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In this study, based on the existing high-temperature measurement and calibration equipment, calibration experiments using the spectral emissivity of intrinsic element particles in the field were designed to achieve the accurate measurement of a temperature field. Laser-induced breakdown spectroscopy was used to select the corresponding elements, and the element doping method was used to approximate the real temperature field. After calibrating the camera, the temperature distribution and spectral emissivity distribution of the flame were calculated. The range of calculated values was determined to be well-consistent with data collected using an infrared thermal imager, which verified the accuracy of the experiment.

Light spectra are a very important source of information for diverse classification problems, e.g., for discrimination of materials. To lower the cost of acquiring this information, multispectral cameras are used. Several techniques exist for estimating light spectra out of multispectral images by exploiting properties about the spectrum. Unfortunately, especially when capturing multispectral videos, the images are heavily affected by noise due to the nature of limited exposure times in videos. Therefore, models that explicitly try to lower the influence of noise on the reconstructed spectrum are highly desirable. Hence, a novel reconstruction algorithm is presented. This novel estimation method is based on the guided filtering technique that preserves basic structures, while using spatial information to reduce the influence of noise. The evaluation based on spectra of natural images reveals that this new technique yields better quantitative and subjective results in noisy scenarios than other state-of-the-art spatial reconstruction methods. Specifically, the proposed algorithm lowers the mean squared error and the spectral angle up to 46% and 35% in noisy scenarios, respectively. Furthermore, it is shown that the proposed reconstruction technique works out of the box and does not need any calibration or training by reconstructing spectra from a real-world multispectral camera with nine channels.

Validation of remote sensing retrievals of aerosol microphysical and optical properties requires in situ measurements of the same properties. We present here an improved imaging nephelometer for measuring the directionality and polarization of light (i.e., polarimetry) scattered at two wavelengths (405 and 660 nm) with high temporal resolution. The instrument was designed for airborne deployment and is capable of ground-based measurements as well. The laser imaging nephelometer (LiNeph) uses two orthogonal detectors with wide-angle lenses and linearly polarized light sources to measure both the phase function, P11(θ), and degree of linear polarization, -P12/P11(θ). In this work, we will describe the instrument function and calibration, as well as data acquisition and reduction. The instrument was first deployed aboard the NASA DC-8 during the 2019 FIREX-AQ campaign. Here, we present field measurements of smoke plumes that show that the LiNeph has sufficient resolution for 0.24 Hz polarimetric measurements at two wavelengths, 405 and 660 nm, at integrated scattering coefficients ranging from 50–8000 Mm−1.

Optical particle counters (OPCs) based on the light extinction measurement scheme are widely used in the industry for monitoring the level of wear debris in lubricating oil systems. In this work it is investigated how model-based size estimation and OPC output data can be correlated. Spherical metal coated 5–20 μm diameter particles were used in a laboratory oil system and monitored using an OPC. The raw OPC output data were extracted with the purpose of estimating the true particle size. Distribution parameters has been deducted from detected minima in output signals for each particle diameter using a half-normal fit centered at the detected kernel peak. Experiments with different sized particles showed that signal minima amplitude distributions differ between particle diameters thus, clearly showing the discrimination ability of the OPC. Furthermore, to obtain OPC based true size determination, the apparent absorption coefficient of the micrometer sized particles must be considered. Thus, reducing the maximum deviation between true and OPC determined diameter to 13%.

