A fast-Fourier-transform method of topography and interferometry is proposed. By computer processing of a noncontour type of fringe pattern, automatic discrimination is achieved between elevation and depression of the object or wave-front form, which has not been possible by the fringe-contour-generation techniques. The method has advantages over moire topography and conventional fringe-contour interferometry in both accuracy and sensitivity. Unlike fringe-scanning techniques, the method is easy to apply because it uses no moving components.

Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry

The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

http://ieeexplore.ieee.org/iel5/6354/16969/00781867.pdf

Photonic crystals

International Technology Roadmap for Semiconductors 2003の要求清浄度について － シリコンウエハ表面と雰囲気環境に要求される清浄度, 分析方法の現状について －

A self-scanned 1024 element photodiode array and minicomputer are used to measure the phase (wavefront) in the interference pattern of an interferometer to lambda/100. The photodiode array samples intensities over a 32 x 32 matrix in the interference pattern as the length of the reference arm is varied piezoelectrically. Using these data the minicomputer synchronously detects the phase at each of the 1024 points by a Fourier series method and displays the wavefront in contour and perspective plot on a storage oscilloscope in less than 1 min (Bruning et al. Paper WE16, OSA Annual Meeting, Oct. 1972). The array of intensities is sampled and averaged many times in a random fashion so that the effects of air turbulence, vibrations, and thermal drifts are minimized. Very significant is the fact that wavefront errors in the interferometer are easily determined and may be automatically subtracted from current or subsequent wavefrots. Various programs supporting the measurement system include software for determining the aperture boundary, sum and difference of wavefronts, removal or insertion of tilt and focus errors, and routines for spatial manipulation of wavefronts. FFT programs transform wavefront data into point spread function and modulus and phase of the optical transfer function of lenses. Display programs plot these functions in contour and perspective. The system has been designed to optimize the collection of data to give higher than usual accuracy in measuring the individual elements and final performance of assembled diffraction limited optical systems, and furthermore, the short loop time of a few minutes makes the system an attractive alternative to constraints imposed by test glasses in the optical shop.

Digital wavefront measuring interferometer for testing optical surfaces and lenses

Fogging occurs when moisture condensation takes the form of accumulated droplets with diameters larger than 190 nm or half of the shortest wavelength (380 nm) of visible light. This problem may be effectively addressed by changing the affinity of a material’s surface for water, which can be accomplished via two approaches: i) the superhydrophilic approach, with a water contact angle (CA) less than 5°, and ii) the superhydrophobic approach, with a water CA greater than 150°, and extremely low CA hysteresis. To date, all techniques reported belong to the former category, as they are intended for applications in optical transparent coatings. A well-known example is the use of photocatalytic TiO2 nanoparticle coatings that become superhydrophilic under UV irradiation. Very recently, a capillary effect was skillfully adopted to achieve superhydrophilic properties by constructing 3D nanoporous structures from layer-by-layer assembled nanoparticles. The key to these two “wet”-style antifogging strategies is for micrometer-sized fog drops to rapidly spread into a uniform thin film, which can prevent light scattering and reflection from nucleated droplets. Optical transparency is not an intrinsic property of antifogging coatings even though recently developed antifogging coatings are almost transparent, and the transparency could be achieved by further tuning the nanoparticle size and film thickness. To our knowledge, the antifogging coatings may also be applied to many fields that do not require optical transparency, including, for example, paints for inhibiting swelling and peeling issues and metal surfaces for preventing corrosion. These types of issues, which are caused by adsorption of moisture, are hard to solve by the superhydrophilic approach because of its inherently “wet” nature. Thus, a “dry”-style antifogging strategy, which consists of a novel superhydrophobic technique that can prevent moisture or microscale fog drops from nucleating on a surface, is desired. Recent bionic researches have revealed that the self-cleaning ability of lotus leaves and the striking ability of a water-strider’s legs to walk on water can be attributed to the ideal superhydrophobicity of their surfaces, induced by special microand nanostructures. To date, the biomimetic fabrication of superhydrophobic microand/or nanostructures has attracted considerable interest, and these types of materials can be used for such applications as self-cleaning coatings and stain-resistant textiles. Although a superhydrophobic technique inspired by lotus leaves is expected to be able to solve such fogging problems because the water droplets can not remain on the surface, there are no reports of such antifogging coatings. Very recently, researchers from General Motors have reported that the surfaces of lotus leaves become wet with moisture because the size of the fog drops are at the microscale—so small that they can be easily trapped in the interspaces among micropapillae. Thus, lotuslike surface microstructures are unsuitable for superhydrophobic antifogging coatings, and a new inspiration from nature is desired for solving this problem. In this communication, we report a novel, biological, superhydrophobic antifogging strategy. It was found that the compound eyes of the mosquito C. pipiens possess ideal superhydrophobic properties that provide an effective protective mechanism for maintaining clear vision in a humid habitat. Our research indicates that this unique property is attributed to the smart design of elaborate microand nanostructures: hexagonally non-close-packed (ncp) nipples at the nanoscale prevent microscale fog drops from condensing on the ommatidia surface, and hexagonally close-packed (hcp) ommatidia at the microscale could efficiently prevent fog drops from being trapped in the voids between the ommatidia. We also fabricated artificial compound eyes by using soft lithography and investigated the effects of microand nanostructures on the surface hydrophobicity. These findings could be used to develop novel superhydrophobic antifogging coatings in the near future. It is known that mosquitoes possess excellent vision, which they exploit to locate various resources such as mates, hosts, and resting sites in a watery and dim habitat. To better understand such remarkable abilities, we first investigated the interaction between moisture and the eye surface. An ultrasonic humidifier was used to regulate the relative humidity of the atmosphere and mimic a mist composed of numerous tiny water droplets with diameters less than 10 lm. As the fog was C O M M U N IC A IO N

