Convex grating types for concentric imaging spectrometers

The properties of convex gratings fabricated by electron-beam lithography are investigated. Three grating types are shown. The first is a single-panel, true blazed grating in which the blaze angle stays constant relative to the local surface normal. This grating provides high peak efficiencies of approximately 88% in the first order and 85% in the second order. The second grating has two concentric panels, with each panel blazed at a different angle. This type permits flexibility in matching the grating response to a desired form. The third type has a groove shape that departs from the sawtooth blazed profile to increase the second-order bandwidth. All these types are difficult or impossible to produce with conventional techniques. The gratings compare favorably with conventional (holographic and ruled) types in terms of efficiency and scatter. Simple scalar models are shown to predict the wavelength response accurately. These gratings allow the optical designer to realize fully the considerable advantages of concentric spectrometer forms.     

Theory of concentric designs for grating spectrometers

A concentric optical design for a grating spectrometer is described. General aberration theory is given for a family of designs of similar form, showing close similarities with the theory for conventional concentric imagers used in microlithography. Control of stray radiation in the concentric grating spectrometer is discussed.     

Noise in microelectromechanical system resonators

Microelectromechanical system (MEMS) and nanoelectromechanical system (NEMS) based resonators and filters, ranging in frequencies from kHz to GHz, have been proposed. The question of how the stabilities of such resonators scale with dimensions is examined in this paper, with emphasis on the noise characteristics. When the dimensions of a resonator become small, instabilities that are negligible in macro-scale devices become prominent. The effects of fluctuations in temperature, adsorbing/desorbing molecules, outgassing, Brownian motion, Johnson noise, drive power and self-heating, and random vibration are explored. When the device is small, the effects of fluctuations in the numbers of photons, phonons, electrons and adsorbed molecules can all affect the noise characteristics. For all but the random vibration-induced noise, reducing the dimensions increases the noise. At submicron dimensions, especially, the frequency noise due to temperature fluctuations, Johnson noise, and adsorption/desorption are likely to limit the applications of ultra-small resonators.     

Accurate wavelength calibration method for flat-field grating spectrometers

A portable spectrometer prototype is built to study wavelength calibration for flat-field grating spectrometers. An accurate calibration method called parameter fitting is presented. Both optical and structural parameters of the spectrometer are included in the wavelength calibration model, which accurately describes the relationship between wavelength and pixel position. Along with higher calibration accuracy, the proposed calibration method can provide information about errors in the installation of the optical components, which will be helpful for spectrometer alignment.     

Review of flexible microelectromechanical system sensors and devices

Today,the vast majority of microelectromechanical system (MEMS) sensors are mechanically rigid and therefore suffer from disadvantages when used in intimately w...     

Two-channel tunable monochromatic illuminator with a concave diffraction grating and an original scanning system

A two-channel monochromatic illuminator with only one diffraction grating and an original scanning system has been designed for multiple applications. This scanning system consists of two rotational plane mirrors that reflect light diffracted by a concave diffraction grating to the ?1 orders of the spectrum. The light reflected by the mirrors goes to two exit slits that correspond to two channels of the device. The positions of the centers of rotation of the mirrors are selected to produce minimal deviation of the direction of the light reflected during the scanning. The aberration characteristics of some variations in the optical mounting of the device made by use of spherical and toroidal holographic diffraction gratings recorded in stigmatic and astigmatic beams, the possibilities for application of the device for measuring the color sensitivity of the human eye, and the possibilities for measuring the efficiency of concave diffraction gratings, are also discussed.     

Interferential scanning grating position sensor operating in space at 4 K

An interferential position sensor for operation in space at a deep cryogenic temperature (4 K) is derived from a commercial sensor. The application is for the Spectral and Photometric Imaging Receiver submillimetric imaging Fourier-transform spectrometer on the Herschel space telescope. This sensor is used to control the displacement of the interferometer's moving mirrors and to sample the interferograms. This development addresses the following points: minimization of the effects of cooling critical optical parts, introduction of a fully redundant focal plane, selection of optoelectronic components efficient at 4 K, and design of a cryogenic preamplifier.     

