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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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The smart electronic unit for precise measurement of refractive index of air in a nano-positioning stage for scanning probe microscopy (SPM)
Hucl, Václav ; Čížek, Martin ; Buchta, Zdeněk ; Mikel, Břetislav ; Lazar, Josef ; Číp, Ondřej
When the traceable measurement of dimensions of samples in scanning probe microscopy is needed the position of the probe tip has to be monitored by a set of laser interferometers. The measurement is done very often during standard atmospheric conditions so the changes of the refractive index of air have an influence to measured values of the length with 1.0exp(-4) relatively. Thus the measurement of the refractive index of air and application of the instantaneous value of the index to all of measurement interferometric axes is necessary. In the work we developed new concept of electronic unit which is able to monitor the refractive index of air on basis of measurement of weather conditions: temperature, humidity and pressure of the air. The unit uses modified Edlen formula for calculation of the refractive index. The next step of the work is verification of accuracy of the measuring capability of the unit. We tested the accuracy with reference unit which measure the refractive index of air by a set of etalon sensors. The expected accuracy of the smart electronic unit falls to the 4.1exp(-7) relatively. The important advantage of the unit is very low power consumption of electronics so the unit causes very small temperature effects to the measuring process.
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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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Laser interference nano-comparator for length sensor calibration in nanometric scale
Číp, Ondřej ; Mikel, Břetislav ; Čížek, Martin ; Šmíd, Radek ; Buchta, Zdeněk ; Lazar, Josef
In the work we present new laser measuring system for precise calibrations of length measuring transducers. This gauge is called nano-comparator because the resolution of the positioning of the measuring probe is in order of nanometers. The gauge works fully self-controlled and it is equipped by control software which is able to calibrate wide area of transducers. We put main stress to compensating of thermal dilatation of the gauge body and to eliminating of imperfection of linear guide ways which are used for positioning of the testing probe of the gauge. The work presents the first records of scale calibration of an incremental transducer.
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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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Absolutní frekvenční posuvy jodem stabilizovaných laserových etalonů zpusobené čistotou jodu absorpčních kyvet
Hrabina, Jan ; Jedlička, Petr ; Číp, Ondřej ; Lazar, Josef
Jodem stabilizované Nd:YAG lasery představují ve spojení se syntezátory optických kmitočtů prostředek k realizaci optických hodin, zařízení dovolujícího dosažení stability optické frekvence stabilizovaného laseru do radiofrekvenčního pásma. V této práci prezentujeme výsledky měření čistoty jodu v absorpčních kyvetách vyrobených na našem ústavu. Čistota byla testována zdokonalenou metodou založenou na indukované fluorescenci s výpočtem Sternovy-Volmerovy formule. Zdokonalení sestavy spočívalo v zařazení prvků ke kompenzaci modových a výkonových nestabilit budicího laseru. Dále byly přímým frekvenčním srovnáváním změřeny absolutní frekvence vybraných hyperjemných jodových přechodů Nd:YAG laseru stabilizovaného pomocí jodových absorpčních kyvet s reprodukovatelností měření pod úrovní 1 kHz. Výsledky obou metod spolu dobře korelují a byly použity ke zdokonalení technologie výroby kyvet na našem ústavu.
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