Dynamic Aberrations Research Articles

Super-oscillation sub-diffraction focusing with emulated atmospheric turbulence

The super-oscillation (SO) phenomena successfully applied to super-resolution optical telescopes have yet to study the existence of atmospheric turbulence (AT). In this paper, we first experimentally investigate the sub-diffraction focusing of the SO light field in the atmospheric-like turbulence. The 137-element adaptive optics (AO) system is utilized to correct the dynamic wavefront aberration produced by the AT and obtain the AO closed-loop RMS of the residual wavefront error ∼λ/15. For a proofed telescope (clear aperture 12 mm and focal length 1000 mm) @λ=632.8 nm, the FWHM of the experimental SO spot under the modest AT (wavefront error RMS ∼0.57λ) is about 0.79 times of the Airy spot compared with the non-AT result of 0.76 times, while the strong AT (wavefront error RMS ∼1.35λ) erases the sub-diffraction focusing effect of the SO field and the average side-lobe intensity increases significantly. This study is promising for super-resolving telescope, synthetic aperture for visible imaging, etc.

Wide Dynamic Range Digital Aberration Measurement and Fast Anterior-Segment OCT Imaging †.

Ocular aberrometry with a wide dynamic range for assessing vision performance and anterior segment imaging that provides anatomical details of the eye are both essential for vision research and clinical applications. Defocus error is a major limitation of digital wavefront aberrometry (DWA), as the blurring of the detected point spread function (PSF) significantly reduces the signal-to-noise ratio (SNR) beyond the ±3 D range. With the aid of Badal-like precompensation of defocus, the dynamic defocus range of the captured aberrated PSFs can be effectively extended. We demonstrate a dual-modality MHz VCSEL-based swept-source OCT (SS-OCT) system with easy switching between DWA and OCT imaging modes. The system is capable of measuring aberrations with defocus dynamic range of 20 D as well as providing fast anatomical imaging of the anterior segment at an A-scan rate of 1.6 MHz.

Large-Dynamic-Range Ocular Aberration Measurement Based on Deep Learning with a Shack-Hartmann Wavefront Sensor.

The Shack-Hartmann wavefront sensor (SHWFS) is widely utilized for ocular aberration measurement. However, large ocular aberrations caused by individual differences can easily make the spot move out of the range of the corresponding sub-aperture in SHWFS, rendering the traditional centroiding method ineffective. This study applied a novel convolutional neural network (CNN) model to wavefront sensing for large dynamic ocular aberration measurement. The simulation results demonstrate that, compared to the modal method, the dynamic range of our method for main low-order aberrations in ocular system is increased by 1.86 to 43.88 times in variety. Meanwhile, the proposed method also has the best measurement accuracy, and the statistical root mean square (RMS) of the residual wavefronts is 0.0082 ± 0.0185 λ (mean ± standard deviation). The proposed method generally has a higher accuracy while having a similar or even better dynamic range as compared to traditional large-dynamic schemes. On the other hand, compared with recently developed deep learning methods, the proposed method has a much larger dynamic range and better measurement accuracy.

Influence of static and dynamic ocular aberrations on full-field optical coherence tomography for in vivo high-resolution retinal imaging.

Under spatially incoherent illumination, time-domain full-field optical coherence tomography (FFOCT) offers the possibility to achieve in vivo retinal imaging at cellular resolution over a wide field of view. Such performance is possible, albeit there is the presence of ocular aberrations even without the use of classical adaptive optics. While the effect of aberrations in FFOCT has been debated these past years, mostly on low-order and static aberrations, we present, for the first time to our knowledge, a method enabling a quantitative study of the effect of statistically representative static and dynamic ocular aberrations on FFOCT image metrics, such as SNR, resolution, and image similarity. While we show that ocular aberrations can decrease FFOCT SNR and resolution by up to 14 dB and fivefold, we take advantage of such quantification to discuss different possible compromises between performance gain and adaptive optics complexity and speed, to optimize both sensor-based and sensorless FFOCT high-resolution retinal imaging.

