Filter Wheel Research Articles

Multi-color two-laser super-resolution structured illumination microscopy for the visualization of multi-organelle in living cells.

In this study, we introduced a novel dual-laser multi-color imaging system. Integrated with a multi-channel filter wheel, this system compared three spectral decontamination algorithms (nonnegative matrix factorization [NMF], RCAN, and PICASSO) showcasing its efficacy in achieving four-color imaging with only two laser sources. Combined with a reliable image reconstruction algorithm, the spatial resolution of four channels super-resolution four-color images reached 130, 125, 133, and 132 nm, respectively. Lipid droplets, mitochondria, lysosomes, and nuclei from the mouse hepatocytes (AML12), human neuroblastoma cells (SH-SY5Y), mouse hippocampal neuronal cells (HT-22), and immortalized murine bone marrow-derived macrophages were imaged. At the same time, the chromatin condensation, nuclear contraction, DNA fragmentation, apoptotic body formation, as well as the fusion of Mito and Lyso involved in mitochondrial autophagy were observed in HT-22 and SH-SY5Y cells suffering oxidative stress. Our multi-color SIM imaging system establishes a powerful platform for dynamic organelle studies and other high-resolution investigations in live cells.

Characterization of a 3D prototyping semi-automated filter holder system for RQR radiation qualities

Characterizing radiation measurement systems, such as diagnostic radiology systems for RQR and RQA, is essential for ensuring reliable results in standardized instrument calibration laboratories. Quality control of dosimetry devices, such as patient dose calibrators (PDCs), a reference meter, is crucial for ensuring accurate measurements. This study demonstrates the use of spectrometry and ionization chambers to characterize a set of semi-automated 3D prototyping filter holder systems, developed in a previously project, designed for applications such as Kerma-Area Product (KAP) meter calibration. The set of 3D prototypes were adjusted to a filter wheel and characterized using an X-ray spectrometer, followed by an ionization chamber, according to international standards. The characterization of radiation qualities from 50 to 150 kV in diagnostic radiology was performed using the substitution method: first with an ionization chamber, then with a PDC. The PDC was calibrated for KAP and Air Kerma quantities, considering the conditions of the X-ray system and factors such as temperature, humidity, and pressure. Spectrometric analysis and the use of an ionization chamber were effective in determining these parameters. Spectral characterization allowed for accurate measurements to establish proper quality control, then it is possible to use the PDC calibrated for calibration procedures for KAP meters. Future studies intend to compare these results with computational simulations using the TOPAS Monte Carlo code to validate the calibration method.

Short Wave Infrared Imaging for Auroral Physics and Aeronomy Studies

Advances in solar-terrestrial physics are generally linked to the development of innovative new sensor technologies, affording us ever better sensitivity, higher resolution, and broader spectral response. Recent advances in low-noise InGaAs sensor technology have enabled the realization of low-light-level scientific imaging within the short-wave infrared (SWIR) region of the electromagnetic spectrum. This paper describes a new and highly sensitive ultra-wide angle imager that offers an expansion of auroral and airglow imaging capabilities into the SWIR spectral range of 900–1,700 nm. The imager has already proven successful in large-area remote sensing of mesospheric temperatures and in providing intensity maps showing the propagation and dissipation of atmospheric gravity waves and ripples. The addition of an automated filter wheel expands the range of applications of an already versatile SWIR detector. Several potential applications are proposed herein, with an emphasis on auroral science. The combined data from this type of instrument and other existing instrumentation holds a strong potential to further enhance our understanding of the geospace environment.

High-throughput fluorescence quantification method based on inner filter effect and fluorescence imaging analysis

