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The surface plasmon resonance (SPR) technique has been widely applied to biosensing technologies for the rapid quantification of biomolecules without enzyme and fluorescent labeling. However, the conventional prism-coupling SPR method generally has a detection area of a few mm2, and the large contribution of the background signal forms a barrier to highly sensitive detection. Based on a highly spatially resolved SPR method, the present study constructed a scanning GC-SPR imaging instrument using an objective lens with a high numerical aperture and a plasmonic chip that could be used for grating-coupled SPR. Focusing light on the diffraction limit can suppress background signals and improve detection sensitivity. SPR imaging can also be performed by scanning a focal spot. Using this method, the refractive index of a mixture of water and dimethyl sulfoxide was measured with a detection accuracy of 2.43 × 10−3 RIU. Polydopamine films prepared with a thickness of <5 nm were also measured, and each film thickness was evaluated with high sensitivity from the effective refractive index detected in a small area of <1 µm2. [ABSTRACT FROM AUTHOR]

3D display technology offers a more realistic visual experience by allowing users to perceive depth and spatial awareness, enhancing interactivity and immersion. Among various approaches, multiview display technology constructs 3D images by offering multiple smooth views along the horizontal plane. Metasurfaces, with ultra‐thin physical structures and flexible functional designs, are positioned to make significant contributions to the evolution of 3D display technologies. Here, a 3D multiview holographic display system based on metasurfaces is proposed. Using generalized Snell's law, a spatially multiplexed metasurface is designed with nine views and achieves 3D display by cascading the metasurface with a spatial light modulator (SLM). By projecting holograms onto different areas of the metasurface via the SLM, corresponding reconstructed images can be observed from specific designed directions. Thanks to the large numerical aperture (NA) of the metasurface, the system successfully achieves nine views within a 120° field of view (FOV, with a theoretical maximum of 180°), validated experimentally. This system promises potential applications in VR/AR display, surgical navigation, geographic information system (GIS), and other fields. [ABSTRACT FROM AUTHOR]

Over the past years, nanostructured metalenses with thin form factors have been extensively studied for their potential in consumer and industrial applications. Despite significant advancements, current metalenses struggle to achieve high numerical aperture (NA), manufacturable structures, broad working bandwidth, and extended depth of focus (DOF) simultaneously. This paper introduces a comprehensive inverse design framework that facilitates the rapid development of polarization‐insensitive 3D metalenses, effective in both frequency and spatial domains. The framework employs shape‐constrained topology optimization to define horizontal ring profiles, along with discrete particle swarm optimization to manage discretized ring heights. Two immersed silicon carbide metalenses are demonstrated to showcase this framework's capability, providing near‐unity NAs for enhanced photon collection. The first design is an extended DOF metalens, exhibiting a DOF over four times the light wavelength and achieving a maximum diffraction efficiency of 23%, close to the theoretical limit. The second design achieves broadband achromaticity, suppressing chromatic aberrations across a wide 300 nm bandwidth (850–1150 nm) while maintaining an average diffraction efficiency of 10%. This methodology serves as a valuable tool for deploying functional metalenses with implications for nanophotonics, quantum optics, and quantum nanotechnology. [ABSTRACT FROM AUTHOR]

Full-colour-sorting metalens using few nanostructured layers have recently generated considerable interest as high-sensitivity colour image sensors because of their reliability and high resolution. Based on the guided mode resonance principle and propagation phase modulation, a full-colour-sorting metalens is designed, which can theoretically obtain any wavelength of light from the incident white light and realize arbitrary wavelength focusing with the same focal length in the visible range. Without the loss of generality, we propose a prototype of such metalens used for sorting blue, green and red light from the visible spectrum commonly used in practical applications. The maximum focussing efficiency is over 50% with a relatively high numerical aperture of 0.7. The proposed full-colour-sorting metalens can be used in many applications, such as colour mixing, colour holography, colour filtering, wavelength division multiplexing and so on. [ABSTRACT FROM AUTHOR]

Long-term observation of single-cell oscillations within tissue networks is now possible by combining bioluminescence reporters with stable tissue explant culture techniques. This method is particularly effective in revealing the network dynamics in systems with slow oscillations, such as circadian clocks. However, the low intensity of luciferase-based bioluminescence requires signal amplification using specialized cameras (e.g., I-CCDs and EM-CCDs) and prolonged exposure times, increasing baseline noise and reducing temporal resolution. To address this limitation, we implemented a cost-effective optical enhancement technique called telecompression, first used in astrophotography and now commonly used in digital photography. By combining a high numerical aperture objective lens with a magnification-reducing relay lens, we significantly increased the collection efficiency of the bioluminescence signal without raising the baseline CCD noise. This method allows for shorter exposure times in time-lapse imaging, enhancing temporal resolution and enabling more precise period estimations. Our implementation demonstrates the feasibility of telecompression for enhancing bioluminescence imaging for the tissue-level network observation of circadian clocks. [ABSTRACT FROM AUTHOR]

This article presents a comprehensive study on the impact of irradiation optical fiber cores with a femtosecond-pulsed laser, operating at a wavelength of 1030 nm, on the signal amplitude in Rayleigh scattering-based optical frequency domain reflectometry (OFDR). The experimental study involves two fibers with significantly different levels of germanium doping: the standard single-mode fiber (SMF-28) and the ultra-high numerical aperture fiber (UHNA7). The research findings reveal distinct characteristics of reflected and scattered light amplitudes as a function of pulse energy. Although different amplitude changes are observed for the examined fibers, both can yield an enhancement of amplitude. The paper further investigates the effect of fiber Bragg grating inscription on the overall amplitude of reflected light. The insights gained from this study could be beneficial for controlling the enhancement of light scattering amplitude in fibers with low or high levels of germanium doping. [ABSTRACT FROM AUTHOR]

The development of bend‐induced effectively single‐mode fiber with a square cross‐section and flat top‐hat intensity distribution is reported using core topology nanostructuring dedicated to femtosecond laser ablation systems. The fiber's core comprises 5419 silica and germanium‐doped silica nanorods with a diameter of 430 nm each arranged into a hexagonal lattice. The distribution of the rods is calculated using in‐house developed code based on the Monte Carlo algorithm to obtain a target shape of mode and intensity distribution. As a proof‐of‐concept, a silica nanostructured fiber with a 24 µm core is developed and verified against the purity of mode guidance, bending, and guiding losses. It is shown that for a wavelength of 1030 nm, the fiber is effectively single‐mode with 96% mode purity when bending with a radius of 20 cm is applied. The fiber has a measured mode area of 360 µm2, numerical aperture of 0.03, and total losses of 0.07 dB m−1. [ABSTRACT FROM AUTHOR]

