Corneal wave aberration from videokeratography: accuracy and limitations of the procedure

A procedure to calculate the wave aberration of the human cornea from its surface shape measured by videokeratography is presented. The wave aberration was calculated as the difference in optical path between the marginal rays and the chief ray refracted at the surface, for both on- and off-axis objects. The corneal shape elevation map was obtained from videokeratography and fitted to a Zernike polynomial expansion through a Gram-Schmidt orthogonalization. The wave aberration was obtained also as a Zernike polynomial representation. The accuracy of the procedure was analyzed. For calibrated reference surface elevations, a root-mean-square error (RMSE) of 1 to 2 microm for an aperture 4-6 mm in diameter was obtained, and the RMSE associated with the experimental errors and with the fitting method was 0.2 microm. The procedure permits estimation of the corneal wave aberration from videokeratoscopic data with an accuracy of 0.05-0.2 microm for a pupil 4-6 mm in diameter, rendering the method adequate for many applications.     

Fabrication of compact turning mirrors in silicon-on-insulator materials

A turning mirror is a key component in compact optical waveguide devices and high-density integrated optics. An improved two-step method for fabrication of high-quality, compact turning mirrors in silicon-on-insulator materials is proposed. First, inductively coupled plasma etching is applied to produce the turning mirror, which keeps the turning mirror compact; then silicon wet anisotropic etching is applied to enhance the quality of the turning mirror by of its polishing surface, correcting its orientation, and improving the verticality. The shape of the turning mirror fabricated by the two-step method is hexagonal or octagonal, matching the optical field of the rib waveguide well. A large effective mirror size to reflect light waves and reduced shrinkage of the mirror size during etching guarantee that a mirror produced by this two-step method will be more compact than previously designed mirrors.     

Φ1.05 m轻量化反射镜设计与制造

针对Ф1.05 m空间光学系统主镜的设计指标要求,提出了轻量化反射镜结构优化设计的新方法,并建立了反射镜结构自动化仿真分析与优化设计平台,基于此平台确定了性能优异的主镜结构设计方案。主镜重量小于50 kg,轻量化率已接近国外先进水平; 主镜在三球铰支撑下的第一阶模态频率为361.2 Hz,自由状态下的一阶非零模态频率为501.9 Hz; 在1 ℃均匀温度变化下,不去离焦和去除离焦之后的面形RMS分别为0.55 nm和0.10 nm; 主镜在30g过载加速度作用下的最大应力为16.1 MPa,均满足设计要求。采用目前最先进的第三代大口径反射镜加工工艺,路线为超精密铣磨—小磨头数控研抛—离子束精修,实现主镜面形误差的确定性去除。为保证面形检测结果的天地一致性,发展了重力卸载技术和面形误差数据后处理技术,剔除重力和其他系统误差对检测的影响。主镜最终面形精度达到0.011λ RMS,获得了高精度的光学面形,也证明了方案的合理性。     

Cryogenic optical performance of the ASTRO-F SiC telescope

The lightweight cryogenic telescope on board the Japanese infrared astronomical satellite, ASTRO-F, which is scheduled to be launched early in 2006, forms an F/6 Ritchey-Chretien system with a primary mirror of 710 mm in diameter. The mirrors of the ASTRO-F telescope are made of sandwich-type silicon carbide (SiC) material, comprising a porous core and a chemical-vapor-deposited coat of SiC on the surface. To estimate the optical performance of the flight model telescope, the telescope assembly was tested at cryogenic temperatures, the total wavefront errors of which were measured by an interferometer from outside a liquid-helium chamber. As a result, the wavefront error obtained at 9 K shows that the imaging performance of the ASTRO-F telescope is diffraction limited at a wavelength of 6.2 microm, which is a little worse than our original goal of diffraction-limited performance at 5.0 microm.     

