Dynamic Aberration Correction Research Articles

Dynamic correction of optical aberrations for height-independent selective laser induced etching processing strategies.

Optical aberrations are a critical issue for tight focusing and high precision manufacturing with ultrashort pulsed laser radiation in transparent media. Controlling the wave front of ultrashort laser pulses enable the correction of low order phase front distortion and significantly enhances the simplification of laser-based manufacturing of 3D-parts in glass. The influence of system-inherent, dominating aberrations such as spherical and astigmatic aberrations affect the focal area, the beam caustic and therefore the focus intensity distribution. We correct these aberrations by means of a spatial light modulator (SLM) for various processing depths in glass thickness of up to 12 mm. This flexible aberration correction significantly simplifies the process control and scanning strategies for the selective laser induced etching process. The influence on the selectivity is investigated by comparing the three different focus conditions of the intrinsic microscope objective aberration corrected, the aberrated and the SLM aberration corrected beam profile. The previously necessary pulse energy adjustment for different z positions in the glass volume is compensated via SLM aberration correction in the end. Furthermore, the spatial extend of the modified and etched area is investigated. In consequence, a simplified scan strategy and depth-independent processing parameters can be achieved for the selective laser induced etching process.

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.

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.

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.

Correction of resonant optical scanner dynamic aberrations using nodal aberration theory.

The rapid oscillation of galvanometric resonant optical scanners introduces linear astigmatism that degrades transverse resolution, and in confocal systems, also reduces signal [V. Akondi et al., Optica 7, 1506, 2020]. Here, we demonstrate correction of this aberration by tilting reflective or refractive optical elements for a single vergence or a vergence range, with and without the use of an adaptive wavefront corrector such as a deformable mirror. The approach, based on nodal aberration theory, can generate any desired third order aberration that results from tilting or decentering optical surfaces.

Adaptive optics in super-resolution microscopy.

Fluorescence microscopy has become a routine tool in biology for interrogating life activities with minimal perturbation. While the resolution of fluorescence microscopy is in theory governed only by the diffraction of light, the resolution obtainable in practice is also constrained by the presence of optical aberrations. The past two decades have witnessed the advent of super-resolution microscopy that overcomes the diffraction barrier, enabling numerous biological investigations at the nanoscale. Adaptive optics, a technique borrowed from astronomical imaging, has been applied to correct for optical aberrations in essentially every microscopy modality, especially in super-resolution microscopy in the last decade, to restore optimal image quality and resolution. In this review, we briefly introduce the fundamental concepts of adaptive optics and the operating principles of the major super-resolution imaging techniques. We highlight some recent implementations and advances in adaptive optics for active and dynamic aberration correction in super-resolution microscopy.

Dynamic Aberration Correction for Conformal Dome Based on Free-Form Lens Array

Dynamic Aberration Correction for Conformal Dome Based on Free-Form Lens Array

Dynamic aberration correction for conformal aircraft windows using the inner window surface and a fixed lens array.

A static solution to dynamic aberrations for conformal aircraft windows with a large range of look angles is reported. The solution uses the inner window surface and a fixed lens array near the image plane to correct the dynamic window aberrations at different look angles. The inner window surface is first used to balance the dynamic aberrations of the full field of regard. Then a lens array is implanted in front of the image, and the dynamic aberrations are corrected by designing the surface shape and rotation direction of each lens unit in the array. The principle of the solution is discussed, and a design example shows that the solution can realize the dynamic aberration correction introduced by the conformal window with a field of regard of ±42∘. Compared to other dynamic or static correctors, this solution takes into account the large field of regard, the light weight and the stability of the optoelectronic system.

Dynamic aberration correction via spatial light modulator (SLM) for femtosecond direct laser writing: towards spherical voxels.

Optical aberrations are a type of optical defect of imaging systems that hinder femtosecond direct laser write machining by changing voxel size and aspect ratio in different sample depths. We present an approach of compensating such aberrations using a liquid crystal spatial light modulator (SLM). Two methods for correcting are explored. They are based on backward ray tracing and Zernike polynomials. Experiments with a long focal distance lens (F = 25 and 50 mm) and microscope objective (100x, 0.9 NA) have been conducted. Specifically, aberration-free structuring with voxels of a constant aspect ratio of 1-1.5 is carried out throughout a 1 mm thick sample. Results show potential in simplifying direct laser writing and enabling new architectures made possible by near-spherical voxels.

