Optical Curvature Research Articles

Cantilever stress measurements for pulsed laser deposition of perovskite oxides at 1000 K in an oxygen partial pressure of 10(-4) millibars.

An in situ stress measurement setup using an optical 2-beam curvature technique is described which is compatible with the stringent growth conditions of pulsed laser deposition (PLD) of perovskite oxides, which involves high substrate temperatures of 1000 K and oxygen partial pressures of up to 1 × 10(-4) millibars. The stress measurements are complemented by medium energy electron diffraction (MEED), Auger electron spectroscopy, and additional growth rate monitoring by a quartz microbalance. A shielded filament is used to allow for simultaneous stress and MEED measurements at high substrate temperatures. A computer-controlled mirror scans an excimer laser beam over a stationary PLD target. This avoids mechanical noise originating from rotating PLD targets, and the setup does not suffer from limited lifetime issues of ultra high vacuum (UHV) rotary feedthroughs.

Design of the active zoom system with three-mirror

In the applications of deep-space exploration, surveillance, threat detection and high resolution investigation on the ground, space optical systems need not only both the high resolution and width of view zoom system, but also the small size, light weight, low power and fast focusing system. As the traditional mechanical zoom system requires complex and precision mechanical motion, many problems are usually caused. Thus, based on active optics, the active optical elements are applied to the imaging system, and it is proposed that the optical element curvature radius should be variable to realize the transition among the different focal lengths. According to third-order aberration theory and dimension calculation of optical system requirement, the active zoom theory is studied, and the third-order aberration equation constraints are confirmed. Then the initial construction parameters of coaxial active zoom system are achieved by solving the equations. The system is optimized with using the optical design software ZEMAX. The system consists of the static primary mirror, the secondary and third mirror with the variable curvature radius, and the plane mirror with zero-power. As two times the light is obscured by the elements in the coaxial active zoom system, the amount of the energy on the image plane will be affected. For this reason, it is proposed that the unobstructed off-axis optimization should be necessary to the coaxial system. The off-axis system design theory is studied and the off-axis active zoom system is designed.

Research on the Residual Error Evaluation Method for Deterministic Polishing of Aspheric Optics

Residual error evaluation method for deterministic polishing of aspheric optics is studied. Two residual error evaluation methods, which are axis-direction error method and normal error method respectively, are researched theoretically. It's inferred that the residual error of aspheric surface should be evaluated by normal error method. A new approach is proposed to calculate normal direction residual error on the basis of the axis-direction residual error of the aspheric surface. There exists difference between these two kinds of error which increases from the center of the aspheric optic to the edge through the comparison of them. Taking bonnet polishing and numerical controlled small tool polishing as examples, experiments are made to quantitatively prove that using axis-direction error method to evaluate residual error in deterministic polishing would introduce different degrees of processing error. It's found that the processing error is positively correlated with the relative aperture of aspheric optics, which is the ratio of the optic's aperture and vertex's curvature radius. Therefore, it is recommended to use axis-direction error method instead of normal error method as the evaluation method of the residual error during deterministic polishing aspheric optics with relatively small relative aperture; the opposite is the other way around.

Orthonormal curvature polynomials over a unit circle: basis set derived from curvatures of Zernike polynomials

Zernike polynomials are an orthonormal set of scalar functions over a circular domain, and are commonly used to represent wavefront phase or surface irregularity. In optical testing, slope or curvature of a surface or wavefront is sometimes measured instead, from which the surface or wavefront map is obtained. Previously we derived an orthonormal set of vector polynomials that fit to slope measurement data and yield the surface or wavefront map represented by Zernike polynomials. Here we define a 3-element curvature vector used to represent the second derivatives of a continuous surface, and derive a set of orthonormal curvature basis functions that are written in terms of Zernike polynomials. We call the new curvature functions the C polynomials. Closed form relations for the complete basis set are provided, and we show how to determine Zernike surface coefficients from the curvature data as represented by the C polynomials.

Method for primary design of superachromats

This work deals with a method for primary optical design of superachromats, where chromatic aberration is corrected for several wavelengths. Equations for the calculation of optical power and curvature radii are described for aplanatic and nonaplanatic optical systems, which are composed of two or three thin lenses in contact. Results of the calculations are presented for chosen optical systems of superachromats with basic design parameters.