Measurement of a fiber-end surface profile by use of phase-shifting laser interferometry

We describe a laser interferometric system in which two objectives are used to measure surface profile on a connectorized fiber-end surface. By the use of the proposed illumination design a He-Ne laser as a point light source is transformed to an extended light source, which is beneficial to localize interference fringe pattern near the test surface. To obtain an optimal contrast of the interference fringe pattern, the flat mirror with an adjustable reflection ratio is used to suit different test surfaces. A piezoelectric transducer attached on the reference mirror can move precisely along the optical axis of the objective and permits implementation of four-step phase-shifting interferometry without changing the relative position between the CCD sensor and the test surface. Therefore, an absolutely constant optical magnification can be accurately kept to capture the interference fringe patterns resulting from a combination of light reflected from both the reference flat mirror and the test surface. The experimental result shows that surface profile on a fiber-end with surface features such as a small fiber diameter of 125 microm and a low reflection ratio of less than 4% are measurable. Measurements on a standard calibration ball show that the accuracy of the proposed setup is comparable with that of existing white-light interferometers and stylus profilometers.     

应力抛光技术加工抛物面的实验研究

大口径非球面加工技术一直是先进光学制造领域研究的前沿课题,本文开展了以大型非球面应力抛光技术(SMP)为核心的相关先进光学制造技术的研究.研究了应力抛光技术的原理及算法,以加工一块口径为φ314mm,F/7的抛物面镜为例,验证应力抛光技术的合理性和有效性.采用干涉仪检测抛光结束的抛物面其峰值(PV)为3.317λ,均方根(rms)为0.489λ.结果表明,应力抛光技术能够以较高精度、快速地形成旋转对称的抛物面,其面形误差满足或接近于非球面面形的精度要求.     

薄反射镜主动光学实验系统

用口径400mm、厚12mm的薄反射镜作为实验镜进行了主动光学实验.支撑系统由背部12个主动支撑点和3个固定支撑点组成,主动支撑点采用由压电陶瓷促动器和压力传感器组成的力促动器,用于控制实验镜面形,固定支撑点用于控制实验镜的定位.通过Shack-Harmann波前传感器测量镜面面形并拟合出Zernike像差,用阻尼最小二乘法计算出校正力,通过PID算法闭环控制各促动器施加力的过程.通过主动校正,将初始支撑状态下的1.16λ(λ=632.8nm)RMS面形精度校正到0.07λRMS,优于镜面抛光后的0.1λRMS.     

Open-loop control of a MEMS deformable mirror for large-amplitude wavefront control

A method is introduced for predicting control voltages that will generate a prescribed surface shape on a MEMS deformable mirror. The algorithm is based upon an analytical elastic model of the mirror membrane and an empirical electromechanical model of its actuators. It is computationally simple and inherently fast. Shapes at the limit of achievable mirror spatial frequencies with up to 1.5 microm amplitudes have been achieved with less than 15 nm rms error.     

Adaptive control of a micromachined continuous-membrane deformable mirror for aberration compensation

The nonlinear response and strong coupling of control channels in micromachined membrane deformable mirror (MMDM) devices make it difficult for one to control the MMDM to obtain the desired mirror surface shapes. A closed-loop adaptive control algorithm is developed for a continuous-surface MMDM used for aberration compensation. The algorithm iteratively adjusts the control voltages of all electrodes to reduce the variance of the optical wave front measured with a Hartmann-Shack wave-front sensor. Zernike polynomials are used to represent the mirror surface shape as well as the optical wave front. An adaptive experimental system to compensate for the wave-front aberrations of a model eye has been built in which the developed adaptive mirror-control algorithm is used to control a deformable mirror with 19 active channels. The experimental results show that the algorithm can adaptively update control voltages to generate an optimum continuous mirror surface profile, compensating for the aberrations within the operating range of the deformable mirror.     

Three-dimensional optical high-resolution profiler with a large observation field: foot arch behavior under low static charge studies

Our aim is to describe a method for detecting small deformations from a three-dimensional (3D) shape of large lateral dimensions. For this purpose the measurement method is based on the simultaneous utilization of several 3D optical systems and the phase-shifting technique. In this way, the following problems appear: optical distortion due to the large field observed, nonlinear phase-to-height conversion, conversion of image coordinates into object coordinates for each 3D optical system, and coordinate unification of all optical systems. The resolution is 50 microm with a field of view of 320 mm x 150 mm. We used this system to study the 3D human foot arch deformation under low loads in vivo. First results indicate the hysteresis behavior of the human foot under a low load (50 to 450 N).     

