共查询到20条相似文献,搜索用时 15 毫秒
1.
We introduce beam-quality metrics for adaptive wave-front control that permit estimation of the degree of laser beam energy concentration on a remotely located extended object based upon the backscattered wave intensity distribution at the receiver. A 37-control-channel adaptive optics system with phase correction of the output wave capable of operating in the presence of speckle-field-induced strong intensity modulation is presented. System operation is based on optimization of the speckle-field-based metric by the stochastic parallel gradient descent technique. Results demonstrate that adaptive wave-front correction using speckle-field-based beam-quality metrics can significantly improve laser beam concentration on extended objects. 相似文献
2.
We demonstrate correction of laser wave-front distortions by use of an adaptive-optical technique based on a light valve. The setup consists of an achromatic and adjustable-sensitivity wave-front sensor and a wave-front corrector relying on an optically addressed liquid-crystal spatial light modulator. Experimental results with strongly aberrated beams focused close to the diffraction limit are presented for the cw regime. Additional experiments with pulses and measurement of damage thresholds show that this approach is relevant for spatial phase correction of ultraintense laser pulses. 相似文献
3.
Hermann B Fernández EJ Unterhuber A Sattmann H Fercher AF Drexler W Prieto PM Artal P 《Optics letters》2004,29(18):2142-2144
Merging of ultrahigh-resolution optical coherence tomography (UHR OCT) and adaptive optics (AO), resulting in high axial (3 microm) and improved transverse resolution (5-10 microm) is demonstrated for the first time to our knowledge in in vivo retinal imaging. A compact (300 mm x 300 mm) closed-loop AO system, based on a real-time Hartmann-Shack wave-front sensor operating at 30 Hz and a 37-actuator membrane deformable mirror, is interfaced to an UHR OCT system, based on a commercial OCT instrument, employing a compact Ti:sapphire laser with 130-nm bandwidth. Closed-loop correction of both ocular and system aberrations results in a residual uncorrected wave-front rms of 0.1 microm for a 3.68-mm pupil diameter. When this level of correction is achieved, OCT images are obtained under a static mirror configuration. By use of AO, an improvement of the transverse resolution of two to three times, compared with UHR OCT systems used so far, is obtained. A significant signal-to-noise ratio improvement of up to 9 dB in corrected compared with uncorrected OCT tomograms is also achieved. 相似文献
4.
The generation of harmonics from the interaction of an ultra-intense laser pulse and a gas jet is strongly influenced by the
intensity and shape of the laser beam. In this work we present a sensor-less optimization procedure of the harmonics yield
based on the use of an adaptive mirror. Because of the limited repetition rate of the laser source, we used a resistive actuator-deformable
mirror which allows a rapid convergence to the optimal laser beam correction without a wave-front measurement. Our approach
demonstrated that this kind of deformable mirror was able to enhance the harmonic yield by a factor of two in about 40 acquisitions. 相似文献
5.
By using adaptive optics to correct the wave-front distortion of a 21-fs, 0.7-mJ, 1-kHz laser, we are able to focus the pulses to a 1-mum spot with an f/1 off-axis parabolic mirror. The peak intensity at the focal position is 1.5x10(18) W/cm(2) , which is to the authors' knowledge the first demonstration of generating relativistic intensity at a kilohertz repetition rate. 相似文献
6.
WANG Zhaohua JIN Zhan ZHENG Jiaan WANG Peng WEI Zhiyi & ZHANG Jie Laboratory of Optical Physics Institute of Physics Chinese Academy of Sciences Beijing China 《中国科学G辑(英文版)》2005,48(1):122-128
We developed an adaptive optics system to correct the wave-front distortion of an intense fs laser beam from our multi-TW laser system, Jiguang II. In this paper, the instruments of the adaptive optical system are described and the experimental results of the closed-loop wave-front correction are presented. A distorted laser wave-front of 20 wavelengths of P-V values was corrected to 0.15 wavelength of P-V values. The beam quality of the laser system varies from 3.5 diffraction limit to 1.5 diffraction limit. 相似文献
7.
Villoresi P Bonora S Pascolini M Poletto L Tondello G Vozzi C Nisoli M Sansone G Stagira S De Silvestri S 《Optics letters》2004,29(2):207-209
We present a method for the optimization of high-order harmonic generation based on wave-front correction of the driving laser beam. The technique exploits wave-front adaptive control by means of a deformable mirror, governed by an optimization procedure. 相似文献
8.
9.
10.
