Aberration Correction Research Articles

Deep tissue super-resolution imaging with adaptive optical two-photon multifocal structured illumination microscopy

Visualization of axons and dendritic spines is crucial in neuroscience research. However, traditional microscopy is limited by diffraction-limited resolution and shallow imaging depth, making it difficult to study neuronal dynamics. Two-photon multifocal structured illumination microscopy (2P-MSIM) provides super-resolution imaging along with a reasonably good penetration, but it is vulnerable to optical aberrations in deep tissues. Herein we present a novel non-inertial scanning 2P-MSIM system incorporated with adaptive optics (AO) which allows for super-resolution imaging with effective aberration correction. Our strategy is designed to correct both laser and fluorescence paths simultaneously using a spatial light modulator and a deformable mirror respectively, providing better results than the individual path corrections. The successful implementation of adaptive optical two-photon multifocal structured illumination microscopy (AO 2P-MSIM) has allowed for the super-resolution imaging of neuronal structures in a mouse brain slice at great depths and dynamic morphological characteristics of zebrafish motoneurons in vivo.

Ion-optical updates and performance analysis of High energy FRagment Separator (HFRS) at HIAF

The High energy FRagment Separator (HFRS), a new generation in-flight radioactive separator, is under construction at the high-intensity Heavy Ion Accelerator Facility (HIAF) in China. To further optimize the separator performance and consider the manufacturing technology, the specifications of some magnetic elements of the HFRS separator have been modified from the original design reported earlier, and prototypes of partial magnetic elements have been fabricated and tested. In this paper, updates of magnetic parameters, test results of prototypes, and development of ion-optical calculation are presented. The high-order correction of aberrations is demonstrated. The performance of the separator is studied using fission reactions and fragmentation reactions of relativistic 238U projectiles. This work will guide the forthcoming experiments in the future HFRS separator.

Accurate piecewise centroid calculation algorithm for wavefront measurement in adaptive optics.

Adaptive optics using direct wavefront sensing (direct AO) is widely used in two-photon microscopy to correct sample-induced aberrations and restore diffraction-limited performance at high speeds. In general, the direct AO method employs a Sharked-Hartman wavefront sensor (SHWS) to directly measure the aberrations through a spot array. However, the signal-to-noise ratio (SNR) of spots in SHWS varies significantly within deep tissues, presenting challenges for accurately locating spot centroids over a large SNR range, particularly under extremely low SNR conditions. To address this issue, we propose a piecewise centroid calculation algorithm called GCP, which integrates three optimal algorithms for accurate spot centroid calculations under high-, medium-, and low-SNR conditions. Simulations and experiments demonstrate that the GCP can accurately measure aberrations over a large SNR range and exhibits robustness under extremely low-SNR conditions. Importantly, GCP improves the AO working depth by 150 µm compared to the conventional algorithm.

FMMAS-OCT: Aberration correction for high-resolution cellular imaging

In optical coherence tomography (OCT), spatial resolution and signal strength often suffer due to aberrations from both the imaging system and the sample. In this work, we introduce a novel method, FMMAS (Forward-Model Multiple Aperture Synthesis), which effectively compensates for these aberrations. It combines forward-model (FM) based method for transverse resolution restoration and multiple aperture synthesis (MAS) to mitigate depth domain aberrations. Our proof-of-concept experiment demonstrates a significant improvement in the mean transverse full width at half maximum (FWHM) of microparticles by 46.1 %. Compared to original OCT and FM method, FMMAS produces sharper, 'pencil beam'-like imaging, resolving cell nuclei in swine esophagus ex vivo and human blood cells in vivo, suggesting a potential for significant enhancements in OCT image quality.

