Real-time Alignment Research Articles

Increasing the Tokamak Pressure Limit: Tearing Mode Experiments in DIII-D

Since its reconfiguration in 1986, DIII-D has performed a number of experiments involving resistive magnetohydrodynamic (MHD) stability. These were and are directed to understand the conditions in which confinement and beta reducing tearing mode islands form, how to avoid them, and if unavoidable, how to stabilize them. Coils for correction of toroidal nonaxisymmetry have been developed to avoid error field locked mode islands. Basic classical tearing mode stability physics has been confirmed with a state-of-the-art ensemble of profile diagnostics, MHD equilibrium reconstruction, and stability code analysis. Neoclassical tearing mode thresholds and seeding are now much better understood with future large higher field devices expected to be “metastable.” DIII-D is the leader in sophisticated real-time alignment of stabilizing electron cyclotron current drive on otherwise unstable rational surfaces. In all, DIII-D experiments are showing how higher stable beta with good confinement can be maintained without tearing mode islands limiting the plasma pressure.

Fluorescence correlation microscopy with real-time alignment readout

In confocal fluorescence correlation microscopy (FCM) it is important to ensure that the correlation measurement is actually performed at the chosen location of the three-dimensional image of the specimen. We present a confocal FCM design that provides an automatic real-time readout of the location in the confocal microscopic image, which is aligned with the detector of the fluorescence correlation spectrometer. The design accomplishes this without using any special positioning device. The design is based on an apertured fluorescence detector placed close to the back aperture of the objective lens and can be easily incorporated into virtually any confocal microscope. We demonstrate the method by performing FCM measurements of a dye diffusing on a cell membrane.

Computational tools for Brassica–Arabidopsis comparative genomics

Recent advances, such as the availability of extensive genome survey sequence (GSS) data and draft physical maps, are radically transforming the means by which we can dissect Brassica genome structure and systematically relate it to the Arabidopsis model. Hitherto, our view of the co-linearities between these closely related genomes had been largely inferred from comparative RFLP data, necessitating substantial interpolation and expert interpretation. Sequencing of the Brassica rapa genome by the Multinational Brassica Genome Project will, however, enable an entirely computational approach to this problem. Meanwhile we have been developing databases and bioinformatics tools to support our work in Brassica comparative genomics, including a recently completed draft physical map of B. rapa integrated with anchor probes derived from the Arabidopsis genome sequence. We are also exploring new ways to display the emerging Brassica–Arabidopsis sequence homology data. We have mapped all publicly available Brassica sequences in silico to the Arabidopsis TIGR v5 genome sequence and published this in the ATIDB database that uses Generic Genome Browser (GBrowse). This in silico approach potentially identifies all paralogous sequences and so we colour-code the significance of the mappings and offer an integrated, real-time multiple alignment tool to partition them into paralogous groups. The MySQL database driving GBrowse can also be directly interrogated, using the powerful API offered by the Perl Bio∷DB∷GFF methods, facilitating a wide range of data-mining possibilities.

Coordination in coteaching: Producing alignment in real time

In coteaching, two or more teachers take collective responsibility for enacting a curriculum together with their students. Past research provided some indication that in the course of coteaching, not only the teaching practices of the partners become increasingly alike but also do unconsciously produced ways of moving about the classroom, hand gestures, and body movements. In this study, we investigate the possible sources of occurrence for the coordination of social and physical practices and provide exemplary episodes at a fine-grained level from one coteaching pair. Drawing on key concepts from cultural sociology, we show how participants continuously create material and social resources that allow for new forms of agency in subsequent moments. Such resources include physical, temporal, and social spaces and meaning-making entities (language, inscriptions). We show how in productive coteaching, participants deploy and take advantage of these resources in synchronized and coordinated ways. The synchronization operates both at the temporal level, where coteachers work in concert like experienced jazz musicians in a jam session, and at a substantive level, where the practices of one look like those of the other. As coteachers generally are not aware that they adopt the ways of their partners as we articulate them here, there are considerable consequences, for better or worse, that arise from teaching with another person. © 2005 Wiley Periodicals, Inc. Sci Ed, 89:675–702, 2005

