Dark-Line Atomic Resonances in Micrometric Rb-Vapor Layer

Abstract

Email:Compact frequency references become increasingly important for many applications in recent years [1]. We present measurements of dark-line resonances excited in Rb atomic vapor confined in micrometric cells (MC). The width and contrast of the resonances were measured for cell lengths below 100 ptm. As the size of the vapor cell is reduced, the lifetime of the ground-state coherence becomes shorter because of collisions of the atoms with the cell windows. Hence, in the case of MC one could expect that the effect of electromagnetically induced transparency (EIT) will vanish (note, that neither an additional buffer gas [1] nor paraffin coating has been used). Nevertheless, it was predicted in [2] that even in the case of pure vapor a narrow EIT resonance can be observed. Moreover, it has been demonstrated that in the case of nonzero detuning of the coupling laser, the EIT resonance and velocity-selective optical pumping (VSOP) resonance are shifted with respect to each other on the frequency scale, which makes it possible to observe a competition between the two effects (this is not possible to realize in an ordinary cm-size cell (OC)). In our work, the A-systems on D2 line of 85Rb have been studied with the use of bi-chromatic radiation of two separate narrowband diode lasers (2 z780 nm) (Fig. 1). In Fig.2 we show the transmission spectrum of the probe laser when the couple is red shifted by 90 MHz from Fg=2 -*Fe=2 transition (upper curve) and is resonant with Fg=2 -*Fe=3 transition (middle curve), while the probe laser frequency is scanned across Fg 3 -> Fe=2, 3, 4 transitions (Qc, Qp -0.5 F, Fr 6 MHz , L 1 O ptm. The lower curve is the reference spectrum of the ETC for L X [3]. EIT CU 3--___ -~~--efrece 2-+ 63MHz 121 MHz F ig.1 Fig.2 Frequency DifferenceThere are several dramatic distinctions in formation of EIT and VSOP resonances in MC as compared with OC. Particularly, in the case of MC the most narrow EIT resonance is formed when the couple is resonant with the corresponding atomic transition (middle curve, YEIT < 7MHz), The increase of the couple detuning leads to the rapid linewidth broadening (upper curve, YEIT -I I MHz), while in the case of OC the effect is vice versa. Note that in the upper and middle curves the VSOP resonances are of the opposite sign. A theoretical model describing EIT effect and VSOP behavior in MC is developed, and the comparison with the experiment will be presented.[1] S. Knappe, L. Hollberg, and J. Kitching, Opt. Lett. 29, 388 (2004) [2] D. Petrosyan and Yu. Malakyan, Phys. Rev. A 61, 053820 (2000) [3] A. Sargsyan, D. Sarkisyan, and A. Papoyan, Phys. Rev. A 73, 033803 (2006).