Optical Laboratory Research Articles

Study of Neural Network Architectures for Determining Gas Concentrations by Spectra

A study of a number of neural networks of different architectures for determining gas concentrations from spectra obtained using an optical emission gas analyzer, which measures the spectrum of electromagnetic radiation emitted by gases when excited by an electric discharge, is presented. The neural network is trained on data from the optical spectroscopy laboratory and is able to predict gas concentrations from spectra at high speed. The research concerned the deep neural network architectures with convolutional and recurrent layers. Convolutional layers highlight the features of the spectra, while recurrent layers take into account the consistent structure of the data. The quality of the neural network is evaluated by the R2 coefficient of determination, and the comparison between networks by the RMSE indicator between the predicted and real gas concentrations.

Calculating the focal length of a concave mirror computerically using mathematical algorithms using MATLAB

This study proposes the use of digital image processing technology to determine the focal lengths of simple concave mirror , as well as spherical mirrors. This method is simpler, faster to implement, and more accurate in calculating the focal length by taking several pictures at different distances for the image formed by the lens, then calculating the least point spread function for these pictures at that distance to determine the best image. In this work Image No. (7) represents the image that carries the least (psf) that was determined by algorithms and special mathematical equations through the (Matlab) program, then the focal length is calculated by employing algorithms and mathematical equations specific to calculating the focal length. A comparison was made with the traditional method by taking measurements of a group of students at the Optics laboratory of University of Wasit, College of Science (which depends on view to choose the best image). This method has proven to be superior in measuring the focal length of lenses. A statistical analysis was conducted for these measurements for the group of students and it was found that there was differences measurements with an error rate, which confirms the feasibility of this method in terms of measurement accuracy and time saving. Experimental results have confirmed this.

Temperature stabilization of a lab space at 10 mK-level over a day.

Temperature fluctuations over long time scales (≳ 1h) are an insidious problem for precision measurements. In optical laboratories, the primary effect of temperature fluctuations is drifts in optical circuits over spatial scales of a few meters and temporal scales extending beyond a few minutes. We present a lab-scale environment temperature control system approaching 10mK-level temperature instability across a lab for integration times above an hour and extending to a day. This is achieved by passive isolation of the laboratory space from the building walls using a circulating air gap and an active control system feeding back to heating coils at the outlet of the laboratory's Heating-Ventilation-Air-Conditioning (HVAC) unit. These techniques together result in 20 dB suppression of the temperature power spectrum across the lab at 10-4Hz-approaching the limit set by statistical coherence of the temperature field-and 10mK Allan deviation around 15 °C after an hour of averaging, which is an order of magnitude better than any previous report for a full laboratory.

Peering inside the biological nano-universe

Barbora Špačková, who is setting up a new single-molecule optics lab in Prague, talks to Laura Hiscott about moving from theoretical to experimental physics, developing a technique for seeing the invisible, and the joy of refining her technology for real-world applications.

Chiral media and optical rotatory dispersion by means of a simple polarimetric experiment for undergraduate students

A simple experiment taking into account media with natural optical activity and their characterization by means of Mueller polarimetry is proposed for undergraduate Optics and Photonics laboratories. The objectives are, first, to review how to characterize dielectric and homogeneous media with natural optical activity by means of a Mueller matrix, taking into account the variation of these characteristics with wavelength, and combining concepts such as polarimetry, natural optical activity, and rotatory dispersion. Secondly, a complete and simple experiment is proposed to characterize a chiral medium by means of its Mueller matrix for different wavelengths. This experiment can be performed by undergraduate students in a standard optics laboratory. As a particular example of a chiral medium, a quartz crystal is used. The experimental results are compared with those published for crystalline quartz to validate the experiment.

Machine Learning Constructed Based on Patient Plaque and Clinical Features for Predicting Stent Malapposition: A Retrospective Study.

