Space-charge lens for focusing negative ion beams by means of an additional electron ionizer

A space-charge lens created at the Institute of Physics, National Academy of Sciences of Ukraine, to focus negative ion beams using an additional electron ionizer is investigated. In the previous version of the lens, in which the gas was ionized by the ion beam itself, the focal power was quite high (the focal length was ? ≤ 20 cm) but the gas pressure was too great (P ～ 10^?3 torr), which resulted in significant charge-exchange losses of the beam ions. The experimental and theoretical study reported here shows that the use of a 100-eV electron beam as an auxiliary ionizer allows the working pressure in the lens to be significantly reduced. As a result, a simple, inexpensive, and efficient lens has been developed that can be used in systems for transportation of negative ion beams.     

Dual laser flow cytometry: focal length compensation when focussing through a single lens

Dual laser operation of flow cytometers, using a single focussing lens for both beams, requires compensating for chromatic aberration of the lens. By using a prefocussing lens at a fixed position in one of the laser beams, complete focal length compensation is obtained without any loss in system performance.     

Focusing of heavy ion beams by a high-current plasma lens

Results are presented from studies of the focusing of wide-aperture low-energy (100–400 eV) and moderate-energy (5–25 keV) beams of heavy-metal ions by a high-current electrostatic plasma lens. It is found experimentally that, because of the significant electron losses, the efficient focusing of such beams can be achieved only if the external potentials at the plasma-lens electrodes are maintained constant. Static and dynamic characteristics of the lens are studied under these conditions. It is shown that, as the beam current and the electrode voltage increase, the maximum electrostatic field in the lens tends to a certain limiting value because of the increase in the spatial potential near the lens axis. The role of spherical and moment aberrations in the focusing of wide-aperture low-divergence ion beams is revealed. It is shown that, even when spherical aberrations are minimized, unremovable moment aberrations decrease the maximum compression ratio of a low-energy heavy-ion beam because of the charge separation of multiply charged ions in the focal region. At the same time, as the ion energy increases, the role of the moment aberrations decreases and the focusing of high-current heavy-ion beams by a plasma lens becomes more efficient than the focusing of light-ion (hydrogen) beams. This opens up the possibility of using electrostatic plasma lenses to control ion beams in high-dose ion implanters and high-current accelerators of heavy ions.     

Multiple-Wavelength Focusing and Demultiplexing Plasmonic Lens Based on Asymmetric Nanoslit Arrays

A multiple-wavelength focusing and demultiplexing plasmonic lens based on asymmetric nanoslit arrays is designed. The nanoslit arrays are perforated in a gold film and act as metal–insulator–metal plasmonic waveguides. By manipulating the widths of the slit arrays, the plasmonic lens can concentrate two incident plane wave beams to two separated focal points corresponding to their wavelengths. The full wave simulation is performed to verify the designed lens. This work provides a way to design more compact and integrated wavelength-division multiplexing plasmonic devices for nanophotonic communication and spectral imaging.     

Space-charge lens for focusing a negative-ion beam

Results are presented from experimental and theoretical studies of a space-charge lens for focusing a negative-ion beam. The space-charge field and the beam ion trajectories are numerically calculated for the lens used in the experiments. The results of calculations are compared with the experimental data. It is shown theoretically and experimentally that the proposed device allows one to achieve the main operating conditions of the space-charge lens: the inertial confinement of positive ions and the removal of electrons by an external electric field. The focusing field of the lens attains ～100 V/cm, which provides a focal length of <20 cm.     

Spherical aberration of the fish lens: interspecies variation and age

Summary Spherical aberration of the eyes of a spectrum of freshwater fishes was determined by photographing the refractive effects of excised crystalline lenses on multiple parallel split laser beams. In general, spherical aberration is minimized by the developmentally related variation in lens refractive index. However, spherical aberration is marked and non-monotonic in a non-visual species such as the bullhead. Furthermore, the size and variability of the aberration appears to be related to visual need as indicated by diet and feeding habits. For example, the lenses of predatory sight feeders such as the pike (Esox lucius) or rock bass (Ambloplites rupestris) are optically superior to that of an omnivorous feeder as the carp (Cyprinus carpio).The effect of age was tested by examining rock bass lenses from fish two to seven years of age. Lens quality, as indicated by the amount of change in posterior focal length for beams of varying eccentricity from the optic axis, is optimum in lenses from five year old fish. The significance of this variation in lens quality is uncertain and requires further study with greater attention to specimens of advanced age.     