Optical sensors are among the sensors that are often used for distance measurements. An optical distance sensor is basically made of a light emitter (Tx) such as a light emitting diode (LED), a light receiver (Rx) such as a photosensitive transistor, and a circuit supporting the operation of the Tx and Rx. The distance measurement is made using the reflection technique in which the Tx emits a light to a target and the Rx receives the reflected light from the target. When designing such a sensor, the factors that affect the performance of measurements need to be taken into account. Among them are light intensity and wavelength. The purpose of this thesis project is to investigate and evaluate the optical sensors, in application towards distance measurement. To this purpose, three pairs of LEDs and phototransistors are selected which three distance sensors are made of. The lights from three LEDs have the wavelengths of 830, 880, and 940 nm, respectively, which are all in the infrared (IR) spectrum. A circuit was made for each sensor in order to read the measurements and then calculate the distances, and then tested in a testbench. The testbench has a metal plate used as a measurement target which can be moved up and down by a motor. Each of the circuits was placed on the testbench’s base, and a microcontroller (Arduino Uno R3) was used to read the measurement of voltage (proportional to the light intensity) from the Rx as the distance to the target changes up to one meter. The measurement data is then presented on a graphical interface to analyse the relationship of light intensity with distance. Curve fitting and optimization techniques are applied to the data to construct a smooth function that approximately fits the data. An operating range where the distance can be reliably determined is determined for each unit. The circuit design and technique was proven to work for operating ranges up to one meter. A limited moving range of the testbench does not allow for experiments at distances higher than one meter and the microcontroller is ill fit for measuring low voltages, but these can be addressed by improving the measuring environment without changing the underlying technique. The test results of the distance measurement reveal that the three sensors give similar distance estimations between different configurations over an operating range of up to 0.9 meters. Future work should consider improving the circuit design to reduce power ripple and increasing operating range.

The Extreme Universe Space Observatory - Super Pressure Balloon (EUSO-SPB2) mission will fly two custom telescopes that feature Schmidt optics to measure \v{C}erenkov- and fluorescence-emission of extensive air-showers from cosmic rays at the PeV and EeV-scale, and search for tau-neutrinos. Both telescopes have 1-meter diameter apertures and UV/UV-visible sensitivity. The \v{C}erenkov telescope uses a bifocal mirror segment alignment, to distinguish between a direct cosmic ray that hits the camera versus the \v{C}erenkov light from outside the telescope. Telescope integration and laboratory calibration will be performed in Colorado. To estimate the point spread function and efficiency of the integrated telescopes, a test beam system that delivers a 1-meter diameter parallel beam of light is being fabricated. End-to-end tests of the fully integrated instruments will be carried out in a field campaign at dark sites in the Utah desert using cosmic rays, stars, and artificial light sources. Laser tracks have long been used to characterize the performance of fluorescence detectors in the field. For EUSO-SPB2 an improvement in the method that includes a correction for aerosol attenuation is anticipated by using a bi-dynamic Lidar configuration in which both the laser and the telescope are steerable. We plan to conduct these field tests in Fall 2021 and Spring 2022 to accommodate the scheduled launch of EUSO-SPB2 in 2023 from Wanaka, New Zealand.

In this presentation a review about the current state of the art concerning the application of deterministic single photon sources for absolute radiometry, i.e. the calibration of single photon detectors, is given. At the Physikalisch-Technische Bundesanstalt, the German national Metrology institute, an extensive research is carried out to optimize single photon sources for this purpose. Different single photon sources are currently under investigation, these are sources based on defect centres in (nano-)diamonds, on molecules and on semiconductor quantum dots.

We developed a system to measure the internal profile of small diameter hole. The minimum measurable diameter is 0.14 mm and the maximum measureable depth is 2 mm. The system can measure the roundness, straightness, cylindricity, and roughness. The main difficulty to measure the small diameter hole is in the relative positioning and aligning between hole and sensor probe. We discuss the principle of alignment, and also the calibration method for the sensor with fine fiber probe.

We present a compact, diffuser-assisted, single-pixel computational camera. A rotating ground glass diffuser is adopted, in preference to a commonly used digital micro-mirror device (DMD), to encode a two-dimensional (2D) image into single-pixel signals. We retrieve images with an 8.8% sampling ratio after the calibration of the pseudo-random pattern of the diffuser under incoherent illumination. Furthermore, we demonstrate hyperspectral imaging with line array detection by adding a diffraction grating. The implementation results in a cost-effective single-pixel camera for high-dimensional imaging, with potential for imaging in non-visible wavebands., Comment: 5 pages, 4 figures

