Focusing Lens Research Articles

A Monocular Projector-Camera System Using Modular Architecture.

This paper presents a monocular projector-camera (procam) system using modular architecture based on relay optics. Conventional coaxial procam systems cannot support (1) online changes to lens settings (zoom and focus) and (2) wide-angle projection mapping. We develop design guidelines for a proposed procam system that would solve these restrictions and address the proposed system's unique technical issue of crosstalk between the camera and projector pixels. We conducted experiments using prototypes to validate the feasibility of the proposed framework. First, we confirmed that the proposed crosstalk reduction technique worked well. Second, we found our technique could achieve correct alignment of a projected image onto a moving surface while changing the zoom and focus of the objective lens. The monocular procam system also achieved radiometric compensation where a surface texture was visually concealed by pixel-wise control of a projection color based on the captured results of offline color pattern projections. Finally, we demonstrated the high expandability of our modular architecture, through the creation of a high dynamic range projection.

Pros and Cons of soft contact lens power mapping

Purpose. To provide an overview of currently available meth- ods and instruments for the measurement of soft contact lens power maps, together with their advantages and potential shortcomings. Material and Methods. The three leading measurement prin- ciples of Moiré Fringe, Shack-Hartmann and Phase Shifting Schlieren were identified, and the relevant literature reviewed and technical specifications summarised. To demonstrate some of the potential deficiencies associated with optical power mapping, a series of measurements were conducted on toric, multifocal and extended depth of focus lenses, using one representative instrument. Raw measured data were analysed using various analysis tools and parameters. Results. Power maps and power profiles are presented for the various lens types. Different smoothing filter settings resulted in significantly different power profiles near the optical centre. The ‘Power versus Azimuth’ profiles showed unexpected results. Conclusion. While all three methods are generally reliable and easy to use, there are still some limitations which need to be considered when interpreting the results. In particular, the profile filter settings need to be chosen carefully for multifocal and extended depth of focus lenses. The need for accurate refractive index data for lens material and solution was demonstrated. Keywords Soft contact lenses, power maps, power profiles, Moiré Fringe, Shack-Hartmann, Phase Shifting Schlieren

A Manufacturability‐Driven Method for Designing Metamaterial Focusing Acoustical Lenses

Herein, a method for designing and fabricating acoustic metamaterial focusing lenses for imaging applications such as nondestructive testing is proposed. First, a refractive index distribution is designed using the time delay method for a target focal length. Second, unit cell structures that can achieve the required refractive indices are found using the effective property retrieval method. At this point, factors such as fabrication cost and manufacturing limitations are considered. Finally, the pressure field from the designed lens is calculated using finite element (FE) modelling and iterated until the required focusing performance is achieved. To increase manufacturability, the unit cells necessarily become larger than required for the homogeneous regime. As an example, a lens of focal length 200 ± 10 mm at a frequency of 40 kHz is designed using cross‐shaped unit cells and fabricated using three‐dimensional printing. The design methodology leads to 2.4 mm (wavelength/3.6) unit cells which operate near the cut‐off frequency of the first mode. The lens is experimentally tested, achieving a focal length of 208 mm and a focal width of 12 mm (1.4 × wavelength), and showing good agreement with an FE model. The focusing ability of the lens is demonstrated by measuring the size of various holes in thin plates.

The state of research on Ghana’s oil and gas resources: Themes and future directions

Research on Ghana's oil and gas resources has flourished since the country discovered oil in 2007. Yet, the existing body of knowledge is scattered across scientific journals and other outlets without any attempts to synthesize and distill key themes and future research directions. Furthermore, prior efforts to synthesize existing research did not use robust methods to select and analyze the articles. Building on past work, we conducted a meta- review of empirical oil and gas articles published in English Language journals between 2007 and 2020. We generated nineteen search terms to select articles from Google Scholar and Web of Science and developed a codebook to manually code thirteen variables for analysis. The findings demonstrate an extensive diversity of authors with local and international institutional affiliations. Additionally, the frequency of publications has increased though the distribution is uneven across time. The dominant research topics are sustainable and economic development, environmental management, and energy governance. Finally, most of the studies are theory-driven and apply qualitative data collection and analytical methods. In conclusion, we propose that future research on oil and gas in Ghana should incorporate more policy process focal lenses, combine diverse theoretical frameworks, advance comparative analysis, and leverage mixed methods and hypothesis testing techniques.