The application of the inner filter effect (IFE) in fluorescent substance determination is gaining popularity. In this paper, a theory of the fluorescence distribution along with the excitation light path is derived from our previous research about the spatial micro-element method. According to the relationship between the summation of fluorescence intensities along the vertical direction at a certain position on the excitation light path and the position, a high-concentration and wide-range fluorescent substance quantification method based on the IFE and fluorescence imaging analysis is proposed. Correspondingly, a high-throughput fluorescent substance quantification detection system is constructed. In order to validate the method, solutions of rhodamine B in different concentrations are used for principle validation, concentration prediction, and experimental investigation on the influence of integration time and lens distortion. The high-throughput system enables the simultaneous measurement of six samples, realizing the high-concentration and wide-range quantification of rhodamine B (100–600 mg/L) with high precision (R2 = 0.9992, MRE = 2.34 %). By setting the filter wheel, the system can measure the concentration of fluorescent substances with different emission wavelengths. The improvement of experimental device is expected to reduce the single sample capacity to tens of microliters and increase the overall sample quantity to tens or even hundreds. The proposed method and system are beneficial to fluorescence measurement in fields such as biomedicine and dye research and to the improvement of high-throughput fluorescence quantitative PCR instruments.

Stellar interferometer experiment by measuring visibilities at different wavelengths

In this work we develop an experiment wherein the variation of the fringe visibilities with wavelength provides insights into the geometry of various stellar sources or components. The experiment is based on the Michelson stellar interferometer in which a filter wheel has been inserted between a detecting camera and a telescope obscured by a double-aperture lid. The spatial and temporal incoherent light emitting from stellar sources has been simulated using polymer optical fibres and a broadband light-emitting diode. By measuring the visibilities of the central fringe at different wavelengths we are able to determine the morphology of the analysed light sources, provided that the baseline used is sufficiently long. The experiment is suitable for postgraduate students seeking to delve deeper into light coherence theory and to gain practical experience in optical stellar interferometry.

Slitless spectrophotometry with forward modelling: Principles and application to measuring atmospheric transmission

Context. In the next decade, many optical surveys will aim to answer the question of the nature of dark energy by measuring its equation-of-state parameter at the per mill level. This requires trusting the photometric calibration of the survey with a precision never reached so far on many sources of systematic uncertainties. The measurement of the on-site atmospheric transmission for each exposure, or for each season or for the full survey on average, can help reach the per mill precision for the magnitudes. Aims. This work aims at proving the ability to use slitless spectroscopy for standard-star spectrophotometry and its use to monitor on-site atmospheric transmission as needed, for example, by the Vera C. Rubin Observatory Legacy Survey of Space and Time supernova cosmology program. We fully deal with the case of a disperser in the filter wheel, which is the configuration chosen in the Rubin Auxiliary Telescope. Methods. The theoretical basis of slitless spectrophotometry is at the heart of our forward-model approach to extract spectroscopic information from slitless data. We developed a publicly available software called Spectractor, which implements each ingredient of the model and finally performs a fit of a spectrogram model directly on image data to obtain the spectrum. Results. We show through simulations that our model allows us to understand the structure of spectrophotometric exposures. We also demonstrate its use on real data by solving specific issues and illustrating that our procedure allows the improvement of the model describing the data. Finally, we discuss how this approach can be used to directly extract atmospheric transmission parameters from the data and thus provide the base for on-site atmosphere monitoring. We show the efficiency of the procedure in simulations and test it on the limited available data set.

High-speed fluorescence excitation-scanning hyperspectral imaging microscopy using thin-film tunable filters.

Hyperspectral imaging (HSI) technologies have enabled a range of experimental techniques and studies in the fluorescence microscopy field. Unfortunately, a drawback of many HSI microscope platforms is increased acquisition time required to collect images across many spectral bands, as well as signal loss due to the need to filter or disperse emitted fluorescence into many discrete bands. We have previously demonstrated that an alternative approach of scanning the fluorescence excitation spectrum can greatly improve system efficiency by decreasing light losses associated with emission filtering. Our initial system was configured using an array of thin-film tunable filters (TFTFs, VersaChrome, Semrock) mounted in a tiltable filter wheel (VF-5, Sutter) that required ~150-200 ms to switch between wavelengths. Here, we present a new configuration for high-speed switching of TFTFs to allow rapid time-lapse HSI microscopy. A TFTF array was mounted in a custom holder that was attached to a piezoelectric rotation mount (ThorLabs), allowing high-speed rotation. Switching between adjacent filters was achieved using the internal optics of a DG-4 lightsource (Sutter Instrument), including a pair of off-axis parabolic mirrors and galvanometers. Output light was coupled to a liquid lightguide and into an inverted widefield fluorescence microscope (TI-2, Nikon Instruments). Initial tests indicate that the HSI system provides a 15-20 nm bandwidth tunable excitation band and ~10-20 ms wavelength switch time, allowing for high-speed HSI imaging of dynamic cellular events. This work was supported by NIH P01HL066299, R01HL169522, NIH TL1TR003106, and NSF MRI1725937.

