Lens Assembly Research Articles

Development and commissioning of ion-optical elements for ion and antiproton beams with energies up to 5 keV

In nuclear and atomic physics experiments, charged ion beams often need to be guided from the ion production to the experimental site. In the PUMA experiment, an ion source beamline was developed, which can be operated with up to 5 keV beam energy at a base pressure of 10-9 mbar or better. In this technical report, a low-energy pulsed drift tube for beam energy modification, a hybrid einzel lens assembly for beam focusing and steering and an iris shutter assembly for separating beamline sections with different vacuum requirements are described with their design principles and performances.

Application of deep learning in active alignment leads to high-efficiency and accurate camera lens assembly

Application of deep learning in active alignment leads to high-efficiency and accurate camera lens assembly

Design and characterization of a compact Einzel lens for portable quadrupole mass spectrometry (QMS)

Quadrupole mass spectrometry (QMS) offers better resolution, selectivity and sensitivity than the metal-oxide, field effect transistors and thermal-based gas sensors. However, existing QMS systems are unsuitable for field applications. The miniaturized QMS requires dimensionally scaled components with comparable performance to the conventional bulky systems. For a portable quadrupole mass spectrometry, a compact focusing ion system is required to transfer the maximum number of ions from the ion source to the filter. The present paper discusses the design of a miniature focusing Einzel lens and the effect of design parameters on its performance. The three-cylindrical axially symmetric compact Einzel lens assembly was designed using commercially available software. The relationship between the design parameters is explored for compact and low-powered ion optics. The beam focal length was tuned by varying the bias voltage. The dimensions, as well as voltages across the Einzel lens, were reduced significantly to open a new way for portable point-of-care applications. At an applied voltage of 70 V, the focal length of the ions is 11 mm without being scattered, which is favorable for a portable quadrupole mass filter. The designed Einzel lens was fabricated using micromachining techniques and characterized at a vacuum of 3.05 × 10−4 mbar. The developed lens system shows a current output of 0.114 µA at 72 V lens voltage. A current of 94.8 µA is observed with a background noise of 0.01 µA for the system with nitrogen (28 amu) as the sample.

Novel plenoptic Imager for 3D Particle Tracking Velocimetry for Fluid Structure Interactions

We show a novel plenoptic camera architecture and demonstrate its ability to perform three-dimensional three-component velocimetry using standard multi camera processing techniques. The novel architecture needs only a custom lens assembly with no modification to the camera body. This allows the use of any camera with an appropriate sensor size. The architecture directly creates multiple views of a scene side by side on the camera sensor which can be separated and treated as if they originated from independent cameras. Standard calibration techniques for creating 3D to 2D correspondence on the images can then be implemented to reconstruct 3D scene information. For this case we focus on performing 3D PTV using the commercial software DaVis and the "shake-the-box" algorithm. We look at the flow induced by an oscillating rod and compare the results with the analytical solution to validate the results.

Optical degradation correction of manufacturing-perturbed glass-plastic hybrid lens systems via a joint hardware-software optimization framework.

Glass-plastic hybrid lens systems are increasingly critical in various optical applications due to their unique advantages and growing demands. Due to limitations in manufacturing processes and costs, the yield rate of glass-plastic hybrid lens systems in mass production struggles to match that of mature all-plastic ones. In this work, we propose a pioneering joint hardware-software optimization framework designed for correcting optical degradation in manufacturing-perturbed glass-plastic hybrid lens systems. Our framework begins with the establishment of a differentiable imaging simulation system that is capable of simulating various manufacturing errors. This system facilitates the preliminary estimation of manufacturing deviations across individual lenses without precise measurements. Subsequently, from the perspective of the hardware assembly process, we integrate active alignment of the glass aspherical lens to mitigate degradation caused by these deviations. Moreover, we introduce a novel and lightweight degradation correction network as post-processing software to address residual optical degradation without fine-tuning for each manufacturing-perturbed lens system, significantly reducing deployment costs for mobile devices. Extensive experiments validate the efficacy of our joint hardware-software optimization framework, showing substantial improvements in imaging quality and enhanced yield rates in mass production. Overall, our framework establishes a new paradigm for optical degradation correction in glass-plastic hybrid lens systems by synergizing the front-end lens assembly process with the back-end degradation correction method. This new paradigm represents an inaugural effort within the optical engineering domain.

