8-inch photomultiplier tubes. An optical calibration system has been designed and built to calibrate and monitor these photomultiplier tubes allowing the veto system to reach its required efficiency and thus ensuring that LUX-ZEPLIN meets its target sensitivity.

SPRINT, system parameters recurrent invasive tracking: a fast and least-cost online calibration strategy for adaptive optics

ABSTRACT Future large adaptive telescopes will trigger new constraints for the calibration of adaptive optics (AO) systems equipped with pre-focal deformable mirrors (DMs). The image of the DM actuator grid, as seen by the wavefront sensor (WFS), may evolve during the operations because of the flexures of the opto-mechanical components present in the optical path. This will result in a degraded AO performance that will affect the scientific operation. To overcome this challenge, it will be necessary to regularly monitor and compensate for these DM/WFS mis-registrations, either by physically realigning some optical components or by updating the control matrix of the system. In this paper, we present a new strategy to track mis-registrations using a pseudo-synthetic model of the AO system. The method is based on an invasive approach where signals are acquired on-sky, before or during the scientific operations, and fed to the model to extract the mis-registration parameters. We introduce a method to compute the most sensitive modes to these mis-registrations that allows us to reduce the number of degrees of freedom required by the algorithm and to minimize the effect on the scientific performance. We demonstrate that, by using only a few of these well-selected signals, the method provides very good accuracy for parameter estimation, well under the targeted accuracy, and has a negligible effect on the scientific path. In addition, the method appears to be very robust to varying operating conditions of noise and atmospheric turbulence and it performs equally for both pyramid and Shack–Hartmann WFSs.

Reference materials for optic nanosensor systems: reduced glutathione and chloramphenicol

The research provides enterprise reference material (ERM) development approach for nanosensor system on the basis of dynamic light scattering and fluorescence for qualitative and quantitative determination of nutrition pollutant - chloramphenicol antibiotic (laevomycetin), as well as marker of ischaemic stroke and a number of other diseases - reduced glutathione.ERM candidate materials were chosen chloramphenicol and reduced glutathione. The attestation procedure based on calculating-experimental approach by preparation procedure was used to determine the certified value of ERM. During the tests there were determined metrological characteristics of reference material. The certified value of ERM for reduced glutathione mass fraction is 98,5 %, the expanded uncertainty of certified value with coverage factor k=2 is ± 0,3 %. The certified value of ERM for chloramphenicol mass concentration is 10,0 g/dm3, the expanded uncertainty of certified value with coverage factor k = 2 is ± 4,0 %.The implementation of the developed ERMs showed their appropriateness for optic nanosensor systems calibration on the base of dynamic light scattering and fluorescence.We suppose that the developed enterprise reference materials further may be certified as CRM (certified reference material) and used for verification, calibration and graduation of compact detection devices of the «point of care diagnostics» type under development, which are intended for express analysis on the sampling site directly.

A Swift Fix for Nuclear Outbursts

Abstract In November 2020, the Swift team announced an update to the UltraViolet and Optical Telescope calibration to correct for the loss of sensitivity over time. This correction affects observations in the three near-ultraviolet (UV) filters, by up to 0.3 mag in some cases. As UV photometry is critical to characterizing tidal disruption events (TDEs) and other peculiar nuclear outbursts, we recomputed published Swift data for TDEs and other singular nuclear outbursts with Swift photometry in 2015 or later as a service to the community. Using archival UV, optical, and infrared photometry, we ran host SED fits for each host galaxy. From these, we computed synthetic host magnitudes and host-galaxy properties. We calculated host-subtracted magnitudes for each transient and computed blackbody fits. In addition to the nuclear outbursts, we include the ambiguous transient ATLAS18qqn (AT2018cow), which has been classified as a potential TDE on an intermediate-mass black hole. Finally, with updated bolometric light curves, we recover the relationship of Hinkle et al., where more-luminous TDEs decay more slowly than less-luminous TDEs, with decreased scatter compared to the original relationship.

Astrosource: automating optical astronomy measurement, calibration and analysis for variable stellar sources from provided photometry

Fitzgerald et al., (2021). astrosource: automating optical astronomy measurement, calibration and analysis for variable stellar sources from provided photometry. Journal of Open Source Software, 6(58), 2641, https://doi.org/10.21105/joss.02641

Broad dual-band temporal compressive imaging with optical calibration.