Remote focusing with dynamic aberration elimination by model-based adaptive optics

Remote focusing using a deformable mirror (DM) provides a rapid and responsive technique for performing axial scanning. However, to maintain the laser focusing quality, the aberrations within the system must be adequately controlled. Accordingly, the present study proposes a low control complexity model-based adaptive optics (AO) approach for remote focusing with zero aberrations. Based on the Zernike coefficients measured by a self-built Shack-Hartmann wavefront sensor (SHWS), 15 independent closed-loop controllers (one for each Zernike mode according to Wyant expansion scheme) execute a three-step DM identification process to determine the control vectors required to actuate the DM in such a way as to restore the Zernike coefficients of the wavefront to their required values. The experimental results show that the controllers converge within four time steps (20 ms) and reduce the converged wavefront variance by nearly 475 times. Moreover, the controller used to manipulate the Z3 (defocus) Zernike coefficient converges within just three time steps (15 ms). Given a static disturbance of the wavefront, the proposed AO control method enables the defocus laser spot to be driven precisely along a target sinusoidal trajectory while maintaining all the other Zernike modes at zero. The control system shows a similar performance in compensating the dynamic aberrations produced by a low-frequency thermal disturbance within the system. Overall, the results indicate that the proposed model-based AO controller facilitates remote focusing with simultaneous aberration elimination and improves the central intensity of the focus laser spot by around 3.1 times compared to the case in which the controller is not applied.

Phase aberration compensation via a self-supervised sparse constraint network in digital holographic microscopy

Phase aberration compensation is of great significance for the quantitative phase imaging in digital holographic microscopy. Least-square-based fitting algorithms are the most common options except for the double exposure method. However, they either require perturbation hypothesis, image segmentation, or an extra object-free hologram, leading to additional efforts for aberration elimination. In addition, supervised learning-based networks are mostly applied to create object-free masks automatically, but suffer from laborious label preparation and limited generalization capability. In this study, we propose a self-supervised sparse constraint network (SSCNet) for aberration compensation without the perturbation hypothesis, as well as an additional label or mask. Zernike model enhancement and sparse constraints are introduced for fitting aberration with only a single measured hologram. Simulation and experiment demonstrate that our proposed SSCNet can accurately compensate the phase aberration without object-free masks, and is more stable than other algorithms. It can be generalized to other samples with high accuracy and little time requirement. Moreover, SSCNet has advantage in the adaptive compensation of dynamic aberration in continuous measurement. Finally, it is an effective and practical fitting algorithm for phase aberration compensation.

A Systematic Approach to Understanding Acid-Base Disorders in the Critically Ill.

The objective of this review is to discuss acid-base physiology, describe the essential steps for interpreting an arterial blood gas and relevant laboratory tests, and review the 4 distinct types of acid-base disorders. A comprehensive literature search and resultant bibliography review of PubMed from inception through March 7, 2023. Relevant English-language articles were extracted and evaluated. Critically ill patients are prone to significant acid-base disorders that can adversely affect clinical outcomes. Assessing these acid-base abnormalities can be complex because of dynamic aberrations in plasma proteins, electrolytes, extracellular volume, concomitant therapies, and use of mechanical ventilation. This article provides a systematic approach to acid-base abnormalities which is necessary to facilitate prompt identification of acid-base disturbances and prevent untoward morbidity and mortality. Many acid-base disorders result from medication therapy or are treated with medications. Pharmacists are uniquely poised as the medication experts on the multidisciplinary team to assist with acid-base assessments in the context of pharmacotherapy. The use of a systematic approach to address acid-base disorders can be performed by all pharmacists to improve pharmacotherapy and optimize patient outcomes.

A mathematical framework for nonlinear wavefront reconstruction in adaptive optics systems with Fourier-type wavefront sensing