Comparison of bilateral implantation of an extended depth of focus lenses and a blend approach of extended depth of focus lenses and bifocal lenses in cataract patients

BackgroundTo compare the visual outcomes, spectacle independent rate and stereopsis in patients who underwent bilateral implantation of extended depth of focus (EDOF) intraocular lens (IOL), or a blend approach of EDOF and bifocal IOL.MethodsA total of 60 cataract patients, who were scheduled for phacoemulsification and intraocular lens implantation in both eyes in West China Hospital of Sichuan University, were enrolled and divided into Micro monovision group(-0.5D~-1.0D), Non-micro monovision group (< 0.5D) with Symfony IOL, and Mixed group with Symfony and ZMB00 IOLs. Three months postoperatively, we compared the visual acuity, modulation transfer function (MTF), defocus curve, stereopsis, spectacle independence, and photic phenomena among the three groups.ResultsCompared to the Non-micro monovision group (UNVA: 0.07 ± 0.04), Micro monovision group (UNVA: 0.00 ± 0.07, P < 0.001) and Mixed group (UNVA: -0.02 ± 0.06, P < 0.001) showed improvement in binocular uncorrected near visual acuity (UNVA). Additionally, Mixed group exhibited lower MTF10 (MTF10: 0.38 ± 0.24) and point spread function (PSF: 0.192 ± 0.269) results in their non-dominant eye compared to both Micro monovision group (MTF10: 0.56 ± 0.21, P = 0.027; PSF: 0.417 ± 0.282, P = 0.034) and Non-micro monovision group (MTF10: 0.55 ± 0.19, P = 0.038; PSF: 0.408 ± 0.285, P = 0.003). Spectacle independence for near vision were higher in both the Micro monovision (45%) and Mixed (55%) group compared to the Non-micro monovision group (40%). The Mixed group also reported higher incidence of photic phenomena (25%). However, there were no significant differences in stereoscopic function among the three groups.ConclusionBoth micro monovision and mix-and-match methods can help patients to obtain better visual outcomes at different distances. Mix-and-match method has better near visual acuity, while micro monovision method has better intermediate visual acuity. Non-micro monovision methods will affect patients’ near vision outcomes. Binocularly implanted EDOF IOL has better contrast sensitivity.Clinical trial registrationRegistration date:11/07/2023. Trial registration number: ChiCTR2300073433. Trial registry: West China Hospital of Sichuan University retrospectively registered.

Exploring the Femtosecond Filamentation Threshold in Liquid Media Using a Mach-Zehnder Interferometer.

We experimentally studied the supercontinuum induced by femtosecond filamentation in different liquid media. Using a Mach-Zehnder interferometer, we determined the relative filamentation thresholds (Pth) of these media. Research has shown that the value of the filamentation threshold is greater than that of Pcr (critical power for self-focusing), which can mainly be attributed to the strong dispersion effect. Changing the focal length of the focusing lens affects filamentation dynamics, thereby affecting the measured results regarding the filamentation threshold. With shorter focal lengths, the linear focusing (i.e., geometrical focusing) regime dominates, and the measured values of Pth for different liquid media are almost the same; as the focal length becomes larger, self-focusing starts to play a role, making the values of Pth for different media different from each other. This study presents an efficient method for investigating the femtosecond filamentation phenomenon in liquid media, helpful to provide further insights into the physical mechanism of supercontinuum generation via femtosecond filamentation in liquid media.

