Study on spectral features of electromagnetically induced absorption in degenerate two-level system of 85Rb atoms

Abstract

We present experimental and theoretical studies on spectral profile variations of weak probe beam transmission signal from hyperfine level between the ground 5 S1/2 and excited 5 P3/2 D2 lines of 85Rb atom at room temperature with degenerate magnetic sublevels in the case of polarization configurations, powers, and directions of control and probe beams. The probe laser frequency is fixed and locked at the Fg = 3 → Fe = 4 degenerate two level system of 85Rb atom while the control beam is scanned through F” = 2 and 3 → F” = 1, 2, 3, and 4. In degenerate two-level system polarizations of probe and control laser fields play important roles to transfer of population from excited states. Consequently variation in absorption and transmission signal profiles including EIA and EIT-like signal have been observed when the polarization state of control and probe lasers fields were changed. In case of weak probe and strong coupling laser field we observed double structure transmittance spectrum, a narrow due to coherence and broad due to optical pumping in cycling transition. The experimental results are compared with the results calculated by solving time-dependent density-matrix equations including the optical and Zeeman coherences connected via multi-photon interactions process between magnetic levels and match well with the calculated signal profiles. We also present theoretical and experimental study of EIA for different hyperfine transitions of 85Rb-D2 line. The calculated result in case of cycling transition of 85Rb show that EIA signal have ultra-narrow feature in low power of coupling beam in both stationary and thermal atoms. In case of thermal atom the ultra-narrow EIA signal due to high coupling power beam still remained in ultra-narrow state in the same polarization configuration. Ultra-narrow EIA spectral features of thermal 85Rb atom with respect to coupling Rabi frequencies in a degenerate Zeeman multiplet system have been unraveled in the cases of same (σ+-σ+, π∥π) and orthogonal (σ+-σ-,π⊥π) polarization configurations. The EIA signals with subnatural linewidth of ~ 90 kHz even in the cases of same circular and linear polarizations of coupling and probe laser have been obtained for the first time theoretically and experimentally. In weak coupling power limit of orthogonal polarization configurations, time-dependent transfer of coherence plays major role in the splitting of the EIA spectra while in strong coupling power, Mollow triplet-like mechanism due to strong power bring into broad split feature. The experimental ultra-narrow EIA features using one laser combined with an AOM match well with simulated spectra obtained by using generalized time-dependent optical Bloch equations |결합광과 조사광의 편광, 파워, 방향에 따른 축퇴된 상온 셀내에 있는 루비듐 원자의 기저준위와 여기준위 D2 사이의 초미세 구조에서 약한조사빔의 투과 신호의 분광선에 대한 실험적, 이론적 고찰을 본 논문에서 연구한다. 조사광은 Fg =3→Fe =4 에 주파수 잠금되고, 결합광은기저준위 Fg = 2와 3에서 여기준위 Fe= 1, 2, 3, 4 사이를 주사 한다. 축퇴된 이원자 준위에서 조사광과 결합광의 편광은 여기준위로부터의 밀도 이전,EIA 혹은 EIT 신호 의 분광선 모양 등에 중요한 역할을 한다. 약한 조사광과 강한 결합광의 경우에 닫혀진 계에서 좁은 선폭과 넓은 선폭을 가지는 이중 구조 분광선이 광펌핑에 의해 얻어진다. 이러한 광펌핑 효과 등이 광 밀도 방정식에 의해 얻어진 분광선과 실험적으로 얻어진 분광선과 비교되었다. 또한, 상온에서 매우 좁은 분광선 선폭을 가지는 EIA 신호가 얻어졌다. 이러한 매우 좁은 선폭을 가지는 분광선이 같은 편광 (σ+-σ+, π∥π) 과수직 편광 (σ+-σ-,π⊥π) 구도에서 연구되었다. 같은 편광의 경우 ~90 kHz 정도의 EIA 신호가 처음으로 실험적, 이론적으로 확인되었다. 이러한좁은 선폭을 가지는 EIA 신호를 연구하기 위해 파워와 편광이 일반화된 광 밀도 방정식의 해의 결과와 실험적으로 얻은 결과와 비교한 결과,매우 잘 일치함을 확인하였다.