表面波布拉格声光互作用耦合波方程的研究

定义了压电晶体的增劲声光系数，它反映压电晶体中声光、电光和压电效应共同作用的结果。从参量互作用基本理论出发，同时考虑声光效应、电光效应和压电效应三个因素，用一个压电增劲声光系数来表示三种因素的共同作用，导出表面波声光布拉格互作用的耦合波方程。并求解得出相应衍射效率的计算公式。该式说明在弱声光互作用条件下，衍射导光波强度与超声功率成正比。表面波声光器件具有体积小、工作稳定、能耗小、易于集成等优点。可以用作光偏转器、光调制器、滤光器。在光通信以及各类实时信号处理，如相关、卷积、频谱分析、矩阵光计算等领域具有广泛的应用前景。     

Adaptive optics optical coherence tomography for retina imaging

When optical coherence tomography (OCT) is used for human retina imaging, its transverse resolution is limited by the aberrations of human eyes. To overcome this disadvantage, a high resolution imaging system for living human retina, which consists of a time domain OCT system and a 37-elements adaptive optics (AO) system, has been developed. The AO closed loop rate is 20 frames per second, and the OCT has a 6.7-μm axial resolution. In this paper, this system is introduced and the high resolution imaging results for retina are presented.     

A high precision phase reconstruction algorithm for multi-laser guide stars adaptive optics

Adaptive optics(AO) systems are widespread and considered as an essential part of any large aperture telescope for obtaining a high resolution imaging at present.To enlarge the imaging field of view(FOV),multi-laser guide stars(LGSs) are currently being investigated and used for the large aperture optical telescopes.LGS measurement is necessary and pivotal to obtain the cumulative phase distortion along a target in the multi-LGSs AO system.We propose a high precision phase reconstruction algorithm to estimate the phase for a target with an uncertain turbulence profile based on the interpolation.By comparing with the conventional average method,the proposed method reduces the root mean square(RMS) error from 130 nm to 85 nm with a 30% reduction for narrow FOV.We confirm that such phase reconstruction algorithm is validated for both narrow field AO and wide field AO.     

Acousto-optic modulation in magnetised diffusive semiconductors

The modulation of an intense electromagnetic beam induced by the acousto-optic (AO) effect has been analysed in a transversely magnetised semiconductor-plasma medium. The effect of carrier diffusion on the threshold field and gain profile of the modulated wave has been extremely investigated using coupled mode theory. The origin of the AO interaction is assumed to lie in the induced nonlinear diffusion current density of the medium. By considering the modulation process as a four wave parametric interaction an expression for effective third-order AO susceptibility describing the phenomena has been deduced. The modulation is greatly modified by propagation characteristics such as dispersion and diffraction due to dielectric relaxation of the acoustic mode. The threshold pump field and the steady state growth rates are estimated from the effective third-order polarisation in the plasma medium. Analytical estimation reveals that in the presence of enhanced diffusion due to excess charge carriers the modulated beam can be effectively amplified in a dispersionless acoustic wave regime. The presence of an external dc magnetic field is found to be favourable for the onset of diffusion induced modulational amplification of the modulated wave in heavily doped regime. Received 5 November 2001     

Polarization changes and beam profile deformation of light during acousto-optic interaction in isotropic media

A spatial Fourier transform approach is proposed to investigate the effects of polarization changes and beam profile deformation of light during acousto-optic (AO) interaction in isotropic media. The behaviour of the total scattered optical fields inside the AO cell can be properly described by a vector wave equation of which the permittivity is perturbed by an acoustic wave propagating inside the medium. In the Bragg regime, using a spatial Fourier transform approach, two coupled differential equations can be derived from the wave equation to depict AO interaction in the spatial frequency domain. Analytic solutions, which comprise the effects of changing polarization, beam deformation and propagating diffraction, can be found from the coupled equations. Detailed numerical simulations, including Fourier transforming the incident light profile to calculate the spectra of the scattered light beams and, hence, their profiles in space using the inverse transform, are presented.     

Adaptive-optics ultrahigh-resolution optical coherence tomography

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.     