Plasma treatment for restoration of dielectric multilayer mirrors in short-wavelength free-electron lasers

Dielectric multilayer mirrors, degraded through irradiation by high-energy undulator radiation, were successfully restored by surface treatment with RF-induced O(2) plasma. The mirror loss, which had been increased up to ~1000 parts in 10(6) (ppm) through the mirror degradation, was drastically reduced to ~100 ppm during the treatment. Such a mirror-restoration technique has been desired especially in short-wavelength free-electron lasers (FEL's), because the laser gain is so small that even a mirror loss as small as ~1000 ppm interferes with the FEL oscillation. The mirror degradation is most likely caused by the deposition and doping of carbon atoms onto the dielectric surface. The surface analysis by the x-ray photoelectron spectroscopy revealed that the plasma treatment effectively removed the carbon contamination covering the mirror surfaces without serious surface damage by high-energy particles from the plasma.     

光学镜面化学镀银中的敏化工艺研究

介绍了光学镜面化学镀银工艺的基本流程及对膜层质量影响较大的敏化工序的原理和工艺,并对该工序中的喷水量进行了理论计算和实验验证。对一块Φ365mm口径的次镜进行镀膜实验。实验结果表明,均匀喷雾35s左右能洗净敏化液中的Cl-,并使水解生成的Sn(OH)2胶体均匀残留于镜面,镀制的Ag膜层质量较好。膜层检测结果为:反射率为92%,厚度为60nm,对面形的影响:PV=λ/45,RMS=λ/250,满足该次镜的检测精度要求。     

On-line fourier transform infrared detection in capillary electrophoresis

The coupling of Fourier transform infrared (FT-IR) spectroscopy as a new on-line detection principle in capillary electrophoresis (CE) is presented. To overcome the problem of total IR absorption by the fused-silica capillaries that are normally employed in CE separations, a micromachined IR-transparent flow cell was constructed. The cell consists of two IR-transparent CaF2 plates separated by a polymer coating and a titanium layer producing an IR detection window, 150 microm wide and 2 mm long, with a path length of 15 microm. The IR beam was focused on the detection window using an off-axis parabolic mirror in an optical device (made in-house) attached to an external optical port of the spectrometer. The connections between the fused-silica capillaries and the flow cell were made by a small O-ring of UV-curing epoxy adhesive on the sharply cut ends of the capillaries, allowing the capillaries to be easily replaced. Aqueous solutions comprising mixtures of adenosine, guanosine, and adenosine monophosphate were used to test the system's performance. Conventional on-line UV detection was employed to obtain reference measurements of analytes after the IR detection flow cell. The limit of FT-IR detection for all analytes (in absolute amounts) was in the nano- to picogram range corresponding to concentrations in the low-millimolar range.     

Parabolic liquid mirrors in optical shop testing

A parabolic liquid mirror obtained by the rotation of a mercury bath around a vertical axis has been built and its optical surface characteristics measured to demonstrate that it can be used in optical shop testing as a reference surface. A linear Hartmann test allowed us to check that the focal length is well related to the rotation velocity, following the theory, and that no spherical aberration is present, as assumed by previous authors. The spherical aberration has been found to be smaller than λ/50 at 633 nm. An interferometric test of the mirror compared with a null lens gave information about the quality of the optical surface for which the rms wave-front error, when the random errors are averaged, is ~λ/25. Because modifying the mirror diameter is cheap and fast and adjusting its focal length within a large range is straightforward, the parabolic liquid mirror can become a highly adaptable tool in optical metrology. In particular, it can be used in optical shop testing as a reference surface to test null correctors, to check any system developed to control the shape of large parabolic or quasiparabolic top-quality solid-state mirrors, or to make holographic references of such surfaces.     

Detection of short-lived electrogenerated species by Raman microspectrometry

Raman microprobe spectrometry has been applied to the characterization of unstable species generated electrochemically at a microelectrode (radius in the 10 microm range). The ability of the spectroelectrochemical method to detect short-lived intermediates is directly related to its capability to probe small volumes. Raman microprobe spectrometry is appropriate for electrochemical applications because it allows the analysis of approximately 1 microm3 of solution. In spectroelectrochemical experiments, such a volume corresponds to a reaction layer of 1 microm thickness. Potentially, this technique can allow the observation of species with lifetimes of the order of 1 ms. To enhance the capabilities of this spectroscopic technique, we utilized it in combination with steady-state voltammetry at a microelectrode, to increase the concentration of unstable intermediates near the electrode surface. To determine the detection limit of this combined technique, we varied the base concentration as a means for varying the lifetime the radical cation electrogenerated from 9,10-dichloroanthracene. Well-resolved resonance Raman spectra were obtained for this radical cation when the lifetime was > or = 0.1 ms. This short time resolution achieved with micro-Raman spectroelectrochemistry makes this technique a powerful tool for the characterization of short-lived intermediates that are generated electrochemically in solution.     