Thermal design and experimental verification of the space ultraviolet wide field of view multi-channel scanning imager

In order to ensure the optimal imaging quality of the space ultraviolet wide field of view multi-channel scanning imager, it is imperative to conduct a comprehensive investigation into the thermal control system. First, we shall present the structure and performance index of the imager. The determination of the heat dissipation surface's position follows an analysis of the imager's exterior heat discharge. Subsequently, the thermal control design for every individual component of the imager is determined, considering the challenges associated with thermal management. The accuracy of the initial thermal design is verified by doing thermal simulation studies. Subsequently, the thermal equilibrium test was performed. The test results reveal that the temperature of the lens assembly varied between 20.0 °C and 25.6 °C, the horizontal bracket ranged from 19.7 °C to 21.7 °C, the vertical bracket exhibited temperatures between 11.2 °C and 15.4 °C, the U-frame experienced temperatures ranging from 15.1 °C to 17.4 °C, the motor showed temperatures between 6.6 °C and 26.3 °C, the detector recorded temperatures between 21.4 °C and 25.9 °C, and the high voltage module exhibited temperatures ranging from 8.9 °C to 19.9 °C. The temperature of each component is within the designated thermal control range. Extensive evidence has been presented to demonstrate the effectiveness and precision of thermal design.

A wide-field-of-view metalens array for CMOS image sensors’ conical light focusing

Microlens array combined with CMOS sensors have recently been the subject of intensive research due to their ability to significantly enhance imaging sensitivity. However, existing microlens arrays suffer from a limited field-of-view, necessitating complex lens assemblies that increase system cost, size and weight. In this study, we present a novel approach utilizing a single layer metalens array composed of low loss and high-index α-Si materials. The metalens array was designed using a phase compensation method to efficiently focus conical light with arbitrary cone angles onto the center pixels of the CMOS sensor. Theoretical analysis demonstrates that the metalens is capable of focusing ± 20° conical light with an impressive efficiency of 83.6 %, which can be extended to arbitrary cone angles. Experimental results reveal a measured focusing efficiency of 73 % under an incidence angle of ± 8.3° for conical light, representing an improvement of 8 % compared to parallel light incidence. This research presents a promising solution for wide-field-of-view metalens arrays in integrated CMOS imaging systems.

Cantilever enhanced fiber-optic photoacoustic microprobe for diffusion detection of sulfur dioxide

A cantilever enhanced fiber-optic photoacoustic microprobe with the cavity volume of only 119 μL is designed to detect SO2, which has the obvious advantages of passive sensing, anti-electromagnetic interference and low cost. A UV multi-mode fiber and a single-mode fiber are applied to transmit excitation light emitted by UV-LED and probe light, respectively. The lens assembly based on a collimating lens and a focusing lens is added to improve the light energy of UV-LED coupling into UV-fiber. Based on theoretical analysis and finite element method, a photoacoustic cavity with a radius of 1.5 mm and a length of 15 mm is designed, which is conducive to the realization of photoacoustic enhancement and rapid response at high frequencies. SO2 gas diffuses into the PA cavity through a hole with the diameter of 0.5 mm and a gap of the cantilever with the width of 0.5 µm. A fiber-optic cantilever based on F-P interference is adopted to detect sound pressure. The frequency characteristic and response time of the sensor in different backgrounds of SF6 and N2 are analyzed experimentally. Compared with N2, the photoacoustic microprobe operates in SF6 background with lower resonance frequency and longer response time, which is due to the high density and low thermal diffusivity of SF6 gas. With the flow rate of 250 SCCM in the external cavity, the response time of the photoacoustic microprobe to SO2/SF6 and SO2/N2 are 96 s and 40 s, respectively. The detection limits of SO2 in SF6 and N2 background are 35 ppb and 5 ppb, respectively.

All-optical photoacoustic detection of SF6 decomposition component SO2 based on fiber-coupled UV-LED

An all-optical photoacoustic sensor for measuring the concentration of SF6 decomposition derivative SO2 was designed, whose detection limit was in the order of ppb-level. An UV-fiber and a single-mode fiber were utilized to transmit excitation light and probe light, respectively. The technical scheme of all-optical gas sensing has realized the competitive advantages of long-distance detection and anti-electromagnetic interference. As an UV-LED was the excitation light, the challenge of designing all-optical SO2 sensor was to effectively couple UV-LED with large divergence angle into an UV- fiber. Theoretical calculation and experiment have proved that the lens assembly as an effective strategy to realize the efficient coupling and beam collimation, which can achieve high excitation power and low solid photoacoustic background interference. The lens assembly with high focusing property was the key to improve the signal-to-noise ratio (SNR) by 5.2 times. To detect photoacoustic pressure with high sensitivity, a fiber optic cantilever acoustic sensor based on F-P interference was designed. Based on the demodulation algorithm of white light interference, dynamic cavity length of F-P was demodulated with high-resolution. Allan-Werle analysis result indicate that the detection limit of SO2 gas was 48 ppb with an averaging time of 100 s

Optical performance of commercial liquid lens assemblies in microgravity

Optical performance of commercial liquid lens assemblies in microgravity

Dynamic detection of ppb-level SO2 based on a differential photoacoustic cell coupled with UV-LED.