The dry-style antifogging properties of mosquito compound eyes and artificial analogues prepared by soft lithography: a superhydrophobic state with high adhesive force

In the semiconductor industry, a device that can measure the surface-profile of photoresist is needed. Since the photoresist surface is very smooth and deformable, the device is required to measure vertical direction with nanometer resolution and not to damage it at the measurement. We developed the apparatus using multi-cantilever and white light interferometer to measure the surface-profile of thin film. But, this system with scanning method suffers from the presence of moving stage and systematic sensor errors. So, in this paper, an error separation approach used coupled distance sensors, together with an autocollimator as an additional angle measuring device, was consulted the potentiality for self-calibration of multi-cantilever. Then, according to this method, we constructed the experimental apparatus and do the measurement on the resist film. The results demonstrated the feasibility that the constructed multi-ball-cantilever AFM system combined with an autocollimator could measure the thin film with high accuracy.

Intelligent Profile Measurement for Wide-Area Resist Surface Using Multi-Sensor AFM System

Metal cylindrical shaft parts are critical components in industrial manufacturing that require high standards for roundness error and surface roughness. When using the self-developed multi-beam angle sensor (MBAS) to detect metal cylindrical shaft parts, the distorted multi-spots degrade the measurement accuracy due to the nonlinear distortion caused by the metal material's reflective properties and surface roughness. In this study, we propose a spot coordinate prediction network (SCPNet), which is a deep-learning neural network designed to predict spot coordinates, in combination with Hough circle detection for localization. The singular value decomposition (SVD) model is employed to eliminate the tilt error to achieve high-precision, three-dimensional (3D) surface reconstruction of metal cylindrical shaft parts. The experimental results demonstrate that SCPNet can effectively correct distorted multi-spots, with an average error of the spot center of 0.0612 pixels for ten points. The proposed method was employed to measure metal cylindrical shaft parts with radii of 10 mm, 20 mm, 35 mm, and 50 mm, with resulting standard deviation (STD) values of 0.0022 µm, 0.0026 µm, 0.0028 µm, and 0.0036 µm, respectively.

SCPNet-based correction of distorted multi-spots for three-dimensional surface measurement of metal cylindrical shaft parts.