For applications such as remote sensing and bio-imaging, images from multiple bands can provide much richer information compared to a single band. However, most multispectral imaging systems have difficulty in acquiring images for high-speed moving objects. In this paper, we use a DMD-based temporal compressive imaging (TCI) system to obtain high-speed images of moving objects over a broad dual-band spectral range, in the visible and the near-infrared (NIR) bands simultaneously. To deal with the degraded reconstruction caused by the optics, four nonuniform calibration strategies are studied, which can also be implemented into other compressive imaging systems. Moving objects covered by paint or through a diffuser are reconstructed to demonstrate the superior performance of the calibrated broad dual-band TCI system.

Optical system calibration for 3D measurements in a hydrodynamic tunnel

For non-contact 3D measurements in hydrodynamic tunnels by photogrammetry methods, it is necessary to refine the standard model of image formation in the camera by taking into account an effect of refraction of rays at the boundaries of optical media, namely, at an air-glass boundary and glass-working fluid boundary. The article presents a model of image formation for shooting in a working environment that includes various optical media and methods for calibrating an optical system for 3D measurements of the coordinates of scene objects, while taking into account the real boundaries of the optical media. Experimental results on calibrating the system of three-dimensional measurements when an object image is formed by rays passing through two optical boundaries are discussed.

Characterization and calibration of shape sensors based on multicore optical fibre

Abstract In order to provide high accuracy in shape measurement with multicore optical fibres, characterization and calibration procedures are an important part of sensor preparation. Some procedures can be considered mandatory for adequate shape reconstruction, while others can help to enhance the measurement accuracy. Several of such procedures are discussed and experimentally applied for demonstrating the possible performance enhancement of curvature sensing, a fundamental phase of the shape reconstruction process. The maximum error observed in curvature calculation for a test object has been proved to be almost halved, decreasing from 2.48% to 1.36%, by applying such calibration corrections. The overall average relative accuracy of curvature measurement was improved from 0.89% to 0.5% (an improvement of 44%).

Optical Butting of Plane Array Sensors for PA-LiDAR

In order to expand the field of view and improve the resolution, a method of optical butting was proposed for two plane array sensors using beam splitter prism in this paper. The principle of optical butting, the optical design, calibration and focusing technology, and alignment method were presented and analyzed. In addition, the gray image stitch and point cloud data registration were also realized. To prove the concept of the optical butting method, we built a prototype system for experiment. The splicing of two <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$320\times240$ </tex-math></inline-formula> sensors of plane array laser imaging detection and ranging (PA-LiDAR) was implemented. After optical butting, the total effective pixel number was <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$320\times480$ </tex-math></inline-formula> , the total effective area was <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$6.4\times4.8$ </tex-math></inline-formula> mm, and the field of view was <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$22\,\,^{\circ }\times 15\,\,^{\circ }$ </tex-math></inline-formula> . Compared with the conventional laser radar system, the optical butting system can improve the field of view and resolution by a factor about <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2\times 1$ </tex-math></inline-formula> . This method had the advantages of simple constitution, easy accomplishment, small space and high assembly precision which guaranteed the operating requirement of the PA-LIDAR sensor.

Research and evaluation of the measurement uncertainty with the two-dimensional optical calibration plate

As a portable standard, two-dimensional optical calibration plate is playing an increasingly important role in precision industry measurement. Therefore, it is of great scientific significance and obvious socioeconomic benefits to carry out the research of comparator. This paper was based on rich experience with the institute in the field of the geometric measurement technology for a long time, the measurement uncertainty of the optical calibration plate was studied, and the measurement uncertainty of the instrument has been researched. The measurement uncertainty of the error of the calibration plate’s setting and marking value was U= (0.14+ 0.015L) m k=2 L: mm.

