Correction Of Wavefront Distortion Research Articles

Wavefront distortion correction in scanning tunneling microscope image.

We report an algorithm to identify and correct distorted wavefronts in atomic resolution scanning tunneling microscope images. This algorithm can be used to correct nonlinear in-plane distortions without prior knowledge of the physical scanning parameters, the characteristics of the piezoelectric actuator, or individual atom positions. The 2D image is first defined as a sum of sinusoidal plane waves, where a nonlinear distortion renders a curve for an otherwise ideal linear wavefront. Using the Fourier transforms of local areas of the image, the algorithm generates a wavefront vector field. The identified wavefronts are subsequently linearized for each plane wave without changing lattice orders, giving rise to distortion corrections. Our algorithm is complementary to conventional post-processing algorithms that require prior detection of real space features, which can also be used to correct nonlinear distortions in 2D images acquired by other microscopy techniques.

Analysis of satellite-to-ground quantum key distribution with adaptive optics

Future quantum communication infrastructures will rely on both terrestrial and space-based links integrating high-performance optical systems engineered for this purpose. In space-based downlinks in particular, the loss budget and the variations in the signal propagation due to atmospheric turbulence effects impose a careful optimization of the coupling of light in single-mode fibers required for interfacing with the receiving stations and the ground networks. In this work, we perform a comprehensive study of the role of adaptive optics (AO) in this optimization, focusing on realistic baseline configurations of prepare-and-measure quantum key distribution, with both discrete and continuous-variable encoding, and including finite-size effects. Our analysis uses existing experimental turbulence datasets at both day and night time to model the coupled signal statistics following a wavefront distortion correction with AO, and allows us to estimate the secret key rate for a range of critical parameters, such as turbulence strength, satellite altitude and ground telescope diameter. The results we derive illustrate the interest of adopting advanced AO techniques in several practical configurations.

Two-photon excitation fluorescence in ophthalmology: safety and improved imaging for functional diagnostics.

Two-photon excitation fluorescence (TPEF) is emerging as a powerful imaging technique with superior penetration power in scattering media, allowing for functional imaging of biological tissues at a subcellular level. TPEF is commonly used in cancer diagnostics, as it enables the direct observation of metabolism within living cells. The technique is now widely used in various medical fields, including ophthalmology. The eye is a complex and delicate organ with multiple layers of different cell types and tissues. Although this structure is ideal for visual perception, it generates aberrations in TPEF eye imaging. However, adaptive optics can now compensate for these aberrations, allowing for improved imaging of the eyes of animal models for human diseases. The eye is naturally built to filter out harmful wavelengths, but these wavelengths can be mimicked and thereby utilized in diagnostics via two-photon (2Ph) excitation. Recent advances in laser-source manufacturing have made it possible to minimize the exposure of in vivo measurements within safety, while achieving sufficient signals to detect for functional images, making TPEF a viable option for human application. This review explores recent advances in wavefront-distortion correction in animal models and the safety of use of TPEF on human subjects, both of which make TPEF a potentially powerful tool for ophthalmological diagnostics.

A Novel SPGD Algorithm for Wavefront Sensorless Adaptive Optics System

Stochastic parallel gradient descent (SPGD) is the most frequently used optimization algorithm for correcting wavefront distortion in the wavefront sensorless adaptive optics(WFS-Less AO)system. However, the convergence speed of the SPGD algorithm becomes slow rapidly as increasing of distortion, and the probability of falling into local optimum is rising owing to the fixed gain coefficient. It cannot meet the requirement of real-time wavefront distortion correction. Therefore, a novel algorithm is proposed in this paper, called as adaptive gain stochastic parallel gradient descent (AGSPGD) based on the AMSGrad optimizer in the deep learning, to improve the convergence speed of the algorithm and to reduce the probability of falling into local optimum. The AGSPGD algorithm adopts the first-order moment and the second-order moment of the performance index, which are combined to dynamically adjust the gain. The numerical simulations are completed in this paper. The results of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$D/r_0=2.5$</tex-math></inline-formula> conditions demonstrate that the AGSPGD can reduce the number of iterations by 25%, and the probability of the algorithm falling into local optimum is reduced from 16% to 4%. In addition, the AGSPGD still outperforms the SPGD as <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$D/r_0$</tex-math></inline-formula> increasing.