Amorphous 1-D nanowires of calcium phosphate/pyrophosphate: A demonstration of oriented self-growth of amorphous minerals

Amorphous inorganic solids are traditionally isotropic, thus, it is believed that they only grow in a non-preferential way without the assistance of regulators, leading to the morphologies of nanospheres or irregular aggregates of nanoparticles. However, in the presence of (ortho)phosphate (Pi) and pyrophosphate ions (PPi) which have synergistic roles in biomineralization, the highly elongated amorphous nanowires (denoted ACPPNs) form in a regulator-free aqueous solution (without templates, additives, organics, etc). Based on thorough characterization and tracking of the formation process (e.g., Cryo-TEM, spherical aberration correction high resolution TEM, solid state NMR, high energy resolution monochromated STEM-EELS), the microstructure and its preferential growth behavior are elucidated. In ACPPNs, amorphous calcium orthophosphate and amorphous calcium pyrophosphate are distributed at separated but close sites. The ACPPNs grow via either the preferential attachment of ∼2 nm nanoclusters in a 1-dimension way, or the transformation of bigger nanoparticles, indicating an inherent driving force-governed process. We propose that the anisotropy of ACPPNs microstructure, which is corroborated experimentally, causes their oriented growth. This study proves that, unlike the conventional view, amorphous minerals can form via oriented growth without external regulation, demonstrating a novel insight into the structures and growth behaviors of amorphous minerals.

Use of Control Systems in the Correction of Static and Thermal Aberrations

Use of Control Systems in the Correction of Static and Thermal Aberrations

Poster Session II: Investigating photoreceptor function in disease-affected retinas using optoretinography.

Assessing the functional response of photoreceptors is vital in understanding retinal disease progression. Traditional subjective methods like visual acuity and visual fields, and objective ones like electroretinography, have limitations. An ideal complement to these techniques is optoretinography (ORG), which images the retina and tests its function at once. ORG utilizes the phase of the optical coherence tomography (OCT) signal to quantify nanometer-scale changes, measuring subtle photoreceptor responses to stimuli. Efforts to observe stimulus-evoked responses in human cone photoreceptors began with adaptive optics (AO) and common path interferometry, enabling the resolution and tracking of individual cells. Advances in OCT systems with cellular resolution through AO or digital aberration correction successfully measured ORG responses from single cones and rods. This method tracks phase differences between outer segment tips (COST or ROST) and the inner-outer segment junction (IS/OS) to assess individual cell responses. A novel velocity-based method recently demonstrated the feasibility of measuring ORG signals with clinical-grade OCT systems. In the present work, we implemented this technique on disease-affected human retinas, revealing lower magnitudes of response compared to healthy retinas, and highlighting its potential clinical applications.

Cross-Layer Feature Fusion and Decentration Aberration Correction of Circular Points for Automated Guided Vehicle Terminal Positioning

Cross-Layer Feature Fusion and Decentration Aberration Correction of Circular Points for Automated Guided Vehicle Terminal Positioning

Vectorial adaptive optics

Adaptive optics normally concerns the feedback correction of phase aberrations. Such correction has been of benefit in various optical systems, with applications ranging in scale from astronomical telescopes to super-resolution microscopes. Here we extend this powerful tool into the vectorial domain, encompassing higher-dimensional feedback correction of both polarisation and phase. This technique is termed vectorial adaptive optics (V-AO). We show that V-AO can be implemented using sensor feedback, indirectly using sensorless AO, or in hybrid form combining aspects of both. We validate improvements in both vector field state and the focal quality of an optical system, through correction for commonplace vectorial aberration sources, ranging from objective lenses to biological samples. This technique pushes the boundaries of traditional scalar beam shaping by providing feedback control of extra vectorial degrees of freedom. This paves the way for next generation AO functionality by manipulating the complex vectorial field.

Potential vision tester using adaptive optics, Maxwellian view, and small pupil.