White LED modules encapsulation features

The behaviour and causes of changes for correlated color temperature (CCT) and radiant spectral power in white LED modules of different design at their encapsulation by optical compounds are investigated. It is shown that CCT of original white LED radiation can both decrease and increase after polymeric covering application. The ССT variation direction is determined mainly by primary lens presence on LED. The variation value of color parameters of white LED modules is determined by created optical surface curvature and spectral characteristics of deposited polymer.

Altering the Mechanical Properties of Sn Films by Alloying with Bi: Mimicking the Effect of Pb to Suppress Whiskers

Stress is believed to be the main driving force for whisker formation in Sn coatings on Cu. This suggests that whiskering can be suppressed by enhancing stress relaxation in the Sn layer, which is believed to be the reason why Sn-Pb alloys do not form whiskers. However, Pb is no longer acceptable for use in electronics manufacturing. As an alternative, we used pulsed plating to create Sn-Bi coatings with an equiaxed microstructure similar to that of Sn-Pb alloys. An optical wafer curvature technique was used to measure stress relaxation kinetics in Sn, Sn-Pb and Sn-Bi alloy thin films during thermal cycles. The results show that Sn-Bi films have significantly enhanced stress relaxation relative to pure Sn films. Comparison between Sn-Bi samples with equiaxed and columnar microstructures shows that both microstructure and alloy composition play a role in enhancing the stress relaxation.

Stress Evaluation on Hetero-Epitaxial 3C-SiC Film on (100) Si Substrates

SiC is a candidate material for micro- and nano-electromechanical systems (MEMS and NEMS). In order to understand the impact that the growth rate has on the residual stress of CVD-grown 3C-SiC hetero-epitaxial films on Si substrates, growth experiments were performed and the resulting stress was evaluated. Film growth was performed using a two-step growth process with propane and silane as the C and Si precursors in hydrogen carrier gas. The film thickness was held constant at ~2.5 µm independent of the growth rate so as to allow for direct films comparison as a function of the growth rate. Supported by profilometry, Raman and micro-machined free-standing structures, this study shows that the growth rate is a fundamental parameter for low-defect and low-stress hetero-epitaxial growth process of 3C-SiC on Si substrates. Stress analysis performed by modify Stoney’s equation trough optical curvature measurement, Raman shift analysis and micro-machining of free-standing structures that shows apparent disagreement about the nature of the stress. These odds between the experimental data can be explained assuming a strong stress field located in the substrate and related to defects generated in the silicon during the growth process.

An Optical Actuation System and Curvature Sensor for a MR-compatible Active Needle.

A side optical actuation method is presented for a slender MR-compatible active needle. The needle includes an active region with a shape memory alloy (SMA) wire actuator, where the wire generates a contraction force when optically heated by a laser delivered though optical fibers, producing needle tip bending. A prototype, with multiple side heating spots, demonstrates twice as fast an initial response compared to fiber tip heating when 0.8 W of optical power is applied. A single-ended optical sensor with a gold reflector is also presented to measure the curvature as a function of optical transmission loss. Preliminary tests with the sensor prototype demonstrate approximately linear response and a repeatable signal, independent of the bending history.

A high sensitivity three-dimensional-shape sensing patch prepared by lithography and inkjet printing.

A process combining conventional photolithography and a novel inkjet printing method for the manufacture of high sensitivity three-dimensional-shape (3DS) sensing patches was proposed and demonstrated. The supporting curvature ranges from 1.41 to 6.24 × 10−2 mm−1 and the sensing patch has a thickness of less than 130 μm and 20 × 20 mm2 dimensions. A complete finite element method (FEM) model with simulation results was calculated and performed based on the buckling of columns and the deflection equation. The results show high compatibility of the drop-on-demand (DOD) inkjet printing with photolithography and the interferometer design also supports bi-directional detection of deformation. The 3DS sensing patch can be operated remotely without any power consumption. It provides a novel and alternative option compared with other optical curvature sensors.