37-element solar adaptive optics for 26-cm solar fine structure telescope at Yunnan Astronomical Observatory

A 37-element solar adaptive optics （AO） system was built and installed at the 26-cm solar fine structure telescope of Yunnan Astronomical Observatory. The AO system is composed of a fine tracking loop with a tip/tilt mirror and a correlation tracker, a high-order correction loop with a 37-element deformable mirror, a correlating Shack-Hartmann wavefront sensor based on the absolute difference algorithm, and a real time controller. The system was completed on Sep. 28, 2009 and was used to obtain AO-corrected high-resolution solar images. The contrast and resolution of the images are clearly improved after wavefront correction by AO. To the best of out knowledge, this system is the first solar AO system in China.     

声光自适应信号处理技术在扩频通信中的应用

研究了声光滤波的工作原理,用布拉格器件作模拟抽头延迟线完成横向滤波。讨论了LMS自适应滤波的基本方法,给出了声光自适应LMS滤波的实现方法并用于扩频通信的窄带干扰抑制中。对扩频通信进行干扰抑制的滤波过程通常是一个自适应过程,采用声光自适应滤波技术,不仅能抑制窄带干扰,而且能提高系统的处理增益和分辨率。     

声电光效应的耦合波方程理论

将声光效应与电光效应的耦合波方程相结合，统一为声电光效应的耦合波方程，并对之进行求解，给出声电光效应的衍射效率公式。     

High resolution mosaic image of capillaries in human retina by adaptive optics

Adaptive optics (AO) has been proved as a powerful means for high resolution imaging of human retina.Because of the pixel number of charge-coupled device (CCD) camera, the field of view is limited to 1°.In order to have image of capillaries around vivo human fovea, we use mosaic method to obtain high resolution image in area of 6°× 6°. Detailed structures of capillaries around fovea with resolution of 2.3μm are clearly shown. Comparison shows that this method has a much higher resolution than current clinic retina imaging methods.     

Evidence for preferential reactivity of the atomic oxygen with hydrogenated diamond (111) facets

Chemical bonding configuration of the adsorbed oxygen on diamond polycrystalline hydrogenated surface was investigated by high resolution electron energy loss spectroscopy (HR-EELS). Hot filament chemical vapor deposited diamond films with sub-micron grain size have been exposed in-situ to thermally activated atomic oxygen (AO) and annealed in ultra-high vacuum in the range of 600–900 °C. HR-EELS features comparison of as-deposited and AO exposed diamond surface as a function of thermal annealing suggests that AO preferentially adsorbs on hydrogenated (111) facets keeping hydrogenated (100) ones intact.     

Nonlinear effects in acousto-optic imaging

Acousto-optic (AO) imaging is a promising technique that is able to reveal optical properties in the millimeter range inside scattering media by tagging the photon paths with an ultrasonic beam. To increase both the contrast and the resolution of the AO images, we have explored the possibility of using the nonlinear response of the speckle modulation. Variation of the second-harmonic signal as the square of the ultrasonic amplitude has been found, and strong reduction of the tagged zone size has been demonstrated.     

Lucky averaging: quality improvement of adaptive optics scanning laser ophthalmoscope images

Adaptive optics (AO) has greatly improved retinal image resolution. However, even with AO, temporal and spatial variations in image quality still occur due to wavefront fluctuations, intraframe focus shifts, and other factors. As a result, aligning and averaging images can produce a mean image that has lower resolution or contrast than the best images within a sequence. To address this, we propose an image postprocessing scheme called "lucky averaging," analogous to lucky imaging [J. Opt. Soc. Am. 68, 1651 (1978)] based on computing the best local contrast over time. Results from eye data demonstrate improvements in image quality.     

Adaptive optics in astronomy

Since Galileo’s first observations in 1609, telescopes have grown dramatically in size. Larger telescopes collect more light, allowing astronomers to detect fainter sources and to look further back in time towards the birth of the universe. The angular resolution of these telescopes, however, has been limited by turbulence in the earth’s atmosphere. This limitation can be dramatically reduced with the use of adaptive optics (AO) to measure and correct the blurring introduced by atmospheric turbulence. AO is now routinely used for science observations on the world’s largest telescopes and is providing a much more detailed view of our universe.     

