engleski

Direct frequency comb spectroscopy: time and frequency domain approach

Optical frequency comb brings revolutionary advances in frequency metrology and spectroscopy. Its frequency spectrum consists of a series of equidistant modes, whose frequencies can be described by the simple formula: fn = nfrep + f0: (1) Here, fn is the optical frequency of the n-th comb mode, frep is the repetition rate of the mode- locked laser and f0 is the carrier-envelope o set frequency. By measuring and controlling frep and f0 it is possible to control the frequencies of all comb modes, providing excellent spectroscopic tool over hundreds of teraherz of the comb bandwidth. Direct frequency comb spectroscopy (DFCS) employs frequency combs to directly interrogate atoms or molecules. One class of experiments use a frequency comb excitation of an atomic system to study the time-dependent quantum coherence. Uni cation of the time- and frequency- domain treatments, based on the coherence accumulation effects in systems characterized by the relaxation times longer than the laser repetition period was reported for cold rubidium atoms [1]. In Doppler-broadened rubidium vapor accumulation e effects in the time domain lead to a comb-like velocity distribution in the excited state and velocity selective population transfer in the alkali ground-state [2]. We will present the results of the experimental and theoretical investigations of the Doppler-broadened rubidium vapor excited by frequency comb, which gives us novel information about the accumulative effects in multilevel atoms and about the frequency comb used for the excitation [3]. In one of the most powerful alternative implementations of DFCS the interaction of the frequency comb with the sample is enhanced by the use of a high fi nesse optical cavity. Precise control of the optical frequency comb allows highly efficient coupling of the individual comb modes to the corresponding cavity resonances, while the long cavity lifetime enhances the effective interaction length between the light field and intracavity sample. As a result, Cavity-enhanced direct frequency comb spectroscopy (CE-DFCS) combines broad spectral bandwidth, high spectral resolution, precise frequency calibration and ultrahigh detection sensitivity [4]. Here, we will present the results of the CE-DFCS in the near-infrared wavelength region using a scanning Fourier transform spectrometer as a detection system [5, 6]. In addition to the other CE-DFCS advantages, the newly developed cavity-enhanced frequency comb Fourier transform spectrometer provides fast acquisition times, which all together brings it to the frontier of many interesting applications such as trace gas detection, breath analysis and other medical applications, environmental and atmospheric science, ... References [1] A. Marian et al., Science 306, 2063 (2004) [2] D. Aumiler et al., Phys. Rev. Lett. 95, 233001 (2005) [3] T. Ban et al., Phys. Rev. A 80, 023425 (2009) [4] F. Adler et al., Annu. Rev. Anal. Chem. 3, 175 (2010) [5] F. Adler et al., Opt. Express 18, 21861 (2010) [6] A. Foltynowicz et al., Faraday Disc., DOI:10.1039/C1FD00005E

uency comb spectroscopy; time and frequency domain

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