Optical methods for monitoring the micro-geometry of a surface

Optical methods of checking for defects in the exterior part of an object on the basis of micro-geometric features and of the surface are considered by means of an analysis of the radiation reflected by the surface, where the information parameters of this radiation are related by means of a parameter R _q . The advantages in terms of the sensitivity of these optical methods over other methods are evaluated on the basis of a theorem proved in the present article. The theorem demonstrates that the mean values of the derivatives of the roughness parameters R _q and R _a depend on the length of the estimator.     

补偿器优化设计法线模拟反射面的确定

补偿器是大口径非球面主镜补偿检验的关键元件。随着主镜口径和相对口径的增大,由于高阶像差的影响,补偿器的优化结果与初始结构偏离也相应增大,此时若能用法线模拟反射面代替主镜,将检验时的自准光路简化为单次通过补偿器的光路,则优化过程将大大简化,且易获得好的补偿效果。用法线模拟反射面代替主镜时,光源位于主镜顶点曲率中心,模拟面的系数由主镜参数决定。设计结果表明,这种模拟面对F/1的主镜法线都有很好的符合精度。     

Error correction for free-space optical interconnects: space-time resource optimization

We study the joint optimization of time and space resources withinfree-space optical interconnect (FSOI) systems. Both analyticaland simulation results are presented to support this optimization studyfor two different models of FSOI cross-talk noise: diffraction froma rectangular aperture and Gaussian propagation. Under realisticpower and signal-to-noise ratio constraints, optimum designs based onthe Gaussian propagation model achieve a capacity of 2.91 x10(15) bits s(-1) m(-2), while therectangular model offers a smaller capacity of 1.91 x10(13) bits s(-1) m(-2). We alsostudy the use of error-correction codes (ECC) within FSOIsystems. We present optimal Reed-Solomon codes of various length, and their use is shown to facilitate an increase in both spatialdensity and data rate, resulting in FSOI capacity gains in excess of8.2 for the rectangular model and 3.7 for the Gaussian case. Atolerancing study of FSOI systems shows that ECC can provide toleranceto implementational error sources. We find that optimally codedFSOI systems can fail when system errors become large, and we present acompromise solution that results in a balanced design in time, space, and error-correction resources.     

Optical multilayers for LED-based surface plasmon resonance sensors

We address a structure for surface plasmon resonance (SPR) sensing supporting a symmetric bound surface plasmon, which results in a SPR feature narrower by a factor of 2 compared with that for the conventional configuration. We demonstrate that it enables a low-cost and low-power-consumption LED to be used as a polychromatic light source, which leads to a decrease in the sensor cost and an increase in the sensor miniaturization potential. Further, we show that these advancements are not at the expense of sensor performance in terms of its sensitivity and resolution. We show that the sensor can be designed to have similar sensitivity and even better resolution compared with those for a conventional configuration.     

An adaptive response surface method for crashworthiness optimization

Response surface-based design optimization has been commonly used for optimizing large-scale design problems in the automotive industry. However, most response surface models are built by a limited number of design points without considering data uncertainty. In addition, the selection of a response surface in the literature is often arbitrary. This article uses a Bayesian metric to systematically select the best available response surface among several candidates in a library while considering data uncertainty. An adaptive, efficient response surface strategy, which minimizes the number of computationally intensive simulations, was developed for design optimization of large-scale complex problems. This methodology was demonstrated by a crashworthiness optimization example.     

Adaptive improved response surface method for reliability-based design optimization

Reliability-based design optimization (RBDO) requires the evaluation of probabilistic constraints (or reliability), which can be very time consuming. Therefore, a practical solution for efficient reliability analysis is needed. The response surface method (RSM) and dimension reduction (DR) are two well-known approximation methods that construct the probabilistic limit state functions for reliability analysis. This article proposes a new RSM-based approximation approach, named the adaptive improved response surface method (AIRSM), which uses the moving least-squares method in conjunction with a new weight function. AIRSM is tested with two simplified designs of experiments: saturated design and central composite design. Its performance on reliability analysis is compared with DR in terms of efficiency and accuracy in multiple RBDO test problems.     

Automatic parameter optimization of the local model fitting method for single-shot surface profiling

The local model fitting (LMF) method is a single-shot surface profiling algorithm. Its measurement principle is based on the assumption that the target surface to be profiled is locally flat, which enables us to utilize the information brought by nearby pixels in the single interference image for robust LMF. Given that the shape and size of the local area is appropriately determined, the LMF method was demonstrated to provide very accurate measurement results. However, the appropriate choice of the local area often requires prior knowledge on the target surface profile or manual parameter tuning. To cope with this problem, we propose a method for automatically determining the shape and size of local regions only from the single interference image. The effectiveness of the proposed method is demonstrated through experiments.     

Optical coating design approaches based on the needle optimization technique

Design approaches for optical thin films that recognize the key role of a design's total optical thickness are presented. These approaches are based primarily on the needle optimization technique but also utilize other optimization procedures. Using the described design approaches, an optical coating engineer can obtain a set of theoretical designs with different combinations of principal design metrics (merit function value, number of layers, and total design optical thickness); this extends opportunities for choosing the most practical and manufacturable design. We also show that some design problems have multiple solutions with nearly the same combinations of principal design metrics.     