Alignment and focusing unit for dual-laser excitation in the fluorescence-activated cell sorter

The two laser beams in a dual-laser fluorescence-activated cell sorter FACS-II can be aligned and focused independently on the sample stream with an additional unit, which can be fitted easily on the optical bench of the FACS. The unit consists of two spherical lenses, which have been mounted in separate holders and can be moved in three directions by way of micrometer gauges. The lenses, which have different focal lengths, have been cut off on one side so each laser beam only passes one lens. The setup has been tested using the flow analysis of a suspension of double-stained chicken red blood cells. The histograms of both fluorescence signals showed normal distributions with a coefficient of variation of approximately 6%. After willful interference with the adjustments, the laser beams could be readily readjusted within five minutes.     

Super-Resolution Long-Depth Focusing by Radially Polarized Light Irradiation Through Plasmonic Lens in Optical Meso-field

In this paper, we propose a novel plasmonic lens design consisting of an annular slit and concentric grooves. The simulation results show that under radially polarized illumination, a super-resolution long depth of focus (DOF) spot can be achieved in optical meso-field due to the constructive interference of scattered light by the concentric grooves. We also analyze the influence of depth-tuned annular grooves on focusing performance, including focal length, DOF, and full-width half-maximum. Moreover, focusing efficiency can be enhanced (～350 %) by introducing a circular metallic grating which surrounds the annular slit. This plasmonic lens has potential applications in nano-imaging and nano-photolithography.     

Plasmonic Lens with Multiple-Turn Spiral Nano-Structures

In this paper, we investigate the focusing properties of a plasmonic lens with multiple-turn spiral nano-structures, and analyze its field enhancement effect based on the phase matching theory and finite-difference time-domain simulation. The simulation result demonstrates that a left-hand spiral plasmonic lens can concentrate an incident right-hand circular polarization light into a focal spot with a high focal depth. The intensity of the focal spot could be controlled by altering the number of turns, the radius and the width of the spiral slot. And the focal spot is smaller and has a higher intensity compared to the incident linearly polarized light. This design can also eliminate the requirement of centering the incident beam to the plasmonic lens, making it possible to be used in plasmonic lens array, optical data storage, detection, and other applications.     

Comparison of focal and afocal optics in insect eyes

Recent experiments suggest that an afocal lens system may occur in insect apposition eyes which are traditionally believed to contain focal systems. We present a theoretical analysis of lens-photoreceptor systems with focal and afocal optics. A simple parameterization of the systems is obtained and formulas are given for calculating receptor response to on-axis incident light and angular sensitivity. The simple parameterization and formulas allow the different lens photoreceptor systems to be compared: both systems may be similarily optimized for a given wavelength, but the focal lens may be marginally superior over a range of wavelengths. Possible refinements to the theory are discussed.     

Lens optical properties in the eyes of large marine predatory teleosts

The optical properties of the crystalline lenses were studied in a variety of large predatory teleosts (bony fishes) that forage in the open ocean, some of them at considerable depths. We found the first fish lenses that are free of measurable longitudinal spherical aberration, i.e., are perfectly monofocal, in contrast to the multifocal lenses that are typical for smaller fishes living close to the surface. In fact, none of the lenses investigated in this study were clearly multifocal. Most, but not all, of the lenses had long normalized focal lengths (focal length/lens radius) of up to 3.3 lens radii. A monofocal lens of long focal length, combined with spectrally suitably placed cone pigments, may be the optimal solution for vision of high spatial and spectral resolutions in a habitat where the available spectrum of light is limited.     

Near-infrared Plasmonic Far-field Nanofocusing Effects with Elongated Depth of Focus based on Hybrid Au–Dielectric–Ag Subwavelength Structures

In this paper, we propose a new far-field nanofocusing lens with elongated depth of focus (DOF) under near-infrared (NIR) wavelength. The surface plasmons can be excited by using the hybrid metal–insulator–metal (MIM) subwavelength structure under the NIR wavelength. The constructive interference of surface plasmons launched by the subwavelength MIM structure can form a nanoscale focus that is modulated by the novel metal grating from the near field to the far field. The numerical simulations demonstrated that a nanoscale focal spot (in plane focal area 0.177λ ²) with elongated DOF (3.358λ) and long focal length (5.084λ) can be realized with reasonably designing parameters of the lens. By controlling the positions of the inner radii of each slit ring and the grating width, the focal length, focal spot, and DOF can be tuned easily. This design method, which can obtain the nanoscale focal spot and micron DOF in far field under NIR illumination, paved the road for utilizing the NIR plasmonic lens in superresolution optical microscopic imaging, optical trapping, biosensing, and complex wavefront/beam shaper.     