Aberrations of a Gaussian laser beam focused by a zone plate

We discuss the Seidel-type wavefront aberrations which degrade the quality of the Gaussian beam focused by a zone plate. First we examine the diffraction of a complex-source-point spherical wave through the zone plate, while the terms of up to fourth order in aperture variables are under consideration. Then we find an explicit formula for the diffracted beam that is represented in terms of Seidel-type wavefront aberrations. We also evaluate the effects of aberrations on the quality of the diffracted beam through the zone plate. If the axis of the incident beam is inclined slightly with respect to the optic axis, both spherical aberration and field curvature affect the beam quality in the sagittal section of the focal plane, whereas the beam quality in its meridian section is under the influence of all Seidel-type aberrations. The fourth order theory of propagation of a slightly inclined Gaussian beam as described here may be applied to evaluate the degradation in the quality of the Gaussian beam focused by a zone plate.

Curvature measurement of optical surface using digital holography

Abstract In this paper, an optical surface curvature measurement technique based on digital holography is proposed. Unlike the previous digital holographic methods, which only involve a small part of the measured data for parameter estimation, the proposed method adopts more of them using least square method. Hence, the analyzed result is not affected by data extraction direction and less sensitive to imperfect phase compensation. The proposed method is demonstrated with a sample of reflection mirror in laser resonator, and verified by comparing the measurement result with that of the white light interferometer.

H- and O-induced compressive surface stress on Pt(111): Experiments and density functional theory calculations

Surface-stress changes induced by the adsorption of oxygen and hydrogen on clean Pt(111) are measured at 320 K under UHV conditions with an optical crystal curvature method and are calculated using density-functional theory. A compressive surface-stress change is measured upon exposure of Pt(111) to either ${\text{H}}_{2}$ or ${\text{O}}_{2}$. The magnitude of the adsorbate-induced surface-stress change is in quantitative agreement with our calculations. Our results indicate that both electropositive (H) and electronegative (O) adsorbates may induce a compressive surface-stress change. The significance of these results for the understanding of adsorbate-induced surface stress is discussed.

Compact optical curvature sensor with a flexible microdisk laser on a polymer substrate

We demonstrate a chip-scale compact optical curvature sensor. It consists of a low threshold InGaAsP microdisk laser on a flexible polydimethylsiloxane polymer substrate. The curvature dependence of lasing wavelength was characterized by bending the cavity at different bending radii. The measurements showed that the lasing wavelength decreases monotonously with an increasing bending curvature. A good agreement between experiment and three-dimensional finite-difference time-domain simulation was also obtained. The sensitivity of the compact device to the bending curvature is -23.7 nm/mm from the experiment.

Nonlinear magnetoelastic coupling of epitaxial layers of Fe, Co, and Ni on Ir(100)

The effective magnetoelastic coefficients ${B}_{i}^{\text{eff}}$ are measured for epitaxial layers of Fe, Co, and Ni on Ir(100). Mechanical stress during film growth and stress during magnetization processes are measured directly by the optical cantilever curvature technique. Our results indicate that the effective magnetoelastic coupling coefficients ${B}_{1}^{\text{eff}}$ and ${B}_{2}^{\text{eff}}$ of Fe, Ni, and Co deviate from the respective bulk values, and we propose that strain may play an important role for this nonbulklike magnetoelastic behavior. The impact of the magnetoelastic coupling on the magnetic anisotropy is explored by magneto-optic Kerr effect measurements. The measurements reveal that the easy magnetization axis is in plane for Fe and Co layers on Ir(100). It changes from out of plane to in plane for Ni at about 15 monolayer with increasing film thickness. This spin reorientation transition can be well described by the measured magnetoelastic coupling coefficients. The result of nonbulklike magnetoelastic coupling is discussed in view of recent theoretical work on the calculation of magnetoelastic coupling in strained systems.

Research on electrostatic deformation of space membrane mirror

薄膜反射镜将解决反射镜孔径与重量相互制约的问题. 采用静电拉伸法控制薄膜反射镜面形, 具有结构简单、反射镜面形易于控制等优点, 其原理为利用静电场上库仑力作用使薄膜产生面形变化, 生成所需的光学曲面. 由于薄膜变形力学, 以及静电场理论的复杂性, 目前薄膜成形及其面形控制在理论分析上仍未有定量的结果. 本文主要以单电极静电场中的薄膜反射镜面形为考察因素, 通过数值计算的方法得到薄膜反射镜上的静电力分布, 运用有限元分析获得该分布下的反射镜面形, 并将其与理想面形进行比较. 提出采用多电极闭环控制可获得更高的控制精度, 对静电拉伸薄膜的研究具有一定的指导意义.

