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This work is to investigate the instrumentation implementing issues of back focal plane (BFP)-typed apertometer. Firstly, we introduce a general instrument architecture of the BFP-typed apertometer, including the hardware (optics and mechanics) of the system, operation procedures of control and measurement system, and also the digital image processing algorithm/software. Secondly, we are the first to discuss the gradual rising effect of total-internal-reflection (TIR) phenomenon, the criteria on how to “exactly” locate the reference ring on BFP images, and the corresponding accuracies. As a significantly important complement, we further discuss three important issues: 1) the influence of Goos–Hänchen shift on numerical aperture (NA) measurement; 2) comparison of one-dimension and two-dimension identification algorithms; and 3) comparison of center locating using Fourier correlation analysis (FCA) and Hough transformation (HT) algorithms. [ABSTRACT FROM AUTHOR]

In this article, a Shack–Hartmann wavefront sensor is combined with a mechatronic positioning system to overcome the limited dynamic range of the Shack–Hartmann sensor (SHS) by repositioning and reorienting the SHS. Feedback loops to ensure a tangential orientation of the wavefront sensor in every measurement position and a measurement strategy that compensates for tip and tilt between wavefront and sensor are described and implemented. A framework that estimates the admissible measurement trajectories by relating the positioning errors caused by misalignments of the stages to the parameters of the wavefront sensor is developed. It is demonstrated that the setup is capable of directly measuring a highly divergent optical wavefront by combining wavefront data and positioning data acquired along the wavefront generated by a microscope objective with numerical aperture (NA) of 0.45. [ABSTRACT FROM AUTHOR]

Solar simulators are a fundamental instrument to characterize solar cells parameters, as they can reproduce the operating conditions under which the solar cells are going to work. However, these systems are frequently big, heavy, and expensive, and a small solar simulator could be a good contribution to test small prototyping devices manufactured in research labs, especially if it could manage the irradiation at any wavelength interval in a custom way. We have designed, developed, and calibrated a small solar simulator made entirely with LEDs, no optics inside, and electronically controlled through a PC using an Arduino microcontroller. The whole structure is 3-D printed in black PLA plastic. The electrical current through the LEDs, and thus the spectral irradiance of the simulator, is controlled with a very intuitive LabVIEW interface. As our calibration proves, we have built an easily reproducible and low-cost Class AAA solar simulator in a central illumination area of 1 cm2, according to the IEC60904-9 standard. This means that the homogeneity in that area is under a 2% deviation in spatial terms, below 0.5% in temporal terms, and is a factor of a 3% close to the AM1.5G sun reference spectrum. The system can be built and used in any research lab to get quick tests of new small solar cells of any material. [ABSTRACT FROM AUTHOR]

In human–robot coexisting environment, one of the primary objectives is to equip robots with the facilities of detecting and following a human being in front, using various sensors. Within this genre, developing algorithms for vision sensor-based shoe detection and subsequently following is considered an active problem. Considering that the shoe poses, during the pursuit, undergo different transformations, this paper presents how the vision sensor based shoe detection problem can be treated as analogous to template matching under general conditions. This paper first shows how a popular fast randomized template-matching algorithm, called FAsT-Match algorithm, and its contemporary variant for color images, called CFAsT-Match algorithm, can be implemented in real robots with success for detecting shoes in subsequent frames. Then, this paper proposes a new density-based clustering method, called ordering points to identify the clustering structure (OPTICS), based template-matching algorithm that is specifically developed to overcome several implementation problems associated with the FAsT-Match and CFAsT-Match algorithms, in real life. Experimental results and performance evaluations demonstrate the superiority of the proposed OPTICS-based algorithm for shoe detection during human tracking in human–robot coexisting environments. [ABSTRACT FROM AUTHOR]

Surface defects on precision optical elements must be carefully inspected since they impact the normal operation of an optical system. It is a challenge to inspect defects of large-aperture optical elements using an imaging system because of efficiency and accuracy. This paper designs a novel and effective inspection instrument with two imaging systems for large-aperture optical elements. They are the dark-field imaging system (DFIS) with a line scan camera in 10- \mu \textm resolution and the bright-field (BF) imaging system with a microscopic camera in a 0.85- \mu \textm resolution. To keep the clarity of the DFIS in large-scope quickly scanning, an adaptive scan path planning method is proposed. A set of novel algorithms is proposed to process a large number of dark-field images. Due to the limitations of the DFIS in scattering effect, the corresponding BF images are obtained according to the dark-field images. The classification of flaws and their sizes measurement based on BF images are also presented. The experiments show that the instrument can scan an optical element with the size of 810~\textrm mm\times 460 mm in less than 6 min and the inspection precision can reach 3 \mu \textm . [ABSTRACT FROM PUBLISHER]