We design a photoacoustic (PA) SO2 sensor based on the coupling of a differential photoacoustic cell (DPAC) and cost-effective UV-LED, which realized the dynamic monitoring of SO2 gas at the ppb level. Aiming at the limitation of UV-LED divergence, a light source combination module with high condensing efficiency was devised based on a lens through theoretical derivation and experimental analysis. The PA signal with the optimum matching of the lens was 20-times larger than the direct coupling of the UV-LED. Due to the excellent beam collimation effect of the lens assembly, the background interference was only 1 ppm. In addition, the DPAC gathered the merits of doubling the PA signal and reducing the flow noise interference. The analysis of Allan-Werle deviation showed that the detection limit of SO2 was 1.3 ppb with the averaging time of 100 s.

Development of Structural Design Method for Twisted Wires Suspension

Copper alloy suspension wires are used in the optical pickups and image stabilization mechanisms of mobile cameras. The durability of suspension wires used in mobile cameras is greatly affected by the increase in the weight of the lens assembly as makers improve the image quality of the camera. Therefore, the durability of the wire needs improvement. In this study, the stress reduction effect of twisted suspension wires was investigated using finite element method (FEM) analysis. In addition, a practical equation was obtained to facilitate the structural design. From this study, the following conclusions were obtained. In contrast to the conventional single-wire structure, the twisted wire structure enables a significant reduction in the stress generated while maintaining the stiffness. A simple formula that approximates the results of many FEM analyses was developed to enable rapid product design.

Performance evaluation of Littrow lens assembly for Visible Emission Line Corongraph (VELC) on board Aditya-L1 mission

Performance evaluation of Littrow lens assembly for Visible Emission Line Corongraph (VELC) on board Aditya-L1 mission

Optical centering method for lens assembly based on fiber point diffraction interferometry

Centering error in lens assembly reduces the image quality. We proposed an optical centering method based on fiber point diffraction interferometry (FPDI) in this paper. Two fiber point-light-sources (PLSs) interfere longitudinally. The intersection of the line connecting the two PLSs with an imaging plane occurs where the optical path difference (OPD) is an extremum. The line of these two PLSs defines a virtual reference axis. A lens group can be centered by mounting and adjusting lenses piece by piece between the two PLSs and keeping the OPD extremum point as unchanged as possible in this process. Introducing an auxiliary lens can enhance the sensitivity of this method to centering errors. We centered a lens group and showed the effectiveness of the proposed method. Compared with the autocollimation method, the FPDI method does not need to rotate lens elements and is always effective in testing centering errors. In contrast to the calculation of wavefront aberration in the computer-aided alignment (CAA) method, the FPDI method just determines the centering error through the coordinate offset of the OPD extremum point. It utilizes a reference axis that can be precisely positioned by interferometry. The theoretical assembly accuracy can reach micron and arcsec levels.

Development of a fabrication process for production of diffractive optics.

In this study, a novel fabrication process, to the best of our knowledge, was developed to fabricate a glass harmonic diffractive lens. In this process, a polymethylmethacrylate master of the diffractive lens was machined using single-point diamond turning. Then an electrolytic plating process was conducted to grow a reverse nickel (Ni) mold. Precision compression molding was performed using the Ni mold to replicate the diffractive lens structures onto a glass surface. Surface measurements and optical testing show that the replicated diffractive lenses by the proposed method have high tolerances and require optical performance, demonstrating a high-volume, high-precision, and cost-effective process. The proposed method will be critical for consumer products where glass optics are increasingly used in lens assemblies.

Ghost imaging lidar system for remote imaging.

Research towards practical applications of ghost imaging lidar system especially in longer sensing distance has been urgent in recent years. In this paper we develop a ghost imaging lidar system to boost an extension of remote imaging, where the transmission distance of the collimated pseudo-thermal beam can be improved hugely over long range and just shifting the adjustable lens assembly generates wide field of view suiting for short-range imaging. Based on the proposed lidar system, the changing tendency of illuminating field of view, energy density, and reconstructed images is analyzed and verified experimentally. Some considerations on the improvement of this lidar system are also discussed.

