[seminar] Seminar na IF-u, 19. veljace 2016. u 11:00 h

[Natasa Vujicic]

      Institut za fiziku, Bijenicka cesta 46,

      predavaonica u zgradi Mladen Paic

      petak, 19. veljace 2016., u 11:00 sati
     
      New Techniques for Broadband and Higly-Precise Spectroscopic Measurements  

       
     
      Dr. Piotr Maslowski
     
       

      Institute of Physics, Nicolaus Copernicus University, Torun, Poland 

      E-mail: pima at fizyka.umk.pl
     
       

      A great potential of cavity-enhanced absorption spectroscopy (CEAS) in application to ultrasensitive spectra measurements comes from significant elongation of optical path inside the high-finesse cavity. Cavity Ringdown Spectroscopy (CRDS) is an established technique based on variation of interaction time of the laser light with the optical cavity [1]. Insensitivity to the laser power fluctuations and negligible instrumental function make it powerful tool for sensitive trace gas detection or detailed spectral line-shape analysis. 

       

      The photon lifetime in the optical cavity, is directly related to the spectral width of the cavity resonant modes.  This phenomenon is exploited in a relatively new technique called cavity mode-width spectroscopy (CMWS) [2] in which absorption spectrum can be retrieved by precise measurements of half-widths of the cavity modes. Qualitative analysis of CRDS and CMWS methods reveals their complementarity in terms of achievable accuracies  at different levels of intracavity absorption.

       

      The absorption is always associated with dispersion, manifested as shifting of the resonant modes in the cavity-enhanced experiment. Measurement of dispersion mode shifts provides another way for potentially very accurate quantitative spectroscopy. Since frequency is a physical constant that can be measured most accurately, direct measurement of absolute or differential mode frequencies to obtain absorption coefficient in cavity mode dispersion spectroscopy (CMDS) should eliminate potential problems with nonlinearities of detection system and minimize contribution of systematic instrumental errors of measured spectra [3].

       

      Absorption spectroscopy based on optical frequency comb (OFC) allows measurements of molecular absorption spectra in wide spectral range with high signal-to-noise ratios, removing the limits of cw-laser spectroscopy caused by its step-like operation and usually limited tuning range. Fourier transform spectrometers (FTS)based on OFCs allow detection of broadband spectra within acquisition times orders of magnitude shorter than traditional FTIRs based on thermal sources. Moreover, the resolution of OFC-based FTS is not limited by the maximum optical path difference (OPD) between the interferometer's arms [4]. It makes it suitable to simultaneous acquisition of tens of molecular lines in wide pressure range. On the other hand, the setups  based on dispersive elements and detector arrays [5], have the advantage of fast acquisition, down to single microseconds. In both cases the sensitivity can be increased by coupling the OFC light to the optical enhancement cavities [6].

       

      In the talk, the basics of the techniques mentioned above will be presented, together with the results of experiments performed in the Institute of Physics in Torun based on those approaches. Also, the recent results obtained with Sr optical clock  will be shortly presented [7].

       

       

      References:

      1. A. Cygan et al., Eur.Phys. J.-Spec. Top. 222, 2119 (2013).

      2. A. Cygn et al., Opt. Express 21, 29744 (2013).

      3. A. Cygan et al., Opt. Express 23, 14472 (2015) 

      4. P. Maslowski et al., Phys. Rev. A, 93, 021802(R) (2016).

      5. G. Kowzan et al., Opt. Letters, accepted.

      6. A. Foltynowicz et al., Phys. Rev. Lett. 107, 233002 (2011).

      7. P. Morzynski et al., Sci. Rep. 5, 17495 (2015), M. Bober et al., Meas. Sci. Technol. 26, 0075201 (2015).

       
     
       

      Voditelji seminara IF-a: Natasa Vujicic i Damir Staresinic 

       
     
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