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Absolutní frekvenční posuvy jodem stabilizovaných laserových etalonů zpusobené čistotou jodu absorpčních kyvet
Hrabina, Jan ; Jedlička, Petr ; Číp, Ondřej ; Lazar, Josef
Results of measurement of purity of a set of iodine cells for laser stabilization made at our institute are presented. The purity was tested by improved method based on measurement of induced fluorescence and evaluation by the Stern-Volmer formula. This method was improved by innovation of the fluorescence detection system by introducing compensation for the pumping laser spectral and power instabilities. Further the absolute frequencies of selected iodine hyperfine transitions were measured in direct laser frequency comparison performed with a set of iodine-stabilized Nd:YAG laser etalons with the reproducibility well below the kHz level. The results indicating the iodine cell purity are presented with relation to the absolute frequency shifts. This highlights the influence of iodine cell quality onto the stability and absolute frequency of lasers etalons and also shows the way towards improvements of the iodine cell manufacturing technology.
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Měření čistoty jódu v absorpčních kyvetách pro frekvenční stabilizaci laserů
Hrabina, Jan ; Petrů, František ; Jedlička, Petr ; Číp, Ondřej ; Lazar, Josef
In the contribution we present a system for measurement of iodine purity by means excitation of a selected strong transition, measurement of induced fluorescence and evaluation by the Stern-Volmer formula. The arrangement is based on a pumping Ar-ion laser tuned to the transition of interest but its linewidth far exceeds the transition. Frequency noise of the laser is effectivelly reduced by monitoring the fluorescence in a second, reference iodine cell and together with monitoring of the laser power enables cancelation of the frequency noise influence which generates errors by demodulating on the absorption profile. The level of the scattered light is subtracted as well. All the measured data are digitally processed and the experiment is fully computer controlled.
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Construction of laser source for precision measurements
Mikel, Břetislav ; Urban, F. ; Číp, Ondřej
We describe a new laser head with Vertical Cavity Surface Emitting Laser (VCSEL) diode. The VCSEL lasers at 760 nm with mode-hop free tuning range above 1 nm are affordable now. The VCSEL's are fabricated as circulary-symetric lasers; the circular aperture is of particular value as it implies a circular beam profile. The linewidth and the optical noise of the VCSEL laser diode depend on the stability of the current source controller and on the quality temperature control system. We developed a digital temperature control system with temperature stability below 1 mK and high stability current source controller.
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New method for direct measurement of refraction index of air with He-Ne lasers
Matoušek, Vít ; Číp, Ondřej
Interferometer methods are used for the high accuracy measurement of distance by specifying the measurement of the air index, since the measurement of the refraction index of air is in atmosphere, the refraction index of air is dependant upon temperature, pressure and humidity. For the measurement of the refraction index of air, Eden's formula is usually used. The formula depends upon the atmospheric values and the CO2 concentration.
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Řídící systém pro absolutní interferometrii s plynule přeladitelným polovodičovým laserem
Mikel, Břetislav ; Číp, Ondřej ; Lazar, Josef
In the work, we oriented to development of the absolute distance interferometer with narrow-linewidth tunable VCSEL laser (Vertical-Cavity Surface-Emitting Laser) at 760 nm and a wavelength-scanning interferometry technique improved by an amplitudě division of interference fringe. We built a high precision current source with respect to high sensitivity of the VCSEL laser diodes. An operating temperature of the VCSEL laser housed in a specially designed copper mount is stabilized below l mK by a fast digital temperature controller. With respect to a highsensitivity of the emitted wavelength to the injection current fluctuation, we provided the stabilization of laser frequency by means of an electronic frequency lock to modes of the Fabry-Perot glass etalon. The PC controls the scanning process, so that, after l nm scan of the wavelength we obtains records of coursed interference fringes and Fabry-Perot resonance modes at the same time
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Vláknové mřížky pro zvýšení stability polovodičových laserů
Mikel, Břetislav ; Číp, Ondřej
The industrial production of Vertical Cavity Surface Emittíng Laser (VCSEL) diodes started several years ago. They have a wide range of applications in laser interferometry and spectroscopy. At present VCSELs become very attractive in optical communications in Wavelength Division Multiplexing (WDM) systems. The influence of the external optical feedback on spectral characteristics of VCSELs has been studied. At present the most interesting solution of this external feedback is to use an external fiber with fíber grating. Thanks to advances in technology of fabrication of fiber gratings they can be used as the external cavity for edge emitting laser diodes and as well as for VCSELs. Study of linewidth improvement, frequency stability, and mechanical stability are growing in importance in connection with fiber gratings
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Porovnání metod pro výpočet srdečního výdeje ze signálu impedanční kardiografie
Jurák, Pavel ; Halámek, Josef ; Vondra, Vlastimil ; Kára, T. ; Nykodým, J. ; Číp, Ondřej ; Eisenberger, M. ; Leinveber, P. ; Fráňa, P. ; Meluzín, J. ; Souček, M.
The goal of the study is to compare various methods of non-invasive stroke volume (SV) assessment from a raw impedance cardiography (IC) signal. IC detects changes in cardiac haemodynamic function using thoracic electrical bioimpedance technology. Corresponding changes of impedance are used along with ECG and blood pressure to measure and calculate haemodynamics parameters
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