Absence of SPARC in lens epithelial cells results in altered adhesion and extracellular matrix production in vitro

The matricellular protein SPARC (also known as osteonectin and BM-40) is expressed abundantly in lens epithelium. That SPARC-null mice exhibit early cataractogenesis, indicates a role for SPARC in the maintenance of lens transparency. Comparison of cultured wild-type and SPARC-null lens epithelial cells revealed significant changes in adhesion to different substrates. SPARC-null lens cells displayed enhanced attachment and spreading, focal adhesion formation, and resistance to trypsin detachment in comparison to wild-type cells. In the absence of SPARC, there was increased deposition of the ECM protein laminin-1 (LN-1). Proteins associated with focal adhesions were increased in SPARC-null versus wild-type lens cells: levels of alpha6-integrin heterodimers, talin, and paxillin phosphorylated on tyrosine were enhanced significantly, as was the association of beta1-integrin with talin and paxillin. Restoration of the wild-type phenotype in SPARC-null cultures was accomplished through genetic rescue by stable transfection of SPARC cDNA. Our findings indicate that SPARC is counter-adhesive for murine lens epithelial cells and demonstrate that multiple factors contribute to this activity. We also identify SPARC as a modulator of LN-1 secretion and deposition by these cells, an activity important in epithelial cell-ECM interactions in the ocular lens.     

Optical quality of the ocular lens of the sea lamprey (<Emphasis Type="Italic">Petromyzon marinus</Emphasis>) during the mature and transformer periods of life

While larval sea lampreys exist as eyeless filter feeders for several years, they transform into free-swimming juveniles (transformers) that attach parasitically to prey fish as they develop sexual maturity. This study examines lamprey lens development and optics and, since the lens is often the only refractive component of an aquatic eye, the data also provide an indication of visual ability during transformer and adult periods of life. Seven adult sea lampreys (0.40–0.55 m) and eight transformers (0.15–0.18 m) were sacrificed, the eyes removed and lenses dissected, measured, and placed in an automated laser scanning instrument. Back vertex focal length (spherical aberration) was measured for 14 beam positions across each lens by using a digital camera to record the position of the refracted beam. Transformer lenses exhibit positive spherical aberration, with average focal lengths varying from about 2.40 mm near the lens center and 1.06 mm at the lens periphery. On the other hand, the lenses from adults are largely corrected for spherical aberration, with average focal lengths varying from 2.19 mm to 2.44 mm. This result indicates that the younger lenses do not have a gradient refractive index necessary to mitigate the aberration and that further study of this model may reveal the relation between lens embryology and the development of such a gradient.     

Rapid three-dimensional isotropic imaging of living cells using Bessel beam plane illumination

A key challenge when imaging living cells is how to noninvasively extract the most spatiotemporal information possible. Unlike popular wide-field and confocal methods, plane-illumination microscopy limits excitation to the information-rich vicinity of the focal plane, providing effective optical sectioning and high speed while minimizing out-of-focus background and premature photobleaching. Here we used scanned Bessel beams in conjunction with structured illumination and/or two-photon excitation to create thinner light sheets (<0.5 μm) better suited to three-dimensional (3D) subcellular imaging. As demonstrated by imaging the dynamics of mitochondria, filopodia, membrane ruffles, intracellular vesicles and mitotic chromosomes in live cells, the microscope currently offers 3D isotropic resolution down to ～0.3 μm, speeds up to nearly 200 image planes per second and the ability to noninvasively acquire hundreds of 3D data volumes from single living cells encompassing tens of thousands of image frames.     

Far-Field Focusing of Spiral Plasmonic Lens

In this paper, we study the nanoscale-focusing effect in the far field for a spiral plasmonic lens with a concentric annular groove by using finite-difference time domain simulation. The simulation result demonstrates that a left-hand spiral plasmonic lens can concentrate an incident right-hand circular polarization light into a focal spot at the exit surface. And this spot can be focused into far field due to constructive interference of the scattered light by the annular groove. The focal length and the focal depth can be adjusted by changing the groove radius and number of grooves within a certain range. These properties make it possible to probe the signal of spiral plasmonic lens in far field by using conventional optical devices.     