Dust orientation has been an ongoing investigation in recent years. Its potential proof will be a paradigm shift for dust remote sensing, invalidating the currently used simplifications of randomly oriented particles. Vertically resolved measurements of dust orientation can be acquired with a polarization lidar designed to target the off-diagonal elements of the backscatter matrix which are nonzero only when the particles are oriented. Building on previous studies, we constructed a lidar system emitting linearly and elliptically polarized light at 1064 nm and detecting the linear and circular polarization of the backscattered light. Its measurements provide direct flags of dust orientation, as well as more detailed information of the particle microphysics. The system also has the capability to acquire measurements at varying viewing angles. Moreover, in order to achieve good signal-to-noise ratio in short measurement times, the system is equipped with two laser sources emitting in an interleaved fashion and two telescopes for detecting the backscattered light from both lasers. Herein we provide a description of the optical and mechanical parts of this new lidar system, the scientific and technical objectives of its design, and the calibration methodologies tailored for the measurements of oriented dust particles. We also provide the first, preliminary measurements of the system during a dust-free day. The work presented does not include the detection of oriented dust (or other oriented particles), and therefore the instrument has not been tested fully in this objective.

In this paper, we described a metrological AFM in order to calibrate step height standards used as transfer artefacts for commercial AFMs. With X, Y and Z axes laser displacement interferometers installed, related calibrated results are directly traceable to the SI of metre definition. The step height measurement accuracy was verified using several step heights up to 2000 nm. Corresponding measurement uncertainty in step height standard calibration was estimated in line with the Guide to the Expression of Uncertainty in Measurement (GUM). The expanded measurement uncertainty (k = 2) was better than 2.5 nm over a full range of up to 2000 nm. This suggests that the developed metrology system is capable of conducting nano-scale metrological standard calibration which is applicable to disseminating accuracy and traceability to commercial AFMs and optical microscopes in application of surface topography measurement.

IXPE scientific payload comprises of three telescopes, each composed of a mirror and a photoelectric polarimeter based on the Gas Pixel Detector design. The three focal plane detectors, together with the unit which interfaces them to the spacecraft, are named IXPE Instrument and they will be built and calibrated in Italy; in this proceeding, we will present how IXPE Instrument will be calibrated, both on-ground and in-flight. The Instrument Calibration Equipment is being finalized at INAF-IAPS in Rome (Italy) to produce both polarized and unpolarized radiation, with a precise knowledge of direction, position, energy and polarization state of the incident beam. In flight, a set of four calibration sources based on radioactive material and mounted on a filter and calibration wheel will allow for the periodic calibration of all of the three IXPE focal plane detectors independently. A highly polarized source and an unpolarized one will be used to monitor the response to polarization; the remaining two will be used to calibrate the gain through the entire lifetime of the mission., 11 pages, 8 figures

An interferometric self-calibration method for the evaluation of the pitch deviation of scale grating has been extended to evaluate the pitch deviation of the long-range type linear scale by utilizing the stitching interferometry technique. Following the previous work, in which the interferometric self-calibration method was proposed to assess the pitch deviation of the scale grating by combing the first-order diffracted beams from the grating, a stitching calibration method is proposed to enlarge the measurement range. Theoretical analysis is performed to realize the X-directional pitch deviation calibration of the long-range linear scale while reducing the second-order accumulation effect by canceling the influence of the reference flat error in the sub-apertures’ measurements. In this paper, the stitching interferometry theory is briefly reviewed, and theoretical equations of the X-directional pitch deviation stitching are derived for evaluation of the pitch deviation of the long-range linear scale. Followed by the simulation verification, some experiments with a linear scale of 105 mm length from a commercial interferential scanning-type optical encoder are conducted to verify the feasibility of the self-calibration stitching method for the calibration of the X-directional pitch deviation of the linear scale over its whole area.

Overlay metrology measures pattern placement between two layers in a semiconductor chip. The continuous shrinking of device dimensions drives the need to explore novel optical overlay metrology concepts that can address many of the existing metrology challenges. We present a compact dark-field digital holographic microscope that uses only a single imaging lens. Our microscope offers several features that are beneficial for overlay metrology, like a large wavelength range. However, imaging with a single lens results in highly aberrated images. In this work, we present an aberration calibration and correction method using nano-sized point scatterers on a silicon substrate. Computational imaging techniques are used to recover the full wavefront error, and we use this to correct for the lens aberrations. We present measured data to verify the calibration method and we discuss potential calibration error sources that must be considered. A comparison with a ZEMAX calculation is also presented to evaluate the performance of the presented method.

