Calibration Of Optical Systems Research Articles

LANTERN: A multichannel light calibration system for cryogenic detectors

Recent advancements in low-energy rare-event searches rely on the use of cryogenic calorimeters in order to reach extremely low energy thresholds. When attempting to accurately characterize their responses within the region of interest (ROI) these detectors face severe challenges due to the fact that traditional radioactive calibration sources produce signals above the ROI and cannot be used in low background environments.LANTERN, an optical calibration system, can instead be used to accurately study the ROI of cryogenic detectors. It utilizes LED pulses to generate photon signals to perform detector calibration. LANTERN’s current LED matrix allows for a fast characterization of up to 64 calorimeters independently, spanning energies from a few eV to hundreds of keV. Its minimal electronics and optics make it a cost-effective and customizable solution and it will be employed by the BULLKID, NUCLEUS and CRAB experiments.

In‐Situ Wavefront Correction via Physics‐Informed Neural Network

AbstractWavefront distortions pose a significant limitation in various optical applications, hindering further advancements in optical system performance. In this study, a novel generic calibration model based on Zernike‐fitting neural network (ZFNN) is proposed, which enables insitu wavefront correction with just a single‐shot measurement. The experimental setup follows a standard or equivalent focal‐field imaging optical path, allowing calibration without the need to remove any components from the optical system. The ZFNN, a physics‐informed neural network, offers the advantage of not requiring prior training, eliminating the need for extensive labeled data. With a fully connected network architecture and a modest number of neurons (469), the ZFNN achieves exceptionally fast optimization speed and meets the basic requirements for real‐time calibration. Consequently, this approach holds great potential for applications such as rapid calibration of optical systems, high‐precision light field modulation, and various advanced imaging techniques.

Optical calibration system for refractometers

An optical calibration system for refractometers was designed and built using a singlet lens and a translatable detector that induces spherical error, making it a simple and easy-to-use system. The system was calibrated using spectacles and then validated by correcting blurred images created by a series of ophthalmic test lenses. A linear regression model of the correction of the ophthalmic test lenses showed nearly direct correlation with an offset of 0.12 D and an R2 value of 0.9998. An updated version of the system was designed in Zemax OpticStudio with a singlet lens, which could induce spherical error accurate to that of the human eye within ≤ 0.05 D. In future work, this system will be manufactured and tested in the lab.

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 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.

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.

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.

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.

Optical calibration system of NIPR for aurora and airglow observations

Calibration of optical instruments is important for accurate measurement of the absolute emission intensity of aurora and airglow. The National Institute of Polar Research (NIPR), Japan, has been operating a facility for the optical calibration which consists of three independent calibration systems to share with collaborating researchers. This paper introduces an outline of the facility and specifications of each system, calibration procedures, and examples of calibration results. With this facility, we can obtain the calibration data for the absolute sensitivity of optical instruments with an accuracy of about 2% within a wavelength range between 420 and 1050 nm. In addition, it is possible to calibrate transmission of optical filters and also relative sensitivity of optical instruments as a function of wavelengths. Current facility, upgraded in 2012, has been used by many researchers to calibrate their various optical instruments.

Heuristic Analysis for In-Plane Non-Contact Calibration of Rulers Using Mask R-CNN

Determining an object measurement is a challenging task without having a well-defined reference. When a ruler is placed in the same plane of an object being measured it can serve as metric reference, thus a measurement system can be defined and calibrated to correlate actual dimensions with pixels contained in an image. This paper describes a system for non-contact object measurement by sensing and assessing the distinct spatial frequency of the graduations on a ruler. The approach presented leverages Deep Learning methods, specifically Mask Region proposal based Convolutional Neural Networks (R-CNN), for rulers’ recognition and segmentation, as well as several other computer vision (CV) methods such as adaptive thresholding and template matching. We developed a heuristic analytical method for calibrating an image by applying several filters to extract the spatial frequencies corresponding to the ticks on a given ruler. We propose an automated in-plane optical scaling calibration system for non-contact measurement.

