A nondegenerate four-level N-type scheme was experimentally implemented to observe electromagnetically induced transparency (EIT) at the 87 Rb D 2 line. Radiations of two independent external-cavity semiconductor lasers were used in the experiment, the current of one of them being modulated at a frequency equal to the hyperfine-splitting frequency of the excited 5 P 3/2 level. In this case, apart from the main EIT dip corresponding to the two-photon Raman resonance in a three-level L-scheme, additional dips detuned from the main dip by a frequency equal to the frequency of the HF generator were observed in the absorption spectrum. These dips were due to an increase in the medium transparency at frequencies corresponding to the three-photon Raman resonances in four-level N-type schemes. The resonance shapes are analyzed as functions of generator frequency and magnetic field.
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.
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.
Summary form only given. In the D/sub 1/ transition in the isotope 87 rubidium atom with no magnetic field present, electromagnetically induced transparency (EIT) can occur due to destructive quantum interference in the lambda transition between the two ground hyperfine states, |F=1, m/sub F/=+1), |F=1, m/sub F/=1), and the single electronically excited hyperfine state |F'=1, m/sub F/=0), when an elliptically polarized laser beam propagates through a rubidium vapor cell. The stronger circularly polarized /spl sigma//sup +/ component of this light beam, which connects the ground hyperfine state |F=1, m/sub F/=1) to the excited hyperfine state, can be considered as the "coupling" laser, and the weaker circularly polarized /spl sigma/ component, which connects the ground hyperfine state |F=1, m/sub F/=+1) to the excited hyperfine state, can be considered as the "probe" laser. An adiabatic increment in the probe laser intensity (with the coupling laser intensity held fixed) causes an adiabatic population transfer between the two ground hyperfine states. As pointed out by Imamoglu et al., if a fourth nearby level is added to this three-level lambda scheme, two new resonantly-enhanced effects can be produced, i.e., a Kerr effect and a two-photon absorption effect.
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.