First data and preliminary experimental results from a new Doppler backscattering system on the MAST-U spherical tokamak

A new Doppler backscattering (DBS) system, consisting of Q-band and V-band, has been installed and achieved its first data on the MAST-U spherical tokamak. The Q-band and V-band have separate microwave source systems, but share the same optical front-end components. The Q-band and V-band sources simultaneously generate eight (34, 36, 38, 40, 42, 44, 46 and 48 GHz) and seven (52.5, 55, 57.5, 60, 62.5, 65 and 67.5 GHz) fixed frequency probe beams, respectively. These frequencies provide a large range of radial positions from the low-field-side edge plasma to the core, and possibly to the high-field-side edge, depending on the plasma conditions. The quasi-optical system consists of a remotely-tunable polarizer, a focusing lens and a remotely-steerable mirror. By steering the mirror, the system provides remote control of the probed density fluctuation wavenumber, and allow the launch angle to match the magnetic field. The range of accessible turbulence wavenumbers (kθ ) is reasonably large with normalized wavenumber kθρs ranging from <0.5 to 9. The first data acquired by this DBS system is validated by comparing with the data from the other DBS system on MAST-U (introduced in ref. [21]). An example of measuring the velocity profile spanning from the edge to the center in a high-density plasma is presented, indicating the robust capabilities of the integrated Q-band and V-band DBS systems.

Clinical Performance of Extended Depth of Focus (EDOF) Intraocular Lenses – preliminaryresults

Purpose: Extended depth of focus (EDOF) lenses are the bridge that connects monofocal IOLs to IOLs with multifocal designs. This retrospective study aimed to analyze visual outcomes 3 months after bilateral implantation of the new EDOF intraocular lens in routine cataract surgery. Methods: Visual function was evaluated for near, intermediate, and far distance in 12 patients (24 eyes), bilaterally implanted with an EDOF artificial intraocular lens (IOL). Visual acuity at distance (5m), intermediate (70 cm) and near distance (40 cm) with and without refractive correction was measured. Subjective outcomes regarding visual function, independence from glasses and lighting, presence of light phenomena such as dysphotopsia, and overall patient satisfaction three months after phacoemulsification were also evaluated. Results: The mean age of the patients was 68 years. The mean IOL power was 21.5 ± 2.50 D. Three months after surgery, the mean uncorrected distance (UCDVA), intermediate (UCIVA) and near (UCNVA) visual acuities were 0,9, 0,9 and 0,8. Patient satisfaction was high, with a low occurrence of dysphotopsia. Conclusion: The EDOF IOLs showed satisfactory visual performance after cataract surgery, with high patient satisfaction and a low occurrence of visual disturbances. It resulted in good distance and intermediate vision, but might require spectacles for small print at a near distance.

Terahertz ellipsometry based on the long-distance diffraction-free beam

We introduce a long-distance terahertz (THz) diffraction-free beam (DFB) to the quasi-optical THz ellipsometry. Due to the distinctive characteristics of DFBs, the reflected arm of the ellipsometer does not need a focusing lens to enhance the signal detected. Since the radiation emitted from the generator is linearly polarized, there is no need to place a polarizer on the incident arm. The THz ellipsometry with the lensless reflected arm completed the thickness measurements of non-absorbent films with thicknesses in the wavelength order. The measured values are consistent with the results measured by the micrometer. In addition, we quantitatively analyzed errors that commonly occur in this ellipsometry. The DFB generating system, which consists of two lens-axicon doublets, is fairly simple to implement. We firmly believe that the proposed approach can be easily transplanted to other types of THz ellipsometry.

Scanning single molecule localization microscopy (scanSMLM) for super-resolution volume imaging