Beat frequency measurement of the stabilized He-Ne laser 633 nm calibration in SNSU-BSN

In the metrology area, typical stabilized lasers are used as length primary standard. KIM-1, i.e. the iodine stabilized He-Ne laser in National Measurement Standards Laboratory-National Standardization Agency of Indonesia (SNSU-BSN) has been traceable to SI through CCL-K11 inter-laboratory comparison. The result was suitable for KIM-1 to be used as the length primary standard in SNSU-BSN. Beat frequency measurement has been applied in the optical frequency and wavelength calibration system for stabilized He-Ne laser 633 nm using KIM-1 as a reference standard. In the calibration replica, a dual-frequency mode (Agilent 5519B) took a role as DUT laser, which emits a pair of beams with a central wavelength of 632.991 354 nm in the vacuum with frequency difference 3.4 to 4.0 MHz and ±0.02 ppm stability for a typical lifetime. As a measurement result, the beat frequencies of the 1st and 2nd polarized beam of Agilent 5519B against KIM-1 are (121.33±0.06) MHz and (118.59±0.06) MHz.

Performance of a segmented 6Li-loaded liquid scintillator detector for the PROSPECT experiment

This paper describes the design and performance of a 50 liter, two-segment 6Li-loaded liquid scintillator detector that was designed and operated as prototype for the PROSPECT (Precision Reactor Oscillation and Spectrum) Experiment. The two-segment detector was constructed according to the design specifications of the experiment. It features low-mass optical separators, an integrated source and optical calibration system, and materials that are compatible with the 6Li-doped scintillator developed by PROSPECT. We demonstrate a high light collection of 850±20 PE/MeV, an energy resolution of σ = 4.0±0.2% at 1 MeV, and efficient pulse-shape discrimination of low dE/dx (electronic recoil) and high dE/dx (nuclear recoil) energy depositions. An effective scintillation attenuation length of 85±3 cm is measured in each segment. The 0.1% by mass concentration of 6Li in the scintillator results in a measured neutron capture time of τ = 42.8±0.2 μs. The long-term stability of the scintillator is also discussed. The detector response meets the criteria necessary for achieving the PROSPECT physics goals and demonstrates features that may find application in fast neutron detection.

A Study of Comparison between Window Glass and Mirror on Flatness Measurement in RCM LIPI

Optical calibration system established in RCM LIPI uses monochromatic lamp and optical flat as standard. In the calibration system, optical to be tested and optical standard are contacted together. The monochromatic lamp illuminates both optical. It helps to generate a dark light pattern called fringe. The fringe pattern can be seen through a window glass screen. The fringe pattern indicates the optical flatness. The fringe is still read using human eyes. It causes human error factor on subjectivity for determining edge of fringe. An improvement to the calibration system is presented by image processing technique. The improvement needs some trials and studies to get the right images. The previous studies review on camera setting to capture fringe pattern. This research presents to study of comparison between window glass and mirror as screen. The result will be used to design the housing system. An experiment is set using window glass and mirror to the existing system. The fringe that appears on both screen are captured by digital camera. The images captured are processed with early edge detection program that built in Matlab. It is obtained that measurement system using window glass gives the best edge detection, but the camera setting can’t be auto mode. It can capture fringe images using manual mode with some adjustment on aperture, shutter time, and ISO. On the contrary, auto mode can be applied on measurement system using mirror as screen.

A novel dynamical 3D smile measurement method to evaluate the effects of face-lifting surgery: Based on the optical structured light strategy

BackgroundAssessment of plastic surgery is important for the therapy evaluation while there is no widespread accepted objective method used. This study proposes a novel optical technique to acquire the dynamical data of face muscle with potential to objectively evaluate the effect of surgery. MethodsThis approach is based on the optical structured light measurement with the colored encoded stripe pattern. Through the calculation of the image phase shift of those projected stripe on the face and the optical system calibration, we get the accurate height of the face surface. 10 young subjects are involved. One high-speed camera is used to record their smile procedure and then data of each captured frame are calculated. ResultsAll the results, which are at subpixel level, are accurate to 0.1mm and all the error s is below 5%, which is considered as enough accuracy. Meanwhile, a significantly high correlation between optical measurement and traditional standard measuring approach is observed (r2=0.99, p=2.97×10−12). ConclusionsBased on the results, our dynamical optical smile measurement shows enough high accuracy of in acquiring the moving information of every point on smile face. No secondary pollution would happen in the measurement technique with no touching or contacting the surgery area, which thus might induce a safer and cleaner way for the clinical evaluation of the face-lifting surgery with high spatial and temporal resolution.

