Comparison of Electromagnetically Induced Transparency (EIT) Spectra for Six-level Lambda
Λ and Five-level V-type Systems
Electromagnetically induced transparency (EIT) is experimentally studied in a rubidium vapour cell (without buffer gas, both
87Rb and
85Rb present according to their natural abundance) kept within two-layers of
μ(μ)-metal shields to avoid the effect of Earth's magnetic field on the energy levels of atomic rubidium. An external cavity diode laser (ECDL), used as a low power probe laser, is locked to the hyperfine cross-over peak of
F=2→F′=2,3 transitions of
87Rb. The frequency of another ECDL, the pump laser, is set to scan the
F=1→F′=0,1,2 transitions of
87Rb. These form the
Λ-type six level system. In the V-type system, both the pump and the probe lasers share the same
F=2 ground level. The probe beam coming out of the cell is detected by a low noise fast photodetector. The resulting spectra show signature of EIT in the "peak" for the
Λ-type system and in the "dip" for the V-type system. Numerical calculation based simulated spectra are also compared with the experimental spectra. In both the cases very narrow EIT linewidth
(Γt<Γ) is observed even at high value of pump Rabi-frequency
(Ωc≫Γ). Narrower value of EIT linewidth is due to Doppler averaging phenomena.
The absorption features of a probe field propagating through a six-level inverted-Y type atomic system in presence of two additional coherent fields are investigated under both Doppler-free and Doppler-broadened conditions resembling the 87Rb 5S1⁄2 → 5P3⁄2 → 44D5⁄2 (Tr-I) through numerical simulation. A comparative study in the probe absorption is also made with the 87Rb 5S1⁄2 → 5P3⁄2 → 7S1⁄2 transition (Tr-II). Under thermal averaging five velocity selective optically pumped absorption peaks (VSOPAP) appear for both the transitions (Tr-I and Tr-II). An interesting feature noticed in the simulated absorption profile is that under thermal averaging we get two extra electromagnetically induced transparency (EIT) dips for Tr-I compared to Tr-II where only two EIT dips are noticed.
Electromagnetically induced transparency (EIT) effect has been studied using an extremely thin cell (ETC) with the thickness of an Rb vapor column of the order of light wavelength λ(780 nm) and varying in the range of 0.5λ-2.5λ. Λ-systems on the D2 line of 85Rb and 87Rb have been studied experimentally. Along with EIT resonance, we study the peculiarities of velocity-selective optical pumping/saturation (VSOP) resonances, which accompany the EIT resonance and, as a rule, are spectrally broader. It is demonstrated that size-conditioned strongly anisotropic contribution of atoms with different velocities in an ETC causes several dramatic differences of the EIT and VSOP resonances formation in the ETC as compared with an ordinary 1-10 cm long cell. Particularly, in the case of the ETC, the EIT linewidth and contrast dramatically depend on the coupling laser detuning from the exact atomic transition. A theoretical model taking into account the peculiarities of transmission spectra when L=nλ and L=(2n+1)λ/2 (n is an integer) has been developed. The experimental transmission spectra are well described by the theoretical model developed. The possibility of EIT resonance formation when atomic column thickness is of the order of L=0.5λ and less is theoretically predicted.
Laser spectroscopy experiments are reported on rubidium atoms by using two or three external cavity diode lasers to study multiple resonance transitions in Λ- and V-type systems as well as on (Λ+V)-type system. Electromagnetically induced transparency (EIT) peaks having sub-natural line-widths are found on the Doppler broadened transmission backgrounds with velocity selective enhanced absorption dips. In the presence of a pump laser, probe spectrum shows enhancement of EIT signal by tuning the control laser frequency when the Λ- and V-type EIT signals are made to overlap. Theoretical analysis is carried out by solving the optical Bloch equations for five-level atomic model under Λ configuration. With the numerically simulated spectra, variation of EIT transmission peak with ground state decay rate and excited state spontaneous decay rate are investigated. Effect of pump Rabi frequency on the transmission peak is also shown.
Abstract Coherent probe field (L A ) propagation through an eight-level inverted Y-type atomic system, in the presence of two additional coherent radiation fields termed the field L C (control or pump field) and the field L B (repump field), is investigated by using the parameters of 87 Rb 5 S 1 / 2 → 5 P 3 / 2 → 7 S 1 / 2 transitions. The system has two ground energy levels, four intermediate energy levels, and two uppermost energy levels. A theoretical model based on the density matrix method is used for numerical simulation of the probe response under different conditions. Simulated probe absorption spectra under a Doppler-free condition as well as under thermal averaging exhibit electromagnetically induced transparency (EIT). The position and line shape of this EIT profile change with different detunings of the control and repump fields. When the three coherent fields share a common level, a funnel-like EIT window appears in the simulated probe absorption curve. Velocity selective optically pumped absorption peaks are seen in the simulated probe response at room temperature.
An electromagnetically induced transparency is observed at one arm of a three-level \ensuremath{\Lambda}-type system in a rubidium D1 line (794.8 nm) with an 85% reduction in absorption, when a pumping field is present at the other arm. This reduction in absorption for the weak probe field is due to the atomic coherence produced by the strong pumping field. This experiment is done in a Rb vapor cell at room temperature with cw diode lasers for both pumping and probe beams in a Doppler-free configuration. A simple theoretical treatment including Doppler broadening is in good qualitative agreement with the experimental measurement.