Over the last decade, single-molecule localization microscopy (SMLM) has developed into a set of powerful techniques that have improved spatial resolution over diffraction-limited microscopy and demonstrated the ability to resolve biological features down to a few tens of nanometers. We introduce a single molecule-based scanning SMLM (scanSMLM) system that enables rapid volume imaging. Along with epi-illumination, the system employs a scanning-based 4f detection for volume imaging. The 4f system comprises a combination of an electrically-tunable lens and high NA detection objective lens. By rapidly changing the aperture (or equivalently the focus) of an electrically-tunable lens (ETL) in a 4f detection system, the selectivity of the axial object plane is achieved, for which the image forms in the image/detector plane. So, in principle, one can scan the object volume by just altering the aperture of ETL. Two schemes were adopted to carry out volume imaging: cyclic scan and conventional scan. The cyclic scheme scans the volume in each scan cycle, whereas plane-wise scanning is performed in the conventional scheme. Hence, the cyclic scan ensures uniform dwell time on each frame during data collection, thereby evenly distributing photobleaching throughout the cell volume. With a minimal change in the system hardware (requiring the addition of an ETL lens and related electronics for step-voltage generation) in the existing SMLM system, volume scanning (along the z-axis) can be achieved. To calibrate and derive critical system parameters, we imaged fluorescent beads embedded in a gel-matrix 3D block as a test sample. Subsequently, scanSMLM is employed to visualize the architecture of actin-filaments and the distribution of Meos-Tom20 molecules on the mitochondrial membrane. The technique is further exploited to understand the clustering of Hemagglutinin (HA) protein single molecules in a transfected cell for studying Influenza-A disease progression. The system, for the first time, enabled 3D visualization of HA distribution that revealed HA cluster formation spanning the entire cell volume, post 24 hrs of transfection. Critical biophysical parameters related to HA clusters (density, the number of HA molecules per cluster, axial span, fraction of clustered molecules, and others) are also determined, giving an unprecedented insight into Influenza-A disease progression at the single-molecule level.

Non-contact optical probe with nanometer resolution and large measurement range based on the astigmatism method

In the measurement field of micro/nano devices, many instruments have a contradiction between high resolution and large measurement range. This paper developed a non-contact optical nanometer probe based on the astigmatism method. This probe employs a high numerical aperture (NA) focusing lens to achieve nanometer resolution of the longitudinal measurement. Meanwhile, a longitudinal scanning measurement method based on two focus error signal (FES) curves is proposed to break the limit of low measurement range caused by high NA value. Therefore, it enables the probe to achieve the nanometer resolution of longitudinal measurement and large measurement ranges. The experiment results show that the longitudinal measurement resolution of the proposed probe is better than 1 nm, and the repeatability error is 17 nm. Combined with the high-precision microstage, the longitudinal range is greater than 15 μm. The proposed probe can be used for large-range longitudinal non-contact measurements with nano-scale measurement requirements.

Underwater Wireless Video Communication Using Blue Light

Interest in wireless blue light communication is increasing because this technology shows promise for realizing high-speed, long-distance and full-duplex underwater communication. Here, we demonstrate an underwater wireless communication system, OceanLink, to establish full-duplex data transmission using blue light. Both the transmitter and receiver are housed together to independently transmit and receive data simultaneously. To obtain a longer transmission distance and better light field distribution, the transmitter is composed of an array of three light-emitting diode (LED) units with the dominant emission peak wavelength centered around 452 nm, each of which merges four LEDs in series. These LEDs are synchronously driven via a main processing unit to pulse blue light using a nonreturn-to-zero on-off keying modulation scheme. At the receiver, light passes through a neutral density (ND) filter and a focus lens to hit the transducer, which converts light signals into electrical signals. The waterproof OceanLink achieves a bidirectional communication rate of 4 Mbps with a wireless transmission distance of 12 m in a swimming pool, wherein the ND factor is 256 and the nephelometric turbidity unit is 1.7. Thus, real-time full-duplex underwater video communication is experimentally demonstrated.

Compact and modular system architecture for a nano-resonator-mass spectrometer.

Mass measurements in the mega-to giga-Dalton range are essential for the characterization of natural and synthetic nanoparticles, but very challenging to perform using conventional mass spectrometers. Nano-electro-mechanical system (NEMS) based MS has demonstrated unique capabilities for the analysis of ultra-high mass analytes. Yet, system designs to date included constraints transferred from conventional MS instruments, such as ion guides and high vacuum requirements. Encouraged by other reports, we investigated the influence of pressure on the performances of the NEMS sensor and the aerodynamic focusing lens that equipped our first-generation instrument. We thus realized that the NEMS spectrometer could operate at significantly higher pressures than anticipated without compromising particle focusing nor mass measurement quality. Based on these observations, we designed and constructed a new NEMS-MS prototype considerably more compact than our original system, and which features an improved aerodynamic lens alignment concept, yielding superior particle focusing. We evaluated this new prototype by performing nanoparticle deposition to characterize aerodynamic focusing, and mass measurements of calibrated gold nanoparticles samples. The particle capture efficiency showed nearly two orders of magnitude improvement compared to our previous prototype, while operating at two orders of magnitude greater pressure, and without compromising mass resolution.