MEASUREMENT UNCERTAINTY OF THE OPTICAL WAVELENGTH CALIBRATION 633 nm BY BEAT FREQUENCY MEASUREMENT METHODS

Measurement traceability is one of the critical aspects in metrology area. The measurement uncertainty had been evaluated to assure reliability of the optical wavelength calibration system for stabilized He-Ne laser 633 nm in SNSU-BSN. Beat frequency measurement was applied as a calibration method by utilizing KIM-1 as a reference standard that traceable to SI unit through CCL-K11 key comparison. Best measurement capability declares with a relative uncertainty of ±1.3×10 -10 by excluding UUC effect. The calibration replica was performed as a validation process, dual mode laser head Agilent 5519B took a role as UUC. As calibration result, beat frequency of KIM-1 and UUC is (122.931±0.060) MHz. Among all of the uncertainty sources, KIM-1 uncertainty most significant influence to the beat frequency uncertainty and the optical wavelength of the UUC laser in vacuum condition. Based on the evaluation result, the calibration system of stabilized He-Ne laser can be validated and trace back with documented unbroken calibration chain to the primary standard of length, KIM-1 where established in SNSU-BSN.

Photon-counting-based optical frequency metrology.

Low power can be a concern for the calibration of frequency-stabilized lasers by traditional heterodyne beating at a photodiode. On the other hand, time-correlated photon counts in a Hong-Ou-Mandel interferometer are able to reveal the frequency difference between a pair of few-photon laser sources. This paper evaluates the photon-counting method as a metrological tool for optical frequency calibration traced to radiation standards. Measurement procedure and uncertainty budget are developed. The method's uncertainty is determined as 0.24 MHz from measurements with a pair of frequency-stabilized He-Ne lasers. The optical frequency traces to standard radiation with 2.9 MHz uncertainty, limited by stability of the sources used. Validation measurements using classical heterodyne technique agree within 0.12 MHz, thus establishing the photon-counting approach as a resource for frequency metrology of extremely faint laser sources.

HPIPS: A High-Precision Indoor Pedestrian Positioning System Fusing WiFi-RTT, MEMS, and Map Information.

In order to solve the problem of pedestrian positioning in the indoor environment, this paper proposes a high-precision indoor pedestrian positioning system (HPIPS) based on smart phones. First of all, in view of the non-line-of-sight and multipath problems faced by the radio-signal-based indoor positioning technology, a method of using deep convolutional neural networks to learn the nonlinear mapping relationship between indoor spatial position and Wi-Fi RTT (round-trip time) ranging information is proposed. When constructing the training dataset, a fingerprint grayscale image construction method combined with specific AP (Access Point) positions was designed, and the representative physical space features were extracted by multi-layer convolution for pedestrian position prediction. The proposed positioning model has higher positioning accuracy than traditional fingerprint-matching positioning algorithms. Then, aiming at the problem of large fluctuations and poor continuity of fingerprint positioning results, a particle filter algorithm with an adaptive update of state parameters is proposed. The algorithm effectively integrates microelectromechanical systems (MEMS) sensor information in the smart phone and the structured spatial environment information, improves the freedom and positioning accuracy of pedestrian positioning, and achieves sub-meter-level stable absolute pedestrian positioning. Finally, in a test environment of about 800 m2, through a large number of experiments, compared with the millimeter-level precision optical dynamic calibration system, 94.2% of the positioning error is better than 1 m, and the average positioning error is 0.41 m. The results show that the system can provide high-precision and high-reliability location services and has great application and promotion value.

Response of the mode Grüneisen parameters with anisotropic compression: A pressure and temperature dependent Raman study of β -Sn

The lattice dynamic response of body-centered tetragonal $\ensuremath{\beta}\text{\ensuremath{-}}\mathrm{Sn}$ $(I{4}_{1}/amd)$ under high-pressure and -temperature conditions is determined using experimental optical vibration modes. Raman scattering is used to map the phase stability region of $\ensuremath{\beta}\text{\ensuremath{-}}\mathrm{Sn}$ to perform mode Gr\uneisen analysis, and we demonstrate the necessity of an optical intensity calibration for Raman thermometry. The Gr\uneisen tensor is evaluated along a set of isotherms to address shortcomings of single-mode Gr\uneisen parameters with respect to anisotropic deformations of this tetragonal structured soft metal. The changes observed here in the Gr\uneisen tensor as a function of temperature are related to anharmonicity and denote potential criteria for the onset of premelting.