Large-mode-area anti-resonant fibers (LMA ARF) with high beam quality have the potential to revolutionize mid-infrared high-power laser delivery by mitigating mode instabilities and nonlinear degradation. However, their tens-of-microns mode field diameters and small numerical aperture significantly increase the mode field mismatch and coupling complexity, respectively. In this work, an LMA all-solid anti-resonant fiber-microlens with a robust operation of high beam quality in the mid-infrared region was designed and prepared. It can significantly stabilize the efficiencies of coupling and transmission at a large radial offset. Consequently, this AS-ARF demonstrates substantial potential for advancing mid-infrared laser power delivery via fiber, ensuring exceptional beam quality throughout the process. [ABSTRACT FROM AUTHOR]

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Significance: Rapid acquisition of large imaging volumes with microscopic resolution is an essential unmet need in biological research, especially for monitoring rapid dynamical processes such as fast activity in distributed neural systems. Aim: We present a multifocal strategy for fast, volumetric, diffraction-limited resolution imaging over relatively large and scalable fields of view (FOV) using singlecamera exposures. Approach: Our multifocal microscopy approach leverages diffraction to image multiple focal depths simultaneously. It is based on a custom-designed diffractive optical element suited to low magnification and large FOV applications and customized prisms for chromatic correction, allowing for wide bandwidth fluorescence imaging. We integrate this system within a conventional microscope and demonstrate that our design can be used flexibly with a variety of magnification/numerical aperture (NA) objectives. Results: We first experimentally and numerically validate this system for large FOV microscope imaging (three orders-of-magnitude larger volumes than previously shown) at resolutions compatible with cellular imaging. We then demonstrate the utility of this approach by visualizing high resolution three-dimensional (3D) distributed neural network at volume rates up to 100 Hz. These demonstrations use genetically encoded Ca2þ indicators to measure functional neural imaging both in vitro and in vivo. Finally, we explore its potential in other important applications, including blood flow visualization and real-time, microscopic, volumetric rendering. Conclusions: Our study demonstrates the advantage of diffraction-based multifocal imaging techniques for 3D imaging of mm-scale objects from a single-camera exposure, with important applications in functional neural imaging and other areas benefiting from volumetric imaging. [ABSTRACT FROM AUTHOR]

Significance: Hair-thin multimode optical fiber-based holographic endoscopes have gained considerable interest in modern neuroscience for their ability to achieve cellular and even subcellular resolution during in-vivo deep brain imaging. However, the application of multimode fibers in freely moving animals presents a persistent challenge as it is difficult to maintain optimal imaging performance while the fiber undergoes deformations. Aim: We propose a fiber solution for challenging in-vivo applications with the capability of deep brain high spatial resolution imaging and neuronal activity monitoring in anesthetized as well as awake behaving mice. Approach: We used our previously developed M3CF multimode-multicore fiber to record fluorescently labeled neurons in anesthetized mice. Our M3CF exhibits a cascaded refractive index structure, enabling two distinct regimes of light transport that imitate either a multimode or a multicore fiber. The M3CF has been specifically designed for use in the initial phase of an in-vivo experiment, allowing for the navigation of the endoscope's distal end toward the targeted brain structure. The multicore regime enables the transfer of light to and from each individual neuron within the field of view. For chronic experiments in awake behaving mice, it is crucial to allow for disconnecting the fiber and the animal between experiments. Therefore, we provide here an effective solution and establish a protocol for reconnection of two segments of M3CF with hexagonally arranged corelets. Results: We successfully utilized the M3CF to image neurons in anaesthetized transgenic mice expressing enhanced green fluorescent protein. Additionally, we compared imaging results obtained with the M3CF with larger numerical aperture (NA) fibers in fixed whole-brain tissue. Conclusions: This study focuses on addressing challenges and providing insights into the use of multimode-multicore fibers as imaging solutions for in-vivo applications. We suggest that the upcoming version of the M3CF increases the overall NA between the two cladding layers to allow for access to high resolution spatial imaging. As the NA increases in the multimode regime, the fiber diameter and ring structure must be reduced to minimize the computational burden and invasiveness. [ABSTRACT FROM AUTHOR]

Skin cancer is a disorder marked by inappropriate skin cell proliferation, which is frequently brought on by UV radiation exposure from tanning booths or the sun. It can present as melanoma, squamous cell carcinoma, or basal cell carcinoma, with varying levels of malignancy and available therapies. Our newly developed photonic crystal fiber (PCF) has exceptional efficacy in the identification of skin cancer. The proposed US model has a heptagonal core and a clad surface with a heptagonal pattern. The PCF analyzer that has just been released shows a maximum relative sensitivity (RS) of 95.35% as well 94.29% for the basal (cancer) alongside basal (normal), respectively. For the aforementioned cells, we also looked at the confinement loss (CL) of 1.74 × 10–14 dB/m, 5.98 × 10–13 dB/m, plus the effective material loss (EML) of 0.0077 cm−1, 0.0088 cm−1. Rapid identification in skin cancer allows for improved results, tailored treatment, and prompt intervention. Early detection of cancer makes milder medications available, which lessens the need for aggressive treatment. Moreover, increasing the treatment of patients and simplifying the continual sickness monitoring process. Accurate evaluation also helps with research into developments that enhance global recognition as well as treatment options. The new PCF, with its exceptional detecting capacity, may have been instrumental in the prompt discovery of such harmful organisms. In summary, there are a lot of opportunities in the medical field. [ABSTRACT FROM AUTHOR]

As an integrable micro-optical device, micro lens arrays (MLAs) have significant applications in modern optical imaging, new energy technology, and advanced displays. In order to reduce the impact of laser modification on wet etching, we propose a technique of femtosecond laser penetration-induced modification-assisted wet etching (FLIPM-WE), which avoids the influence of previous modification layers on subsequent laser pulses and effectively improves the controllability of lens array preparation. We conducted a detailed study on the effects of the laser single pulse energy, pulse number, and hydrofluoric acid etching duration on the morphology of micro lenses and obtained the optimal process parameters. Ultimately, two types of fused silica micro lens arrays with different focal lengths but the same numerical aperture (NA = 0.458) were fabricated using the FLPIM-WE technology. Both arrays exhibited excellent geometric consistency and surface quality (Ra~30 nm). Moreover, they achieved clear imaging at various magnifications with an adjustment range of 1.3×~3.0×. This provides potential technical support for special micro-optical systems. [ABSTRACT FROM AUTHOR]