Phase measuring deflectometry (PMD) is a competitive method for specular surface measurement that offers the advantages of a high dynamic range, non-contact process, and full field measurement, furthermore, it can also achieve high accuracy. Camera calibration is a crucial step for PMD. As a result, a method based on the calibration of the entrance pupil center is introduced in this paper. Then, our proposed approach is compared with the most popular photogrammetric method based on Zhang’s technique (PM) and Huang’s modal phase measuring deflectometry (MPMD). The calibration procedures of these three methods are described, and the measurement errors introduced by the perturbations of degrees of freedom in the PMD system are analyzed using a ray tracing technique. In the experiment, a planar window glass and an optical planar element are separately measured, and the measurement results of the use of the three methods are compared. The experimental results for the optical planar element (removing the first 6 terms of the Zernike polynomial) show that our method’s measurement accuracy reached 13.71 nm RMS and 80.50 nm PV, which is comparable to accuracy values for the interferometer.

Improving sensitivity and spatial resolution in small animal Positron Emission Tomography imaging instrumentation constitutes one of the main goals of nuclear imaging research. These parameters are degraded by the presence of gaps between the detectors. The present manuscript experimentally validates our prototype of an edge-less pre-clinical PET system based on a single LYSO:Ce annulus with an inner diameter of 62 mm and 10 outer facets of 26 × 52 mm(2). Scintillation light is read out by arrays of 8 × 8 SiPMs coupled to the facets, using a projection readout of the rows and columns signals. The readout provides accurate Depth of Interaction (DOI). We have implemented a calibration that mitigates the DOI-dependency of the transaxial and axial impact coordinates, and the energy photopeak gain. An energy resolution of 23.4 ± 1.8% was determined. Average spatial resolution of 1.4 ± 0.2 and 1.3 ± 0.4 mm FWHM were achieved for the radial and axial directions, respectively. We found a peak sensitivity of 3.8% at the system center, and a maximum NECR at 40.6 kcps for 0.27 mCi. The image quality was evaluated using reconstructed images of an array of sources and the NEMA image quality phantom was also studied.

Publisher Copyright: IEEE Absolute thickness and free-water-content gradients in gelatin-based corneal phantoms with physiologically accurate radii of curvature and aqueous backing were extracted via coherent submillimeter-wave reflectometry at 220-330 GHz. Fourier-domain-based calibration methods, utilizing temporal and spatial gating, were developed and yielded peak-to-peak amplitude and phase clutter of 10-3 and 0.1°, respectively, for signal-to-noise ratios (SNRs) between 40 and 50 dB. Total 12 phantoms were fabricated. Calibration methods enabled quantification of target sphericity that strongly correlated with optical-coherence tomography-based sphericity metrics via image segmentation. The extracted free-water volume fraction varied less than 5% in the five phantoms whose fabrication yielded the most spherical geometry. Submillimeter-wave-based thickness accuracy was better than 111 μm (∼λ/9) with an average of 65 μm (∼λ/17) and standard deviation of 44 μm (∼λ/25) for phantoms with physiologically relevant geometry. Monte-Carlosimulations of measurement noise and uncertainty limits agree with the experimental data analysis and indicate a lower thickness accuracy limit of 33 μm, and water-content sensitivities of 0.5% and 11.8% for the anterior and posterior segments, respectively. Numerical analysis suggests that the measurement fidelity was SNR limited and identified optical path length ambiguities within the cornea where a continuum of thickness/water gradient pairs produces statistically insignificant differences in complex reflection coefficient for finite SNR. This is the first known submillimeter-wave measurement technique, which is able to extract both the thickness and water-content gradients from a soft-tissue phantom, with a water backing, without the need for ancillary measurements.