Microperimetry — comparison between the micro perimeter 1 and scanning laser ophthalmoscope — fundus perimetry

To compare microperimetry using the scanning laser ophthalmoscope (SLO, Rodenstock, Germany) and the recently introduced Micro Perimeter 1 (Nidek Technologies, Italy). Prospective comparative observational study. Fundus perimetry with static threshold perimetry was performed using the SLO and the MP1 in 68 eyes of 40 consecutive patients with different retinal diseases for example, central serous chorioretinopathy, macular dystrophy, and age-related macular degeneration. With both instruments, an automated 4-2-1 staircase strategy with Goldmann III stimuli and a comparable number of stimuli were applied. The depth and size of the detected scotomata as well as the location and stability of fixation were compared between both instruments. There was good concordance of results, with 75% (51 of 68 eyes) showing an equal defect. Whereas the MP1 showed larger defects (depth and size) in 23.5% (16/68) of eyes studied than the SLO, the defects appeared larger with the SLO in 1 eye. Concerning fixation analysis, similar results were found for fixation stability with stable fixation in 47.1% (MP1: 32/68) and 48.5% (SLO: 33/68) and likewise for the location of fixation with foveal fixation in 54.4% (37/68) with the MP1 and the SLO. Whereas the average number of stimuli was similar for both instruments (MP1 56.8 +/-16.1, SLO 62.9 +/- 17.0), examination time was prolonged with the MP1 (MP1: 11m 35s +/- 3m 47s, SLO: 10m 29s +/- 3m 23s). Throughout all examinations, fundus visualization with the SLO was superior to the MP1. For automated threshold microperimetry the MP1 provides results comparable to our SLO perimetry. Both instruments enable detection of sensitivity loss of the central visual field and an analysis of fixation behavior during microperimetry. Nevertheless, the MP1, with its automated real-time image alignment, facilitates examination. Additionally, the enlarged field allows testing in an area of 44 x 36 degrees instead of the 33 x 21 degree-area of the SLO. However, in comparison to our SLO-software, the current software of the MP1 requires improvements before exact measurements of defined retinal diseases are possible.

Development and test of a new grating-polarimeter and its application in ellipsometric measurements

An original configuration of a photo-polarimeter with a blazed diffraction grating as central element is proposed for a newel ellipsometric set up. It produces two measurement beams corresponding to the grating diffraction orders ±1. The third beam, corresponding to the diffraction order 0, is back-reflected for the real time alignment of the photo-polarimeter by the autocollimation method. Each of the two diffracted beams passes through a beam splitter to be resulted in the four beams required for the measurement. The light intensity is measured by either four silicon detectors or four small photomultipliers and data are collected by four parallel ADC channels. In order to evaluate the measurement speed of the ellipsometer constructed using these new polarimeters, the change of the polarization state produced by a photo-elastic modulator oscillating at 50 kHz was measured in real time.

The RASNIK real-time relative alignment monitor for the CDF inner tracking detectors

We describe the design and operation of the RASNIK optical relative alignment system designed for and installed on the CDF inner tracking detectors. The system provides low-cost minute-by-minute alignment monitoring with submicron precision. To reduce ambiguities, we modified the original three-element RASNIK design to a two-element one. Since the RASNIKs are located within 10– 40 cm of the beam line, the systems were built from low-mass and radiation-hard components and are operated in a mode which reduces damage from radiation. We describe the data-acquisition system, which has been running without interruption since before the CDF detector was rolled into its collision hall in March 2001. We evaluate what has been learned about sources of detector motion from almost 2 years of RASNIK data and discuss possible improvements to the system.

High-precision measurement of angular dispersion in a CPA laser

Angular dispersion is measured with the accuracy of 0.2 μrad/nm by a new method based on spectrally resolved interferometry. It is linear, simple and allows for real-time alignment of the stretcher-compressor system of CPA lasers.