Study on the Difference of Wavefront Distortion on Beams Caused by Wavelength Differences in Weak Turbulence Region

In dual-wavelength free-space optical communication systems, the wavefront distortion differences caused by the wavelength difference of the signal and beacon lights cannot be completely corrected. In this study, according to the method of geometric optics, the relationship between the wavefront phases of the signal and beacon lights is analyzed by establishing a mathematical model of the cross-correlation ratio of the arrival-angle fluctuation and phase relationship of different Gaussian-beam wavelengths under weak turbulence near the surface. The numerical results show that after Gaussian beams of different wavelengths propagate through the same atmospheric channel, the cross-correlation number of the arrival-angle fluctuation decreases with an increase in the wavelength difference, waist radius, and turbulence intensity, and increases with an increase in propagation distance. The beam-wavefront phase difference increases with an increasing wavelength difference. Finally, a wavefront distortion correction experiment of a dual-wavelength adaptive optical system verified the correctness of the wavefront phase-difference relationship between the signal light and beacon light established in this study.

Wavefront distortion correction of superposed optical vortices based on deep multi-branch compensation network

Optical vortices with orbital angular momentum play a crucial role in many fields such as target detection, quantum entanglement, and space optical communication. However, the wavefront distortion of optical vortices caused by atmospheric turbulence during free-space transmission is a major obstacle to practical applications. In this work, a deep-learning-based method is proposed for wavefront correction of distorted superposed optical vortices under various turbulence intensities. First, the Zernike polynomial expansion method is used to numerically simulate the atmospheric turbulence phase screen conforming to the Kolmogorov statistical law which assumes that turbulence is locally uniform and isotropic, in which the first 10 Zernike polynomials are adopted. Then, according to the distinct wavefront distortion features of different polynomials, a deep multi-branch compensation network (DMCN) is designed to adaptively and more accurately learn the mapping relationship between the intensity distribution profile of distorted optical vortices and the corresponding turbulent phase screen. The distorted superposed optical vortices dataset for network training is obtained by experimental measurement. Finally, the turbulence compensation screen predicted by the trained DMCN is verified experimentally and the results show that our wavefront distortion correction method based on DMCN can accurately predict the turbulent compensation screen and improve the mode purity of superposed optical vortices to more than 80% within 40 ms when using a workstation computer under various turbulence intensities, which has apparent advantages compared with traditional algorithms.

A Neural Network-Based Method for Fast Capture and Tracking of Laser Links between Nonorbiting Platforms.

In this paper, a neural network approach is used to conduct an in-depth study and analysis of the fast capture tracking method for laser links between nonorbiting platforms. The experimental platform of the convolutional neural network- (CNN-) based free-space optical communication (FSO) wavefront correction system is built indoors, and the wavefront distortion correction performance of the CNN-based wavefront correction method is investigated. The experimental results show that the coupling power loss can be reduced to small after the CNN method correction under weak and strong turbulence. The accuracy of the above model is verified by comparing the simulation data with the experimentally measured data, thus realizing the coordinate decoupling of the coarse aiming mechanism and weakening the influence of structural factors on the tracking accuracy of the system. The tracking correlation equation of the influence of beam far-field dynamic characteristics on the tracking stability of the link is established, and the correlation factor variance of beam far-field dynamic characteristics is used to provide a quantitative analysis method for the evaluation and prediction of the comprehensive performance of the link tracking stability. The influence of beam divergence angle, wavefront distortion, detector accuracy, and atmospheric turbulence disturbance on the correlation factor variance of beam far-field dynamic characteristics of laser link beacons is modelled, and the link tracking stability optimization method is proposed under the requirement of link tracking accuracy, which provides an effective solution analysis method to realize the improvement of laser link tracking stability.

Adaptive optimization of SPGD method in wavefront distortion correction of space light

Adaptive optimization of SPGD method in wavefront distortion correction of space light

Nesterov-accelerated adaptive momentum estimation-based wavefront distortion correction algorithm

In order to improve the wavefront distortion correction performance of the classical stochastic parallel gradient descent (SPGD) algorithm, an optimized algorithm based on Nesterov-accelerated adaptive momentum estimation is proposed. It adopts a modified second-order momentum and a linearly varying gain coefficient to improve iterative stability. It integrates the Nesterov momentum term and the modified Adam optimizer to further improve the convergence speed, correct the direction of gradient descent in a timely fashion, and avoid falling into local extremum. Besides, to demonstrate the algorithm's performance, a wavefront sensorless adaptive optics system model is established using a 6×6 element deformable mirror as wavefront corrector. Simulation results show that, compared with the SPGD algorithm, the proposed algorithm converges faster, and its Strehl ratio after convergence is nearly 6.25 times that of the SPGD algorithm. Also, the effectiveness and superiority of the proposed algorithm are verified by comparing with two existing optimization algorithms.