ELSSIE: A compact stereo spectral imager for planetary surface morphology and composition

Here we describe the design, prototyping, testing, and simulations that were conducted to demonstrate the technology for a concept of the next generation landed planetary spectral imager, the Europa Lander Stereo Spectral Imaging Experiment (ELSSIE). The concept was developed originally for a Europa Lander mission, but the design is applicable, with simplifications, to any ocean world of the outer solar system or to non-icy bodies, including Enceladus, the Moon, Mars, or the surface of Ceres. ELSSIE's design consists of two subassemblies. A Sensor melds a high-resolution, 20-filter, 0.4–3.65 μm, adjustable-focus multispectral stereo imager with a 0.8–3.6 μm point spectrometer, sharing a radiation-shielded single Teledyne H2RG 2048 × 2048 pixel focal plane array (FPA). Each camera includes two 6-position filter wheels with 5 filters and a blank position, providing 10 bandpasses for each of the 2 stereo eyes, and uses 700 × 700 pixels of the FPA. The point spectrometer uses a 6 ×350 pixel strip of the FPA. The Sensor provides stereo and imaging/spectroscopic measurements of reflected light from visible to medium wave-infrared (MWIR) wavelengths to characterize surface morphology, search for pyroclastic plumes, search for organics, identify salts and possible biominerals, characterize crystalline vs. amorphous ice and ice grain sizes, and map the distributions of key phases. In addition to addressing important geologic questions, these measurements support selection of a site for in situ sampling and analysis. A Data Processing Unit (DPU) performs mitigation of radiation that penetrates the shielding using sets of same-filter image frames or spectra of a single spot by removing image spatial pixels with radiation hits, and coadding the remainder for the same spatial pixel, improving signal-to-noise ratio (SNR). The DPU also performs onboard calibration of imager and spectrometer data, co-registration of multispectral images, and calculation of spectral index (“summary parameter”) images for efficient use of lander downlink. Co-registered multispectral image sets and spectra are retained onboard and can be downlinked upon query.

Spinning metasurface stack for spectro-polarimetric thermal imaging

Spectro-polarimetric imaging in the long-wave infrared (LWIR) region plays a crucial role in applications from night vision and machine perception to trace gas sensing and thermography. However, the current generation of spectro-polarimetric LWIR imagers suffers from limitations in size, spectral resolution, and field of view (FOV). While meta-optics-based strategies for spectro-polarimetric imaging have been explored in the visible spectrum, their potential for thermal imaging remains largely unexplored. In this work, we introduce an approach for spectro-polarimetric decomposition by combining large-area stacked meta-optical devices with advanced computational imaging algorithms. The co-design of a stack of spinning dispersive metasurfaces along with compressive sensing and dictionary learning algorithms allows simultaneous spectral and polarimetric resolution without the need for bulky filter wheels or interferometers. Our spinning-metasurface-based spectro-polarimetric stack is compact (<10×10×10cm) and robust, and it offers a wide field of view (20.5°). We show that the spectral resolving power of our system substantially enhances performance in machine learning tasks such as material classification, a challenge for conventional panchromatic thermal cameras. Our approach represents a significant advance in the field of thermal imaging for a wide range of applications including heat-assisted detection and ranging (HADAR).

Assembly and Testing of Ground Layer Adaptive Optics (GLAO) for ARIES Telescopes

This project is focused on evaluating the slowly-varying ground layer seeing component at the optical telescopes of ARIES. To achieve this, we assembled the instrument, consisting of a filter wheel, a CCD camera, and a tip-tilt enabled transparent glass plate integrated within an off-the-shelf unit termed as the AO (Adaptive Optics) unit. The instrument developed by us was deployed on the 1.04-m f/13 Sampurnanand telescope at Manora Peak and the 1.3-m f/4 telescope at Devasthal. This instrument measures the average instantaneous slope (tip/tilt) of the incoming wavefront over the telescope aperture via a fast (within the atmospheric coherence time) sampled image and corrects it via a software-controlled oscillating (tipping/tilting) single thin glass plate. The night observations revealed that the slowly-varying seeing component is significant at both observatories and can be effectively controlled to enhance the sharpness of the celestial images at the two sites. The most significant improvement was measured from 5 arcsec of uncorrected FWHM of a star to 3.4 arcsec of corrected FWHM in the 1.04-m telescope in the evening hours.