Advanced adaptive optics (AO) instruments have applications in ophthalmic imaging, free-space optical communications and the future generation of extremely large telescopes. These AO systems are designed to perform real-time corrections of dynamic wavefront aberrations. The corrections can be performed by converting wavefront measurements into deformable mirror (DM) actuator commands. The role of the DM is to mitigate aberrations by restoring a planar wavefront. Optimal DM actuator commands therefore require precise phase measurements across the entire wavefront. Reconstructing a wavefront from wavefront sensor (WFS) data is an inverse problem that depends on the type of WFS implemented. Nonlinear Fourier-type WFSs are included in the design of many current and upcoming AO systems. Conventionally, these sensors perform AO control based on simplifications and linearisations of the underlying models. However, in nonlinear regimes, approximation errors critically degrade image quality. This study looks at overcoming nonlinear wavefront sensing regimes by introducing a nonlinear, iterative algorithm for Fourier-type wavefront reconstruction. The algorithm used is well-known in the field of inverse problems. The underlying mathematical theory for modelling Fourier-type WFSs is provided, along with how these models can be used to perform nonlinear wavefront reconstruction. A significant advantage of the analysis presented is its generalised applicability to any Fourier-type sensor. The only input required is the mathematical expression for the optical element transfer function. The generalised and full mathematical model of Fourier-type WFSs is introduced in a Sobolev space setting. Necessary inputs are derived for the nonlinear iterative algorithms, such as Fréchet derivatives and adjoints. The generalised theory is then expanded to solve the inverse problem of wavefront reconstruction for all Fourier-type WFSs. Moreover, the study concentrates on the pyramid WFS (PWFS)—one of the most well-known Fourier-type WFSs—and shows a Hilbert transform representation of the amplitude of the incoming light on its detector. The developed theory is demonstrated using a simulated PWFS to measure an example wavefront.

Data-driven modeling and control of an X-ray bimorph adaptive mirror.

Adaptive X-ray mirrors are being adopted on high-coherent-flux synchrotron and X-ray free-electron laser beamlines where dynamic phase control and aberration compensation are necessary to preserve wavefront quality from source to sample, yet challenging to achieve. Additional difficulties arise from the inability to continuously probe the wavefront in this context, which demands methods of control that require little to no feedback. In this work, a data-driven approach to the control of adaptive X-ray optics with piezo-bimorph actuators is demonstrated. This approach approximates the non-linear system dynamics with a discrete-time model using random mirror shapes and interferometric measurements as training data. For mirrors of this type, prior states and voltage inputs affect the shape-change trajectory, and therefore must be included in the model. Without the need for assumed physical models of the mirror's behavior, the generality of the neural network structure accommodates drift, creep and hysteresis, and enables a control algorithm that achieves shape control and stability below 2 nm RMS. Using a prototype mirror and ex situ metrology, it is shown that the accuracy of our trained model enables open-loop shape control across a diverse set of states and that the control algorithm achieves shape error magnitudes that fall within diffraction-limited performance.

Aberration correction for multiphoton microscopy using covariance matrix adaptation evolution strategy

Multiphoton microscopy is the enabling tool for biomedical research, but the aberrations of biological tissues have limited its imaging performance. Adaptive optics (AO) has been developed to partially overcome aberration to restore imaging performance. For indirect AO, algorithm is the key to its successful implementation. Here, based on the fact that indirect AO has an analogy to the black-box optimization problem, we successfully apply the covariance matrix adaptation evolution strategy (CMA-ES) used in the latter, to indirect AO in multiphoton microscopy (MPM). Compared with the traditional genetic algorithm (GA), our algorithm has a greater improvement in convergence speed and convergence accuracy, which provides the possibility of realizing real-time dynamic aberration correction for deep in vivo biological tissues.

Dynamic Aberrations of Scanning Imaging System with Cascaded Microlens Arrays

Dynamic Aberrations of Scanning Imaging System with Cascaded Microlens Arrays

Analysis of Telescope Wavefront Aberration and Optical Path Stability in Space Gravitational Wave Detection

Space-based gravitational wave detection programs, such as the Laser Interferometer Space Antenna (LISA) or Taiji program, obtain gravitational wave signals by measuring the change in the distance between three satellites by laser. The telescope is an important part of the measurement system, and its function is to transmit and receive laser signals. Due to changes in the space environment, the telescope will inevitably introduce additional dynamic aberrations, which will bring optical path errors to the inversion of gravitational wave signals. Taking LISA as an example, to achieve pm-level measurement accuracy at the detection frequency of 0.1 mHz–1 Hz, the stability requirements of the telescope are less than 1 pm/Hz1/2. This paper theoretically deduces the aberration types that affect the telescope’s stability and conducts simulation analysis according to the actual phase demodulation method, which verifies the theory’s correctness. In addition, using this theory, it can be concluded that under the condition that the total size of the telescope aberration is determined to be stable, reducing the ratio of rotationally symmetric aberrations such as “spherical aberration” and “defocusing” among common aberrations can significantly improve the stability of the telescope. The conclusion guides the optical system design of LISA or Taiji.