We derive the bit error rate (BER) of inter-satellite laser communication (lasercom) links with on-off-keying systems in the presence of both wave-front aberrations and pointing error, but without considering the noise of the detector. Wave-front aberrations induced by receiver terminal have no influence on the BER, while wave-front aberrations induced by transmitter terminal will increase the BER. The BER depends on the area S which is truncated out by the threshold intensity of the detector (such as APD) on the intensity function in the receiver plane, and changes with root mean square (RMS) of wave-front aberrations. Numerical results show that the BER rises with the increasing of RMS value. The influences of Astigmatism, Coma, Curvature and Spherical aberration on the BER are compared. This work can benefit the design of lasercom system. 相似文献
11.
Dynamic wave-front correction is applied before each shot on a 100-TW, 30-J/300-fs high-power laser facility by use of an adaptive-optics system. This system allows us to increase the repetition rate of high-energy lasers while maintaining excellent and constant beam focusability with a Strehl ratio of >0.75 despite the amplifiers' not being in thermal equilibrium. The best results in terms of the highest Strehl ratio and intensities are obtained when locking the system on wave-front sensing after pulse recompression. 相似文献
12.
在惯性约束聚变系统中,改进G-S算法设计的连续相位板能够对波前发生畸变的激光进行束匀滑处理,以改善远场分布。由于连续相位板对不同畸变状态的波前进行处理后的效果不一样,因此针对连续相位板的束匀滑容差能力进行了系统分析。鉴于畸变光束的传输特性,采用波前均方根梯度来量化波前畸变量,定量计算了不同畸变光经过匀滑处理后的远场光强分布情况。并比较了不同入射畸变光通过连续相位板后的远场焦斑顶部均匀性,结果表明:当入射波前畸变的均方根梯度小于0.32 wave/mm 时,连续相位板具有很好的束匀滑效果。 相似文献
13.
Y. L. Wang Z. W. Lu Y. Li P. Wu X. M. Fan Z. X. Zheng W. M. He 《Applied physics. B, Lasers and optics》2010,99(1-2):257-261
The strong wave-front aberrations compensated by stimulated Brillouin scattering phase conjugate mirror (SBS-PCM) in a high power laser were investigated experimentally. The wave-front fluctuation of the 10 Hz 500 mJ Nd:YAG laser is 0.5λ. Transmitting through a random phase plate (RPP), it increases to 8.6λ. While using SBS-PCM in place of a high reflection mirror, the distortion induced by the RPP is compensated, and the wave-front fluctuation becomes 0.9λ. At the same time, obvious breakdown phenomena in the SBS cell were observed, and the reflectivity is unstable. A rotating wedge plate is introduced into the phase conjugating mirror to make the focus of the SBS cell rotate and optical breakdown is avoided effectively. The reflectivity becomes stable around about 70% and the instability is changed from ±4.1% to ±0.9%. Besides, the compensated wave-front fluctuation is only 0.6λ, which is near to the original wave-front distribution. The results show that the reflectivity of the SBS-PCM is very high and stable when there are no other nonlinear effects such as optical breakdown. Thus the compensating effects for strong wave-front errors are perfect. 相似文献
14.
用于人眼视网膜成像照明的激光消散斑技术研究 总被引:6,自引:2,他引:4
以近红外激光(808 nm)作为人眼波前像差探测的信号光和视网膜成像的照明光,液晶空间光调制器(LCOS)作为波前校正器,用哈特曼波前探测器探测人眼像差,构建了人眼像差自适应校正的视网膜成像系统.利用模拟眼分析了激光散斑对相机成像的影响和对哈特曼波前探测器进行像差探测的影响,同时验证了利用旋转散射体的方法消除激光散斑的可行性和有效性;用活体人眼进行了激光消散斑前后照明视网膜进行成像的对比实验,并进一步利用自适应光学技术实现了对人眼像差的动态校正和视网膜细胞的连续成像.校正后,系统波前像差的均方根值小于0.1λ.实验表明激光消散斑后可以同时作为人眼像差探测的信号光和视网膜成像的照明光,从而可以进行连续自适应校正和成像. 相似文献
15.
Our work presents a theoretical analysis of aberration properties of a simple single-channel deformable mirror from both the aspect of modeling the shape of the mirror reflecting surface and the mechanisms of wave-front correction using such mirror. The proposed mirror can be used for a compensation of rotationally symmetrical wavefronts, e.g. focusing of optical beams, adaptive change of resonator parameters in laser technology, phase shifting, etc. The detailed analysis of possibilities of wave-front correction was performed. 相似文献
16.