Optical Calibration of SNO+

SNO is being upgraded to SNO+, which has as its main goal the search for neutrinoless double-beta decay. The upgrade is defined by filling with a novel scintillator mixture containing 130Te. With a lower energy threshold than SNO, SNO+ will be sensitive to other exciting new physics. Here we are describing new optical calibration system that meets new, more stringent radiopurity requirements has been developed.

Extended depth of field in images through complex amplitude pre-processing and optimized digital post-processing

Many applications require images with high resolution and an extended depth of field. Directly changing the depth of field in optical systems results in losing resolution and information from the captured scene. Different methods have been proposed for carrying out the task of extending the depth of field. Traditional techniques consist of optical-system manipulation by reducing the pupil aperture along with the image resolution. Other methods propose the use of optical arrays with computing-intensive digital post-processing for extending the depth of field. This work proposes a pre-processing optical system and a cost-effective post-processing digital treatment based on an optimized Kalman filter to extend the depth of field in images. Results demonstrate that the proposed pre-processing and post-processing techniques provide images with high resolution and extended depth of field for different focalization errors without requiring optical system calibration. In assessing the resulting image through the universal image quality index, this technique proves superior.

Non-bar, an optical calibration system for five-axis CNC machine tools

Five-axis CNC machine tools comprise three linear axes and two rotary axes, enabling the fabrication of complex workpieces, such as dies, turbo blades, and cams. Improved measurement methods are continually being researched to increase the accuracy of five-axis CNC machine tools. This paper presents a novel optical calibration system, called non-bar, with no linkage bars. The system comprises a master detector module, a ball lens module, and a signal module. The proposed measurement system was implemented according to ISO/CD 10791-6 to measure A-type, B-type, and C-type five-axis CNC machine tools from three different manufacturers. The results demonstrate that the proposed non-bar measurement scheme provides high accuracy, high reproducibility, and simultaneous multi-axis measurement.

R&D of Lhaaso-Wcda

As one of the important parts of the LHAASO Project, the Water Cherenkov Detector Array (WCDA) is planned to be built in Yangbajing, Tibet, China soon. In order to fully understand the engineering issues and the basic performance of the water Cherenkov detection technique, a prototype water Cherenkov detector has been built and operat- ed in Beijing, and an engineering array has been constructed on site. With the help of the prototype detector, performance related to cosmic muon signals and water quality maintenance has been studied and acquired. Studies of the engineering array are also progressing smoothly: nine 8-in PMTs and their electronics and DAQ systems have been deployed; an optical calibration system, a water recycling and purification system, and a slow control system, have been installed; the data taking started, and the data analysis is going on. These studies will offer a great help to the future work of the full array.

Developing robust vision modules for microsystems applications

In this work, several robust vision modules are developed and implemented for fully automated micromanipulation. These are autofocusing, object and end-effector detection, real-time tracking and optical system calibration modules. An image based visual servoing architecture and a path planning algorithm are also proposed based on the developed vision modules. Experimental results are provided to assess the performance of the proposed visual servoing approach in positioning and trajectory tracking tasks. Proposed path planning algorithm in conjunction with visual servoing imply successful micromanipulation tasks.

Multiple optical calibration system–based effective multiviews video processing

A new multiple optical calibration system (MOCS)-based effective multiview video processing (MVP) is proposed. The proposed MOCS can be classified as intracamera processing and intercamera processing (IP). In IP, unequal brightness intensity is rectified by using a brightness difference map, and geometric distortion of the optical lens is corrected. In IP, several important factors, such as unequal camera sensor location, tilt degree of lens mount, and focal length, among multiple cameras are calibrated. Furthermore, an effective disparity matching algorithm, called an as adaptive-based disparity matching algorithm (A-DMA), is proposed for MVP. The proposed A-DMA enhances the performance of MVP in terms of accuracy of disparity estimation and computational overhead.