We demonstrate a free-space, trolley-mounted potential vision tester (PVT), designed to study and improve the accuracy of visual acuity (VA) measurements in the aging eye. Key features include a high-resolution visual display presented in Maxwellian view, a 3 mm pupil to limit wavefront (WF) aberrations, and a moderate cost deformable mirror to induce or correct higher order optical aberrations. The visual display supported accurate measurement of visual acuities down to 20/5. The moderate cost, piezo deformable mirror induced seven nominal aberrations, calibrated as 0, -0.32, -0.23, + 0.27, and +0.39 microns spherical aberration; + 0.49 microns Y coma; and -0.51 microns X coma. A custom Hartmann Shack (HS) calibration (HSc) system demonstrated that induced aberrations were repeatable and stable. A Badal optometer provided the coarse focus. WF aberrations were measured for five normal subjects with a commercially available HS device (HSP) (OCULUS Pentacam AXL Wave), providing estimates of WF errors for 3 mm and other pupil sizes. VA was measured using four alternative forced-choice for a single black on white E stimulus in each trial. Using the method of constant stimuli yielded robust standard deviation measurements. The 50% fit for VA plotted against induced aberration resulted in linear functions for each subject for the range of our positive and negative spherical aberration data. Subjects differed, but higher order terms were unnecessary to describe data across spherical aberrations.

Tandem aberration correction optics (TACO) in wide-field structured illumination microscopy.

Structured illumination microscopy (SIM) is a powerful super-resolution imaging technique that uses patterned illumination to down-modulate high spatial-frequency information of samples. However, the presence of spatially-dependent aberrations can severely disrupt the illumination pattern, limiting the quality of SIM imaging. Conventional adaptive optics (AO) techniques that employ wavefront correctors at the pupil plane are not capable of effectively correcting these spatially-dependent aberrations. We introduce the Tandem Aberration Correction Optics (TACO) approach that combines both pupil AO and conjugate AO for aberration correction in SIM. TACO incorporates a deformable mirror (DM) for pupil AO in the detection path to correct for global aberrations, while a spatial light modulator (SLM) is placed at the plane conjugate to the aberration source near the sample plane, termed conjugate AO, to compensate spatially-varying aberrations in the illumination path. Our numerical simulations and experimental results show that the TACO approach can recover the illumination pattern close to an ideal condition, even when severely misshaped by aberrations, resulting in high-quality super-resolution SIM reconstruction. The TACO approach resolves a critical traditional shortcoming of aberration correction for structured illumination. This advance significantly expands the application of SIM imaging in the study of complex, particularly biological, samples and should be effective in other wide-field microscopies.

Optical fiber-integrated achromatic metalens based on catenary metasurfaces.

A challenge in all-fiber-integrated metasurface devices is to efficiently control dispersion in the limited fiber end area to build metasurfaces, therefore, the design of metasurfaces with a special structure becomes crucial to meet the demands of dispersion control. A unique phase response of circularly polarized light in catenary metasurfaces can offer new opportunities for polarization-sensitive arbitrary chromatic dispersion control. Herein, we proposed an optical achromatic metalens based on equal width catenary metasurfaces integrated on the large-mode optical fiber (LMF) end. To reduce phase distortions, the LMF is designed to generate quasi-plane waves (QPW), and then QPW converts from catenary metasurfaces to realize achromatic focusing. A notable feature of this device is its axial focal length shift as low as 0.09% across the working wavelength range from 1.33 µm to 1.55 µm, commonly used in optical fiber communication, demonstrating its excellent dispersion control capability. Furthermore, the device exhibits exceptional capabilities to break through the diffraction limit of the output field. This research has potential applications in the fields of achromatic devices, chromatic aberration correction, fiber lasers, and optical communication and modulation.

Atmospheric Turbulence Aberration Correction Based on Deep Learning Wavefront Sensing.

In this paper, research was conducted on Deep Learning Wavefront Sensing (DLWS) neural networks using simulated atmospheric turbulence datasets, and a novel DLWS was proposed based on attention mechanisms and Convolutional Neural Networks (CNNs). The study encompassed both indoor experiments and kilometer-range laser transmission experiments employing DLWS. In terms of indoor experiments, data were collected and training was performed on the platform built by us. Subsequent comparative experiments with the Shack-Hartmann Wavefront Sensing (SHWS) method revealed that our DLWS model achieved accuracy on par with SHWS. For the kilometer-scale experiments, we directly applied the DLWS model obtained from the indoor platform, eliminating the need for new data collection or additional training. The DLWS predicts the wavefront from the beacon light PSF in real time and then uses it for aberration correction of the emitted laser. The results demonstrate a substantial improvement in the average peak intensity of the light spot at the target position after closed-loop correction, with a remarkable increase of 5.35 times compared to the open-loop configuration.