Fibre bundle (FB)‐based endoscopes are indispensable in biology and medical science due to their minimally invasive nature. However, resolution and contrast for fluorescence imaging are limited due to characteristic features of the FBs, such as low numerical aperture (NA) and individual fibre core sizes. In this study, we improved the resolution and contrast of sample fluorescence images acquired using in‐house fabricated high‐NA FBs by utilising generative adversarial networks (GANs). In order to train our deep learning model, we built an FB‐based multifocal structured illumination microscope (MSIM) based on a digital micromirror device (DMD) which improves the resolution and the contrast substantially compared to basic FB‐based fluorescence microscopes. After network training, the GAN model, employing image‐to‐image translation techniques, effectively transformed wide‐field images into high‐resolution MSIM images without the need for any additional optical hardware. The results demonstrated that GAN‐generated outputs significantly enhanced both contrast and resolution compared to the original wide‐field images. These findings highlight the potential of GAN‐based models trained using MSIM data to enhance resolution and contrast in wide‐field imaging for fibre bundle‐based fluorescence microscopy. Lay Description: Fibre bundle (FB) endoscopes are essential in biology and medicine but suffer from limited resolution and contrast for fluorescence imaging. Here we improved these limitations using high‐NA FBs and generative adversarial networks (GANs). We trained a GAN model with data from an FB‐based multifocal structured illumination microscope (MSIM) to enhance resolution and contrast without additional optical hardware. Results showed significant enhancement in contrast and resolution, showcasing the potential of GAN‐based models for fibre bundle‐based fluorescence microscopy. [ABSTRACT FROM AUTHOR]

A nonlinear robust motion control strategy was proposed to achieve precise movement of objective motion carrier in context of large numerical aperture microscopy imaging technology, which required a long stroke, high precision, and large load capabilities. An optical path system and a virtual prototype of a large numerical aperture microscope were designed. In addition, a ball-screw-driven objective motion carrier was designed, and the backlash of ball-screw was eliminated by double nut preloading method. To achieve finite-time convergence of system state and improve system robust¬ness, an adaptive technology was employed in nonsingular terminal sliding mode control. Further¬more, to address nonlinear friction effect in ball-screw transmission mechanisms, TDE technology was employed to realize online estimation and real-time compensation of friction forces. TDE technolo¬gy and adaptive nonsingular terminal sliding mode control were adopted to achieve model-free control characteristics. The stability of closed-loop system was proved by Lyapunov theory. Consequently, a high-resolution optical microscope was developed to achieve precise movement of objective motion car¬rier, and microscopic images of mouse cardiac muscle cells were acquired to demonstrate the effective¬ness of the proposed algorithm [ABSTRACT FROM AUTHOR]

We present deep-ultraviolet Fourier ptychography (DUV-FP) for high-resolution chemical imaging of biological specimens in their native state without exogenous stains. This approach uses a customized 265-nm DUV LED array for angle-varied illumination, leveraging the unique DUV absorption properties of biomolecules at this wavelength region. We implemented a robust feature-domain optimization framework to overcome common challenges in Fourier ptychographic reconstruction, including vignetting, pupil aberrations, stray light problems, intensity variations, and other systematic errors. By using a 0.12 numerical aperture low-resolution objective lens, our DUV-FP prototype can resolve the 345-nm linewidth on a resolution target, demonstrating at least a four-fold resolution gain compared to the captured raw images. Testing on various biospecimens demonstrates that DUV-FP significantly enhances absorption-based chemical contrast and reveals detailed structural and molecular information. To further address the limitations of conventional FP in quantitative phase imaging, we developed a spatially coded DUV-FP system. This platform enables true quantitative phase imaging of biospecimens with DUV light, overcoming the non-uniform phase response inherent in traditional microscopy techniques. The demonstrated advancements in high-resolution, label-free chemical imaging may accelerate developments in digital pathology, potentially enabling rapid, on-site analysis of biopsy samples in clinical settings. [ABSTRACT FROM AUTHOR]

Spectral confocal sensors are effective for measuring displacements. The core of the spectral confocal measurement system is a dispersive objective lens that uses optical dispersion to establish a one-to-one correspondence between the focusing position and wavelength, achieving high-resolution measurements in the longitudinal direction. Despite significant progress in dispersive objective lenses for spectral confocal sensor systems, challenges such as a limited dispersion range, high cost, and insufficient measurement accuracy persist. To expand the measurement range and improve the accuracy of the spectral confocal sensor, we designed a compact, long-axial dispersion objective lens. This lens has a simple structure that requires only six lens elements, two of which form cemented doublets. The system length is 58 mm, with a working distance of 46 ± 6 mm and a dispersion range of 12 mm within the wavelength range of 450–656 nm. The lens has an object-side numerical aperture (NA) of 0.22 and an image-side NA between 0.198 and 0.24, ensuring high light energy utilization. Finally, a spectral confocal measurement system was constructed based on the designed dispersive objective lens, and performance evaluation tests were conducted. The test results showed that the system achieved a resolution of 0.15 μm and a maximum linear error of ±0.7 μm, demonstrating high-precision measurement capabilities. The proposed lens design enables the development of more portable and cost-effective spectral confocal sensors. [ABSTRACT FROM AUTHOR]

We demonstrate a technique for flexibly controlling subwavelength focusing and scanning, by using the Fourier translation property of a topology-preserved flat lens. The Fourier transform property of the flat lens enables converting an initial phase shift of light into a spatial displacement of its focus. The flat lens used in the technique exhibits a numerical aperture of 0.7, leading to focusing the incident light to a subwavelength scale. Based on the technique, we realize flexible control of the focal positions with arbitrary incident light, including higher-order structured light. Particularly, the presented platform can generate multifocal spots carrying optical angular momentum, with each focal spot independently controlled by the incident phase shift. This technique results in a scanning area of 10 μm × 10 μm, allowing to realize optical scanning imaging with spatial resolution up to 700 nm. This idea is able to achieve even smaller spatial resolution when using higher-numerical-aperture flat lens and can be extended to integrated scenarios with smaller dimension. The presented technique benefits potential applications such as in scanning imaging, optical manipulation, and laser lithography. [ABSTRACT FROM AUTHOR]