This paper introduces a new type of icing detector for aircraft applications. Unlike the well-known icing detectors that are based on optics, the new detector uses \alpha particles. An \alpha-particle source is attached to the wing of the aircraft, and a detector that mainly depends on a MOSFET transistor is placed a few centimeters away from the source. As the \alpha particles strike the detector, they deposit their positive charges on the gate of the MOSFET (n-channel), and the transistor turns ON. If, however, a layer of ice builds up on the wing and prevents the \alpha particles from reaching the detector, the MOSFET shuts OFF. The new detector is more reliable than optics-based detectors because it is an integral part of the wing and hence cannot miss the formation of ice. [ABSTRACT FROM PUBLISHER]

In order to improve the safety, lifetime, and energy efficiency of turbomachines, the dynamic behavior of the rotor has to be analyzed. Blade vibrations have to be monitored during operation to optimize the rotor design and to validate numerical models. However, measuring the vibration amplitude and frequency of the blades is a challenging task for metrology, since the blades to be measured are rotating quickly, and noncontact measurements are demanded. To solve this problem, we present a measurement system consisting of four laser Doppler sensors that have been mounted around the circumference of the rotor. These sensors measure simultaneously and contactlessly the in-plane velocity and the out-of-plane position of laterally moving objects. By analyzing the variation of the blade tip velocities, the vibration amplitude and frequency of the blades were estimated. Blade vibration measurements down to amplitudes of only 20 \mum in tangential direction have been carried out. We achieved a standard uncertainty of approximately 400 nm for these experiments. [ABSTRACT FROM PUBLISHER]

This paper presents an algorithmic method for measurements of relaxed statistical properties of point processes (PPs). In particular, this method makes it possible to determine the probability density function of the residual waiting time, which is the distance between an arbitrary origin and the first point of the PP posterior to this origin and also the probabilities of counting n points of the PP in an interval open by an instant independent of the PP. These quantities are rarely accessible from a theoretical calculation. However, in the cases where this is possible, various experiments show quite good agreement with the theory. [ABSTRACT FROM PUBLISHER]

In this paper, details are given on a novel measurement device for radio propagation-channel measurements. To avoid measurement errors due to the conductive cables on small terminal antennas, as well as to improve the handling of the prototypes under investigation, an optical measurement device has been developed. It utilizes thin, light, and flexible glass fibers as opposed to heavy, stiff, and conductive coaxial cables. This paper looks at the various system parameters such as overall gain, noise figure, and dynamic range and compares the solution to other methods. An estimate of the device accuracy is also given. Selected parts of the circuitry are given in more detail. Typical measurement results are also shown. [ABSTRACT FROM AUTHOR]

In this paper, we present a novel procedure for the on-the-field autocalibration of triaxial micro accelerometers, which requires neither any equipment nor a controlled environment and allows increasing the accuracy of this kind of microsensor. The procedure exploits the fact that, in static conditions, the modulus of the accelerometer output vector matches that of the gravity acceleration. The calibration model incorporates the bias and scale factor for each axis and the cross-axis symmetrical factors. The parameters are computed through nonlinear optimization, which is solved in a very short time. The calibration procedure was quantitatively tested by comparing the orientation produced by MEMS with that measured by a motion capture system. Results show that the MEMS output, after the calibration procedure, is far more accurate with respect to the output obtained using factory calibration data and almost one order of magnitude more accurate with respect to using traditional calibration models. [ABSTRACT FROM AUTHOR]

In sinusoidal parameter-estimation problems for measurement applications, discrete spectra with high dynamic range are often under investigation. To suppress unwanted interference effects ("leakage") in the discrete Fourier transform (DFT) spectrum, the application of data windows is common practice. In this paper, the influence of windowing on the bias and variance of the frequency and phase estimates, calculated via the DFT, is investigated. Furthermore, the effect of choosing different sampling start times on both the bias and the variance is discussed. [ABSTRACT FROM AUTHOR]

This paper describes the development of a new type of microwave power standard based on atomic resonances. An atomic Rabi frequency is proportional to the magnetic field strength of the resonant microwave; the proportionality constant is determined only from fundamental constants and atomic quantum theory. The microwave field strength that corresponds to microwave power is thus uniquely determined by the Rabi frequency. The proportionality constant can thus serve as the basis for a new microwave power standard. This paper confirmed that the Rabi frequency of cesium-133 (133Cs) atoms in a rectangular cell is proportional to the incident microwave field strength. A rectangular Cs glass cell was developed and inserted into a WR90 waveguide--an industrially practical waveguide that permits the impedance analysis necessary to measure microwave power. The microwave field strength in the Cs cell can be adjusted to arbitrary values proportional to the Rabi frequency. The relative expanded uncertainties of the effective microwave magnetic field strength Heff for the coverage factor k = 2, which is typically less than 7%, averaged 4%. The dynamic range of the available Rabi frequency was 31.9 dB. [ABSTRACT FROM AUTHOR]