Multigas nonresonant photoacoustic spectroscopy sensor based on a broadband radiation source

AbstractMultigas detection is in demand for a wide range of environmental and industrial applications. In this work, a sensitive and selective multigas photoacoustic spectroscopy (MG‐PAS) sensor was developed by employing a nonresonant photoacoustic spectroscopy technique combining a broadband radiation source. Six gases including CO, CO2, CH4, C2H2, C2H4, and C2H6 were selected as target measurement molecules. Selectivity of the MG‐PAS was realized by using six mid‐infrared narrow‐band filters which integrated in a homemade filter wheel. A minimum concentration detection limits of 0.2 ppm for CO, 0.05 ppm for CO2, 0.12 ppm for CH4, 0.1 ppm for C2H2, 0.81 ppm for C2H4, and 0.05 ppm for C2H6 were obtained, respectively, with a 1‐s integration time. Measurements of six gas mixtures showed that the average measurement error of the MG‐PAS sensor was within 2%.

Switchable LED-based laparoscopic multispectral system for rapid high-resolution perfusion imaging.

Multispectral imaging (MSI) is an approach for real-time, quantitative, and non-invasive tissue perfusion measurements. Current laparoscopic systems based on mosaic sensors or filter wheels lack high spatial resolution or acceptable frame rates. To develop a laparoscopic system for MSI-based color video and tissue perfusion imaging during gastrointestinal surgery without compromising spatial or temporal resolution. The system was built with 14 switchable light-emitting diodes in the visible and near-infrared spectral range, a 4K image sensor, and a 10mm laparoscope. Illumination patterns were created for tissue oxygenation and hemoglobin content monitoring. The system was calibrated to a clinically approved laparoscopic hyperspectral system using linear regression models and evaluated in an occlusion study with 36 volunteers. The root mean squared errors between the MSI and reference system were 0.073 for hemoglobin content, 0.039 for oxygenation in deeper tissue layers, and 0.093 for superficial oxygenation. The spatial resolution at a working distance of 45mm was . The effective frame rate was 20fps. High-resolution perfusion monitoring was successfully achieved. Hardware optimizations will increase the frame rate. Parameter optimizations through alternative illumination patterns, regression, or assumed tissue models are planned. Intraoperative measurements must confirm the suitability during surgery.

Toward Compact Motorized Lens: Switch and Focus a Filter Wheel with Single Piezoelectric Tube

AbstractMultispectral cameras (MSCs) have the capability of detecting and analyzing features invisible to human eyes and are of interest for many applications. However, the traditional MSC suffers from bulkiness since the light filtering and optical focusing mechanisms are independent. Herein, it proposed an integrated strategy that implements two functions through a tunable filtering‐focusing mechanism (TFFM), driven by two degrees of freedom (two‐DOF) piezoelectric tube actuator (PTA). The TFFM can realize light filtering and optical focusing through the rotary and linear motions of PTA. The configuration of PTA is presented, and the working principle is discussed. Then, prototypes of PTA and TFFM are developed, weighing merely 5.5 and 8 g, sizing of Ø7 × 21.4 mm and Ø35 × 7 mm, demonstrating the merits of lightweight and miniaturization. Experiments validate the effectiveness of TFFM, including multispectral images acquired with 0.1 s through rotary motion, focused images obtained with a linear speed of 60.2 mm−1s, and a series of images with different sharpness and wavelengths. The sharpness evaluation algorithms are adopted to determine the sharpest image. The work contributes to reducing the volume of MSC systems with multifunctionalities while keeping the devices simple, providing a practical and effective solution for the integrated design of MSC.

Electron Temperature Measurements Using a Two-Filter Soft X-ray Array in VEST.