The common methods used for correcting chromatic aberration are typically based on multi‐lens and multi‐material systems, resulting in lens thicknesses that are several orders of magnitude greater than the wavelength and complex combination designs. A method to achieve the singlet achromatic microlens of the wavelength‐scale thickness by utilizing high refractive index materials with an aspherical profile is proposed. A theoretical model based on the dispersion effect is developed to guide the selection of materials and the design of thicknesses for achieving chromatic aberration correction in singlet microlenses of a given diameter and numerical aperture. H‐ZLaF68N (68N) glass, sapphire, and fused silica with relatively high to low refractive index are selected to prepare the singlet achromatic microlenses to verify the validity of the model. The thicknesses of three microlenses are 573, 737 nm, and 1.27 µm, respectively, and all of them have achieved achromatic correction as designed. This indicates that the high refractive index material not only achieves achromatic aberration but also reduces the thickness by ≈50% compared with the conventional low refractive index material of silica glass. The presented wavelength‐scale singlet achromatic microlens hold significant promise for compact wearable devices, dynamic holography, and color projection displays. [ABSTRACT FROM AUTHOR]

In this work, an imaging spectrometer with a diffraction-limited resolution of 0.043 nm is designed by using two manufacturable gradient-index (MGRIN) lenses with a linear refractive index distribution to suppress the aberrations. The MGRIN lenses are made from a combination of two separate base materials that their refractive indices are determined by the fractional composition of each base material at any point. The volume fraction of each base material in both lenses changes linearly from the front edge to the rear vertex of the lens. The input light to the spectrometer originates from a single-mode fiber with a core diameter of 9 μm and a numerical aperture of 0.1. The parallel rays after passing through the collimator are diffracted by a diffraction grating with a number of grooves of 1200 g/mm. The criteria determining the quality of the image show that the aberrations of the image have been optimally controlled. Comparing the results of this design with some similar studies done by other researchers shows that the root-mean-square radius of the spot diagram and Airy disk radius are significantly smaller than those designs. In addition, the modulation transfer function diagram has a better fit with the diffraction limit curve. These results make our proposed spectrometer have a stronger resolution than those in previous studies. [ABSTRACT FROM AUTHOR]

Wide‐field imaging is widely adopted due to its fast acquisition, cost‐effectiveness, and ease of use. Its extension to direct volumetric applications, however, is burdened by the trade‐off between resolution and depth of field (DOF), dictated by the numerical aperture of the system. It is demonstrated that such trade‐off is not intrinsic to wide‐field imaging, but stems from the spatial incoherence of light: images obtained through spatially coherent illumination are shown to have resolution and DOF independent of the numerical aperture. This fundamental discovery enables to demonstrate an optimal combination of coherent resolution‐DOF enhancement and incoherent tomographic sectioning for scanning‐free, wide‐field 3D microscopy on a multicolor histological section. [ABSTRACT FROM AUTHOR]

Filamentation of high-power femtosecond laser pulses in air is accompanied by a fairly strong release of optical energy into the propagation medium due to laser-induced ionization of air molecules and production of an underdense plasma of charged species. We present the results of our laboratory experiments and numerical simulations aimed at estimating the energy deposition amount by laser filament upon propagation in air depending on the conditions of spatial focusing, pulse energy, and radiation wavelength. Importantly, our study reveals a more than 50% decrease in the filament energy deposited in air in the range of moderate numerical aperture values, approximately from 0.003 to 0.007, at carrier wavelengths of 740 and 470 nm. We attribute such a considerable reduction in the laser pulse energy release for femtosecond plasma to the competing effects of Kerr self-focusing and geometric divergence of focused laser pulse. [ABSTRACT FROM AUTHOR]

A 2D numerical model based on the finite-difference time-domain (FDTD) method had been developed to investigate the correspondence between the spatio-temporal aspects and intensity evolution of a focused laser beam after the propagation through micro-structured dispersive materials under the pulse duration variation in the few-cycle regime. In parallel with the laser field intensification investigations, a spatio-temporal analysis of the electromagnetic field in the focal point is elaborated as a function of the relative spatial extension of the pulse in order to provide a complex description of this approach. The numerical computations indicate that shorter and more intense pulses may be obtained in well-defined conditions. Also, the major contribution played by the input laser beam profile, numerical aperture, and the dispersive material features in the intensity enhancement process in the focal point is pointed out. The present approach can be used as a versatile method for field intensification in various ultra-short and ultra-intense few-cycle laser pulse experiments. [ABSTRACT FROM AUTHOR]

K9 glass is a classical transparent material widely used in high-power optical systems due to its high-temperature resistance. However, the precision machining of K9 glass is difficult. The laser processing method, characterized by being non-contact, having a small heat-affected zone, and having high processing precision, is commonly employed for processing intricate structures. In this study, the vector diffraction model is employed to simulate the internal electric field inside the material when focused by objective lenses with varying numerical apertures. Furthermore, the temperature field is simulated. The simulation considered the nonlinear absorption of the material, the stretching of the focal dot due to spherical aberration, and the energy loss of the laser during the focusing process. The experiment indicated that the ablated area consists of numerous small, ablated dots and that multiple ablated areas emerged under an NA of 0.6. This study can provide valuable references for the research of the interaction between lasers and glass materials. [ABSTRACT FROM AUTHOR]

The correction of chromatic aberration and achievement of high numerical aperture (NA) are two main issues for the realistic application of metalenses in imaging and display systems. In this work, we design a broadband achromatic metalens (BAM) with high NA, which is composed of hybrid all-dielectric meta-atoms in the visible region. By simultaneously and independently manipulating the geometric phase and propagation phase, meta-atoms can focus the incident lights on the same spot. Besides, a large phase compensation can be obtained through the variation in structural parameters of the hybrid meta-atom, which is essential to achieve high-NA BAM. For demonstration, the achromatic metalens with NA of 0.68 over the spectrum from 420 to 700 nm is numerically simulated. The metalens possessing high NA, broad bandwidth, and diffraction-limited achromatic focusing performance can be potentially applied in the field of imaging, spectroscopy, display, etc. [ABSTRACT FROM AUTHOR]

