Frequency-modulation high-precision spectroscopy of coherent dark resonances

Abstract

ABSTRACT The results of frequency-modulation (FM) spectroscopy of coherent dark resonances from the Zeeman sublevelsof the transition F =2 $ F =1 of D 1 line in absorption of 87 Rb atoms are presented and discussed in detail.By contrast with the conventional spectroscopy of coherent dark resonances employing two laser beams, relativefrequency of which can be varied, these data has been obtained with the help of a single frequency-modulatedlaser ¯eld. Variation of the modulation frequency plays then similar role with variation the relative frequencyin conventional spectroscopy. Experimental data are ¯t to the theoretical calculations, which are based onthe theory of FM spectroscopy of coherent dark resonances recently developed by us. Feasibility of using suchexperimental technique for accurate measurements of magnetic ¯elds is also discussed.Keywords: Coherent population trapping, absorption, dark resonance, magnetometry, metrology 1. INTRODUCTION The coherent population trapping (CPT) is one of the most intriguing quantum interference phenomena thatcan be most vividly seen in a three-level system in ¤-con¯guration. In this system, if two monochromaticpumping ¯elds are tuned into the resonance with the respective transitions, all the population is captured in thecoherent superposition of two low-lying levels, which gives the name of the phenomenon|coherent populationtrapping [1]. This means that the media of such three-level atoms under CPT will not emit °uorescence and donot absorb photons. In absorption spectra it is revealed as a narrow sharp dip in the absorption pro¯le whilescanning frequency of one of the pumping laser ¯elds. These resonances are called the coherent dark resonances.Due to the rather small spectral width of the dark resonances they found applications in precision spectroscopicapplications, such as metrology,