Piezoelectric forceps actuator: Theory and experiments

This paper studies the characteristic performances of a novel piezoelectric forceps actuator (PFA) that has several potential applications for minimally invasive surgery and assembly lines of semiconductor industries. The first part of the paper treats the PFA model, which is comprised of a piezoelectric slightly curved composite beam derived using Hamilton's principle. In the latter part of the paper, the distributed transfer function method is applied to evaluate the transfer function formulation of the cantilevered PFA associated with its boundary conditions. This method will be used to resolve the radial displacements and natural frequencies of the PFA in an exact and closed-form solution, which is validated by in situ fiber optic curvature sensing measurements. The theoretical model predicted the natural frequencies of the first- and second-mode responses of the experimental quite accurately. For a cyclical low-field input, the field-induced displacement appears approximately linear, which seems comparable to the theoretical prediction and reflects primarily the converse piezoelectric effect. A cyclical high-field butterfly-shaped displacement behavior is also analogous to the behavior predicted by the model in that it demonstrates the range of validity of the linear converse piezoelectric effect without consideration of the ferroelectric domain switch effect.

Vibration control of a single-link flexible manipulator using an array of fiber optic curvature sensors and PZT actuators

This paper presents a novel distributed sensing and actuation approach for actively suppressing vibrations within flexible link manipulators. Through vibration suppression, the method acts to regulate the shape of flexible links and, consequently, improves the performance of any independent trajectory controller being employed over the manipulator joints. To demonstrate the approach, a series of piezoceramic actuators (PZTs) are bonded to the surface of a single-link flexible manipulator. Slewing of the flexible link induces vibrations in the link that persist long after the hub stops rotating. The vibration suppression is achieved through a combined scheme of PD-based hub motion control and a PZT actuator controller that is a composite of linear and angular velocity feedback controllers. A Lyapunov approach is used to synthesize the composite controller, and a unique, commercially-available sensor, called ShapeTape ™, that provides the linear and angular velocity feedback. The sensor array is comprised of a series of fiber optic curvature sensors that are laminated on a long, thin ribbon tape which can be embedded into the flexible link and measures the bend and twist of the link’s centerline. Simulation and experimental results show the effectiveness of the proposed approach and the ability of the new sensor to provide the requisite feedback.

Sensor error modeling and compensation for range images captured by a 3D ranging system

The improvements in structured lighting-based 3D optical camera measurement systems have made the non-contact data acquisition (3D ranging) systems more applicable. A major critical issue in range image acquisition concerns the data accuracy. In this paper, factors that affect accuracy are carefully considered for a specific range image acquisition system, the four-dimensional imager system. The surface point distance errors, due to the optical distortion, field curvature and depth of field of the ranging system, have been studied. Two model-based methods, the area model (AM) and line model (LM), are proposed to model the systematic errors at different distances and orientation angles. An error lookup table is built with these models and used to reduce the systematic error of acquired data. The experimental results show that the proposed algorithm effectively improves ranging accuracy. Up to half of the systematic errors can be reduced using the AM method and almost all the systematic errors with the LM method.

파이버 브래그 격자를 이용한 곡률 측정

본 논문에서는 곡률을 측정하기 위해 파이버 브래그 격자를 이용한 곡률 센서에 대해 연구하고자 한다. 곡률의 변화를 측정하기 위해 브래그 공진파장의 이동 변화를 측정하였다. 실험견과로부터 곡률이 <TEX>$0\;m^{-1}$</TEX>에서 <TEX>$10\;m^{-1}$</TEX>까지 증가함에 따라 반사 스펙트럼은 감소하나. 브래그 공진 파장의 변화량은 선형적으로 증가함을 알 수 있었으며, 기울기는 대략 <TEX>$8.8\;pm/m^{-1}$</TEX> 이었다. 한편, 반사 스펙트럼은 곡률이 증가함에 따라 감소하였다. To measure the curvature, in this paper, we investigate an optical curvature sensor based on the fiber Bragg gratings. We observed the variation of the Bragg resonant wavelength shift to measure the curvature change. From the experimental results, we knew that the Brags resonant wavelength shift was lineally increased with the increase of the curvature from <TEX>$0\;m^{-1}$</TEX> to <TEX>$10\;m^{-1}$</TEX>. It's slope is about <TEX>$8.8\;pm/m^{-1}$</TEX>. On the other hand, the spectral reflection decreased with the increase of the curvature.