Rolling-element bearings are widely used in various mechanical and electrical systems. A reliable online bearing fault-diagnostic technique is critically needed to prevent the system's performance degradation and malfunction. In this paper, an extended wavelet spectrum analysis technique is proposed for a more positive assessment of bearing health conditions. Two strategies have been suggested for different wavelet function implementation. Two statistical indexes are proposed to quantify the resulting wavelet (coefficient) functions. Based on the information provided by these indexes, the wavelet functions can be deployed more effectively over the designated frequency bands. An extended Shannon function is proposed to synthesize the wavelet coefficients over selected bandwidths to enhance feature characteristics. An averaged autocorrelation power spectrum is adopted to highlight bearing characteristics. The viability of the developed technique is verified by online experimental tests corresponding to different bearing conditions. [ABSTRACT FROM AUTHOR]

The novelty of this paper is indicated by a series of experimental measurements aimed at enhancing the detectability of targets immersed in scattered solutions. The experimental results clearly show that polarimetric images of superior quality can be obtained by doping the background surrounding the target with polar or high-dielectric molecules, yielding an enhanced contrast and specificity of the target. In addition, it is observed that degree of linear polarization (DOLP) images exhibit superior image characteristics with respect to total intensity (S0) images with the increase in the concentration of the optical scattering agents. [ABSTRACT FROM AUTHOR]

Two microcellular environments, which are the regular and chaflane street corners, are compared using a ray-launching engine based on the uniform theory of diffraction and geometric optics. This paper includes a study on the signal-to-noise ratio (SNR), K factor, correlation, and multiple-input multiple-output capacity. Two situations, which are the line-of-sight (LoS) and the non-LoS (NL0S), are distinguished and studied separately. In NLoS, the influence of the SNR is higher than the effect of the correlation. However, in LoS, the SNR is comparable in both environments, and correlation determines capacity. [ABSTRACT FROM AUTHOR]

Two 171Yb+ single-ion optical frequency standards operating at 688 THz (436 nm) are compared in order to investigate systematic frequency shifts in the subhertz range. In the absence of externally applied perturbations, a mean relative frequency difference of 3.8 · 10-16 is observed. Using a femtosecond frequency comb generator based on an Er3+-doped fiber laser, the frequency of the 171Yb+ standard is measured with a relative systematic uncertainty of 3.1 · 10-15 and a statistical uncertainty of 0.6 · 10-15. [ABSTRACT FROM AUTHOR]

We report on the frequency stabilization of extended-cavity diode lasers against rotovibrational absorption lines of water vapor at around 0.94 μm, by means of the frequency modulation spectroscopy technique. A minimum frequency instability of ∼30 kHz has been obtained for integration times in the range from 1 to 100 s. [ABSTRACT FROM AUTHOR]

We present the results of a joint project to identify the origin of a discrepancy between the value of the Si lattice-parameter obtained by the Istituto Nazionale di Ricerca Metrologica and that obtained by the National Metrology Institute of Japan. The re-evaluation of diffraction in the laser interferometry indicates that misalignment of the interfering beams could account for the observed difference. [ABSTRACT FROM AUTHOR]

In this paper, we report our systematic study of a promising absolute-calibration technique of analog photodetectors based on the properties of parametric down conversion. Our formal results and a preliminary uncertainty analysis show that the proposed method can be effectively developed with interesting applications to metrology. [ABSTRACT FROM AUTHOR]

The uncertainty in the evaluation of the frequency shift caused in the Cs hyperfine transition by the alternating current Stark effect due to blackbody radiation is presently the dominant term in the accuracy budget of Cs fountain frequency standards. The bias is calculated with a formula wherein it is proportional to a coefficient β. The latter must be known to the nearest 1% if the accuracy goal is in the low 10-16. This, in turn, has required 10-16 uncertainty in frequency measurements used to evaluate β. The novel technique discussed here relaxes this latter requirement by shifting the burden to the short-term stability of the experiment, hence allowing that kind of accuracy on β even if the accuracy of the standard is lower. The method is based on fast temperature cycling of the drift tube while keeping everything else at a constant temperature. In this way, all frequency biases, other than the one under study, are rejected as common mode in a differential measurement, and the uncertainty on the relative shift can be better than the accuracy of the frequency standard. [ABSTRACT FROM AUTHOR]