Decentralized Youla parameterized adaptive regulation with application to surface shape control for magnetic fluid deformable mirrors

The magnetic fluid deformable mirror (MFDM) is a new type of wavefront corrector which has advantages compared to conventional wavefront correctors, such as higher stroke and lower fabrication cost. In this paper, a Youla (Q) parameterized adaptive regulation approach is proposed for the MFDM to correct both random and deterministic dynamic aberrations based on the dynamic model of the MFDM. The parameter Q is tuned online by a recursive least squares (RLS) algorithm so that it converges to the desired value. An adaptive optical system with a prototype MFDM is setup to verify the effectiveness of the adaptive controller. The control performance is also compared with a H∞ controller to show the improvement of the wavefront residue RMS error. The result illustrates that the proposed adaptive control method can effectively control the mirror surface for the unknown dynamic aberration correction, especially to the deterministic disturbances in adaptive optics systems.

Effect of Simulated and Real Spherical and Astigmatism Defocus on Visual Acuity and Image Quality Score.

Image simulation is a useful and efficient tool to explore the impact of spherical and astigmatic blur on visual acuity (VA) and image gradation. It could help to design new optical corrections more efficiently and rapidly. The purpose of this study was to compare the effects of simulated (convolution by an artificial eye) and real spherical and astigmatic defocus on VA and image gradation. Experiments were performed under highly controlled conditions: dynamic correction of the subjects' aberrations at 1 Hz and application of an artificial pupil. In experiment 1, Landolt C VA was measured in various conditions of spherical and astigmatism defocus. The amounts of spherical or positive astigmatic defocus oriented at 45° that gives a Landolt C VA of 0.0, 0.2, and 0.5 logMAR were measured in experiment 2. In experiment 3, the subjects scored the quality of the perceived image (three high-contrast 0.4 logMAR letters) with a five-item continuous grading scale. Simulated blur was always more detrimental than optical blur. We measured a difference of 0.08 ± 0.03 and 0.11 ± 0.05 logMAR between both conditions, respectively, in presence of spherical and astigmatism defocus. An average ± standard deviation difference of 0.16 ± 0.06 D (i.e., spherical defocus) and 0.24 ± 0.15 D (i.e., astigmatism defocus) was observed between simulated and real optics blur to provide a given VA. The differences of image quality score between both conditions were, respectively, 15.13 ± 9.63 and 13.33 ± 4.83 for spherical and astigmatism defocus. Most of the differences were statistically significant. We observed a difference of about 20 and 35% between simulated and real optics blur, respectively, in presence of spherical and astigmatism blur. However, the difference between both methods remains equal to or below the clinically significant difference.

Universal membrane-based tunable liquid lens design for dynamically correcting spherical aberration over user-defined focal length range.

A novel membrane-based tunable liquid aspherical lens design capable of dynamically reducing spherical aberration over certain focal length tuning range is presented. Different from conventional treatment using elastic membrane with uniform thickness, in current case, the membrane's cross-section is designed to be a plano-convex shape with well-defined aspherical contour. A brand new design flow combining optical ray-tracing and mechanical finite element analysis is especially developed, in which through properly selecting the initial focal length and the center membrane thickness with respect to particularly designed figure of merit (FOM), the membrane can be flexibly optimized to achieve dynamic spherical aberration correction capability over the desired focal length range. For proof of concept demonstration, a tunable aspherical lens with clear aperture of 4 mm is designed. Compared with conventional counterpart, after being individually optimized using current design strategy, lenses with distinctly reduced spherical aberration have been successfully achieved over different focal length tuning ranges. Besides, no special refractive index matching between the filling liquid and the membrane is required, making current design more practical in real applications.