提高大口径金属主镜面形精度的方法

分析了影响Ｒｉｔｃｈｅｙ－Ｃｈｒｅｉｔｉｅｎ光学系统中金属主反射镜面形精度因素，采用有限元法对立交易的加工过程及其安装进行了模拟，指出提高主镜的面形镜度，既要合理主镜材料的热处理工艺，也要对加工参数进行控制。良好的稳定化处理可以有效地消除材料内部的残余应力，保证主镜尺寸的稳定性。提高加工基准的精度，并采用组合加工镜面，可以大大提高主镜的面形精度，最后，给出了主镜的干涉仪检测结果。     

Adaptive Control of a Micromachined Continuous Membrane Deformable Mirror for Aberration Compensation

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Immobilized diaphorase surfaces observed by scanning electrochemical microscope with shear force based tip-substrate positioning

Imaging of a coimmobilized diaphorase and albumin surface was investigated by scanning electrochemical microscopy (SECM) with shear force based tip-substrate distance control. A microelectrode tip was attached to a commercially available tuning fork to detect the shear force between the microelectrode tip and the surface. We used the standing approach mode, which repeats an approach and retraction at each data point of the surface to obtain simultaneous current and topographic images. To check the performance of our SECM system, we imaged a platinum-patterned array electrode and a diaphorase/albumin coimmobilized glass surface. Since the system acquires current when the tip is retracted to a desired distance, this mode is useful for a relatively large microelectrode (approximately 10 microm) and for scanning a large area (few hundreds of micrometers). Furthermore, by retracting the tip when the tip moves laterally to the next data point to avoid contact between the tip and sample surface, we successfully imaged the surface without destroying its morphology.     

TMC系统主镜的平板补偿自准检验方法

针对TMC(三镜卡塞格林)光学系统凹椭球面主镜的检验,本文提出了一种平板补偿的自准检验方法.该方法克服了OFFENER零位补偿器本身性能难以检验,只能靠加工和装调保证精度的问题.针对TMC主镜面形与抛物面接近的特点,对平板补偿的自准检验方案进行了理论分析,利用二次非球面的法线像差性质推导了检验光路中球差的表达式,并利用最小剩余球差进行补偿平板参数的确定.对某TMC系统顶点曲率1 589mm,二次系数-0.983,口径φ500 mm的主镜检验,设计了尺寸仅为φ34.2 min×9.126 5 mm的补偿平板.在ZEMAX中计算的结果表明,经平板补偿后的检验光路波像差RMS值为0.003λ,可满足TMC主镜的高精度检验要求.对补偿平板的检验方法,以及加工和使用中应当采取的措施也进行了考虑.与常用检验方法相比,本文方法具有容易对平板性能进行检验,成本低、研制周期短等优点.     

Hydrodynamics of rotating liquid mirrors. I. Synchronous disturbances

The effects of axis alignment errors, planetary rotation, and tidal forces on rotating liquid mirrors are analyzed. These produce a surface distortion that decreases exponentially with distance inward from the rim with a characteristic length l= square root of 3hf/2, where h is the thickness of the fluid and f is the focal length. Even a small tilt of the rotation axis can produce a significant deformation of the optical surface. The maximum surface height error is 3epsilonl, where epsilon is the tilt angle and is typically of the order of 1.5 microm for a 1 arc sec tilt. The main optical effect of the wave is to produce a ring, with angular diameter 6epsilon, offset by half of the diameter in the direction opposite the tilt. This diamond ring aberration can be avoided by accurate alignment of the rotation axis or by masking the outer few centimeters of the mirror. Planetary rotation produces a small deformation of the order of 100 nm for a 10 m telescope at low latitude on Earth. This deformation can be canceled by a small tilt of the rotation axis. Tidal forces produced by the Moon, or by the Earth in the case of a lunar telescope, produce an inconsequential, subnanometer, surface deformation.