Optical ray tracing is a computationally intensive operation that is central both to the design of optical systems and to analyzing their performance once built. The authors have previously reported on the use of parallel digital signal processors (DSPs) to reduce the time required to perform ray tracing in analyzing the performance of the moderate resolution imaging spectroradiometer (MODIS), which is presently in orbit on multiple spacecraft. The earlier work was incomplete, providing only a conservative estimate of the performance improvement that could be achieved with one to four DSPs. This paper reports on the completed project and extends the earlier work to eight DSPs. As predicted in the earlier paper, not all rays make it through the entire optical system. Many are lost along the way. This is one factor that led to reduced processing time. Another is the use of an optimizing compiler. In this paper, the authors present results showing the separate effect of each of these two independent factors on the overall processing time. The most significant finding is the extraordinarily linear relationship between the number of DSPs available and the speed of the ray tracing. By using eight DSPs, the processing time is reduced from two weeks to less than one and a half days, an improvement of nearly a whole order of magnitude. Low-cost high-speed ray tracing is now feasible using off-the-shelf plug-in processor boards. [ABSTRACT FROM AUTHOR]

An instrumentation based on a silicon monolithic array of 60 photon counters [single-photon avalanche diode array (SPADA)] for state-of-the-art measurements of fast transient phenomena and adaptive optics (AO) is presented. The fabricated solid-state photon counters are rugged, easy to be integrated in the optical system, free from read-out noise, and provide very fast frame rates (> 10 kHz) and nanosecond electronic gating. The detection electronics includes an integrated active-quenching circuit (AQC) for each pixel of the array. The real-time data- processing board is implemented into a field programmable gate array (FPGA) and a digital signal processor (DSP) and is configurable for dealing with different applications: acquisition and processing of two-dimensional (2-D) images with fast frame rate and extraction of the curvature wavefront for adaptive optics applications. The optical and electrical characterization of the detectors and the associated electronics is reported. [ABSTRACT FROM AUTHOR]

A major challenge for light scattering techniques is the ability to simultaneously collect data over a wide angular range. This is of particular interest if light scattering is used for medical diagnostics of biological cells. The intricate relationship between scattered light and cellular morphological structure is especially visible over the whole scattering regime. Unfortunately, intensity levels of the scattered light display large variations over scattering angles. Consequently, low and high angles of scattering cannot be concomitantly imaged in one single test. Repeated measurements over a series of angles are time consuming and inefficient. On the other hand, preferential sampling of only a few scattering angles results in overlooking important information contained in other angular ranges. We propose the use of an interference filter for selective attenuation of scattered light Our approach is to employ a commercial shortwave-pass filter. We discuss how to obtain adequate contrast between scattering peaks to enable detection over a wide angular range. The filter is incorporated into the design of a microchip-based optical device for single cell medical diagnostics. It is expected that this inexpensive device will provide advantages arising from simultaneous imaging of a wider angular range. [ABSTRACT FROM AUTHOR]

The pulse parameters of amplitude and transition duration are dependent on the waveform epoch and transition occurrence instant of the pulse transition in the waveform epoch. The primary explanations for the observed variations are the pulse aberrations and settling behavior of both the pulse generator and the measurement instrument (sampling oscilloscope). Measurement results are included for three pulse generators and two sampling oscilloscopes. [ABSTRACT FROM AUTHOR]

Today's very deep submicron IC technology enables high-performance analog and digital applications to be integrated on a single piece of silicon. For this effort, a design of 2.5 giga sample per second (GSPS) receiver-on-a-chip (ROC) is presented. For our design, we take advantage of a compensation technique to reduce spurs and improve instantaneous dynamic range. A major goal is to produce a low-cost, small, and lightweight, and low-power ROC. Our design will cover a 1-GHz bandwidth (125-1125 MHz), and it will correctly process two simultaneous signals by detecting their frequency, pulsewidth (PW), and time of arrival (TOA). The single or dual signal, spur-free dynamic ranges and two signal instantaneous dynamic ranges of our design are high. The minimum frequency separation of two signals is 10 MHz (one channel width), and the maximum amplitude separation (dynamic range) of two signals is 18 dB with the second signal false alarm less than 1%. [ABSTRACT FROM AUTHOR]

A jitter-free vector frequency-domain measurement technique to characterize optical reference receivers is presented. The system is based on a Mach-Zehnder integrated-optic modulator (IOM). Results from this new technique and those obtained by optical impulse and heterodyne methods are compared up to 76 GHz An IOM down-conversion scheme was used to measure the heterodyne beat frequency to >106 GHz. [ABSTRACT FROM AUTHOR]