A multichannel soft X-ray (SXR) array has been developed to measure the electron temperature in the Versatile Experiment Spherical Torus (VEST). To estimate electron temperature using the two-filter method applied to SXR intensity, we designed a pinhole camera that has two photodiode arrays with different metallic filters. We also adopted a filter wheel and tested various filter parameters to find the optimal filter set. Through tests, the combination of aluminum and beryllium was found to be the most suitable for the current experimental conditions in VEST. The filtered SXR signals were acquired with a low-noise preamplifier, exhibiting sufficient signal-to-noise ratios for electron temperature estimation based on the intensity ratio of two signals obtained with different filters. The estimated electron temperature from the developed two-filter SXR array showed reasonably matched levels and consistent trends with Thomson scattering measurements. Error contribution from impurity line emission is also discussed.

Tangential extreme ultraviolet and soft x-ray diagnostic system for time-resolved temperature measurement on the High Beta Tokamak-Extended Pulse.

The High Beta Tokamak-Extended Pulse has recently incorporated a tangential multi-energy extreme ultraviolet and soft x-ray diagnostic system. This system enables measurements of the electron temperature and the examination of mode dynamics within the tokamak. While other systems have been built for poloidal views over similar temperature ranges, this is the first multi-energy tangential-view system designed to work in a temperature range below 200eV in a tokamak. To facilitate these measurements, a filter wheel comprising five distinct groups of dual-filters has been developed and implemented. By employing a combination of 0.1μm aluminum and 0.2μm titanium filters, the system allows estimation of electron temperature profiles through reconstruction of the emission profile using the standard "double-foil" technique. The influence of impurities and filter oxide layers on measurement outcomes is examined. Results reveal that, while the absolute electron temperature values may exhibit some deviations, key characteristics like the electron temperature profile shape and inversion radius during sawtooth events remain consistent. This consistency confirms the system's suitability for core plasma studies. This system has proven effective in detecting and analyzing internal magnetohydrodynamic phenomena, such as sawteeth.

4K × 4K CCD Imager for the 3.6 m DOT: Recent Up-gradations and Results

The 4K × 4K CCD Imager is the first light instrument for the 3.6[Formula: see text]m Devasthal Optical Telescope and is producing broad-band imaging observations of many Galactic and extra-galactic sources since 2015–2016. Capabilities of the CCD Imager are demonstrated recently through several publications using the well-calibrated multi-band deep photometric results as expected from other similar facilities globally. In this paper, we summarize some of the recent up-gradations made to improve the Imager, i.e. mounting the new filter wheel casing, replacing stray light baffles and discussing the fringe pattern corrections in redder filters. Some of the new science initiatives like galaxy-embedded faint point sources including WR stars and the observations of low surface brightness galaxy clusters are also discussed.

Combining laser speckle imaging and spatially modulated visible illumination to study the effect of anesthetic drugs on the optical and physiological parameters of brain

This work employs an integrated optical imaging system to evaluate the effect of anesthetic drugs on several brain parameters including absorption, scattering, oxygen saturation, and cerebral blood flow (CBF). Two anesthetic drugs, namely ketamine-xylazine (KX) and thiopental, frequently used by researchers in mouse experiments, were investigated herein. The combined system is based on spatially modulated visible light illumination and a laser speckle based-technique. With this apparatus, a series of structured light (sinusoidal patterns) with phase shifts at each of two spatial frequencies (low and high) are projected onto the surface of a mouse brain and diffusely reflected light is acquired by a camera. A six-position filter wheel, equipped with five visible bandpass filters, is placed at the output of the projector. Then, structured illumination is blocked and a laser source illuminates the tissue while the diffusely reflected light is captured by the same camera through the remaining open hole in the wheel. In this manner, visible and laser speckle images are captured and processed off-line to reconstruct the cerebral tissue features. This work's major findings are six-fold: first, over a specific range of the spectrum a difference of more than 20% was found in the absorption coefficient presumably as a sensitivity to hemoglobin. Second, a difference of more than 20% was observed between drug types in the scattering coefficient along the entire spectral range. Third, CBF varied considerably in thiopental anesthesia throughout the experiment. Fourth, oxygen saturation level remains stable in both anesthetics. Fifth, thiopental keeps blood glucose in normal range while with KX glucose level increases. Sixth, the co-registered system is capable of revealing quantitative functional contrast and may be an attractive method in a variety of biomedical applications. Overall, these findings suggest that the choice of KX or thiopental should be carefully considered as a component of study design in research utilizing animal models.