Stent malapposition (SM) following percutaneous coronary intervention (PCI) for myocardial infarction continues to present significant clinical challenges. In recent years, machine learning (ML) models have demonstrated potential in disease risk stratification and predictive modeling. ML models based on optical coherence tomography (OCT) imaging, laboratory tests, and clinical characteristics can predict the occurrence of SM. We studied 337 patients from the Affiliated Hospital of Zunyi Medical University, China, who had PCI and coronary OCT from May to October 2023. We employed nested cross-validation to partition patients into training and test sets. We developed five ML models: XGBoost, LR, RF, SVM, and NB based on calcification features. Performance was assessed using ROC curves. Lasso regression selected features from 46 clinical and 21 OCT imaging features, which were optimized with the five ML algorithms. In the prediction model based on calcification features, the XGBoost model and SVM model exhibited higher AUC values. Lasso regression identified five key features from clinical and imaging data. After incorporating selected features into the model for optimization, the AUC values of all algorithmic models showed significant improvements. The XGBoost model demonstrated the highest calibration accuracy. SHAP values revealed that the top five ranked features influencing the XGBoost model were calcification length, age, coronary dissection, lipid angle, and troponin. ML models developed using plaque imaging features and clinical characteristics can predict the occurrence of SM. ML models based on clinical and imaging features exhibited better performance.

Custom-made spherical fluorescent tracer particles for laser Velocimetry Laboratory Experiments

This article introduces a method for creating custom-made spherical fluorescent particles tailored for fluid mechanics optical velocimetry laboratory measurements techniques such as Particle Image Velocimetry (PIV) and Particle Tracking Velocimetry (PTV) measurement techniques. The incorporation of the fluorescent dye Rhodamine B into the particle bulk significantly reduces direct light reflections and enhances particle detection when enlightened by a laser and using a band-pass filter on the optical measurement device. Furthermore, the study offers a clear guide for adjusting particle diameter by modifying various parameters such as the stirrer used, its stirring speed, the surfactant concentration, and the type of polymer. This allows for the customization of particles best suited for water multiphase flow characterization and transport studies. The resulting particles exhibit excellent sphericity, making them suitable for a wide range of fluid mechanics investigations, from small to large scale. Experimental validations, including size measurements, density assessments, emission spectra analyses, and applicability in a confined flow affirm the effectiveness of the proposed methodology by exhibiting a signal-to-noise ratio four to five times higher than fluorescent surface-stained and non-fluorescent particles.

Prescription lens partners

Optician's updated annual guide to optical labs throughout the UK and Ireland

Remotely operated optical lab equipment for education: a DIY approach

Remotely operated optical lab equipment for education: a DIY approach

Optical turbulence profiling at the Table Mountain Facility with the Laser Communication Relay Demonstration GEO downlink

We report the first measurement of the atmospheric optical turbulence profile using the transmitted beam from a satellite laser communication terminal. A ring image next generation scintillation sensor (RINGSS) instrument for turbulence profiling, as described in Tokovinin [MNRAS 502, 747 (2021)10.1093/mnras/staa4049], was deployed at the NASA/Jet Propulsion Laboratory’s Table Mountain Facility (TMF) in California. The optical turbulence profile was measured with the downlink optical beam from the Laser Communication Relay Demonstration (LCRD) geostationary satellite. LCRD conducts links with the Optical Communication Telescope Laboratory ground station and the RINGSS instrument was co-located at TMF to conduct measurements. Turbulence profiles were measured at day and night and atmospheric coherence lengths were compared with other turbulence monitors such as a solar scintillometer and Polaris motion monitor. RINGSS sensitivity to boundary layer turbulence, a feature not provided by many profilers, is also shown to agree with a boundary layer scintillometer at TMF (R = 0.85). Diurnal evolution of optical turbulence and measured profiles are presented. The correlation of RINGSS with other turbulence monitors (R = 0.75 − 0.86) demonstrates the concept of free-space optical communications turbulence profiling, which could be adopted as a way to support optical ground stations in a future Geostationary feeder link network. These results also provide further evidence that RINGSS, a relatively new instrument concept, correlates well with other instruments in daytime and nighttime turbulence.