SOHO State of the Art Updates and Next Questions | Mechanisms of Resistance to BCL2 Inhibitor Therapy in Chronic Lymphocytic Leukemia and Potential Future Therapeutic Directions.

Chronic lymphocytic leukaemia (CLL) constitutively overexpresses B-cell lymphoma 2 (BCL2) with consequent dysregulation of intrinsic apoptosis leading to abnormal cellular survival. Therapeutic use of BCL2 inhibitors (BCL2i, eg, venetoclax) in CLL, as both continuous monotherapy or in fixed duration combination, has translated scientific rationale into clinical benefit with significant rates of complete responses, including those without detectable minimal residual disease. Unlike with chemotherapy, response rates to venetoclax do not appear to be influenced by pre-existing chromosomal abnormalities or somatic mutations present, although the duration of response observed remains shorter for those with traditional higher risk genetic aberrations. This review seeks to describe both the disease factors that influence primary venetoclax sensitivity/resistance and those resistance mechanisms that may be acquired secondary to BCL2i therapy in CLL. Baseline venetoclax-sensitivity or -resistance is influenced by the expression of BCL2 relative to other BCL2 family member proteins, microenvironmental factors including nodal T-cell stimulation, and tumoral heterogeneity. With selection pressure applied by continuous venetoclax exposure, secondary resistance mechanisms develop in oligoclonal fashion. Those mechanisms described include acquisition of BCL2 variants, dynamic aberrations of alternative BCL2 family proteins, and mutations affecting both BAX and other BH3 proteins. In view of the resistance described, this review also proposes future applications of BCL2i therapy in CLL and potential means by which BCL2i-resistance may be abrogated.

Apparatus and its principle for thermal aberration compensation.

Thermal aberrations caused by absorption of laser beams degrade the image quality of exposure tools during the working process. Many compensators, such as lens movement or lens deformation, are used to compensate for low-order thermal aberrations of optical systems. In this paper, an apparatus with higher-order aberration correction capability is presented. The main principle of the apparatus is to actively heat and cool the lens near the pupil to generate a desired temperature profile to compensate for thermal aberrations. We first introduce the basic concept of the apparatus. Then we establish an analytical model to describe the lens temperature of the apparatus based on its working principle and demonstrate its compensation capability. Finally, an algorithm for dynamic thermal aberrations compensation is proposed to overcome the time lag effects of a thermally controlled lens.

Particle Tracking Velocimetry With Dynamic Aberration Correction For 3D Flow Measurements Through Fluctuating Phase Boundaries

Imaging based flow measurements allow the observation of complex three-dimensional flows with a high temporal resolution. However, at least one optical access with a good imaging quality is needed. In fluids with a dynamic phase boundary, often the only optical access is the dynamic surface (e. g. droplet on opaque surface). In this case, temporally varying aberrations are introduced that can increase the measurement uncertainty significantly. Additionally, many flows in technical systems are three-dimensional and turbulent so that volumetric measurements are desirable. In this contribution, we present the first 3D-3C flow measurement system with dynamic aberration correction and a single optical access. By using a deformable mirror with 69 actuators, a laser guide star and a wavefront sensor, the dynamic aberrations that are introduced by the fluctuating phase boundary can be corrected. By introducing a double-helix point spread function (DH-PSF) with a spatial light modulator (SLM) we achieve three-dimensional flow measurements with only one camera. For demonstration purposes, the flow in a microchannel was measured through an oscillating puddle-like droplet. By applying the adaptive-optics system, the measurement uncertainty could be lowered by 58 % relative to measurements through a static droplet. The technique has the potential to allow three-dimensional flow measurements in droplets on opaque surfaces (e. g. membrane of fuel cell). Thus, new insights about the movement of droplets (e. g. in fuel cells) are made possible.