Comprehensive characterization of PVDF-TrFE thin films for microelectromechanical system applications

This paper presents a comprehensive characterization of a polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) thin film with 75/25 molar ratio for piezoelectric MEMS applications. PVDF-TrFE film was deposited on a silicon substrate using spin coating, and electrodes were formed using sputtering. Dielectric constant and dielectric loss factor were measured at different frequencies. Frequency and temperature dependence of the ferroelectric response was examined to investigate required poling conditions and maximum operating temperature. The lower limit for the coercive field was measured as 55 V/μm at room temperature. Coercive field decreased with temperature with a slope of ?0.1 V/μm K, and ferroelectric to paraelectric transition occurred between 100? and 108?°C. Piezoelectric displacement measurements were performed using an atomic force microscope based method. Average value of the effective piezoelectric d₃₃ coefficient was measured as ?23.9 pm/V. No degradation was observed in this value after 2?×?10⁵ unipolar excitation cycles. On the other hand, significant fatigue was observed in the piezoelectric response due to polarization switching; 1.8?×?10⁵ cycles caused an average reduction of 33% in the effective d₃₃. Presented data corroborates with the previous studies in the literature and can be used in the design of PVDF-TrFE based MEMS devices utilizing its dielectric, ferroelectric, and piezoelectric properties.     

Modulating and driving system for the application of microelectromechanical system infrared source array

A problem demanding to be solved in the development of microelectromechanical system (MEMS) IR source array has been the driving circuit and system. A method that can achieve the requirements of high driving power, high output efficiency, high voltage precision, voltage compensation, and deep frequency modulation for driving and modulating a MEMS IR source array was proposed. A liner DC steady voltage integrated circuit ADP3336 is used to drive the source array directly with a programmable compensation module ensuring the precision of radiation peak wavelength. And a FPGA as the control core of the system modulates the frequency and width of the driving pulse to control the array coding pattern. The engineering value of the system would be increased with the application of the MEMS IR source.     

Calibration of a scanning electron microscope with a diffraction grating

We examine the problem of high accuracy SEM measurement. We have developed a calibration method that eliminates the operator from the procedure and thereby removes the main source of random error.Translated from Izmeritel'naya Tekhnika, No. 9, pp. 33–35, September, 1995.     

On forces in microelectromechanical systems

This paper investigates forces of importance in microelectromechanical systems (MEMS), their origin, effective range of action, proper classification, and formulations. It is shown that because of extremely small sizes of micromechanical structures in MEMS, forces operating at surfaces, across interfaces, and between micromechanical components caused by molecular interactions and by electric and magnetic loadings may become significant to influence behaviors of microelectromechanical devices. It is also shown that interaction forces between material bodies can be effectively of much longer range than those between molecules even though the same type of force may be operating in each case, depending on the shape, size, and material properties of the interacting media. Even quantum electrodynamic effects are shown to play effectively roles in MEMS in certain cases. To identify relative importance of forces in MEMS, a comparison of some major operating forces is made quantitatively with respect to their interaction range of interacting media, and its results are discussed in the paper. Possible effects of forces and their applications are also discussed briefly for MEMS in which a variety of forces may play important roles.     

Nano-strip grating lines self-organized by a high speed scanning CW laser

After a laser annealing experiment on Si wafer, we found an asymmetric sheet resistance on the surface of the wafer. Periodic nano-strip grating lines (nano-SGLs) were self-organized along the trace of one-time scanning of the continuous wave (CW) laser. Depending on laser power, the nano-trench formed with a period ranging from 500 to 800 nm with a flat trough between trench structures. This simple method of combining the scanning laser with high scanning speed of 300 m min(-1) promises a large area of nanostructure fabrication with a high output. As a demonstration of the versatile method, concentric circles were drawn on silicon substrate rotated by a personal computer (PC) cooling fan. Even with such a simple system, the nano-SGL showed iridescence from the concentric circles.     