自适应光学系统几种随机并行优化控制算法比较

 直接对系统性能指标进行优化是自适应光学系统中一种重要的波前畸变校正方法,选择合适的随机并行优化控制算法是该技术成功实现的关键。以32单元变形镜为校正器,基于多种随机并行优化算法建立自适应光学系统仿真模型。从算法的收敛速度、校正效果、局部极值3个方面对遗传算法、单向扰动随机并行梯度下降、双向扰动随机并行梯度下降及模拟退火算法进行了比较。仿真结果表明,遗传算法收敛速度太慢,不适用于需要实时控制的自适应光学系统;双向扰动随机并行梯度下降算法收敛速度、校正效果要优于单向扰动随机并行梯度下降,且能够适应各种情况下的扰动电压;模拟退火几乎以概率1收敛到全局极值附近,且收敛速度是上述算法中最快的。     

Spin‐Orbit Coupling in All‐Electron Mixed Basis Approach

In the evaluation of the spin‐orbit coupling (SOC), the use of the L · S formula is invalid in the interatomic region where the effective potential is not spherically symmetric. This problem occurs in the LCAO, LMTO, and APW methods, while the plane‐wave pseudopotential and PAW methods cannot treat the spin‐orbit splitting (SOS) of core orbitals. To avoid these problems, the all‐electron mixed basis approach is adopted, which uses both plane waves (PWs) and atomic orbitals (AOs) as a basis set. The general form S · ?V × p can be used for PWs, while the standard form L · S can be used for AOs, which are well localized inside the non‐overlapping atomic sphere in the spherical potential region and composed of the numerical radial function on a logarithmic radial mesh and analytic cubic harmonics. The explicit formula of the AO–AO, PW–AO, and PW–PW matrix elements of the SOC for spin‐polarized systems is presented. In particular, the AO–AO matrices are explicitly derived for p, d, and f orbitals. The method is applied to the SOS of core and valence levels in X‐ray photoelectron spectra. The results are in excellent agreement with the available experimental data, which suggests the validity of the present method.     

High sensitivity adaptive optics control of laser beam based on interferometric phase-front detection

We present an upgrade of an adaptive optics (AO) system for the control of geometrical fluctuations in a laser beam, based on the interferometric detection of phase front. Acoustic isolation and suitable design of optical system make the present system very sensitive to laser beam geometrical fluctuations and can be an interesting step toward the active correction of the small perturbations of the input beam of gravitational wave interferometric detectors.     

双倒易边界元拓展于模拟生物组织中热波传播问题

1前言双倒易边界元是一个新发展的纯边界积分数值方法＊，乞今在热波传播问题的应用尚未见到报导。对热波在工程材料中传播的反射和衰减特性已作过一些研究，但它们均局限在快速温度变化及极低温情形．生物组织热波传播问题的研究则尚未见到报导。我们曾用有限差分法考察过一维情况下热波在不同时刻下的演化情况，算例中波形存在锯齿这是由于有限差分误差所致．热波问题的数值模拟，需要对热波及其分解、叠加和反射能进行准确定位与精确捕获。在已发表的有限差分泡括采用了TVD高精度算法）数值解中报道了热波前沿存在严重的数值脉动。边界…     

组合变形镜对板条固体MOPA激光波前畸变校正（英）

提出了一种利用组合变形镜校正板条MOPA固体激光器像差的方法,并通过实验验证其有效性。通过将一个11单元的一维变形镜和一个67单元的二维变形镜组合,有效降低了单个二维变形镜波前校正过程中驱动器间的电压差,从而提高了二维变形镜的使用安全性,并在一定程度上改善了校正后波前畸变的空间分布,降低了波前畸变残差。实验结果表明,一维变形镜与二维变形镜的组合能高效地校正板条MOPA固体激光器的波前畸变,波前残差均方根值小于0.08 m,远场光束质量因子可达1.67。     

自适应光学系统的数值模拟：噪音和探测误差的效应

噪音和探测误差是影响自适应光学系统性能的三个主要因素之一。噪音和探测误差使哈特曼－夏克（Hartmann-Shack)波前传感器所测得的华斜量产生误差,进而影响整个自适应光学系统的性能,建立了对噪声和探测误差对哈特曼－夏克波前传感器的影响进行数值模拟的理论模型,编制了计算程序,与已有的激光大气传输与自适应光学系统的计算程序相衔接,进行了模拟计算,对有限的离散采样,读出噪音和光子噪音的效应作了数值模拟研究,获得了一些对于实际的自适应光学系统的最佳设计有价值的结果。