The study of aerosol optical properties is essential to understand its impact on the global climate. In our recent field measurement carried out in the Gehu area of southwest Changzhou City, a photoacoustic extinctiometer (PAX) and a cavity attenuated phase shift albedo monitor (CAPS-ALB) were used for online aerosol optical properties measurement. Laboratory calibration with gas and particle samples were carried out to correct disagreements of field measurements. During particle calibration, we adopted ammonium sulfate (AS) samples for scattering calibration of nephelometer parts of both the instruments, then combined these with number-size distribution measurements in the MIE model for calculating the value of the total scattering (extinction) coefficient. During gas calibration, we employed high concentrations of NO2 for absorption calibration of the PAX resonator and then further intercompared the extinction coefficient of CAPS-ALB with a cavity-enhanced spectrometer. The correction coefficient obtained from the laboratory calibration experiments was employed on the optical properties observed in the field measurements correspondingly and showed good results in comparison with reconstructed extinction from the IMPROVE model. The intercomparison of the calibrated optical properties of PAX and CAPS-ALB in field measurements was in good agreement with slopes of 1.052, 1.024 and 1.046 for extinction, scattering and absorption respectively, which shows the reliability of measurement results and verifies the correlation between the photoacoustic and the cavity attenuated phase shift instruments.

Objective: Proton range uncertainties can compromise the effectiveness of proton therapy treatments. Water equivalent path length (WEPL) assessment by flat panel detector proton radiography (FP-PR) can provide means of range uncertainty detection. Since WEPL accuracy intrinsically relies on the FP-PR calibration parameters, the purpose of this study is to establish an optimal calibration procedure that ensures high accuracy of WEPL measurements. To that end, several calibration settings were investigated. Approach: FP-PR calibration datasets were obtained simulating PR fields with different proton energies, directed towards water-equivalent material slabs of increasing thickness. The parameters investigated were the spacing between energy layers (ΔE) and the increment in thickness of the water-equivalent material slabs (ΔX) used for calibration. 30 calibrations were simulated, as a result of combining ΔE = 9, 7, 5, 3, 1 MeV and ΔX = 10, 8, 5, 3, 2, 1 mm. FP-PRs through a CIRS electron density phantom were simulated, and WEPL images corresponding to each calibration were obtained. Ground truth WEPL values were provided by range probing multi-layer ionization chamber simulations on each insert of the phantom. Relative WEPL errors between FP-PR simulations and ground truth were calculated for each insert. Mean relative WEPL errors and standard deviations across all inserts were computed for WEPL images obtained with each calibration. Main results: Large mean and standard deviations were found in WEPL images obtained with large ΔE values (ΔE = 9 or 7 MeV), for any ΔX. WEPL images obtained with ΔE ≤ 5 MeV and ΔX ≤ 5 mm resulted in a WEPL accuracy with mean values within ±0.5% and standard deviations around 1%. Significance: An optimal FP calibration in the framework of this study was established, characterized by 3 MeV ≤ ΔE ≤ 5 MeV and 2 mm ≤ ΔX ≤ 5 mm. Within these boundaries, highly accurate WEPL acquisitions using FP-PR are feasible and practical, holding the potential to assist future online range verification quality control procedures.

In this work, a novel 3D-printed biaxial sensor system for tilt measurement, based primarily on the use of four Fiber Bragg Grating (FBG) devices, has been developed and its performance characterized. The tilt sensor system created is of a compact design and relatively small dimensions, making it ideally suited to a variety of industrial applications. In the system developed, the four FBGs used were spliced in a serial formation and attached to four different sides of the sensor structure designed, to allow biaxial measurements to be made. The wavelengths' shift of the FBGs used were monitored as a function of the tilt of the device, using an Optical Spectrum Analyzer (OSA) for this development work. In the sensor, an average FBG-based responsivity of 0.01 nm/° of tilt was measured for each of the different FBGs used. To provide compensation for temperature changes in the system itself, a further FBG-based approach was used (in which they were configured to be insensitive to the effect of the tilt). They were thus calibrated by being exposed to a range of operational temperatures for the system, showing, as a result, a calibration of 0.011 nm/°C. Prior work on the sensor system had proved it to be highly linear in response, over the tilt range of 0° ± 90°. The experimental results obtained from the performance characterization indicate that the small, compact design of this type yields excellent responsivity, compared to other larger and more complex designs discussed in the literature. The sensor system was also relatively easy to fabricate using the 3D-printing method, creating in that way an inexpensive, temperature-compensated tilt monitoring device that had a wide variety of potential industrial applications.