Bit error rate reduction of optical communication by means of Tip/Tilt correction

Abstract One of the parameters for evaluating the free space optical link is BER. The atmospheric turbulence increases BER of telecommunication link. One of the BER reduction methods is the use of correction of dynamic aberrations caused by atmospheric turbulence. In this paper first, by using phase plates, atmospheric turbulence has been simulated. In order to determine the refractive index structure parameter, fluctuation of angle of arrival and fitting curve into probability density function of scintillation beam have been applied. The obtained value of C n 2 , from two methods is of order of 10−14 m − 2 ∕ 3 , which are in good agreement with each other. In the following, BER of free space telecommunication link before and after correction has been measured using the correction of tip and tilt low order aberration in the presence of simulated turbulence at laboratory. In this paper, by indirect method, BER was measured by probability density function of fluctuation beam. Before correction, the value of BER was 3 . 302 × 1 0 − 4 that which reduced to 4 . 276 × 1 0 − 7 after the correction.

Dynamic Aberration Correction for Conformal Window of High-Speed Aircraft Using Optimized Model-Based Wavefront Sensorless Adaptive Optics.

For high-speed aircraft, a conformal window is used to optimize the aerodynamic performance. However, the local shape of the conformal window leads to large amounts of dynamic aberrations varying with look angle. In this paper, deformable mirror (DM) and model-based wavefront sensorless adaptive optics (WSLAO) are used for dynamic aberration correction of an infrared remote sensor equipped with a conformal window and scanning mirror. In model-based WSLAO, aberration is captured using Lukosz mode, and we use the low spatial frequency content of the image spectral density as the metric function. Simulations show that aberrations induced by the conformal window are dominated by some low-order Lukosz modes. To optimize the dynamic correction, we can only correct dominant Lukosz modes and the image size can be minimized to reduce the time required to compute the metric function. In our experiment, a 37-channel DM is used to mimic the dynamic aberration of conformal window with scanning rate of 10 degrees per second. A 52-channel DM is used for correction. For a 128 × 128 image, the mean value of image sharpness during dynamic correction is 1.436 × 10−5 in optimized correction and is 1.427 × 10−5 in un-optimized correction. We also demonstrated that model-based WSLAO can achieve convergence two times faster than traditional stochastic parallel gradient descent (SPGD) method.

Dynamic Correction of Higher-Order Deflection Aberrations in the Environmental SEM

Dynamic Correction of Higher-Order Deflection Aberrations in the Environmental SEM

Multifractality in steady-state accommodation is robust to dynamic correction of aberrations using adaptive optics

When fixating on a stationary object, the human eye exhibits microfluctuations in accommodation. Changes in the magnitude of these fluctuations reflect changes in the accommodation control system. We used adaptive optics to determine the effect of monochromatic aberration dynamics on the control of steady-state accommodation of four subjects. The subjects viewed a stationary stimulus at 2 D while selective Zernike aberrations were corrected. The fluctuations in accommodation were characterised using a wavelet-based multifractal formalism approach. We found that for all subjects, and all experimental conditions, the accommodative fluctuations were multifractal. For one subject, we found that the width of the multifractal spectrum was statistically significantly larger when even-order aberrations were corrected as compared to no aberrations corrected. Hence, in general, for the subjects tested, the multifractal nature of steady-state accommodation control is unaffected by the manipulation of monochromatic aberration dynamics. Averaging across all subjects and experimental conditions, the mean spectrum was right-skewed with a most frequently occurring Hölder exponent of 0.31 ± 0.08. Future applications of multifractal analysis to accommodation control are discussed.

Live imaging using adaptive optics with fluorescent protein guide-stars

Spatially and temporally dependent optical aberrations induced by the inhomogeneous refractive index of live samples limit the resolution of live dynamic imaging. We introduce an adaptive optical microscope with a direct wavefront sensing method using a Shack-Hartmann wavefront sensor and fluorescent protein guide-stars for live imaging. The results of imaging Drosophila embryos demonstrate its ability to correct aberrations and achieve near diffraction limited images of medial sections of large Drosophila embryos. GFP-polo labeled centrosomes can be observed clearly after correction but cannot be observed before correction. Four dimensional time lapse images are achieved with the correction of dynamic aberrations. These studies also demonstrate that the GFP-tagged centrosome proteins, Polo and Cnn, serve as excellent biological guide-stars for adaptive optics based microscopy.