Pretty good measurement for bosonic Gaussian ensembles

The pretty good measurement is a fundamental analytical tool in quantum information theory, giving a method for inferring the classical label that identifies a quantum state chosen probabilistically from an ensemble. Identifying and constructing the pretty good measurement for the class of bosonic Gaussian states is of immediate practical relevance in quantum information processing tasks. Holevo recently showed that the pretty good measurement for a bosonic Gaussian ensemble is a bosonic Gaussian measurement that attains the accessible information of the ensemble [IEEE Trans. Inf. Theory 66(9) (2020) 5634]. In this paper, we provide an alternate proof of Gaussianity of the pretty good measurement for a Gaussian ensemble of multimode bosonic states, with a focus on establishing an explicit and efficiently computable Gaussian description of the measurement. We also compute an explicit form of the mean square error of the pretty good measurement, which is relevant when using it for parameter estimation. Generalizing the pretty good measurement is a quantum instrument, called the pretty good instrument. We prove that the post-measurement state of the pretty good instrument is a faithful Gaussian state if the input state is a faithful Gaussian state whose covariance matrix satisfies a certain condition. Combined with our previous finding for the pretty good measurement and provided that the same condition holds, it follows that the expected output state is a faithful Gaussian state as well. In this case, we compute an explicit Gaussian description of the post-measurement and expected output states. Our findings imply that the pretty good instrument for bosonic Gaussian ensembles is no longer merely an analytical tool, but that it can also be implemented experimentally in quantum optics laboratories.

The TR-icOS setup at the ESRF: time-resolved microsecond UV-Vis absorption spectroscopy on protein crystals.

The technique of time-resolved macromolecular crystallography (TR-MX) has recently been rejuvenated at synchrotrons, resulting in the design of dedicated beamlines. Using pump-probe schemes, this should make the mechanistic study of photoactive proteins and other suitable systems possible with time resolutions down to microseconds. In order to identify relevant time delays, time-resolved spectroscopic experiments directly performed on protein crystals are often desirable. To this end, an instrument has been built at the icOS Lab (in crystallo Optical Spectroscopy Laboratory) at the European Synchrotron Radiation Facility using reflective focusing objectives with a tuneable nanosecond laser as a pump and a microsecond xenon flash lamp as a probe, called the TR-icOS (time-resolved icOS) setup. Using this instrument, pump-probe spectra can rapidly be recorded from single crystals with time delays ranging from a few microseconds to seconds and beyond. This can be repeated at various laser pulse energies to track the potential presence of artefacts arising from two-photon absorption, which amounts to a power titration of a photoreaction. This approach has been applied to monitor the rise and decay of the M state in the photocycle of crystallized bacteriorhodopsin and showed that the photocycle is increasingly altered with laser pulses of peak fluence greater than 100 mJ cm-2, providing experimental laser and delay parameters for a successful TR-MX experiment.