The frequency of the ²Sfrac12; (F = 0, mF = 0) - ²Ffrac72; (F = 3, mF = 0) transition in a single, trapped, laser cooled ion of 171yb+ has been measured with an improved narrow probe laser and a femtosecond laser frequency comb generator. Our best estimate of the frequency is 642 121 496 772.3 ± 0.6 kHz by comparison with earlier measurements. The uncertainty is limited by measurement statistics and by the ac Stark shift. [ABSTRACT FROM AUTHOR]

We report progress toward a Cs-fountain frequency standard operating in the nanokelvin temperature range. We have implemented the Raman sideband cooling in a far-off-resonance optical lattice and observed subrecoil temperatures of 200 nK. We have studied the structure of the lattice and optimized the capture of atoms released from the magneto-optical trap into the lattice. In addition, the atoms, accumulated by the cooling scheme in the stretched magnetic state mF = 3, have been transferred to the magnetically insensitive state mF = 0 by using the adiabatic-passage technique. [ABSTRACT FROM AUTHOR]

We are developing a highly stable optical-microwave frequency link system using an optical frequency comb. We consider the stability degradation factors in the frequency link system to be the synthesis, phase locking, and photo detection system of the repetition frequency. We evaluated these factors by undertaking phase noise measurements and we estimated the stability from these results. These estimations were consistent with experimental results. [ABSTRACT FROM AUTHOR]

We have used a Ti:Sapphire-based fs-comb generator to measure the frequencies of several optical frequency standards available at PTB. The frequency values for HeNe- and frequency- doubled Nd:Yag lasers stablized to iodine hyperfine transitions as well as the frequencies of the ¹S0 - P1, transition of 40Ca at 657.5 mu (456 THz) and the ¹S½ D&frac32; transition of 171Yb+ at 435.5 nm (688 THz) are presented. Comparing our results with previously published data for the frequency variation of transitions of the Hg+ ion and H atom, we have derived a new upper limit of the variation of the fine structure constant α. [ABSTRACT FROM AUTHOR]

The frequency of the ²Sfrac12; (F = 0, mF = 0) - ²Ffrac72; (F = 3, mF = 0) transition in a single, trapped, laser cooled ion of 171yb+ has been measured with an improved narrow probe laser and a femtosecond laser frequency comb generator. Our best estimate of the frequency is 642 121 496 772.3 ± 0.6 kHz by comparison with earlier measurements. The uncertainty is limited by measurement statistics and by the ac Stark shift. [ABSTRACT FROM AUTHOR]

One of the instruments on the sun-synchronous Thrra (EOS AM) and Aqua (EOS PM) spacecraft, the Moderate Resolution Spectroradiometer (MODIS), obtains calibration data once during every orbit. Observations of the sun permit corrections to observations of the earth during the ensuing orbit. Although the instrument was designed to receive uniform sunlight over the entire surface of its detector, the sunlight was in fact not uniform. While this did not adversely affect the calibration, it nonetheless implied a lack of understanding of how the optical system really functioned. To lean what was wrong, NASA used an optical ray-tracing program on a DEC Alpha computer. The results correlated well with the observations made by the instrument itself, hut it took nearly two weeks to complete the computer simulation, a discouragingly long time. This paper describes the algorithm and its implementation in a system with multiple digital signal processor (DSP) chips operating in parallel. Timing data show a highly linear relationship between the number of DSPs present and the speed of the computation. Administrative overhead is negligible compared to the time taken to compute ray trajectories. This implies that many more than just four DSPs could be harnessed before administrative overhead would begin to be significant. [ABSTRACT FROM AUTHOR]

Presents a study that reported on work directed toward the systematic evaluation of an optical frequency standard based on the [sup199]Hg[sup+] ion. Overview on the atomic system; Frequency measurements of the clock transition; Conclusion.

Presents a study that realized an optical frequency standard based on cold neutral calcium atoms released from a magnetooptical trap. Spectroscopic properties of calcium atoms; Experimental setup; Uncertainty of the optical calcium frequency standard.

Celebrates the progress in optical frequency standards and measurement, won by the 40 years of dedicated work of worldwide teams working in frequency standards and frequency measurement. Approaches to optical frequency measurement; Basis for frequency metrology; Illustration of a prototype of an optically-based clock.

Presents a study that reported the capture of cold strontium atoms in a magnetooptical trap at a rate of 3 x 10[sup10] atoms/s. Setup of the sum-frequency generation system; Overview on cold atom source; Conclusion.