Active Focal Length Control of Terahertz Slitted Plane Lenses by Magnetoplasmons

Active plasmonic devices are mostly designed at visible frequencies. Here, we propose an active terahertz (THz) plasmonic lens tuned by an external magnetic field. Unlike other tunable devices where the tuning is achieved by changing the plasma frequency of materials, the proposed active lens is tuned by changing the cyclotron frequency through manipulating magnetoplasmons (MPs). We have theoretically investigated the dispersion relation of MPs of a semiconductor?Cinsulator?Csemiconductor structure in the Voigt configuration and systematically designed several lenses realized with a doped semiconductor slab perforated with sub-wavelength slits. It is shown through finite?Cdifference time?Cdomain simulations that THz wave propagating through the designed structure can be focused to a small size spot via the control of MPs. The tuning range of the focal length under the applied magnetic field (up to 1?T) is ??3??, about 50% of the original focal length. Various lenses, including one with two focal spots and a tunable lens for dipole source imaging, are realized for the proposed structure, demonstrating the flexibility of the design approach. The proposed tunable THz plasmonic lenses may find applications in THz science and technology such as THz imaging.     

Polarization-Controlled Tunable Multi-focal Plasmonic Lens

A polarization-controlled tunable plasmonic lens which can generate different multi-focal combinations with exciting sources of left and right circular polarizations is proposed in this paper. Both position and intensity of each focal point can be adjusted by modulating the structure of the plasmonic lens. It is believed that the polarization-controlled tunable plasmonic multi-focal lens can be potentially used for optical switches and multi-channel couplers in future logic photonic and plasmonic systems.     

High Efficient Far-Field Nanofocusing with Tunable Focus Under Radial Polarization Illumination

We design a new nanofocusing lens for far-field practical applications. The constructively interference of cylindrical surface plasmon launched by the subwavelength metallic structure can form a subdiffraction-limited focus, which is modulated by the dielectric grating from the near field to the far field. The principle of designing such a far-field nanofocusing lens is elucidated in details. The numerical simulations demonstrated that nanoscale focal spot (0.12λ ²) can be realized with 3.6λ in depth of focus and 4.5λ in focal length by reasonably designing parameters of the grating. The focusing efficiency can be 7.335, which is much higher than that of plasmonic microzone plate-like lenses. A blocking chip can enhance the focusing efficiency further as the reflected waves at the entrance would be recollected at the focus. By controlling the number of the grooves in the grating, the focal length can be tuned easily. This design method paved the road for utilizing the plasmonic lens in high-density optical storage, nanolithography, superresolution optical microscopic imaging, optical measurement, and sensing.     

Mutations in laminin alpha 1 result in complex, lens-independent ocular phenotypes in zebrafish

We report phenotypic and genetic analyses of a recessive, larval lethal zebrafish mutant, bal(a69), characterized by severe eye defects and shortened body axis. The bal(a69) mutation was mapped to chromosome 24 near the laminin alpha 1 (lama1) gene. We analyzed the lama1 gene sequence within bal(a69) embryos and two allelic mutants, bal(arl) and bal(uw1). Missense (bal(a69)), nonsense (bal(arl)), and frameshift (bal(uw1)) alterations in lama1 were found to underlie the phenotypes. Extended analysis of bal(a69) ocular features revealed disrupted lens development with subsequent lens degeneration, focal cornea dysplasia, and hyaloid vasculature defects. Within the neural retina, the ganglion cells showed axonal projection defects and ectopic photoreceptor cells were noted at inner retinal locations. To address whether ocular anomalies were secondary to defects in lens differentiation, bal(a69) mutants were compared to embryos in which the lens vesicle was surgically removed. Our analysis suggests that many of the anterior and posterior ocular defects in bal(a69) are independent of the lens degeneration. Analysis of components of focal adhesion signaling complexes suggests that reduced focal adhesion kinase activation underlies the anterior segment dysgenesis in lama1 mutants. To assess adult ocular phenotypes associated with lama1 mutations, genetic mosaics were generated by transplanting labeled bal cells into ocular-fated regions of wild-type blastulas. Adult chimeric eyes displayed a range of defects including anterior segment dysgenesis and cataracts. Our analysis provides mechanistic insights into the developmental defects and ocular pathogenesis caused by mutations in laminin subunits.