Numerous techniques and technologies have been proposed for the detection and identification of hazardous chemicals that can harm the lungs and respiratory system as well as the central nervous system and kidneys when inhaled. Most practical techniques can be carried out by extraordinary professionals in well-equipped facilities. A reliable, simple, highly sensitive, and feasible sensing technique is still required. A potential sensor for these harmful chemicals is the photonic crystal fiber (PCF), which achieves several unique properties. A square-core PCF sensor is proposed in this work for the detection of detrimental gases (tetra-chloro silane, tetra-chloro methane, turpentine, and tin terra-chloride) in the THz region. The cladding region is divided into three rings, and each ring has rectangular and square air holes. Within the operating region, we have found a relatively high sensitivity of 96.185% along with 95.407% core power fraction, 0.2211 numerical aperture, and a low effective area of 154 470 μm2 at 1.9 THz frequency. Ignorable confinement loss of 3.071 × 10−14 cm−1 and effective material loss of 0.007 72 cm−1 have been also found. Additionally, the current manufacturing techniques guarantee the viability of the proposed PCF sensor's manufacture. These obtained results demonstrate that the proposed sensor can be effectively employed for applications involving hazardous chemical compounds, gases, and biosensing. [ABSTRACT FROM AUTHOR]

Polarization plays a crucial role in understanding the interaction of fluorescent molecules in a light field. We report the study on the effect of a field–dipole interaction under polarization light-sheet fluorescence microscopy using the vectorial theory of light. The molecule is suitably modeled as a radiating electric dipole in a polarized electric field (both linear and random), and the system point spread function (PSF) is determined for different orientations of the dipole (both fixed and random). PSF analysis and contour plots suggest distinct nature of a field distribution in each case, indicating the importance of a field–dipole interaction for high-quality fluorescence imaging. The analysis suggests that the field spreads gradually along the polarization axis at a high numerical aperture (NA) of the objective lens, whereas it is more isotropic and homogeneous at low NA. Moreover, fast changes are not observed at low NA (i.e., far from the central lobe in the field contour plots), suggesting the absence of high-frequency components. However, sidelobes are prominent for linear polarized (along x) light. On the other hand, rapid variations are evident for randomly polarized light, depicting the presence of high spatial frequencies in the system optical transfer function. The other significant observation is the distinct frequency spectrum (both k x and k y) for random and fixed dipoles, indicating the significance of dipole orientation in a light-sheet field. Compared to the point-illumination-based fluorescence microscopy, sheet based polarization technique provides a high signal-to-noise ratio, a uniform field, an order large field of view, and critical information (related to the micro-environment of a dipole and its short-range interactions). The study is expected to facilitate polarization-sensitive investigation of large biological specimens (both fixed and live). [ABSTRACT FROM AUTHOR]

Various quartz microlenses were fabricated in two stages with two lasers. A fiber laser at 1.06 µm was employed for the laser ablation, while a CO2 laser at 10.6 µm was used for direct laser writing (DLW). The experimental data demonstrate the formation of spherical, cylindrical microlenses and microlens array (MLA) with an optimum numerical aperture (NA) of 0.55. Theoretical calculations and simulation were conducted to estimate the temperature at the quartz surface during ablation and simulation of the reshaping. A temperature of 2500 K is achieved in the ablation, and 2015 K was established during the reshaping. The ablation depth is 280 µm, the diameter is 150 µm, and the heat affected zone (HAZ) is approximately 1345 µm after 1 s. Due to the controllable laser micromachining, optoelectronics and biological imaging are viable applications for MLAs. [ABSTRACT FROM AUTHOR]

We provide a brief review of the development and application of the Mesolens and its impact on microbiology. Microbial specimens such as infected tissue samples, colonies surfaces, and biofilms are routinely collected at the mesoscale. This means that they are relatively large multimillimetre‐sized samples which contain microscopic detail that must be observed to answer important questions across various sectors. The Mesolens presents the ideal imaging method to study these specimens as no other optical microscope can thanks to its unique combination of low magnification and high numerical aperture providing large field‐of‐view, high‐resolution imaging. We demonstrate the current applications of the Mesolens to microbial imaging and go on to outline the huge potential of the Mesolens to impact other key areas of microbiology. [ABSTRACT FROM AUTHOR]

Ytterbium (Yb)-doped fibers using aluminophosphosilicate (Yb-APS) host glass offer significant advantages over conventional aluminosilicate (Yb-AS) fibers, such as strong photodarkening resistance, higher RE-ion solubility and lower Numerical Aperture (NA), making them ideal for high-power laser applications. However, achieving optimal performance in Yb-APS fiber fabrication poses various challenges, including maintaining a precise Al3+/P5+ ratio (1:1), minimizing the central dip in the refractive index profile (RIP), ensuring proper dopant distribution, and reducing background loss. We introduce a new fabrication method for Yb-APS fiber to address these challenges. This approach entails first synthesizing amorphous Yb³⁺: AlPO 4 particles, then incorporating them into the fiber core using a hybrid technique that merges Vapor Phase Delivery (VPD) with solution doping (SD). We extensively utilized various materials and optical characterizations, including XRD, FTIR, Raman spectroscopy, FESEM, and XPS, to fine-tune the composition of Yb³⁺: AlPO 4. The optical characterization of the developed preform sample, including absorption, emission, and luminescent lifetime measurements, was conducted to assess the fabrication technique's suitability. The results confirmed the successful incorporation of Yb-ions into the preform core, with peaks consistent with reported values. The fiber's attenuation loss was measured, showing approximately 10 dB/km at 1200 nm. This indicates that the particles dissolved smoothly during preform and fiber processing, resulting in minimal scattering loss in the fiber core. The developed fiber demonstrated NA of 0.1, uniform RIP along the preform length with significant reduction of the central dip formation and improved spectral performance (∼1.7X broader bandwidth) compared with an equivalent Yb-AS fiber. These findings suggest the Yb-APS fiber's overall effectiveness and structural robustness, highlighting the potential of the proposed fabrication method for high-power fiber laser applications. [ABSTRACT FROM AUTHOR]