Optical phase-shift detection of surface plasmon resonance

A heterodyne optical measurement system for studying the phase shift of surface plasmon resonance (SPR) is presented. The system utilizes a frequency-stabilized Zeeman laser as a detection light source and is suitable for real-time phase measurement in SPR-sensing applications. The phase shift in an angular dispersion SPR excitation setup was measured ranging from +180 degrees to -120 degrees around the SPR excitation region. The experimental results fit well with the theoretical analysis. Compared with the reflection coefficient variation that is widely investigated in SPR studies, phase shift is estimated to provide a higher sensitivity to sensor systems and more information about the resonance phenomenon.     

Pyrometry inside an arc furnace using a ray-tracing correction for surface emissivity

A general method using a ray-tracing analysis has been developed to improve the accuracy of surface temperatures measured by pyrometry inside a furnace. This method allows temperature correction for enclosed non-ideal black-body surfaces, having temperature gradients, by taking into account the contributions from the reflected fraction of the pyrometer field-of-view. The development has been made possible by the recent availability of internal furnace scanning pyrometry technology for complete temperature profile measurements inside furnaces. The correction method can be expressed in terms of the solution of a square matrix having a dimension corresponding to the number of spatially resolved points in the temperature profile, with the number of non-zero elements depending on the number of field-of-view reflective surface bounce points used in the analysis. The utility of this method is demonstrated for the correction of 19-point temperature profiles measured inside a dc arc furnace. Reflective contributions from two, three, and four field-of-view surface bounce points are considered. Generally, the lower the surface emissivity and the higher the temperatures, the more bounces needed in the analysis. It is shown that there can be significant corrections to internal furnace temperatures measured by pyrometry when temperature gradients exist.     

Optical remote sensing of surface roughness through the turbulent atmosphere

Using a CO(2), cw, coherent lidar, we have measured the surface roughness of diffuse targets through 1000 m of turbulent atmosphere. The technique measures the phase fluctuations of the speckle field at the receiver and relates the measured phase variance to the surface roughness. Measurements were made with aluminum targets that had been sandblasted with 8-, 16-, and 30-grit material and also with a flame-sprayed aluminum target. It was found that a linear relationship exists between the standard deviation (SD) of the unwrapped phase fluctuations and the SD of the target surface-height fluctuations. Good results were obtained with modest transmitter power and small receiver optics in just a few seconds of averaging time.     

Phase aberration correction using ultrasound radiation force and vibrometry optimization

We describe a phase aberration correction method that uses dynamic ultrasound radiation force to harmonically vibrate an object using amplitude modulated continuous wave ultrasound. The phase of each element of an annular array transducer is adjusted to maximize the radiation force and obtain optimal focus of the ultrasound beam. The maximization of the radiation force is performed by monitoring the velocity of scatterers in the focus region. We present theory that shows focal optimization with radiation force has a well-behaved cost function. Experimental validation is shown by correction of manual defocusing of an annular array as well as correcting for a lens-shaped aberrator placed near the transducer. A Doppler laser vibrometer and a pulse-echo Doppler ultrasound method were used to monitor the velocity of a sphere used as a target for the transducer. By maximizing the radiation force-induced vibration of scatterers in the focal region, the resolution of the ultrasound beam can be recovered after aberration defocusing.     

A lexicographic weighted Tchebycheff approach for multi-constrained multi-objective optimization of the surface grinding process

In this article a multi-objective mathematical model is developed to minimize total time and cost while maximizing the production rate and surface finish quality in the grinding process. The model aims to determine optimal values of the decision variables considering process constraints. A lexicographic weighted Tchebycheff approach is developed to obtain efficient Pareto-optimal solutions of the problem in both rough and finished conditions. Utilizing a polyhedral branch-and-cut algorithm, the lexicographic weighted Tchebycheff model of the proposed multi-objective model is solved using GAMS software. The Pareto-optimal solutions provide a proper trade-off between conflicting objective functions which helps the decision maker to select the best values for the decision variables. Sensitivity analyses are performed to determine the effect of change in the grain size, grinding ratio, feed rate, labour cost per hour, length of workpiece, wheel diameter and downfeed of grinding parameters on each value of the objective function.     

Optical reflectance and transmission of a textured surface

The reflectivity of a solar thermal or solar electric device is a key parameter in efficiency. In the recent solar device literature, highly “textured” surfaces have been shown to reduce the reflectivity appreciably. The theoretical model used to describe this phenomenon is light trapping by multiple reflections. Surface roughness has also been considered by others through statistical scattering theory. The range of validity of either model is limited to a scale of texture larger than the wavelength of the light. For the micron scaled texture which is of interest, however, both approaches fall into the category of approximate solutions to approximate models of the surface.We approached the problem differently. We obtained the effects of texture on reflectivity and transmission through an exact calculation of a boundary layer whose complex dielectric constant is an appropriate average of the bulk dielectric constant of the material and air. The calculations were made for arbitrary angles of incidence, polarization and wavelength, as well as for arbitrary spatial variation of the dielectric constant through the boundary layer. We developed the spatial variation through effective medium models for a discontinuous surface layer. Finally, we compared the computer calculation with an exact analytic treatment for normal incidence, as well as with experimental reflectivities on several textured surfaces.