Intrinsic projector calibration is essential in projection mapping (PM) applications, especially in dynamic PM. However, due to the shallow depth-of-field (DOF) of a projector, more work is needed to ensure accurate calibration. We aim to estimate the intrinsic parameters of a projector while avoiding the limitation of shallow DOF. As the core of our technique, we present a practical calibration device that requires a minimal working volume directly in front of the projector lens regardless of the projector's focusing distance and aperture size. The device consists of a flat-bed scanner and pinhole-array masks. For calibration, a projector projects a series of structured light patterns in the device. The pinholes directionally decompose the structured light, and only the projected rays that pass through the pinholes hit the scanner plane. For each pinhole, we extract a ray passing through the optical center of the projector. Consequently, we regard the projector as a pinhole projector that projects the extracted rays only, and we calibrate the projector by applying the standard camera calibration technique, which assumes a pinhole camera model. Using a proof-of-concept prototype, we demonstrate that our technique can calibrate projectors with different focusing distances and aperture sizes at the same accuracy as a conventional method. Finally, we confirm that our technique can provide intrinsic parameters accurate enough for a dynamic PM application, even when a projector is placed too far from a projection target for a conventional method to calibrate the projector using a fiducial object of reasonable size.

This paper presents experimental and numerical studies of erythrocyte stretching, with a focus on the aging of red blood cells in an in vitro environment during storage. The experimental studies were performed using optical tweezers. The laser beam was used to pull and stretch a cell sedimented on a flat surface. A force calibration was obtained via a comparison of the experimental data with results from finite element simulations of the cell stretching. The experiments were performed using blood samples from blood bank donations made by three donors. The experiments were performed over 21 days of storage, and the estimate erythrocyte membrane shear modulus during this period increased from 2.5 to 13 mu N/m.

We apply a novel laser diagnostic technique — Resonant Holographic Interferometry (RHI) to measure the concentration of hydroxyl radical (∼2000 ppm) in a co-flow diffusion flame of diluted hydrogen and air stabilized on a Wolfhard-Parkerburner. This methodology is based upon the dispersion of light of frequency close to an electronic transition of a target molecule. The two-color setup utilized in RHI provides a two-dimensional distribution of the target species concentration and quantitative information can be obtained from the interferogram without requiring any calibration. To provide independent flame data for comparison, a two-dimensional numerical simulation was performed taking into account the effects of detailed chemical kinetics and transport phenomena. In spite of a number of simplifying assumptions made in the simulation, computational and experimental results are in good agreement with respect to the magnitude and width of the region where OH is found. We do observe a difference of approximately 1 mm in the flame position due to the simplifying assumptions made in the simulation. The comparison between the experimental and numerical results clearly demonstrated the potential of RHI in flame diagnostics.

The spectral response of the pixel detector Timepix at the high per-pixel proportional range is examined and calibrated using a simple technique and alpha particles from a standard laboratory source in air. For the detector used, a Timepix ASIC chip equipped with a 300 μ m thick silicon sensor, the spectral range is newly extended up to about 1750 keV per-pixel. This expands and covers the region above 850 keV per pixel which is described and covered by the existing low-energy calibration. The low-energy calibration uses discrete low-energy gamma rays in the range 5-60 keV and is extrapolated over the linear range up to 850 keV/px. Above this level, the per-pixel spectral response changes. At higher energies it undergoes distortion and saturation. The proportional and monotonic response is observed with regions of varying dependence up to nearly 2 MeV. This high-energy region is covered and described by the newly developed calibration method which Uses an alpha source of common low activity (kBq level). Data are collected within one day of total measuring time. Measurements are performed in air at various source-to-distance positions and several sensor bias settings. The developed method together with suitable setting of the sensor bias, which determines the extent of charge sharing, expands the spectral response of Timepix to high energy-loss particles such as alpha particles and light ions in wide energy range. Results are demonstrated on alpha particles, protons and 12C ions. Resulting spectra of deposited energy and cluster pixel height are correctly calibrated and they reproduce expected values.