Modulation of the blood-retina-barrier permeability by focused ultrasound: Computational and experimental approaches

The blood-retina-barrier (BRB) is a critical barrier that protects the retinal neurons. It selectively regulates the permeability of molecules, responds to pathologies, and modulates disease progression. While the BRB prevents harmful molecules from the blood from affecting the neurons and is thus essential for retinal health, it also poses a hurdle for therapeutic agents and impedes treatment. The goals are a non-invasive and well-defined transient increase of the BRB’s permeability by mechanical microscale-induced forces, to visualize the permeability change in real-time, and to computationally model the process for an improved understanding and control of the dynamics of larger molecules passage through the BRB. Our approach combines in vivo animal experiments with computational modeling in silico. The in vivo results are used to continuously and iteratively optimize the COMSOL model. In order to modulate BRB’s permeability, we developed a prototype acoustic lens assembly based on COMSOL simulation calculations for the delivery of ultrasonic pressure waves to targeted regions in the retina under optical guidance by light-based imaging. Our data indicate that lower energy focused ultrasound at a PRFP close to 0.8 MPa rapidly increases the permeability of the retinal vessels in a fashion that can be depicted in a real-time fluorescein angiography.

A high-performance cell-phone based polarized microscope for malaria diagnosis.

We present a cell-phone based polarized microscope for diagnosing malaria through hemozoin recognition over a wide field-of-view (FOV) accompanied with decent image performance. The system is constructed based on attachment method using a lens assembly as objective, two mobile phones and two linear polarizers. A ~0.92 μm resolution across a FOV of ~3.27 mm × 3.27 mm with high imaging quality is realized, demonstrating an increased resolving power, four times improvement in FOV and better imaging quality over mobile-optical-polarization imaging device. Importantly, we also demonstrate it has capability of recognizing hemozoin within the sample for malaria diagnosis by imaging malaria-infected blood samples with similar sensitivity comparable to Leica microscopy. It is more compact, portable, and insensitive to alignment, making it highly suitable for malaria detection in a portable, easy to setup and use way in low-resource areas.

Technology for developing a high-aperture four-mirror lens with aspherical mirrors

Subject of study: Methods for optimizing the design, assembly, and alignment of a high-aperture wide-angle four-mirror axisymmetric lens are presented. Aim of study: The aim is the development of a high-tech lens design considering the relationship between the calculated tolerances for the decentering of mirrors and the technological capabilities of their fabrication, assembly, and alignment. Method: The methods include selection of an image quality criterion and calculation of its permissible decrease, distribution of the fabrication errors between the decentering errors and surface shape errors, and calculation of the tolerances based on the obtained ratios. Moreover, the motivation for choosing a lens design with a minimum number of adjustment stages based on the optimization of the calculated permissible decentering is provided considering the technological tolerances for positioning the optical elements. In addition, the possibilities of the scheme to compensate for the residual aberrations resulting from the fabrication and positioning of the mirrors are investigated. At the final stage, the method of reducing the evaluation function for the final adjustment of the optical elements in the lens is used. Main results: The design and technological solutions enabling the optimization of the requirements for the tolerances for deviation of the surface shape of the mirrors from their calculated profile, as well as decentering of the optical elements considering the technological capabilities of production, are examined. The criteria for the distribution of tolerances for permissible deviations of optical system parameters affecting the image quality are formulated. The possibility of designing a high-tech drop-in structure of a high-aperture four-mirror lens comprising a case of two blocks and a single linear adjustment stage of the second mirror to compensate for residual aberrations is demonstrated using the proposed method. Practical significance: The proposed technical solutions were tested by designing a high-resolution lens comprising four aspherical mirrors. The positive results of fabricating a lens with a high aperture and resolution allow the proposed solutions to be used for the design of multimirror axisymmetric lenses.

Understanding wide field-of-view flat lenses: an analytical solution [Invited

Wide field-of-view (FOV) optics are widely used in various imaging, display, and sensing applications. Conventional wide FOV optics rely on complicated lens assembly comprising multiple elements to suppress coma and other Seidel aberrations. The emergence of flat optics exemplified by metasurfaces and diffractive optical elements (DOEs) offers a promising route to expand the FOV without escalating complexity of optical systems. To date, design of large FOV flat lenses has been relying upon iterative numerical optimization. Here, we derive, for the first time, to the best of our knowledge, an analytical solution to enable computationally efficient design of flat lenses with an ultra-wide FOV approaching 180°. This analytical theory further provides critical insights into working principles and otherwise non-intuitive design trade-offs of wide FOV optics.