Universal adaptive optics for microscopy through embedded neural network control

The resolution and contrast of microscope imaging is often affected by aberrations introduced by imperfect optical systems and inhomogeneous refractive structures in specimens. Adaptive optics (AO) compensates these aberrations and restores diffraction limited performance. A wide range of AO solutions have been introduced, often tailored to a specific microscope type or application. Until now, a universal AO solution – one that can be readily transferred between microscope modalities – has not been deployed. We propose versatile and fast aberration correction using a physics-based machine learning assisted wavefront-sensorless AO control (MLAO) method. Unlike previous ML methods, we used a specially constructed neural network (NN) architecture, designed using physical understanding of the general microscope image formation, that was embedded in the control loop of different microscope systems. The approach means that not only is the resulting NN orders of magnitude simpler than previous NN methods, but the concept is translatable across microscope modalities. We demonstrated the method on a two-photon, a three-photon and a widefield three-dimensional (3D) structured illumination microscope. Results showed that the method outperformed commonly-used modal-based sensorless AO methods. We also showed that our ML-based method was robust in a range of challenging imaging conditions, such as 3D sample structures, specimen motion, low signal to noise ratio and activity-induced fluorescence fluctuations. Moreover, as the bespoke architecture encapsulated physical understanding of the imaging process, the internal NN configuration was no-longer a “black box”, but provided physical insights on internal workings, which could influence future designs.

Direct design method for holographic grating imaging spectrometer and corresponding recording system

The combination of holographic gratings with freeform surface technology has led to a significant breakthrough in terms of the performance of imaging spectrometers. In this paper, a general direct design method that is capable of designing imaging spectrometers that include holographic gratings based on a complex-shaped surface substrate and their corresponding recording systems is proposed. The most important feature of this method is that the recording and imaging systems are designed within one optical system model, thus allowing for an optimal balance to be achieved between the aberration correction capability and the manufacturability of the holographic grating. To illustrate the effectiveness of the proposed method, three imaging spectrometers were designed that used holographic gratings manufactured by a recording system without auxiliary mirrors, a system with a spherical auxiliary mirror, and a system with a freeform auxiliary mirror. Ultimately, these three systems all achieved diffraction-limited imaging quality with minimal distortion.

Analysis and Optical System Design of the Lenslet-Array Integral Field Spectrometer

To address the problem of slit limitation in traditional slit imaging spectrometers, which hampers fast the identification, efficient tracking, and precise avoidance of faint targets in lunar orbit, this article proposes a lenslet-array integral field spectrometer structure that is free of slits, static, and that is fast and efficient for the visible-to-near-infrared wavelength band. Firstly, the field of view segmentation model is analyzed, and the requirement of the telecentric degree of the pre-imaging system is obtained. Secondly, the influence of aberrations, such as spherical aberration and coma distortion on the micro-pupil dispersion model is analyzed. Based on this, the pre-imaging system is designed to meet the requirements of aberration correction and the telecentricity of the system. Finally, the structure of the spectral system is designed, and the integrated system is optimized. The smile of the lenslet-array integral field spectrometer is ±1 nm, and the MTF is greater than 0.7 at 60 lp/mm and close to the diffraction limit.