A high-accuracy length measurement method using an optical frequency comb is developed, which is traceable to the national frequency standards. The repetition frequency is phase-locked to the frequency standards of an Rb frequency clock. Moreover, a laser diode is phase-locked with an offset frequency of ∆1 to one frequency (f1) of the lower optical frequency modes in the optical comb (frequency; about 200 THz), and the second laser diode is phase-locked to another frequency (f2) of the higher optical frequency modes in the optical comb. Therefore, we can generate a high beatfrequency (f1-f2) such as some THz. In this case, the laser diodes have off-set frequencies of ∆1 and ∆2 to the mode of the optical comb, respectively. As a result, we can obtain a super heterodyne frequency of (∆2-∆1)= several tens kHz for length measurements based on the optical frequency comb. For example, 15 THz corresponds to a synthetic wavelength of 20 µm. Also, a unique determination of the fringe order is achieved in the new system. Finally, we can measure an absolute length with an accuracy of 40 nm up to several tens meters.

/pdf/super-hetrodyne-interferometric-length-measurement-using-the-1dl2irxhh5.pdf

Super-hetrodyne interferometric length measurement using the repetition frequency of an optical frequency comb

In recent years, the CMM (Coordinate Measuring Machine) quickly has been spreading in the manufacturing industry. With this phenomenon, the environmental condition and installation site of CMMs has been changed from the temperature control room to the workshop environment and the production line without air conditioning. However, even in severe environment the demand to high accuracy measurements by CMM has been enhancing still more. Therefore, the methods to evaluate and realize the high accuracy measurements by CMM in workshop environment have been investigated. In this paper, we clarify the difference of thermal drift and conventional temperature correction in thermal errors of length and position measurement, and propose the simple model of thermal drift and correction method. Additionally the thermal drift of CMM in workshop environment is tested and corrected experimentally. From these results, we confirmed the availability of the proposed methods.

Study on Improvement Methods of CMM (Coordinate Measuring Machine) in Workshop Environment

Evanescent-wave-based nano-stereolithography, which uses the ultra-thin field distribution of evanescent wave to solidify photosensitive resin, provides a sub-micrometer vertical resolution of each layer. In fabrication process, cured resin (solid state) is submerged in uncured resin (liquid state). The interfaces between the cured and the uncured resin are made up of half-cured resin in a state of the uncompleted polymerization. Due to the gradient boundary directly determines the thickness of each fabrication layer and greatly influences the quality of products, it is of great significance to study the gradient boundary in the fabrication process. We proposed in-process measurement of gradient boundary using the reflection interference technique to monitor the formation of cured resin and investigate the gradient boundary. In this method, the variation of refractive index of resin in curing process has been utilized in the measurement. Measurement light was deduced near the critical angle to obtain a susceptible total internal reflection condition. In the verification experiment, a compact experiment system including fabrication and measurement sections has been developed. Two beams of light in the different wavelength have been delivered into the system as fabrication and measurement light, respectively. Resin exposed by increasing time has been measured by our proposed method at various incident angles near the critical angle. The refractive index distribution and the depth gradient boundary have been successfully measured. The results prove that the refractive index of cured resin is different in the position; the span of gradient is not constant as well. The maximum span of gradient boundary in center was measured in around 250 nm. This work that helps us clearly understand the curing process and the formation of the cured layer in EWNSL provides a research basis for further and detailed research in the nanoscale stereolithography.

Kiyoshi Takamasu

Papers

Intelligent Profile Measurement for Wide-Area Resist Surface Using Multi-Sensor AFM System

SCPNet-based correction of distorted multi-spots for three-dimensional surface measurement of metal cylindrical shaft parts.

Super-hetrodyne interferometric length measurement using the repetition frequency of an optical frequency comb

Study on Improvement Methods of CMM (Coordinate Measuring Machine) in Workshop Environment

In-process Measurement of Gradient Boundary of Resin in Evanescent-wave-based Nano-stereolithography using Reflection Interference Near Critical Angle