High contrast resonances of the coherent population trapping on sublevels of the ground atomic term

Abstract

Received Month X, XXXX; revised Month X, XXXX; accepted Month X, XXXX; posted Month X, XXXX (Doc. ID XXXXX); published Month X, XXXXWe have detected and analyzed narrow, high contrast coherent population trapping resonances, which appear in transmission of the probe monochromatic light beam under action of the counterpropagating two-frequency laser radiation, on example of the nonclosed three level Λ-system formed by spectral components of the Doppler broadened D2 line of cesium atoms (in the cell with the rarefied Cs vapor). These nontrivial resonances are determined directly by the trapped atomic population on the definite lower level of the Λ-system and may be used in atomic frequency standards, sensitive magnetometers and in ultrahigh resolution laser spectroscopy of atoms and molecules.OCIS Codes: 030.1670, 120.4800, 140.3425, 300.6210, 300.6360 At the phenomenon of the coherent population trapping (CPT), a multilevel quantum system subject to decay processes is coherently driven into a superposition state immune from the further excitation, in which the system population is trapped. The CPT is the basis of a number of important applications: ultrahigh resolution spectroscopy, atomic clocks, magnetometry, optical switching, coherent cooling and trapping of atoms and also in some others described, for example in reviews [1][2][3]. In particular, narrow CPT resonances, detected in absorption of a twofrequency laser radiation (and also in the corresponding induced fluorescence spectrum of a gas medium) on three level atomic Λ-systems, are successfully applied in atomic frequency standards [4] and in high sensitive magnetometers [5]. For these applications, researchers use, mainly, vapors of alkali earth atoms (in particular Cs or Rb), whose ground quantum term consists of two sublevels of the hyperfine structure [6]. Resonance excitation of atoms on the Λ-system scheme is realized by means of the two-frequency radiation from given sublevels (Fig.1). Such Λ-systems are not closed because of presence of channels of the radiative decay of the excited state│3 > on some Zeeman sublevels of lower levels which don't interact with the two-frequency radiation [1][2][3]. Therefore highly narrow CPT resonances, recorded by known methods on the population of the upper level │3 > (Fig.1), have a comparatively small contrast on a more wide spectral background of absorption or fluorescence [4]. At the same time, more contrast CPT resonances may appear in dependences of populations of lower long-lived levels│1 > and │2 > of a nonclosed Λ-system (Fig.1) on the frequency difference (ω2 − ω1) of the bichromatic laser pumping. Indeed, let us consider interaction of such a system with 2 monochromatic laser fields. Frequencies ω1 and ω2 of given fields are close to centers Ω31 and Ω32 of electrodipole transitions │1 > − │3 > and │2 > − │3 > respectively (Fig.1). The population of this nonclosed Λ-system will be exhausted at intensification of the twofrequency laser pumping with the exception of a fraction of atoms, which may ...

Coherent population trapping resonances at lower atomic levels of Doppler broadened optical lines

“…Therefore the frequency difference (ω 2 − ω 1 ) may be smoothly scaned around the microwave interval (9192.6 MHz) between hyperfine sublevels of the Cs ground term (Fig.2). Thus the spectral resolution of our improved setup was risen at least on 1 order of the magnitude in comparison with the previous work [14]. As a result, new important features of nontrivial CPT resonances have been discovered.…”

“…The spectral resolution of this installation was risen at least on one order of the magnitude in comparison with our previous paper [14], where we used two independent lasers (with different frequencies ω 1 and ω 2 ) for receipt of necessary pumping and probe beams. Therefore, unlike paper [14], in the present work we detected CPT resonances with characteristic widths much less than 1 MHz.…”

“…In the present work we applied the same method as in our previous paper [14] but with use of only one diode laser, which generates the monochromatic beam with the stabilized frequency ω 2 .The second pumping radiation component (with the frequency ω 1 ) was obtained from this initial beam by the electrooptical modulator. Therefore the frequency difference (ω 2 − ω 1 ) may be smoothly scaned around the microwave interval (9192.6 MHz) between hyperfine sublevels of the Cs ground term (Fig.2).…”

Effect of the coherent population trapping on saturated absorption resonances in Cs vapor

“…Unlike our previous works [7,8], now we will analyze features of sub-Doppler resonances in absorption of the weak probe beam (with the scanned frequency ω 1 ) counterpropagating with respect to the bichromatic pumping radiation with various fixed frequency differences (ω 1 − ω 2 ) near the CPT condition (1). …”

“…Recently we have carried out experimental research of such CPT resonances for nonclosed three level Λ-systems formed by spectral components of the Doppler broadened D 2 line of cesium atoms [7,8]. Given CPT resonances were detected in absorption of the probe monochromatic light beam under action of the counterpropagating two-frequency pumping radiation.…”