High-contrast dark resonance in σ₊ - σ_- optical field

Abstract

The amplitude of Λ resonance in alkali atoms is limited by perturbing cycling transitions in the case of D2 line or by existence of additional trapping states in the case of D1 line. We propose to eliminate these extra trapping states by using two counter-propagating bichromatic fields of orthogonal circular polarizations. The experiment is in accordance with the theoretical proposal. The result refers to small-size cells and is important for applications in miniaturized atomic clocks. The dependence of the CPT signal amplitude on the position of the mirror with respect to the vapor cell

High-contrast dark resonance on the D2-line of 87Rb in a vapor cell with different directions of the pump-probe waves

“…However, there are also inelastic collisions of the alkali atoms with the buffer gas resulting in decrease of the amplitude and significant broadening of the dark resonance. Thus the scheme proposed in [5] yielded practically only a small (1.4-fold) increase of the amplitude [7] compared to the usual copropagating light waves configuration.…”

“…Efforts to design and build CPT-based atomic clocks were undertaken by several scientific groups [3][4][5][6][7][8]. The main advantage of quantum frequency standard based on the CPT effect is that the corresponding RF resonance (so-called dark resonance) is excited by all-optical methods.…”

Cancellation of Doppler shifts in a cold-atom CPT clock

“…When counterpropagating fields are applied to the atoms, the phase of the dark state created from the up and down CPT interrogation fields varies linearly with position as ±k HF ·z [13,14]. The slopes are opposite for the up and down beams.…”

Dark resonance in bichromatic linearly polarized optical field on Cs D<inf>1</inf> line

“…Other approaches to increase the contrast include push-pull optical pumping with alternating circular polarizations [9], counterpropagating waves with orthogonal circular polarizations [10], interrogation with crossed linear polarizations [11], and four-wave mixing [12]. These methods excite a two-photon Λ resonance on the ground-state hyperfine sublevels with |F, m F = 0>, |F + 1, m F = 0> to minimize the frequency shift due to the magnetic field.…”