电动机系统绿色节能发展探讨

随着电动机系统节能技术的不断深入研究和发展,电动机系统节能不仅仅停留于研究和开发单一的高效产品和装置,而是向着电动机系统的优化匹配、节能和绿色设计等方面发展,使电动机系统的寿命周期都达到绿色、节能的效果,最大限度提高系统能源利用率,真正成为低碳经济的重要组成部分。一、国际上电动机系统绿色节能技术发展现状国际上各国政府和组织纷纷     

Double triangular prism filter based on the optical-readout method in a microelectromechanical infrared imaging system

This paper presents a novel filtering method with a double triangular prism in an optical-readout thermal imaging system. First, the working principle of this system is described in detail, followed by the analysis of sensitivity. Then, infrared images of hands are obtained. On the basis of the analysis, it is concluded that this filtering method, whose noise equivalent temperature difference (NETD) can reach 145 mK, is effective in obtaining high-quality images. Finally, comparing the filtering method with a knife-edge filter, we can draw the conclusion that the filtering method can effectively improve image quality (the value of NETD is less than that of a knife-edge filter).     

光栅尺解调的分布式光纤光栅传感系统

提出了一种新的利用光栅尺解调一组光纤光栅布喇格波长移动的系统。当光纤光栅所受的应力或温度发生变化时,光纤光栅的布喇格波长会变化(移动)。本系统利用一组光纤光栅作为敏感元件置于被测场中;利用另一组光纤光栅作为跟踪元件,跟踪从作为敏感元件的光纤光栅反射回来的布喇格波长的移动。当作为跟踪元件的光纤光栅的布喇格波长与作为测量元件的光纤光栅的布喇格波长对准时,探测器探测到最大的光强,此时,记下光栅尺的输出作为系统的测量结果。采用数字化的方法确定反射回来的布喇格波长的峰值点,从而提高系统的测量精度,使系统的测量线性大于0.999。并利用一个测量分辨率为0.01μm的光栅尺读出系统的测量结果,使本系统对光纤光栅布喇格波长移动的测量分辨率小于1μ应变量。     

Mechanical disturbances in Fourier spectrometers

Fourier spectrometers are sensitive to many kinds of disturbance. This focus is mainly on those connected to mechanical vibrations, assessing the relationships between the mechanical inputs and the deriving effects on the spectra. Mechanical vibrations have two main effects on the spectra, the addition of signals due to direct sensitivity to vibrations of the detectors (e.g., through piezoelectric effect) and the changes of the interferogram due to the interferometer optical components motion. The Fourier transform spectrometer considered in this study is based on the constant optical path step sampling achieved by using the interferogram of a reference laser as a trigger so, ideally insensitive to mirrors speed changes, however, the analysis will show how the effects of delays in the sampling chain can compromise the benefits of this configuration. The effects of the vibration of the interferometer optical alignment are considered as well, showing the effect produced on the interferograms and eventually on the spectra. Despite their nonmechanical nature, detector nonlinearity and internal optical reflections are considered as well because their effects, similar to the mechanical ones, could be confused with the latter while in spectra diagnostic it is often important to be able to distinguish between the two. For all the analyzed effects the quantitative relationships between the mechanical disturbances' amplitudes and spectral observed effects are derived.     

Optimization of zero-reference grating considering tip distortions for scanning probe microscopy drift measurement

A nonperiodic grating composed of unevenly distributed step elements on a flat substrate can serve as the calibration grating for scanning probe microscopy (SPM) drift measurements. The grating named zero-reference grating (ZRG) is characterized by the number of step elements t, the number of total grating elements n and the maximum correlation peak contrast D. To optimize the ZRG structures considering tip distortions in SPM images, mathematical morphology and genetic algorithms are adopted. Results show that the optimal step elements tend to distribute orderly under the influence of large tip radius and the contrast D decreases with the increase of tip radius when t < or = n/2. On the contrary, the optimal ZRG structures and the contrast D are insensitive to tip distortions when t > n/2. These differences can be interpreted by the effective code mechanism due to tip dilation. For quantitative drift measurements, the parameter t is suggested to be larger than n/2 since the performances of such optimal ZRGs are more robust to tip distortions.