Wavefront Distortion Correction for the Non-Uniform-Intensity Light Based on Extreme Learning Machine

This paper aims to employ a neural network method of extreme learning machine to solve the problem of laser beam cleanup under the dynamic non-uniform-intensity distribution. This neural network is used to fit the corresponding nonlinear relationship between the slope information detected by the wavefront sensor and the recovery voltage of deformable mirror under the dynamic non-uniform-intensity distribution. The simulation results show that the beam quality after correction is improved from 1.7 to 1.3 times diffraction limit. And the residual wavefront after correction for the proposed method has been reduced by 55%, while the direct gradient method is 17%.

基于改进型SPGD算法的涡旋光波前畸变校正

基于改进型SPGD算法的涡旋光波前畸变校正

A method of wavefront distortions correction for an atmospheric optical link with a small volume of information transmitted through a service channel

The paper describes a method of wavefront distortion correction in a turbulent atmosphere, which allows reducing the volume of information transmitted through a service channel. The correction is carried out with a transparency whose phase mask is calculated by a simple three-layer neural network by intensity distribution obtained at the photoreceiver. The architecture of the network is constructed so that the amount of data transferred over the service channel is reduced to 30 parameters, using which a corrective mask is then constructed.

基于小波分形插值的波前畸变校正

基于小波分形插值的波前畸变校正

Adaptive optics microspectrometer for cross-correlation measurement of microfluidic flows.

.Mapping flows in vivo is essential for the investigation of cardiovascular pathologies in animal models. The limitation of optical-based methods, such as space-time cross correlation, is the scattering of light by the connective and fat components and the direct wave front distortion by large inhomogeneities in the tissue. Nonlinear excitation of the sample fluorescence helps us by reducing light scattering in excitation. However, there is still a limitation on the signal-background due to the wave front distortion. We develop a diffractive optical microscope based on a single spatial light modulator (SLM) with no movable parts. We combine the correction of wave front distortions to the cross-correlation analysis of the flow dynamics. We use the SLM to shine arbitrary patterns of spots on the sample, to correct their optical aberrations, to shift the aberration corrected spot array on the sample for the collection of fluorescence images, and to measure flow velocities from the cross-correlation functions computed between couples of spots. The setup and the algorithms are tested on various microfluidic devices. By applying the adaptive optics correction algorithm, it is possible to increase up to 5 times the signal-to-background ratio and to reduce approximately of the same ratio the uncertainty of the flow speed measurement. By working on grids of spots, we can correct different aberrations in different portions of the field of view, a feature that allows for anisoplanatic aberrations correction. Finally, being more efficient in the excitation, we increase the accuracy of the speed measurement by employing a larger number of spots in the grid despite the fact that the two-photon excitation efficiency scales as the fourth power of this number: we achieve a twofold decrease of the uncertainty and a threefold increase of the accuracy in the evaluation of the flow speed.

受激布里渊散射波前畸变校正仿真实验

受激布里渊散射波前畸变校正仿真实验

Carbazole-based bi-functional photorefractive polyphosphazene for correcting the laser wavefront distortion

Carbazole-based polyphosphazene containing nitro azo chromophore moieties was synthesized first. The photorefractive polyphosphazene was prepared to optical qualitative films and used to correct the laser wavefront distortion under the room temperature without external electric field, pre-poling and addition agent. The results indicate that the photorefractive polyphosphazene film can correct both the diffraction distortion and phase distortion of the laser wavefront. At the same time the high-resolution laser wavefront distortion correction can be achieved. Further, as the result of the effectively correction of the diffraction distortion, the polymer film may be applied in microscale direct image.

相干光照明主动成像波前畸变的数字式快速校正

相干光照明主动成像波前畸变的数字式快速校正

激光主动成像中散斑噪声对波前畸变校正性能的影响

激光主动成像中散斑噪声对波前畸变校正性能的影响

Freeform corrector for laser with large aperture YAG:ND3+ active element

The results of transmitted wavefront distortion correction are presented for a YAG:ND 3+ active element with a diameter 45 mm. Halftone mask and proximity printing were used for fabrication of the freeform corrector. Experimental results show a three-fold decrease of the wavefront distortion. Because the corrector presented a high damage threshold, it can be used with high power laser systems.

Auto-alignment in four-pass amplifier with wavefront correction system

In order to solve the interaction problem between the wavefront distortion correction and optical alignment in a high-power laser system, especially in a multi-pass amplification system, based on fresnel diffraction integral theory, the beam propagation model of 310 mm×310 mm aperture beam in four-pass amplifier is built by analyzing the properties of this system. The problem of excessive amount of calculation, caused by high resolution in traditional calculation, is solved by coordinate transformation method, Using this model, the differences of far-field accuracy among centroid method, circle fitting and pure phase matching filter in beam with wavefront distortion are discussed; what influence the wavefront correction has on focal spot position is analyzed. This article provides an important basis for optimizing collimation adjustment programs in four-pass amplifier.