Flexible optical tactile sensor based on a liquid-membrane lens structure.

Based on the liquid lens focus mechanism, a novel, to the best of our knowledge, optical tactile sensor is designed by taking advantage of the structure simplicity, fast response, and environmental immunity. The design of the tactile sensing mechanism used the liquid-membrane lens structure. To integrate the tactile sensing system, we designed a data acquisition circuit unit. A performance test platform was built, and performance testing and two application demonstrations were conducted. The experiment's result showed that the linear fitting degree was greater than 0.988, the load response time was 0.078s, the target mass was accurately measured, the maximum error was less than 0.02N, and the fine adjustment of the LED light intensity was achieved.

Full aperture backscatter diagnostics for characterization of laser plasma instabilities at the extreme light infrastructure (ELI) beamlines.

We report on the commissioning of a full aperture backscatter diagnostics station for the kilojoule, nanosecond high repetition rate L4n laser operating at a wavelength of 527nm at the Extreme Light Infrastructure (ELI) - Beamlines, Dolni Brezany, Czech Republic. Light scattered back from laser-plasma interaction into the cone of the final focusing lens is captured and split into different channels to measure the signatures of laser plasma instabilities from stimulated Brillouin scattering, stimulated Raman scattering, and two plasmon decay with respect to back scattered energy, its spectrum, and its temporal profile. The performance was confirmed in a commissioning experiment with more than 800 shots at laser intensities ranging from 0.5 × 1013 to 1.1 × 1015Wcm-2. These diagnostics are permanently installed at ELI Beamlines, and can be used to understand the details of laser-plasma interactions in experiments with kJ and 527nm light. The large number of shots that can be collected in an experimental campaign will allow us to study the details of the laser-plasma interaction with a high level of confidence.

Optimal structures for focusing and energy accumulation: mathematical models and intuition

Metamaterials and composite structures are able to manipulate waves and focus fields and currents in desirable directions. Designs based on spatial and temporal variation of material properties create structures forcing fluxes into specified parts of the domain or concentrating energy into arrays of progressively sharpening pulses. The paper discusses examples of focusing structures, mathematical and intuitive considerations that influence optimal design theory. The optimality requirement introduces zones of optimal composites with variable microgeometry. The observed absence of classical solutions motivates the extension of the class of optimal partitions to composites. Such materials also provide a solution to the problem of optimal design of a thermal lens focusing thermal fluxes when the incoming fluxes are not completely known in advance. An extension of designs to dynamical materials such as space–time checkerboard composites introduces metamaterials with additional capabilities that control the accumulation of energy in the propagating waves. The discussed mathematical methods of focusing and suitable properties alternation targeted on optimality are illustrated by physical examples.

Embracing the Technological Metamorphosis: Envisioning Higher Education for Generation Alpha in a Shifting Educational Landscape

The contemporary landscape is witnessing an accelerated technological evolution that is fundamentally altering our conception of knowledge as an open and easily attainable entity. This transformative progression is not only redefining the practical application of competencies, concepts, and insights but also exerting a profound impact on various facets of education. This paradigmatic transition, catalyzed by the pervasive influence of technology, is particularly pertinent in the realm of education, where its metamorphic contributions are conspicuously manifest. As the educational milieu continues to undergo metamorphosis, the future pedagogical and didactic methodologies will inevitably bear the indelible imprint of technological advancements. Concurrently, educators are confronted with the distinctive imperative of effectively engaging the emergent cohort of learners, commonly referred to as Generation Alpha, within the context of higher education. Characterized by a pronounced entrepreneurial disposition, Generation Alpha is notably predisposed to embracing innovation and advancement, with a significant proportion of its members harboring aspirations of pursuing tertiary education. The present study undertakes a proactive stance in envisioning the educational dynamics and prospects that will define the forthcoming landscape of higher education, with a focal lens on the distinctive attributes of Generation Alpha. This entails a comprehensive inquiry into their favored pedagogical modalities, cognitive perspectives, and educational anticipations. The study embraces a robust theoretical framework that is anchored in the distinctive attributes of Generation Alpha, attributes invariably molded by the inexorable march of technological progress. In a complementary manner, the study derives insights from a triad of discrete empirical investigations conducted across diverse locales including Slovakia, Hungary, Australia, and Turkey. Collectively, these empirical explorations synergistically illuminate the complex matrix of challenges and opportunities that underpin the educational edifice concerning Generation Alpha. The research significantly underscores the potency wielded by the realm of social media and interconnectivity in shaping educational discourse. Moreover, it discerns Generation Alpha's inherent prowess in swiftly assimilating and processing information as an invaluable asset that stands to influence forthcoming pedagogical paradigms within the precincts of higher education. Informed by these discerning revelations, the research culminates in the formulation of actionable imperatives directed at institutes of higher learning, with a strategic intent to implement transformative measures aimed at elevating the erudition voyage for the denizens of Generation Alpha. These prescriptive directives are meticulously attuned to the distinct attributes, cognitive configurations, and educational expectations that are emblematic of Generation Alpha, thereby orchestrating an ecosystem conducive to fostering an immersive and resonant traditional odyssey.