Wideband Antennas of Passive Seekers for Anti Radiation Missiles

Suppression of Enemy Air Defence (SEAD) is a fundamental element of Air Power application by means of in protecting friendly air attackers and destroying the enemy’s ability to defend against air attack. Most of the SEAD operation even today relies on Anti-radiation missile (ARM) which is an air-to-surface tactical missile designed to detect, seek, attack and destroy opponent’s radar. Passive seeker of ARM is a miniaturized ESM receiver which is capable of extracting the necessary angular data from the enemy radar emissions. Single head passive seeker covering wide frequency range from L to Ku band is the preferred choice. Wideband antennas have been designed and utilized for Direction Finding applications of ESM/ELINT receivers for ground, air and ship borne platforms. Unlike these platforms, there are several restrictions for passive seeker based compact ESM receiver for missile borne platform specially air to surface missile where lesser diameter is one of the preferred design parameter. This review paper mainly discusses the existing wideband antennas such as spiral, log-periodic, printed circuit vivaldi and all-metal vivaldi antennas and the comparison of their various parameters for passive seeker. The paper also suggests their suitability with respect to their placement on the missile for three configurations: concealed inside the radome, flush-mounted and conformal antenna based. The paper also brought about the specific test facility required for testing and evaluation of passive seeker to characterize it with missile radome which is the most challenging and time consuming task. Among the three passive seeker configuration discussed, conformal antenna based passive seeker using all-metal Vivaldi is the best option avoiding radome aberration correction which is being utilized in the present third generations of ARM. The second commonly and established passive seeker configuration is concealed inside the radome using spiral antennas where handling radome aberration correction is a limitation.

Atomic-scale imaging of electron sensitive zeolites with aberration corrected transmission electron microscopy

The spatial resolution of transmission electron microscopes (TEMs) and scanning transmission electron microscopes (STEMs) has been drastically improved by introducing aberration correction. However, observable range in electron sensitive zeolites are still limited due to electron irradiation damages. Nevertheless, atomic resolution imaging of some zeolites is currently being realized by various developments in electron microscopic hardware, such as high sensitivity cameras. On the other hand, surveying the status of TEM and STEM imaging is very important for further progress in the structural analysis of zeolites. Here, we demonstrate and compare the high-resolution imaging of zeolites with several kinds of imaging modes.

Chalcogenide GRIN glasses with high refractive index and large refractive index difference for LWIR imaging.

Gradient refractive index (GRIN) materials utilize an internally tailored refractive index in combination with the designed curvature of the optical element surface, providing the optical designer with additional freedom for correcting chromatic and spherical aberrations. In this paper, new GRIN materials suitable for the second (3-5 µm) and third (8-12 µm) atmospheric windows were successfully developed by the thermal diffusion method based on Ge20As20Se60-xTex series high refractive index glasses, where the maximum refractive index difference (Δn) at 4 µm and 10.6 µm were 0.281 and 0.277, respectively. The diffusion characteristics and refractive index distribution of the GRIN glass were analyzed by Raman characterization. Furthermore, the performance of GRIN singlet and homogeneous singlet in the LWIR band (8 µm, 10.6 µm (primary wavelength), 12 µm) was compared, and the results showed that the GRIN singlet had better chromatic aberration correction and unique dispersion characteristics.

Design of Electrostatic Aberration Correctors for Scanning Transmission Electron Microscopy.

In a scanning transmission electron microscope (STEM), producing a high-resolution image generally requires an electron beam focused to the smallest point possible. However, the magnetic lenses used to focus the beam are unavoidably imperfect, introducing aberrations that limit resolution. Modern STEMs overcome this by using hardware aberration correctors comprised of many multipole elements, but these devices are complex, expensive, and can be difficult to tune. We demonstrate a design for an electrostatic phase plate that can act as an aberration corrector. The corrector is comprised of annular segments, each of which is an independent two-terminal device that can apply a constant or ramped phase shift to a portion of the electron beam. We show the improvement in image resolution using an electrostatic corrector. Engineering criteria impose that much of the beam within the probe-forming aperture be blocked by support bars, leading to large probe tails for the corrected probe that sample the specimen beyond the central lobe. We also show how this device can be used to create other STEM beam profiles such as vortex beams and probes with a high degree of phase diversity, which improve information transfer in ptychographic reconstructions.