The integration of multiple functional microscopy methods into a single, miniaturized instrument, known as multimodal endomicroscopy, presents significant challenges due to the often conflicting optical requirements of each imaging modality. In this study, the use of 3D nano‐printing based on two‐photon polymerization for the monolithic manufacturing of complete optical MEMS devices is investigated as an enabling platform for multimodal endoscopy. This approach offers unparalleled miniaturization, design flexibility, and alignment precision of micro‐optics and actuators. In particular, the design, fabrication, and characterization of a monolithically 3D nano‐printed bistable microlens actuator are discussed. Bistability allows the microlens to switch between two stable positions, thereby changing the focus distance and numerical aperture. The actuator features two coils with opposing current directions, which create a magnetic field gradient around a polymer micro‐magnet. This configuration allows for robust switching between stable positions with an average axial distance of 168.3 ± 7.3 µm. Experiments conducted to ascertain the optical characterization of the actuator demonstrate its capacity to transition between different optical modes. The beam widths are measured to be in the range of 4.1 ± 0.2 µm in the high‐resolution mode and 11.3 ± 1.1 µm in the extended depth of focus mode. [ABSTRACT FROM AUTHOR]

We develop a new all-dielectric metasurface for designing high quality-factor (Q-factor) quasi-bound states in the continuum (quasi-BICs) using asymmetry kite-shaped nanopillar arrays. The Q-factors of quasi-BICs follow the quadratic dependence on the geometry asymmetry, and meanwhile their resonant spectral profiles can be readily tuned between Fano and Lorentzian lineshapes through the interplay with the broadband magnetic dipole mode. The third-harmonic signals of quasi-BIC modes exhibit a gain from 43.4- to 634-fold enhancement between samples with an axial-length difference of 15 nm and 75 nm when reducing the numerical aperture of the illuminating objective lenses in nonlinear measurement, which is attributed to the increasing illumination spot size and the less contribution from the large oblique incident light for establishing quasi-BIC modes with high-Q spectral profile and strong near-field intensity. The silicon-based metasurfaces with their simple geometry are facile for large-area fabrication and open new possibilities for the optimization of upconversion processes to achieve efficient nonlinear devices. [ABSTRACT FROM AUTHOR]

Fourier ptychographic microscopy (FPM) is a computational imaging technology that can acquire high-resolution large-area images for applications ranging from biology to microelectronics. In this study, we utilize multifocal plane imaging to enhance the existing FPM technology. Using an RGB light emitting diode (LED) array to illuminate the sample, raw images are captured using a color camera. Then, exploiting the basic optical principle of wavelength-dependent focal length variation, three focal plane images are extracted from the raw image through simple R, G, and B channel separation. Herein, a single aspherical lens with a numerical aperture (NA) of 0.15 was used as the objective lens, and the illumination NA used for FPM image reconstruction was 0.08. Therefore, simultaneous multifocal plane FPM with a synthetic NA of 0.23 was achieved. The multifocal imaging performance of the enhanced FPM system was then evaluated by inspecting a transparent organic light-emitting diode (OLED) sample. The FPM system was able to simultaneously inspect the individual OLED pixels as well as the surface of the encapsulating glass substrate by separating R, G, and B channel images from the raw image, which was taken in one shot. [ABSTRACT FROM AUTHOR]

Despite their excellent performance and versatility, the efficient integration of small lasers with other optical devices has long been hindered by their broad emission divergence. In this study, we introduce a novel approach for emission engineering in microdisk lasers, significantly enhancing their vertical emission output by directly integrating specially designed reflective metalenses, referred to as "meta-micromirrors". A 5 μm-diameter microdisk laser is precisely positioned at an 8 μm focal distance on a 30 × 30 μm2 meta-micromirror featuring a numerical aperture (NA) of 0.95, accomplished through micro-transfer printing techniques. Our experiments demonstrated a notable increase in the emission efficiency within an NA of 0.65. Specifically, we observed a 2.68-fold increase in the average emission from ten microdisk lasers. This integration not only enhances the emission efficiency of small lasers but also holds considerable implications for micro- and nano-photonic integrations. The results of this integration open up new possibilities in various fields, including photonic integrated circuits, bio-sensing technologies, and the development of quantum light sources. [ABSTRACT FROM AUTHOR]

Holographic Metasurfaces (HMs) in the visible range enable advanced imaging applications in compact, planarized systems. The ability to control and structure light with high accuracy and a high degree of freedom is particularly relevant in lab‐on‐chip biophotonic applications. Pushing the operation wavelength into the blue region and below is an open challenge. Here, it is demonstrated that Zirconium dioxide (ZrO2) metasurfaces (MSs) are particularly well‐suited to satisfy these requirements. Specifically, MSs are designed for optical trapping applications with a high numerical aperture (NA = 1.2) at a wavelength as low as 488 nm, with trap stiffness >200 pN (µmW)−1. [ABSTRACT FROM AUTHOR]

This paper presents a numerical simulation study on the coupling of lasers and waterjets, focusing on the distribution of the spot power density. The analysis utilized a laser wavelength of 532 nm, chosen for its minimal energy attenuation in water. The key conditions for successful coupling were identified, including the necessity for the spot diameter of the laser beam to be smaller than the nozzle diameter of the waterjet fiber, the numerical aperture of the laser beam to be lower than that of the waterjet fiber, and the divergence angle of the laser to be smaller than the critical angle for total internal reflection. Using the ZEMAX simulation software, various coupling cases were explored, revealing that the radial displacement of the waterjet fiber relative to the laser axis has the most significant impact on the output power density, followed by angular deflection, whereas the axial displacement has the minimal effect. This study also investigates the combined effects of different influencing factors on the peak distribution of the output power density, uncovering distinct characteristics resulting from these deviations. Overall, the research findings provide theoretical insights for achieving effective coupling between fine waterjets and lasers as well as for the design of water-guided laser coupling devices. [ABSTRACT FROM AUTHOR]

This article proposes a novel Si3N4-based five-ring hexa-circular photonic crystal fiber (PCF) that shows a remarkably high nonlinear coefficient (NLC) and birefringence (Br). Several distinctive optical features, including birefringence, nonlinearity, effective area, numerical aperture, confinement loss, dispersion, etc., are investigated utilizing the COMSOL Software. The simulation analysis demonstrates that a zero-crossing dispersion for Y- polarization and an extremely high Br and NLC of 0.22 and 2687.51 W - 1 Km - 1 are reached at the wavelength of 1.55 μ m . The proposed PCF, having extremely high Br and NLC properties, can be useful for prospective future applications in the areas of supercontinuum generation, nonlinear optics, polarization-maintaining, and so on. [ABSTRACT FROM AUTHOR]