Terahertz quasi-perfect vortex beams

We have successfully demonstrated the generation of terahertz (THz) quasi-perfect vortex beams (quasi-PVBs) at 0.3 THz. These THz quasi-PVBs can carry not only an individual orbital angular momentum (OAM) mode but also a multiplexed one. The 3D printed spiral axicon and multiplexed spiral axicon were used to generate THz quasi-PVBs carrying individual and multiplexed OAM modes, respectively. The individual and multiplexed OAM modes are verified using a focal hyperbolic lens method and a modified coordinate transformation method, respectively. A THz quasi-PVB with the multiplexing of multiple different OAM modes holds promise for coupling to a receiver port with a fixed annular index profile, thereby increasing the number of communication channels. These works have potential applications in compact terahertz systems, such as mode division multiplexing, which further enhances the system's capacity.

Characteristics of laser-induced steel plasmas generated with different focusing conditions.

Laser focusing is an important parameter that affects the characteristics of laser-induced plasma. Focusing lenses with different F-numbers form different energy density distributions near the surface of a sample, thus affecting the characteristics of plasma. In this study, the plasma generated by a nanosecond laser ablation of a micro-alloy steel certified sample at 1atm of air was investigated. We compare the spectrally integrated plasma images obtained at different defocusing distances for short- and long-focus lenses and investigate the optical emission spectra of laser-induced plasma on steel alloy by using focusing lenses with different F-numbers. With an increase in the defocusing distance, the plasma plume changes from flat to hemispherical and then splitting occurs. The spectral line intensity increases first and then decreases, then increases slightly, and finally decreases gradually. For the long-focus lens, when the focal point is above the sample surface, the laser beam strongly interacts with air over a longer distance, leading to longer air plasma and weaker sample plasma compared with the short-focus lens. Thus, the relative intensity of the second peak in the spectral line intensity, according to the defocusing distance, gradually decreases with increasing F-number. We also obtain two-dimensional spatial distributions of the spectral line intensity according to the F-number and defocusing distance. The optimal defocusing distances for all focusing lenses occur when the focal point is below the sample surface. The relation between the optimal defocusing distance and F-number follows a single- exponential decay function.

Numerical investigation of ultrasound focusing and bubble collapse

Ultrasound focusing and microbubble collapse are numerically investigated using a level-set interface tracking method for two-phase flows with multiple interfaces. The computations for ultrasound propagating through a spherical lens demonstrate the ultrasound refraction and pressure intensification at the rear of the lens. The focusing of the initial negative pressure wave through the lens induces a converging flow and the focusing of the subsequent positive pressure wave further intensifies the pressure at the lens. Computations are extended to bubble oscillations near the focusing lens and compared with the no-lens case. The lens not only amplifies the bubble expansion and contraction rates significantly but also generates a larger pressure gradient across the bubble. This ultrasound focusing effect contributes to the asymmetric collapse of the bubble and the formation of a liquid jet that penetrates the bubble. The effects of lens size, initial bubble radius and bubble-lens distance on bubble expansion and liquid jet are further investigated.