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Journal of Physics B Atomic Molecular and Optical Physics

Threshold nonlinear absorption in Zeeman transitions

Andal Narayanan, Abheera Hazra, S. N. Sandhya

Published Oct 12, 2010• 0 citations
Publisher

Abstract

We experimentally study the absorption spectroscopy from a collection of gaseous 87Rb atoms at room temperature irradiated with three fields. Two of these fields are in a pump–probe saturation absorption configuration. The third field co-propagates with the pump field. The three fields address Zeeman degenerate transitions between hyperfine levels 5S1/2, F = 1 and 5P3/2, F = 0, F = 1 around the D2 line. We find a sub-natural absorption resonance in the counter-propagating probe field for equal detunings of all three fields. This absorption arises in conjunction with the appearance of increased transmission due to electro-magnetically induced transparency in the co-propagating fields. The novel feature of this absorption is its onset only for the blue of 5P3/2, F = 0, as the laser frequency is scanned through the excited states 5P3/2, F = 0, F = 1 and F = 2. The absorption rapidly rises to near maximum values within a narrow band of frequency near 5P3/2, F = 0. Our experimental results are compared with a dressed atom model. We find the threshold absorption to be a result of coherent interaction between the dressed states of our system.

DOI
10.1088/0953-4075/43/21/215502

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We experimentally study the absorption spectroscopy from a collection of gaseous 87Rb atoms at room temperature irradiated with three fields. Two of these fields are in a pump–probe saturation absorption configuration. The third field co-propagates with the pump field. The three fields address Zeeman degenerate transitions between hyperfine levels 5S1/2, F = 1 and 5P3/2, F = 0, F = 1 around the D2 line. We find a sub-natural absorption resonance in the counter-propagating probe field for equal detunings of all three fields. This absorption arises in conjunction with the appearance of increased transmission due to electro-magnetically induced transparency in the co-propagating fields. The novel feature of this absorption is its onset only for the blue of 5P3/2, F = 0, as the laser frequency is scanned through the excited states 5P3/2, F = 0, F = 1 and F = 2. The absorption rapidly rises to near maximum values within a narrow band of frequency near 5P3/2, F = 0. Our experimental results are compared with a dressed atom model. We find the threshold absorption to be a result of coherent interaction between the dressed states of our system.
We experimentally study the absorption spectroscopy from a collection of gaseous 87Rb^87 Rb87Rb atoms at room temperature irradiated with three fields. Two of these fields are in a pump probe saturation absorption configuration. The third field co-propagates with the pump field. The three fields address Zeeman degenerate transitions between hyperfine levels 5S1/2,F=15S_{1/2}, F = 15S1/2​,F=1 and 5P3/2,F=05P_{3/2}, F = 05P3/2​,F=0 and also between 5S1/2,F=15S_{1/2}, F = 15S1/2​,F=1 and 5P3/2,F=15P_{3/2}, F =15P3/2​,F=1 around the D2 line. We find a sub-natural absorption resonance in the counter-propagating probe field. The novel feature of this absorption is its abrupt onset in the vicinity of 5P3/2,F=05P_{3/2}, F = 05P3/2​,F=0, as the laser frequency is scanned from 5P3/2,F=05P_{3/2}, F = 05P3/2​,F=0 to 5P3/2,F=15P_{3/2}, F =15P3/2​,F=1. The experimental results are compared with the theory modeled after a four level system. There is a qualitative agreement between our theory and experiment. We find the threshold absorption to be a result of the off-resonant interaction of the strong field with nearby hyperfine levels.
We investigate both theoretically and experimentally the electro- magnetically induced transparency (EIT) phenomenon of atomic 87Rb at the room temperature with a static magnetic field lifting the degeneracy of all three involved hyperfine levels. Two collinearly propagating and linearly polarized laser fields (a probe field and a coupling field) are used to couple one hyperfine level (the upper level) of the 5P1/2 state to two hyperfine levels (the lower levels) of the 5S1/2 state, respectively. In the case of zero magnetic fields, we observed a deep EIT window with the contrast of about 66%. Here, the EIT window width is limited by both the spontaneous decay rate of the upper level and the coupling field intensity. When a magnetic field parallel to both laser beams is applied, the EIT window is split into three much narrower sub-windows with contrasts of about 32%. If the magnetic field is perpendicular to the laser beams, however, the EIT window is split into four much narrower sub-windows whose contrasts are 32% or 16%. This is because the decomposition of the linearly polarized optical fields strongly depends on the orientation of the used magnetic field. The underlying physics is that, in the limit of a weak probe field, an ideal degenerate three-level system can be split into three or four sets of independent three-level systems by a magnetic field due to the lifting of magnetic sublevels of the involved hyperfine levels. In this paper the absorption spectra corresponding to different magnetic field directions are clearly shown and compared. And a straightforward but effective theoretical method for analyzing the experimental results is put forward. Our theoretical calculations are in good agreement with the experimental results.