Optically levitated multiple nanoparticles have emerged as a platform for studying complex fundamental physics such as non-equilibrium phenomena, quantum entanglement, and light–matter interaction, which could be applied for sensing weak forces and torques with high sensitivity and accuracy. An optical trapping landscape of increased complexity is needed to engineer the interaction between levitated particles beyond the single harmonic trap. However, existing platforms based on spatial light modulators for studying interactions between levitated particles suffered from low efficiency, instability at focal points, the complexity of optical systems, and the scalability for sensing applications. Here, we experimentally demonstrated that a metasurface which forms two diffraction-limited focal points with a high numerical aperture (∼0.9) and high efficiency (31 %) can generate tunable optical potential wells without any intensity fluctuations. A bistable potential and double potential wells were observed in the experiment by varying the focal points' distance, and two nanoparticles were levitated in double potential wells for hours, which could be used for investigating the levitated particles' nonlinear dynamics, thermal dynamics and optical binding. This would pave the way for scaling the number of levitated optomechanical devices or realizing paralleled levitated sensors. [ABSTRACT FROM AUTHOR]

Trapping and manipulating micro-objects and achieving high-precision measurements of tiny forces and displacements are of paramount importance in both physical and biological research. While conventional optical tweezers rely on tightly focused beams generated by bulky microscope systems, the emergence of flat lenses, particularly metalenses, has revolutionized miniature optical tweezers applications. In contrast to traditional objectives, the metalenses can be seamlessly integrated into sample chambers, facilitating flat-optics-based light manipulation. In this study, we propose an experimentally realized transmissive and polarization-insensitive water-immersion metalens, constructed using adaptive nano-antennas. This metalens boasts an ultra-high numerical aperture of 1.28 and achieves a remarkable focusing efficiency of approximately 50 % at a wavelength of 532 nm. Employing this metalens, we successfully demonstrate stable optical trapping, achieving lateral trapping stiffness exceeding 500 pN/(μm W). This stiffness magnitude aligns with that of conventional objectives and surpasses the performance of previously reported flat lenses. Furthermore, our bead steering experiment showcases a lateral manipulation range exceeding 2 μm, including a region of around 0.5 μm exhibiting minimal changes in stiffness for smoothly optical manipulation. We believe that this metalens paves the way for flat-optics-based optical tweezers, simplifying and enhancing optical trapping and manipulation processes, attributing ease of use, reliability, high performance, and compatibility with prevalent optical tweezers applications, including single-molecule and single-cell experiments. [ABSTRACT FROM AUTHOR]

To realize nanoscale manufacturing based on laser direct writing technology, objective lenses with high numerical apertures immersed in water or oil are necessary. The use of liquid medium restricts its application in semiconductors. Achieving nanoscale features on silicon by laser direct writing in a low refractive index medium has been a challenge. In this work, a microsphere assisted femtosecond laser far-field induced dewetting approach is proposed. A reduction in the full-width at half-maximum of the focused light spot is realized by modulating tightly focused light through microspheres and achieving a minimum feature size of 9 nm on silicon in ambient air with energy smaller than the ablation threshold. Theoretical analysis and numerical simulation of laser processing are performed based on a two-temperature model. Furthermore, we explored the potential of femtosecond laser-induced dewetting in nanolithography and demonstrated its ability to achieve an arbitrary structure on silicon. Our work enables laser-based far-field sub-10-nm feature etching on a large-scale, providing a novel avenue for nanoscale silicon manufacturing. [ABSTRACT FROM AUTHOR]

A novel high‐speed, high‐resolution 3D microscopy technique named BP‐TIDT is presented that quantifies the refractive index (RI) distribution of label‐free, transparent samples. This method combines a bi‐plane detection scheme (BP) with the transport of intensity diffraction tomography (TIDT), effectively circumventing the need for matched illumination conditions under high numerical aperture (NA) objectives, which enables 15 fps volume rates and 326 nm lateral resolution. The effectiveness and accuracy of the proposed approach are validated through high‐resolution imaging of polystyrene microspheres and HepG2 cells. Moreover, the wide‐ranging applicability of BP‐TIDT is demonstrated by investigating subcellular organelle motion, including mitochondria and lipid droplets, as well as the macroscopic apoptosis process in living COS‐7 cells. To the best of current knowledge, this is the first time that high spatial‐temporal resolution dynamic ODT results are obtained in a non‐interferometric and motion‐free manner, highlighting the potential of BP‐TIDT in advancing research on dynamic cellular processes. [ABSTRACT FROM AUTHOR]

The numerical aperture of the spectrometer is crucial for weak signal detection. The transmission lens-based configuration has more optimization variations, and the grating can work approximately in the Littrow condition; thus, it is easier to acquire high numerical aperture (NA). However, designing a large aperture focusing lens remains challenging, and thus, ultra-high NA spectrometers are still difficult to acquire. In this paper, we propose a method of setting image plane tilt ahead directly when designing the large aperture focusing lens to simplify the high NA spectrometer design. By analyzing the accurate demands of the focusing lens, it can be concluded that a focusing lens with image plane tilt has much weaker demand for achromatism, and other monochromatic aberration can also be reduced, which is helpful to increase the NA. An NA0.5 fiber optic spectrometer design is given to demonstrate the proposed method. The design results show that the NA can achieve 0.5 using four lenses of two materials, and the MTF is higher than 0.5 when the spectral dispersion length is 12.5 mm and the pixel size is 25 μm, and thus, the spectral resolution can achieve 6.5 nm when the spectral sampling ratio is 2:1. The proposed method can provide reference for applications when appropriate materials are limited and high sensitivity is necessary. [ABSTRACT FROM AUTHOR]

The optical topology, which serves as a stable spatial electromagnetic structure, offers a new dimension for applications in the field of optical information processing, transmission, and storage. In recent years, there has been an increasing focus on these spatially structured light fields. By reversing the radiation of orthogonal dipole pairs, we propose an approach to generate Meron topologies within the focused light field while also investigating the evolution of the Meron structure along the longitudinal axis. Through introducing a dipole placed along the z -axis, we achieve precise positioning and fine adjustment of the topological center. The stability of Meron under a high numerical aperture objective lens (NA = 0.95) can be effectively demonstrated. [ABSTRACT FROM AUTHOR]