Quantitative analysis of crystalline lens and vitreous opacities

Intraocular light scattering affects the contrast of the image created on the retina thus reducing the vision quality. Although one can consider the ocular components transparent, the microstructural changes (that are associated with aging or other factors) lead to the increase in intraocular light scattering. Therefore, the opacification of ocular structures is associated with vision‐affecting diseases such as corneal dystrophies, crystalline lens cataracts, vitreous floaters etc.Optical coherence tomography (OCT) is a non‐invasive imaging modality enabling generation of micrometre resolution, two‐dimensional (2‐D) cross‐sectional images and three‐dimensional (3‐D) volumetric data presenting internal structure of optically scattering tissues. OCT detects light that is back‐scattered/back‐reflected at the optical in homogeneities within the ocular structures. Due to its high sensitivity, OCT enables detection of ultralow scattered light levels obtained from weakly scattering tissues such as the vitreous body.In this talk, we will demonstrate in vivo enhanced three‐dimensional visualization of vitreous and lens opacities in normal subjects and cataract patients of different ages using a swept source OCT (SS‐OCT) system deployed to the Laboratory of Optics at the University of Murcia, Spain. The instrument operated at the central wavelength of 1050 nm and was optimized to image the anterior segment of the eye. Volumetric images were used to effectively map the opacities and to generate en‐face projection images of opacities.The results revealed the changes in the transparency of the crystalline lens showing lens micro‐ and macro‐scale features related to cataract such as cortical spokes, water clefts and enhanced scattering in the lens nucleus. On the other hand, vitreous imaging with SS‐OCT allowed for visualization of gel vitreous, liquefied lacunae, Berger's space, retrolental laminae and fibrous opacifications.Volumetric OCT data of the lens and retrolental vitreous were used to perform quantitative analysis of light scattering (transparency). We introduced indices describing transparency and optical homogeneity of ocular structures. Later on, we showed that those biomarkers correlate with age. Finally, statistical association between transparency of crystalline lens / vitreous and degradation of visual function was performed.The proposed imaging platform can be a new‐generation ophthalmic diagnostic tool in the fundamental studies as well as for objective clinical evaluation and management of eye diseases.

General education and training of NDT personnel, including NDT Education at Universities. in South Africa

Following the 16th World Conference in Durban, South Africa, The South African Institute for NDT (SAINT) was mandated to invest the monies made from the WCNDT to establish a professional qualification for NDT personnel. In South Africa, a professional qualification must comply with the national qualification framework (NQF) requirements, which stipulate the rules to assure that qualifications for different occupations are at the same level. For NDT this meant, that the qualifications to ISO 9712 (ISO TC 25107 syllabus) would not suffice to serve as a qualification. There exists a requirement that classroom training, classroom practical training and work integrated practical training should each make up at least 30 % of the work. Anybody who had a look at ISO 9712 will realise that 160 hours of classroom training and 180 days (1080 hours) practical training would not cut it, as the training content for the 1080 hours is not defined in any standard. This state of affairs required the definition (curriculum development) of what has to be taught and how. The paper will elucidate this outcome. Concerning university education in South Africa one has to mention the NDT diploma and advanced diploma in NDT offered by the Vaal University of Technology (VUT). These courses focus on teaching NDT theory across a broad spectrum. Students have to undergo work integrated learning (WIL) and then successfully pass the practical examination at NDT Level II in order to be certificated to perform NDT in line with codes and standards. The Tshwane University of Technology (TUT) offer a subject in NDT as part of the applied physics diploma, where the emphasis is on Nuclear Technology and Photonics. At the University of Cape Town (UCT) in the department of mechanical engineering, digital shearography is offered as a research field for master degree studies. They have a well-equipped optical laboratory for this purpose and have manufactured a shearography system which they support and improve on an ongoing basis. At the University Pretoria (UP) the subject Non-destructive Testing was offered at the post graduate degree level, as part of the course work for Asset Integrity Management. Most practical NDT technology development in South Africa is performed in industry at the company’s own costs. Some examples will be mentioned.

Recording changes in biochemical parameters <i>in vivo</i> in the ischemic stroke model

