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Nanometrology coordinate measurement machines uncertainties caused by frequency fluctuations of the laser
Hrabina, Jan ; Lazar, Josef ; Číp, Ondřej
One of considerable sources of displacement measurement uncertainty in nanometrology systems such as multidimensional interferometric positioning for local probe microscopy is the influence of amplitude and especially frequency noise of a laser source which powers the interferometers. We investigated the noise properties of several laser sources suitable for interferometry for micro- and nano-CMMs (coordinate measurement machines) and compared the results with the aim to find the best option. The influences of amplitude and frequency fluctuations were compared together with the noise and uncertainty contributions of other components of the whole measuring system. Frequency noise of investigated laser sources was measured by two approaches – at first with the help of frequency discriminator (Fabry-Perot resonator) converting the frequency (phase) noise into amplitude one and then directly through the measurement of displacement noise at the output of the interferometer fringe detection and position evaluation. Both frequency noise measurements and amplitude noise measurements were done simultaneously through fast and high dynamic range synchronous sampling to have the possibility to separate the frequency noise and to compare the recorded results.
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Differential interferometry with suppression of the influence of refractive index of air for nanometrology
Holá, Miroslava ; Číp, Ondřej ; Hrabina, Jan ; Buchta, Zdeněk ; Lazar, Josef
We present an interferometric technique based on differential interferometry setup for measurement in the subnanometer scale in atmospheric conditions. The motivation for development of this ultraprecise technique is coming from the field of nanometrology. The key limiting factor in any optical measurement are fluctuations of the refractive index of air representing a source of uncertainty on the 1*E-6 level when evaluated indirectly from the physical parameters of the atmosphere. Our proposal is based on the concept of overdetermined interferometric setup where a reference length is derived from a mechanical frame made from a material with very low thermal coefficient on the 1*E-8 level. The technique allows to track the variations of the refractive index of air on-line directly in the line of the measuring beam and to compensate for the fluctuations. The optical setup consists of three interferometers sharing the same beam path where two measure differentially the displacement while the third evaluates the changes in the measuring range acting as a tracking refractometer. The principle is demonstrated on an experimental setup and a set of measurements describing the performance is presented.
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Displacement Interferometry in Passive Fabry-Perot Cavity
Lazar, Josef ; Číp, Ondřej ; Oulehla, Jindřich ; Pokorný, Pavel ; Fejfar, Antonín ; Stuchlík, Jiří
We present techniques oriented to improvement of precision in incremental interferometric measurements of displacements over a limited range where the atmospheric wavelength of the coherent laser source is either directly stabilized to a mechanical reference or is corrected to fit to the reference. This may represent a reduction of uncertainty linking the laser wavelength not to indirectly evaluated refractive index but to the setup mechanics which cannot be completely eliminated. Here we suggest an approach where the traditional interferometers are replaced by a passive Fabry-Perot cavity with position sensing using an intracavity transparent photodetector.
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Optical methods in non-contact velocity measurement
Šmíd, Petr
The paper presents an overview of some interesting methods using optical and sound waves for non-contact velocity measurements. The paper focuses mainly on optical techniques using different optical principles as interferometry, image analysis and processing, and speckle effect.
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Interferometer controlled positioning for nanometrology
Lazar, Josef ; Číp, Ondřej ; Čížek, Martin ; Hrabina, Jan ; Šerý, Mojmír ; Klapetek, P.
We present a system for dimensional nanometrology based on scanning probe microscopy techniques (primarily atomic force microscopy, AFM) for detection of sample profile combined with interferometer controlled positioning. The interferometric setup not only improves resolution of the position control but also ensures direct traceability to the primary etalon of length. The system was developed to operate at and in cooperation with the Czech metrology institute for calibration purposes and nanometrology. The interferometers are supplied from a frequency doubled Nd:YAG laser stabilized by linear absorption spectroscopy in molecular iodine and the interferometric configuration controls the stage position in all six degrees of freedom.
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Preliminary interferometry measurements of flow field around a fluttering NACA0015 profile
Vlček, Václav ; Kozánek, Jan
The paper presents experimental results of the optical measurements of flow field around a fluttering NACA0015 profile elastically supported with two degrees of freedom in subsonic wind flow. The high-speed camera was used for the interferometry visualization of the airflow in different phases of the profile motion. Special care was devoted to the plotting of the fringes near the surface of the profile, which was blurry due to the fast vibration. Examples of the interferograms, pressure and velocity development around the surface of the vibrating body and the phase shift between rotation and translation cycles are presented.
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