We perform saturated absorption spectroscopy on the D2{D}_{2}D2​ line for room temperature rubidium atoms immersed in magnetic fields within the 0.05--0.13 T range. At those medium-high field values the hyperfine structure in the excited state is broken by the Zeeman effect, while in the ground-state hyperfine structure and Zeeman shifts are comparable. The observed spectra are composed by a large number of absorption lines. We identify them as saturated absorptions on two-level systems, on three-level systems in a V\mathsf{V}V configuration, and on four-level systems in an N\mathsf{N}N or double-N\mathsf{N}N configuration where two optical transitions not sharing a common level are coupled by spontaneous emission decays. We analyze the intensity of all those transitions within a unified simple theoretical model. We concentrate our attention on the double-N\mathsf{N}N crossovers signals whose intensity is very large because of the symmetry in the branching ratios of the four levels. We point out that these structures, present in all alkali-metal atoms at medium-high magnetic fields, have interesting properties for electromagnetically induced transparency and slow light applications.
We perform saturated absorption spectroscopy on the D2_22​ line for room temperature rubidium atoms immersed in magnetic fields within the 0.05-0.13 T range. At those medium-high field values the hyperfine structure in the excited state is broken by the Zeeman effect, while in the ground state hyperfine structure and Zeeman shifts are comparable. The observed spectra are composed by a large number of absorption lines. We identify them as saturated absorptions on two-level systems, on three-level systems in a V configuration and on four-level systems in a N or double-N configuration where two optical transitions not sharing a common level are coupled by spontaneous emission decays. We analyze the intensity of all those transitions within a unified simple theoretical model. We concentrate our attention on the double-N crossovers signals whose intensity is very large because of the symmetry in the branching ratios of the four levels. We point out that these structures, present in all alkali atoms at medium-high magnetic fields, have interesting properties for electromagnetically induced transparency and slow light applications.
We present nonlinear spectra of four-level ladder cesium atoms employing 6S 1/2 → 6P 3/2→ 7S 1/2 → 30P 3/2 scheme of a room temperature vapor cell. A coupling laser drives Rydberg transition, a dressing laser couples two intermediate levels, and a probe laser optically probes the nonlinear spectra via electromagnetically induced transparency (EIT). Nonlinear spectra are detected as a function of coupling laser frequency. The observed spectra exhibit an enhanced absorption (EA) signal at coupling laser resonance to Rydberg transition and enhanced transmission (ET) signals at detunings to the transition. We define the enhanced absorption (transmission) strength, H EA (H ET), and distance between two ET peaks, γ ET, to describe the spectral feature of the four-level atoms. The enhanced absorption signal H EA is found to have a maximum value when we vary the dressing laser Rabi frequency Ω d, corresponding Rabi frequency is defined as a separatrix point, Ω dSe . The values of Ω dSe and further η = Ω dSe /Ω c are found to depend on the probe and coupling Rabi frequency but not the atomic density. Based on Ω dSe , the spectra can be separated into two regimes, weak and strong dressing ranges, Ω d ≲ Ω dSe and Ω d ≳ Ω dSe , respectively. The spectroscopies display different features at these two regimes. A four-level theoretical model is developed that agrees well with the experimental results in terms of the probe-beam absorption behavior of Rabi frequency-dependent dressed states.
We have simulated spectra of weak probe absorption from one of two hyperfine structure (hfs) components of an atomic ground state, to a hfs manifold of an upper state. A stronger coupling transition was assumed to bind the other hfs component of the ground state with the same upper hfs manifold. The purpose of this simulation was to study the impact on the spectral features in probe absorption from the presence of a state to which the electric-dipole transition is allowed for coupling, but forbidden for probing. In relation to our other (experimental) work, we considered the D2-line transitions for 85Rb. With coupling from the 5S1/2(F=2) state, as in our experiment, the 5P3/2(F'=1) state is coupled but not-probed from the 5S1/2(F=3) state. In calculations we searched for steady-state solutions of optical Bloch equations assuming a 5-level model and RWA. The collisionless (cold) atoms were considered, and we assumed that decoherence was entirely due to natural decay and exciting lasers' linewidths. We investigated probe absorption spectra as a function of both coupling-field-induced Rabi frequency Ωc, and coupling field detuning from the atomic resonances. The 5-level model spectra were compared with the corresponding spectra result of 4-level model calculations performed by omission of the 5P3/2(F'=1) level. Even for small Ωc values close to the natural linewidth, for some detunings a considerable influence of the 5P3/2(F'=1) state on the spectra was observed which cannot be ignored in interpretations.