Real-time active alignment demonstration for free-space optical interconnections

A real-time active alignment system is reported for short-distance free-space optical interconnections that compensates for dynamical disturbances. Real-time misalignment compensation is a solution to achieve tight alignment tolerances without compromising the spatial density of the optical channels. A piezoelectric microstage and a proportional-integral-derivative (PID) control scheme was implemented in an experimental system and misalignment error compensation was demonstrated up to 118 Hz.

On-line measurement of the straightness of seamless steel pipes using machine vision technique

In this paper, on-line and real-time laser visual alignment measurement technique is studied to measure the spatial straightness of large objects. The basic principle of the visual alignment measurement is detailed. The mathematics models of visual sensor, measurement system and their calibrations are presented. Based on the technique, an experiment system is developed and the straightness of a 1500 mm long seamless steel pipe is inspected. The experiment results show that the measurement technique can achieve total on-line measurement and it offers high precision and stability, which is of practical importance for the application.

A low-power analog correlation processor for real-time camera alignment and motion computation

A design is presented for a low-power switched-current block correlation processor, which produces a set of feature matches between pairs of binary edge images. The novelty and usefulness of the processor stem from the reliability of its outputs. Statistical tests are included to minimize the probability that the correspondences found have occurred by chance. The results may be used without further refinement to accurately compute the epipolar geometry between two camera positions. The primary applications of this processor are computing camera motion and providing coarse alignment of two images acquired from similar sensors. An analog design was chosen to reduce circuit area in order to accommodate both large template blocks and search areas. Switched current sources at each pixel are summed on a single wire, while analog comparators implement the validation tests and track the minimum score. A prototype 5/spl times/5 block processor with a 9/spl times/9 search area was fabricated as a Tiny Chip through MOSIS in a 1.2-/spl mu/m complimentary metal-oxide-semiconductor (CMOS) process. The chip correctly determined the correct matches for the given patterns and dissipated no more than 12 /spl mu/W of static power per pixel in continuous operation. In a full-scale implementation, an array of several large (e.g., 24/spl times/24) block processors could be placed single 1 cm/sup 2/ die. Measurements indicate that the computations for each block offset can be processed in less than 200 ns, implying that a 200/spl times/200 area can be searched in 8 ms.

Development of EXELFS for Nanoscale Atomic Structure Determination

EXELFS spectroscopy contains the same local atomic structural information as XAFS; furthermore, it is readily applied to low Z elements, has high spatial resolution, and the capacity of combining other local WM measurements. Due to hitherto relatively poor quality of the EELS data, the EXELFS technique has not been developed to its full advantage until recently. We introduced various new methods to improve the data acquisition including real-time alignment and accumulation of virtually unlimited number of spectra while monitoring sample drift, radiation damage, and changes in energy resolution. We also developed a systematic data analysis procedure which corrects for the differences between EXELFS and XAFS, and adopts the UWXAFS data analysis software package to perform EXELFS data analysis with the same level of sophistication. The technique is demonstrated for SiC.

Photoacoustic methods for real-time measurement of laser beam diameter and position, and for laser cavity alignment

Photoacoustic signals generated in absorbing media can be used for real-time alignment of laser cavity components, for measurements of positions and diameters of pulsed laser beams, and for control of the degree of overlap of two or more, focused and unfocused pulsed laser beams. The developed techniques require an absorbing medium and a piezoelectric detector. Measurements and control can be performed by real-time inspection of the acoustic signals in an oscilloscope. These methods are convenient for experiments in nonlinear optics in which the power requirements lead to focusing and superposition of the beams, and for alignment of laser cavities in the liquid phase as well as gas and solid state infrared lasers.

エキシマレーザ露光装置用ＴＴＬアライメント法 倍率色収差を補正したリアルタイムアライメントＳＭＡＲＴ

This paper presents a real-time SMART (separated mark TTL alignment) technique for optical lithography systems. The new TTL alignment optical system corrects lateral chromatic aberration which has made impossible reticle-to-wafer real-time alignment (during exposure) at all mark positions. The optical method of correcting lateral chromatic aberration is described. This correcting method was applied to a KrF excimer laser optical lithography aligner to demonstrate the principle of this alignment method. The simulation results of alignment beam positions were similar to the experimental results. At each alignment mark position, the alignment signal level was sufficient to allow detection as a positioning signal, an overlay accuracy of ± 0.05 μm (3σ) was achieved.