Infrared Reflection Absorption Spectroscopy (IRAS) on dielectric single crystals is challenging because the optimal incidence angles for light–adsorbate interaction coincide with regions of low IR reflectivity. Here, we introduce an optimized IRAS setup that maximizes the signal-to-noise ratio for non-metals. This is achieved by maximizing light throughput and by selecting optimal incidence angles that directly impact the peak heights in the spectra. The setup uses a commercial Fourier transform infrared spectrometer and is usable in ultra-high vacuum (UHV). Specifically, the optical design features sample illumination and collection mirrors with a high numerical aperture inside the UHV system and adjustable apertures to select the incidence angle range on the sample. This is important for p-polarized measurements on dielectrics because the peaks in the spectra reverse the direction at the Brewster angle (band inversion). The system components are connected precisely via a single flange, ensuring long-term stability. We studied the signal-to-noise ratio (SNR) variation in p-polarized IRAS spectra for one monolayer of CO on TiO2(110) as a function of incidence angle range, where a maximum SNR of 70 was achieved at 4 cm−1 resolution in a measurement time of 5 min. The capabilities for s polarization are demonstrated by measuring one monolayer D2O adsorbed on a TiO2(110) surface, where a SNR of 65 was achieved at a peak height ΔR/R0 of 1.4 × 10−4 in 20 min. [ABSTRACT FROM AUTHOR]

Nanophotonic devices are optical platforms capable of unprecedented wavefront control. To push the limits of experimental device performance, scalable design methodologies that combine the simplicity and fabricability of conventional design paradigms with the extended capabilities of freeform optimization are required. A novel gradient‐based design framework for large‐area freeform metasurfaces is introduced in which nonlocal interactions between simply shaped nanostructures, placed on an irregular lattice, are tailored to produce high‐order hybridized modes that support customizable large‐angle scattering profiles. Utilizing this approach, multifunctional super‐dispersive metalenses are designed and experimentally demonstrated. The approach to high‐numerical‐aperture radial metalenses capable of diffraction limited focusing and the generation of donut‐shaped point spread functions is also extended. It is anticipated that these concepts will have utility in super‐resolution microscopy, particle trapping, additive manufacturing, and metrology applications that require ultra‐high numerical apertures. [ABSTRACT FROM AUTHOR]

Introducing super‐resolution techniques to imaging through scattering media potentially revolutionizes the technical analysis for many exotic applications, such as cell structures behind biological tissues. The main challenge is scattering media's inhomogeneous structures, which scramble the light path and create noise‐like speckle patterns, hindering object's visualization even at a low‐resolution level. Here, a computational method is proposed relying on the object's spatial and temporal fluctuation to visualize nanoscale objects through scattering media non‐invasively. Taking advantage of the optical memory effect and multiple frames, the point spreading function (PSF) of scattering media is estimated. Multiple images of fluctuating objects are obtained by deconvolution; then, the super‐resolution image is achieved by computing the higher‐order cumulants. Non‐linearity of high order cumulant significantly suppresses artifacts in the resulting images and enhances resolution by a factor of N$\sqrt N $, where N is the cumulant order. The proof‐of‐concept demonstrates a resolution of 266 nm at the 6th‐order cumulant with numerical aperture (NA) of 0.42, breaking the diffraction limit by a factor of 2.45. An adaptive approach is also demonstrated for imaging through dynamic scattering media. The non‐invasive super‐resolution speckle fluctuation imaging (NISFFI) presents a nanoscopy technique with straightforward imaging hardware configuration to visualize samples behind scattering media. [ABSTRACT FROM AUTHOR]

The field of large numerical aperture microscopy has witnessed significant advancements in spatial and temporal resolution, as well as improvements in optical microscope imaging quality. However, these advancements have concurrently raised the demand for enhanced precision, extended range, and increased load-bearing capacity in objective motion carrier (OMC). To address this challenge, this study introduces an innovative OMC that employs a ball screw mechanism as its primary driving component. Furthermore, a robust nonlinear motion control strategy has been developed, which integrates fast nonsingular terminal sliding mode, experimental estimation techniques, and adaptive radial basis neural network, to mitigate the impact of nonlinear friction within the ball screw mechanism on motion precision. The stability of the closed-loop control system has been rigorously demonstrated through Lyapunov theory. Compared with other enhanced sliding mode control strategies, the maximum error and root mean square error of this controller are improved by 33% and 34% respectively. The implementation of the novel OMC has enabled the establishment of a high-resolution bio-optical microscope, which has proven its effectiveness in the microscopic imaging of retinal organoids. • Novel SMC Strategy: To address the limitations of traditional SMC, characterized by high gains and pronounced chattering, a novel SMC strategy is introduced. • Online Estimation and Compensation: The utilization of TDE techniques enables online estimation and real-time compensation of unknown terms. • Biophotonic Microscope Development: The research culminates in the development of a biophotonic microscope, wherein the objective motion carrier plays a crucial role in achieving focal plane movement. [ABSTRACT FROM AUTHOR]

A four-group mechanically compensated continuous-zoom microscope is proposed and designed based on the theory of continuous zoom. The system addresses the limitations of traditional continuous-zoom microscopes, including a small zoom ratio, a short working distance, and the loss of details during 2D–3D switching. The system has a magnification of 0.6×~6.0× under two-dimensional observation, adapts to two-third-inch sensors, has a working distance of 130 mm, and adds a 360-degree rotatable beamsplitter for three-dimensional full-field-of-view observation. The magnification, numerical aperture, and sensor dimensions remain unchanged under both two-dimensional and three-dimensional observation. The design results demonstrate that the system is capable of achieving a high zoom ratio of 10× while maintaining a high level of imaging quality in both two-dimensional and three-dimensional modes. The MTF curves for each magnification are in close proximity to the diffraction limit, the spot diagrams are smaller than the airy disk range, and the zoom cam curves are smooth with no inflection points. Furthermore, the system negates the visual discrepancies and loss of detail that arise when switching observation modes due to alterations in system magnification and numerical aperture, thereby broadening the scope of applications for continuous-zoom microscopes. [ABSTRACT FROM AUTHOR]

Based on the demand for high-power output, a spatial beam combining 7-channel quantum cascade lasers (QCLs) is demonstrated in this paper. A "2 + 3 + 2" stepped structure is designed to convert the seven beam spots into a circular arrangement. An aspherical lens with a large numerical aperture (NA) of 0.85 and a focal length of 1.873 mm is used in each single QCL for collimation, and seven reflectors are utilized in the 7-channel QCLs combined in the spatial beam. After combining the spatial beam, the maximum continuous output power of the system is 3.6 W, and the beam quality M2 is 5.59 in the fast axis and 8.3 in the slow axis, respectively. [ABSTRACT FROM AUTHOR]