Stroke is a significant and socially insidious disease that ranks second among fatal diseases according to the World Health Organization [1]. Understanding the molecular mechanisms behind the pathogenesis of this ailment will enable the development of more effective preventative measures and treatment strategies to minimize the negative consequences of stroke. Despite the abundance of experimental data, most of which were acquired indirectly, the study of the dynamics of biochemical parameters in brain tissue in real time during the acute phase of ischemic stroke is difficult. The use of genetically-encoded sensors creates novel possibilities for monitoring alterations in different biochemical and metabolic parameters in vivo tissues. In this study, we evaluated pH changes, hydrogen peroxide production (an important type of biologically active ROS), and polysulfide synthesis in various types of brain tissue cells of SHR rats during the development of ischemic stroke in real time using sensors such as SypHer3s (for pH detection), HyPer7 (for H2O2 detection), and PersIc (for polysulfide detection). Middle cerebral artery occlusion was used to simulate an ischemic stroke. The in vivo sensor signals were registered with a fiber optic setup that was created in the laboratory of spectroscopy and nonlinear optics at Moscow State University. The studies revealed that in the acute phase of stroke, acidosis occurred in the cytoplasm of neurons in the caudate nucleus, the epicenter of ischemia. The pH mutated from 7.25±0.08 to 6.7±0.15 within the first few seconds after arterial occlusion initiation. A gradual increase in pH was observed after the initial drop, which persisted throughout reperfusion but did not return to the original value in all animals. In the penumbra zone, a wave-like shift in sensor signal was detected, whereas no change in sensor signal was noted in the healthy hemisphere. Investigation of the dynamics of H2O2 formation in the mitochondrial matrix of caudate neurons revealed minimal sensor oxidation during ischemia/reperfusion in the acute phase of stroke, indicating low ROS production. Nevertheless, a substantial increase in the sensor signal was detected after 24 hours following the surgery. Thus, the confirmation of oxidative stress development in the affected hemisphere differed from the commonly accepted view in terms of its dynamics. Previously, it was believed that excessive production of H2O2 leading to oxidative stress and related brain cell death occurred primarily in the acute phase. However, a comparison of hydrogen peroxide production dynamics in neurons and astrocytes revealed differences between these cell populations. It was discovered that as early as 12 hours after middle cerebral artery occlusion, the sensor signal in astrocytes increased more intensely than in neurons. This trend persisted until the end of the measurements, 40 hours after surgery. The observed distinctions may stem from glial cells’ protective function in counteracting the harmful consequences of hydrogen peroxide on neurons, along with their contribution to maintaining the myelin structure in the brain. Additionally, the role of astrocytes in neuroinflammation development is noteworthy. Reactive sulfur species, in addition to reactive oxygen species, appear to be significant contributors to the development of pathological processes. The PersIc sensor signal measurement did not show any disparities between the caudate nucleus of the healthy hemisphere and the hemisphere affected by stroke development in terms of polysulfide and persulfide appearance detection. However, the area surrounding the core infarction is noteworthy due to the observed bouts of acidosis using the SypHer3s sensor. Our findings suggest a potential association between these bouts, spreading depolarization, changes in calcium concentration, and the development of neuroinflammation. These reactions may ultimately lead to the synthesis of polysulfides, known modulators of inflammatory reactions. Thus, our data provides valuable additions to the existing knowledge on metabolic changes that take place during the progression of ischemic brain injury.

An innovative optics lab design for residency training in ophthalmology

Proper understanding of the optical function of the eye is the foundation of clinical understanding of ophthalmologists. Although teaching principals of optics has always been a part of ophthalmology residency curriculum, it seems that successful strategies other than lecture—based methods are needed to engage students and facilitate the understanding of optical principals. A collaborative team of physicists (optics Ph.D.), ophthalmologists and medical education experts designed an optics lab for ophthalmology residents to help them practically simulate different optical phenomena. The educational course consisted of 4 sessions of 90 min to practice the optical tests using the lab instruments. Each class consisted of 6–9 residents, divided into 3 groups with a fully equipped unit, and two mentors (an optics Ph.D. professor and an ophthalmology professor). A quasi-experimental design with pre-post test was used to evaluate the effectiveness of the training workshop in changing the ophthalmology residents’ optical knowledge and attitude. Thirty-five residents participated in the study. The average score of residents' performance before the workshop was 5.21 (out of 100), which increased significantly to 66.1 after the workshop. Also, the average knowledge of residents, which was measured as self-reported, increased significantly from 28.85 to 71.09. The average score of students' attitudes and interest was increased from 40.49 to 74.81. It seems that training workshops and labs are effective to bring about change in knowledge and attitude of ophthalmology residents toward optics as a new teaching strategy that would be implemented in their curriculum.

