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Lenght characterization of a piezoelectric actuator by use of a mode-locked femtosecond laser
Pravdová, Lenka ; Lešundák, Adam ; Šmíd, Radek ; Číp, Ondřej
Modern laser interferometers with high resolution are considered as very precise sensors for length measurement. We assembled a specialized optical resonator using silver mirrors. The femtosecond laser with a repetition frequency of 250 MHz and a central wavelength 1560 nm of supercontinuum is used. Femtosecond laser is stabilized by optical frequency comb technique, ie. the frequency offset fCEO and repetition frequency frep is synchronized by our ultra-stable frequency source - hydrogen maser. The technique of derivative spectroscopy is used for locking the resonance peaks of the resonator component of the supercontinuum. The frequency frep in fine steps in the desired range of values is changed via control electronics. This was achieved by changing the length of the cavity in the order of several hundred of nanometers. Repetition frequency change is carried out so that the entire range of the length of the actuator is tested. Value of the applied voltage is recorded for every measured point of the characteristics. The result is a measured characteristic hysteresis curve of the PZT actuator.
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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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The femtosecond optical frequency comb based tool for spectral analysis of molecular absorbtion gases
Lešundák, Adam ; Šmíd, Radek ; Buchta, Zdeněk ; Mikel, Břetislav ; Lazar, Josef ; Randula, A. ; Číp, Ondřej
The spectral analysis of absorption of molecular gases belongs to very powerful methods for detection of concentration of gases in a tested sample. In case of the human breath it consists of hundreds of molecules of gasses and their concentrations are known as biomarkers. An increased concentration of more of them indicates certain diseases or symptoms. The presenting work covers a pilot experiment where femtosecond pulse probe laser and a detection chain based on cross-correlation makes an analysis of the specimen of the absorption gas. In the pilot experimental set-up the detection part utilizes a Michelson interferometer with movable measuring mirror. We developed a novel digital processing method for precise stabilization of the speed of the mirror during measuring process. The caught optical signals are calculated by the fast Fourier transform from the time to wavelength domain. The first caught spectra of the femtosecond beam passing trough the specimens show absorption lines of one isotope of acetylene which was tested as the first sample. The work proofed positive the possibility of using the femtosecond laser for detection of broadband absorption spectra in the infrared region.
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