Design of a Large-Format Low-Light Imaging System Based on the RGB Filter Wheel

In order to capture true-color information of distant targets under extremely low light, a large-format low-light imaging system is designed based on an RGB filter wheel. By decomposing the system indicators, this study proposes a method for acquiring low-light true-color images using a large-aperture, low-distortion optical lens combined with an RGB filter wheel capable of multi-line sequential exposure. The optical field segmentation is achieved using a four-panel optical reflective prism, and the images from four high-sensitivity SCOMS detectors are stitched together to form a composite image. The working principle of the system is explained, and the low-light imaging capability is thoroughly evaluated. The dimensions and rotation speed of the filter wheel are then calculated in detail, ensuring accurate synchronization of the filter wheel’s speed and exposure time. The calculation method for the parameters of the four-panel reflective prism structure is investigated, mathematical expressions for the geometric parameters of the prism assembly are provided, and a prism assembly suitable for four-way spectral separation is designed. Based on the research and design results, a large-swath-width, low-light true-color imaging system is developed that is suitable for an environmental illuminance of 0.01 lux. The system achieves a ground pixel resolution of 0.5 m (at an altitude of 5 km) and an effective image resolution of 4 K × 4 K, and is capable of accurately reproducing target color information. Laboratory and field flight tests verified that the large-swath-width images obtained by the imaging system are clear, with high contrast and resolution. After image fusion and spectral registration, the color images exhibit full saturation and high fidelity, meeting the requirements of low-light true-color imaging under airborne conditions. The design methodology of this low-light imaging system can serve as a reference for the development of airborne low-light imaging equipment.

Magnetic cleanliness verification of miniature satellites for high precision pointing

The advancement in miniature satellite technology and its increasing usage in scientific and commercial applications presents new and unique challenges, particularly for pointing requirements. These small platforms, often limited in resources, are particularly susceptible to disturbance from residual magnetic dipoles while operating in low earth orbit (LEO). To overcome this issue, the precise identification of a satellite's residual magnetic dipole is crucial to enable the compensation of disturbance torques. However, the use of magnetic materials in modern commercial-off-the-shelf (COTS) technology cannot always be avoided. The pre-launch verification of magnetic cleanliness requirements in a laboratory setting is also a significant challenge for small satellite systems. To address this problem, Fraunhofer Ernst-Mach-Institute (EMI) and Fraunhofer Institute for Physical Measurement Techniques (IPM) have developed a cutting-edge test setup for the precise characterization of small residual dipole moments, with the goal of qualifying the ERNST nanosatellite. This innovative approach aims to provide efficient system verification with minimal time and cost overhead and to establish a dedicated test infrastructure, specifically tailored to tackle the unique challenges and requirements of magnetic cleanliness verification in future miniature space systems. As a promising preliminary result of the first test campaign, the filter wheel mechanism of the ERNST nanosatellite could be optimized, resulting in a significantly reduced magnetic moment of the device, meeting the missions challenging magnetic budget constraints.

The fast camera (Fastcam) imaging diagnostic systems on the DIII-D tokamak

Two camera systems are installed on the DIII-D tokamak at the toroidal positions of 90° (90° system) and 225° (225° system), respectively. The cameras have two types of relay optics, namely, a coherent optical fiber bundle and a periscope system. The periscope system provides absolute intensity calibration stability while sacrificing resolution (10 lp/mm), while the fiber system provides high resolution (16 lp/mm) while sacrificing calibration stability. The periscope is available only for the 90° system. The optics of the 225° system were designed for view stability, repeatability, and easy maintenance. The cameras are located inside optimized neutron, x ray and magnetic shielding in order to reduce electronics damage, reboots, and magnetic and neutron interference, increasing the overall system reliability. An automated filter wheel, providing remote filter change, allows for remote wavelength selection. A software suite automates camera acquisition and data storage, allowing for remote operation and reduced operator involvement. System metadata is used to streamline the data analysis workflow, particularly for intensity calibration. The spatial calibration uses multiple observable wall features, resulting in a reconstruction accuracy ≤2cm.