0.05 µm (3σ) Overlay Accuracy Through-the-lens Alignment in an Excimer Laser Lithography System

This paper presents a through-the-lens (TTL) alignment, called separated mark TTL alignment (SMART), applied to a KrF excimer laser lithography system. This SMART optical system does not require any complicated compensation mechanisms for longitudinal chromatic aberration. Several advanced methods for SMART optics to obtain higher overlay accuracy, such as optical heterodyne interferometry, real-time alignment system, and alignment signal processor, have been developed and adopted. The performance of such an improved SMART in an excimer laser lithography system was experimentally evaluated using dynamic random access memory (DRAM)-processed wafers. An overlay accuracy of 0.05 µm (3σ) has been achieved.

Stabilization of laser beam alignment to an optical resonator by heterodyne detection of off-axis modes

We demonstrate a method for real time alignment of a Gaussian beam to an optical resonator. While thefrequency of a source laser is stabilized to a fundamental cavity mode resonance, phase modulation sidebands are applied at the off-axis mode frequencies. Asymmetrical transmission of the sideband at the frequency of each off-axis mode produces amplitude modulated optical signals and indicates the extent of the misalignments. Phase sensitive detection of these optical signals provides the error signals which are minimized by a control system that steers the input beam. In this way, optimum coupling of an injected source beam can be maintained to the fundamental mode of the resonator. This active alignment technique has demonstrated a sensitivity to tilts of 0.1 nrad/ radicalHz and to lateral beam displacements of 0.08 nm/ radicalHz in the ~1-Hz-1-kHz frequency range. These values correspond to 2 parts in 10(7) radicalHz for both the far-field divergence angle and the beam waist size. Such performance is within a factor of 2 of the shot noise limitation of the error signal measurement for a detected power of 160 microW.

X-ray lithography two-state alignment system

We present a novel alignment system for x-ray lithography. A linear Fresnel zone plate, defined on the mask, is used to focus a laser beam on a wafer mark (a series of dots). A fast electro-optic modulator is used to make the laser beam hop between two positions at the mark edges. The light diffracted by the periodic mark is measured at each position and a misalignment signal is originated when the mark is not illuminated equally in the two states. A signal that is proportional to the misalignment is generated when the error is within the alignment range (±0.2 μm); outside that range a capture signal is present as long as the beam is on the mark, which would be typically 2–4 μm wide. The method is highly sensitive with resolution in excess of 0.003 μm, has a wide capture range, no moving parts, and is suitable for real-time alignment during exposure. Sensitivity to gap changes is highly reduced, making the system ideal for synchrotron-based x-ray lithography aligners.

Femtosecond real-time alignment in chemical reactions

Femtosecond real-time alignment in dissociation reactions is observed experimentally for HgI 2 and ICN. The results are accounted for by the classical theory outlined here. This study adds a new dimension to femtosecond transition-state spectroscopy (FTS), namely the probing of the “vector dynamics” of reactions.

PAC-MAN, A Precision Alignment Control System for Multiple Laser Beams Self-Adaptive through the Use of Noise

A control system is described that aligns the 96 beams of the Aurora KrF laser system to within a pointing accuracy of 5 {mu}rad within 5 min and maintains the alignment in real time. This performance is made possible through a novel use of random noise. The 96 beams, together with optical benchmarks, are imaged on a single television (TV) camera. The pointing angles of those beams are estimated from the arithmetic means of the pixel coordinates within the beam images. The pixel intensities of each TV frame are mapped into a binary decision array based on whether or not the pixel intensity is above or below a threshold criterion. Existing, or introduced, random noise in the TV signal causes the contents of this array to vary from frame to frame, even when the actual beam is stationary. The beam positions are estimated from the pixel coordinates and their associated elements within this array. Finally, the beam angle estimates are updated from these position estimates, each TV frame, in combination with all previous estimates.