A Stimulated Emission Depletion (STED) Microscope of All Trades

Abstract: Super-resolution microscopy gives researchers invaluable opportunities and continues to make great strides in terms of performance and applicability. Clever developments in stimulated emission depletion (STED) microscopy have pushed the doors open wider for many applications. Here, we discuss three examples: first, how time-resolved detection unlocks new information; then, live-cell imaging enabled by intelligent illumination schemes; and finally, deep tissue imaging with dynamic aberration correction. As an outlook, we examine MINFLUX as an approach for molecular resolution with fluorescence.

3D Imaging with Double-Helix Point Spread Function and Dynamic Aberration Correction Using a Deformable Mirror

Imaging-based measurements through fluctuating phase boundaries such as free water surfaces or droplets have usually a higher uncertainty due to the changing refraction of light at the boundary. In this paper, a novel measurement system is presented for both 3D imaging with only one camera and aberration correction of light propagation through one boundary. 3D imaging is achieved by introducing a Double-Helix Point Spread Function (DH-PSF). The dynamically introduced aberrations of the phase boundary are measured with a Fresnel Guide Star (FGS) and are corrected with a deformable mirror in a closed-loop system with low latency. The measurement system and the adaptive optics image correction were characterized by means of a linear actuator and a demonstration measurement through an oscillating droplet. For the latter, the uncertainty of a reference flow could be lowered by 58 % using adaptive optics. The technique has the potential to measure complex three-dimensional flows that are optically difficult to access without modification of the experimental setup. Possible applications are optimizations of fuel cells for reducing the consumption of fossil energy.

The correction of dynamic aero-optical aberration of optical dome at different altitudes using wavefront coding

In our previous published paper [Opt. Commun. 490, 126876 (2021)], we proposed a method to correct the optical dome’s aero-optical aberration using wavefront coding (WFC). The simulation results were carried out under a fixed flight altitude. However, because the missile tracking the target is a dynamic process, the image quality deterioration of the aero-dynamically heated dome is diverse under different altitude. Therefore, it is of great significance to study the correction effect of WFC on dynamic aero-optical aberration of optical dome at different altitudes, which is performed in our new manuscript. The simulation results demonstrate that the WFC could effectively correct the dynamic aero-optical aberration and improve the accuracy of imaging guidance. These results confirm the possibility of the application of WFC imaging technology in missile-borne optical detection systems.

Conformal dome aberration correction based on the integrated design of inner surface and fixed corrector

The ellipsoidal conformal dome is commonly used at present, which is a balanced choice between the aero-dynamic performance and optical imaging performance of the optical dome. The paraboloidal dome has superior aerodynamic performance, but the dynamic aberration correction is far more difficult than that of the ellipsoidal dome which has also become a bottleneck restricting on its application. This paper proposed a dynamic aberration correction method based on integrated design of inner surface and fixed corrector, for which realized the design of the dynamic aberration correction of the paraboloidal dome. Based on the analysis of the Zernike aberration characteristics of the paraboloidal dome, we focused on controlling of the Zernike aberration coefficients Z4, Z5, Z8 and Z9 to execute the dynamic aberration correction of the inner surface. Then, after deriving the Wassermann-Wolf equation (W-W equation) of the paraboloidal conformal dome, the initial surface shape of the fixed corrector was numerically solved combining with the ray tracing method, and the following dynamic aberration correction of the fixed corrector was carried out. Finally, with a specific design example of mid-wave infrared optical system with the paraboloidal dome, the dynamic aberration correction method for the paraboloidal conformal dome optical system was verified. These results show that the design method is feasible to solve the dynamic aberration correction difficulties of the paraboloidal dome, and is of great significance to promote the applications of the paraboloidal conformal dome.

Fast dynamic correction algorithm for model-based wavefront sensorless adaptive optics in extended objects imaging.

A major concern for wavefront sensorless adaptive optics (WFSless AO) is how to improve the algorithm's efficiency which is critical for dynamic aberration correction. For extended objects and dynamic aberration, a typical model-based WFSless AO algorithm is called "3N" which uses three image measurements to estimate each aberration mode and then corrects it immediately. The three images include an initial aberrated image and two biased images with deliberately introduced predetermined positive or negative modal aberrations. In this paper, an improved algorithm called "2N" that requires only one biased image is proposed. The reduction of one biased image is achieved by the estimation of a parameter that is considered unknown in the 3N algorithm. It is demonstrated that the 2N algorithm can achieve convergence with less image measurements and have better performance in dynamic correction.