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Digital signal synthesizer for compensating Doppler effect in fiber-optic lines
Hucl, Václav ; Čížek, Martin ; Pham, Minh Tuan ; Pravdová, Lenka ; Číp, Ondřej
If a highly stable laser standard is distributed over a long fiber-optic line the stability of optical frequency of the laser at the far end is usually degraded due to external influences on the optical fiber. Thermal dilatation or vibrations of the fiber result in Doppler shifts changing the optical frequency of the laser light. A setup based on an unbalanced Mach-Zehnder or a Michelson interferometer with the optical line acting as a measuring arm can be used for detecting Doppler frequency shifts. Once we are able to detect the shifts we can compensate them by detuning the optical frequency of the transmitted laser light in a closed-loop. Our paper presents the method of detecting the frequency shifts in the fiber-optic line together with a digital electronic controller. The controller is based on a digital signal processor and a DDS chip for generating the radiofrequency signal driving the acousto-optic modulator in order to detune the transmitted laser light.
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Optical diagnostic methods for energetics
Hrabina, Jan
This work is oriented to non-contacting laser spectroscopy diagnostic methods for monitoring of combustion processes in coal power plant facilities. These methods can be used for optimalization of combustion process in the chamber, which is neccessary step toward reduction of toxic gases releasing in to the atmosphere, increasing of efficiency of the combustion and reduction of overall costs needed for electricity production.
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Coordinate interferometric system for measuring the position of a sample of the electron lithograph
Holá, Miroslava ; Lazar, Josef ; Čížek, Martin ; Řeřucha, Šimon ; Číp, Ondřej
This project is called "Platform of advanced microscopic and spectroscopic techniques for nano and microtechnology." The coordinator of this project is the Brno University of Technology / Faculty of Mechanical Engineering and the co-investigators are ON Semiconductor Czech Republic, Ltd., Optaglio Ltd., Tescan Brno, Ltd. And the Institute of Scientific Instruments of the CAS, v. v. i.. In this project we are working on a design of an interferometric measuring system, laser source and detection techniques for a coordinate measuring system of the table of the electron beam lithography.
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Distribution of the accurate optical frequency and time via photonic networks in the Czech Republic
Číp, Ondřej ; Čížek, Martin ; Pravdová, Lenka ; Hucl, Václav ; Řeřucha, Šimon ; Hrabina, Jan ; Lešundák, Adam ; Mikel, Břetislav ; Lazar, Josef ; Vojtěch, J. ; Smotlacha, V.
To verify the stability of the frequency of optical clock an intensive research in the transmission of stable frequency via optical fibers is in progress for many years. Interconnection of large cities and metropolitan networks with optical fiber running DWDM allowing to transfer many optical signals in parallel over one fiber at the same time contributes significantly to troubleshoot the problem. Between nodes of ISI Brno and the main center of CESNET there are several dedicated bi-directional channels through the DWDM technology. The first tests are ongoing with the transfer of accurate time, which are using the possibility of bi-directional communication over a single fiber, thus the phase delay including Doppler shift are reflected on the two signals as well. From periodic measurements can subsequently be evaluated daily, weekly and seasonal fluctuations of the delay and after deduction of such data from the measured data a mutual stability of used time normal can be determined. The second technique is a full compensation of phase of the laser wave through active control of phase changes of the wave during its transmission from the ISI to the node of CESNET. At present, a characterization of the behavior of individual system elements, including their commissioning is in progress.
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Laser standards for interferometry and stable frequencies distribution
Hrabina, Jan
Optical frequency references - absorption cells - represent an unique tool for frequency stabilization of the laser sources. Their spectral properies define overall quality of the stabilized laser, so these properties must be precisely controlled and verified. One of the most used absorption media in the visible spectral range is molecular iodine. It offers wide and reach spectra of very narrow and strong transitions so many types of laser standards can be realized on base of this media. Testing of final properties of iodine absorption cells is traditionaly based on two methods - laser induced fluorescence method (LIF) and evaluation of absolute frequency shifts of the iodine stabilized laser (beatnote measurement). Unfortunately both of these methods have few limitations and disadvantages - in case of high-quality cells the LIF method reaches its resolution limits, the beatnote method needs quite complicated optical setup. We present a novel approach for the iodine cells quality evaluation based on measurement of hyperfine transition linewidths - the impurities in absorption media cause line broadening of the transitions. Pilot measurement shows that presented method achieves a very good sensitivity to the iodine purity and together with a need of relatively simple setup can be considered as a novel method for absorption cells quality verification.
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Study of behavior of the refractive index fluctuations to the lenght noise in displacement interferometry
Holá, Miroslava
Nanoscale measurement became one of the key challenges in the field of metrology in last ten years. The international project launched called “Nanotrace” where renowned EU laboratories including the proposer of this project were trying to break the limits of resolution in interferometry. Techniques investigated here have proven that there are chances to achieve significant improvements in resolution of laser interferometry. Measurement of position within a limited range is typical for coordinate measuring system such as nanometrology standards combining scanning probe microscopy (SPM) with precise positioning. In this contribution we evaluate the level of uncertainty associated with spatial shift of two measuring beams and spatial shift of one measuring beam (change of length the measuring beam). Consequently the nature of the fluctuations of the refractive index of air in laser interferometry is investigated anddiscussed with the focus on potential applications in coordinate measuring systems and long-range metrological scanning pro microscopy systems.
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