自适应光学系统随机并行梯度下降控制算法实验研究 总被引:10,自引:3,他引:7
随机并行梯度下降算法是一种极具应用潜力的自适应光学系统控制算法,具有不依赖波前传感器直接对系统性能指标进行优化的特点。基于32单元变形镜、CCD成像器件等建立自适应光学系统随机并行梯度下降控制算法实验平台。考察算法增益系数和扰动幅度对校正效果和收敛速度的影响,验证随机并行梯度下降算法的基本原理。实验结果表明参量选取合适的情况下,随机并行梯度下降控制算法对静态或慢变化的畸变波前具有较好的校正能力。根据实验结果分析了影响随机并行梯度下降算法校正速度的主要因素。 相似文献
17.
A novel adaptive wave-front correction system based on an all-optical feedback interferometer is described. In this system the two-dimensional output fringe intensity from a Mach-Zehnder interferometer with large radial shear is optically fed back to an optically addressed phase-only liquid-crystal spatial light modulator. Consequently, without a separate aberration-free reference wave, the modulator phase approximates the conjugate of the interferometer phase that is directly related to the phase of the input aberrated wave front, so this system is applicable in adaptive optics. We successfully achieved real-time correction of aberrated wave fronts: A diffraction pattern that was seriously distorted because of aberrations was transformed into a diffraction-limited spot immediately after the feedback loop was closed. 相似文献
18.
Thomas Weyrauch Mikhail A. Vorontsov 《Journal of Optical and Fiber Communications Reports》2004,1(4):355-379
Refractive index inhomogeneities of the turbulent air cause
wave-front distortions of optical waves propagating through the
atmosphere, leading to such effects as beam spreading, beam
wander, and intensity fluctuations (scintillations). These
distortions are responsible for severe signal fading in free-space
optical communications systems and therefore compromise link
reliability. Wave-front distortions can be mitigated, in
principle, with adaptive optics, i.e., real-time wave-front
control, reducing the likeliness of signal fading. However,
adaptive optics technology, currently primarily used in
astronomical imaging, needs to be adapted to the requirements of
free-space optical communication systems and their specific
challenges.In this chapter we discuss a non-conventional adaptive optics
approach that has certain advantages with respect to its
incorporation into free-space optical communication terminals. The
technique does not require wave-front measurements, which are
difficult under the strong scintillation conditions typical for
communication scenarios, but is based on the direct optimization
of a performance quality metric, e.g., the communication signal
strength, with a stochastic parallel gradient descent (SPGD)
algorithm.We describe an experimental adaptive optics system that consists
of a beam-steering and a higher-resolution wave-front correction
unit with a 132-actuator MEMS piston-type deformable mirror
controlled by a VLSI system implementing the SPGD algorithm. The
system optimizes the optical signal that could be coupled into a
single-mode fiber after propagating along a 2.3-km near-horizontal
atmospheric path. We investigate characteristics of the
performance metric under different atmospheric conditions and
evaluate the effect of the adaptive system. Experiments performed
under strong scintillation conditions with beam-steering only as
well as with higher-resolution wave-front control demonstrate the
mitigation of wave-front distortions and the reduction of signal
fading. 相似文献
19.
一种新型人眼波前像差测量补偿系统的研究 总被引:1,自引:1,他引:1
离焦是人眼中最主要的像差之一,离焦量过大会严重影响人眼波前像差的测量及矫正精度。为了消除离焦在此方面带来的影响,设计了带有补偿装置的人眼波前像差测量及矫正系统。重点分析了该系统的原理、结构和工作流程。运用Hartmann-Shack波前传感器测量了人眼波前像差,并使用变形反射镜对人眼波前像差进行矫正。对模拟人眼矫正离焦前后的光斑点阵图和波前三维重构图进行了对比分析。研究表明,通过离焦补偿系统对模拟人眼的离焦量进行矫正,使被测量人眼的离焦量由2.020D和-2.035D分别减小到0.011D和-0.007D;通过调焦系统,使显示器上显示出的人眼光斑点阵图由模糊变清晰,提高了信标光在人眼眼底的成像质量。 相似文献
20.
Druon F Chériaux G Faure J Nees J Nantel M Maksimchuk A Mourou G Chanteloup JC Vdovin G 《Optics letters》1998,23(13):1043-1045
Wave-front correction and focal spot improvement of femtosecond laser beams have been achieved, for the first time to our knowledge, with a deformable mirror with an on-line single-shot three-wave lateral shearing interferometer diagnostic. Wave-front distortions of a 100-fs laser that are due to third-order nonlinear effects have been compensated for. This technique, which permits correction in a straightforward process that requires no feedback loop, is also used on a 10-TW Ti:sapphire-Nd:phosphate glass laser in the subpicosecond regime. We also demonstrate that having a focal spot close to the diffraction limit does not constitute a good criterion for the quality of the laser in terms of peak intensity. 相似文献