Development of Computer Vision, Image Processing, and Analysis at the Digital Optics Laboratory of the Institute for Information Transmission Problems of the Russian Academy of Sciences

Development of Computer Vision, Image Processing, and Analysis at the Digital Optics Laboratory of the Institute for Information Transmission Problems of the Russian Academy of Sciences

Computational simulation of the optical performance of an EDOF intraocular lens in post-LASIK eyes.

To evaluate computationally the optical performance of AcrySof IQ Vivity extended depth-of-focus (EDOF) intraocular lenses (IOLs) in post-laser in situ keratomileusis (LASIK) eyes. Visual Optics and Biophotonics Laboratory, Madrid, Spain. Experimental study. Computer pseudophakic eye models were implemented using reported post-LASIK corneal aberrations (refractive corrections from -7.5 to +4.5 diopters [D]) and virtually implanted with monofocal (AcrySof IQ) or EDOF (AcrySof IQ Vivity) IOLs. Retinal image quality was quantified through visual Strehl (VS). The depth of focus (DOF) was calculated from the through-focus VS curves. Halos were estimated from the light spread in the image of a pinhole. Those quantitative parameters were obtained for 5.0 and 3.0 mm pupil diameters. Simulated virgin eyes showed VS of 0.89/0.99 with monofocal IOLs and 0.74/0.52 with EDOF IOLs for 5.0/3.0 mm pupils at best focus. VS decreased with induced spherical aberration (SA) by 25% and with induced SA + coma by 61% on average (3.0 mm pupils). The DOF was 2.50 D in virgin eyes with EDOF IOLs, 1.66 ± 0.30 and 2.54 ± 0.31 D ( P < .05) on average in post-LASIK eyes for 3.0 mm pupils, monofocal and EDOF IOLs, respectively. Halos were more sensitive to SA induction for 5.0 mm pupils, and induction of positive SA (myopic LASIK) resulted in reduced halos with the EDOF when compared with the monofocal IOLs, by 1.62 (SA) and 1.86 arc min (SA + coma), on average. Computer post-LASIK pseudophakic eye models showed that the DOF was less dependent on the presence of SA and coma with EDOF IOLs and that halos were reduced with EDOF IOLs compared with the monofocal IOL for a range of SA.

Remote accessible/fully controllable fiber optic systems laboratory design and implementation

AbstractIn private and expensive experimental laboratory studies, there are problems such as difficulty in accessing measuring devices and materials, space and time problems, and insufficient technical support due to the need for expertise. In this study, a fiber optic laboratory (FOL), which can be used for educational and scientific research purposes, has high installation costs and has difficulty in accessing devices, was designed and realized as a remote accessible/fully controllable. All devices in the proposed laboratory have been virtualized on the MATLAB App Designer platform, and communication protocols have been defined and made remotely accessible and controllable. In the proposed system, the user accessed remotely can perform all device controls, record the measurement results, take the measurement average as much as he wants to increase the measurement accuracy, monitor the experimental setup with a camera, and receive expert support. Afterward, a sample experiment was set up on the system and the results were compared. The proposed laboratory has a high potential to establish international collaborations in remote/flexible work and scientific research. Finally, a scale was applied to FOL undergraduate, graduate, and doctoral student groups. The Cronbach α coefficient showing the reliability of the applied model was found to be .934.

GC Insights: The crystal structures behind mineral properties – a case study of using TotBlocks in an undergraduate optical mineralogy lab

Abstract. Spatial thinking represents an ongoing challenge in geoscience education, but concrete manipulatives can bridge this gap by illustrating abstract concepts. In an undergraduate optical mineralogy lab session, TotBlocks were used to illustrate how crystal structures influence properties such as cleavage and pleochroism. More abstracted properties, e.g., extinction angles, were increasingly difficult to illustrate using this tool.