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Absorption and dispersion in atomic vapours: Applications to interferometery

G. T. Purves

Published Jan 1, 2006• 10 citations
OpenAlex

Abstract

Continuous wave extended cavity diode lasers are used to measure the absorptive and dispersive properties of the 5 2S1/2 → 5 (^2)Рз/2 resonance, at 780 nm, in Rubidium (Rb) vapour. The Doppler-broadened hyperfine transitions are studied both with and without a pump beam. The investigation concentrates on three-level Л-systems, realized in the presence of a pump beam, exhibiting Electromagnetically Induced Transparency (EIT). Electromagnetically Induced Absorption (EIA) IS also seen. The EIT and EIA resonances can be several orders of magnitude narrower than the natural line width of the atomic transitions in the absence of the pump beam. Further, the EIT resonances are sensitive to applied magnetic fields. The narrowest resonances measured in this work have a full-width at half- maximum of 〜 80 kHz. This is limited by the transit time of the atoms through the probe and pump beams. Predictions of theoretical calculations and models are compared to experimental results. The theory of beam splitters and interferometers is developed to enable the implementation of a Sagnac interferometer in a novel "biased" alignment. This allows the dispersion of atomic resonances to be measured directly. The direct measurement of the dispersion of the narrow EIT features in a "biased" Sagnac interferometer is presented. Such a signal is ideally suited to precision measurement applications such 88 inertial sensing and magnetometry.

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The dispersive and absorptive features of a closed transition in atomic cesium are investigated by means of a heterodyne interferometer as a function of the powers of probe and pump laser. Coherent population trapping (CPT) phenomena have raised the interest of the community in recent years. Possible applications of such effects are in the field of slow light propagation and, on the other side, superluminal effects. In particular, special interest has been devoted to the investigation of the refractive index of coherently prepared atoms. The goal of this investigation is the design of new optical media which show either negative or positive dispersion without absorption or with increased anomalous absorption. Such media could be useful ui building white light cavities, opto-optical modulators, and in quantum non-demolition (QND) measurements which are crucial to the development of the future generations gravitational wave detectors. Among these coherency processes we have been studying the phenomenon of electromagnetically induced absorption (EIA) (2) in a closed transition in cesiumatoms. The transition under analysis was the 'CS DZ line at 852 nm, in particular the hyperfine transition 6s zS~/2 F=4 + 6p 2P~/2 F'=5. The system was analyzed by means of a three beam heterodyne interferometer (l). This experimental setup shows high sensitivity to phase measurements and strongly reduced sensitivity to acoustical or vibrational noise. Using a third reference laser which does not interact with the mediumone can perform simultaneous measurements of the phase shift and the absorption of either the probe or the pump laser. The dispersion and the absorption of probe and coupling lasers have been measured as a funcion of the power of the coupling and probe lasers themselves. The power of the lasers are changed in the range of several decades. The halfwidth of the EL4 signal shows an increase with respect to the power of the probe laser while the phase shift of the probe laser decreases. The possibility to extend EIA measurements to a closed four level system in cesium is under analysis and is discussed here. Such possible developments of the experimental setup using a fourth laser or modulating the present reference laser enhance the capability to exploit simultaneous measurements of dispersion and absorption even in the four level system. This work was supported by SFB 407 of the Deutsche Forschungsgemeinschaft (German Research Society).

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Measurement of Dispersive Properties of Electromagnetically Induced Transparency in Rubidium Atoms

Min Xiao, Yongqing Li, Shaozheng Jin +1 more

The dispersive properties of the atomic transition in the rubidium ${D}_{2}$ line ($5{S}_{\frac{1}{2}}\ensuremath{-}5{P}_{\frac{3}{2}}$) at 780.0 nm are measured with a Mach-Zehnder interferometer when an additional coupling field at 775.8 nm is applied to an upper transition ($5{P}_{\frac{3}{2}}\ensuremath{-}5{D}_{\frac{5}{2}}$). This ladder-type system is observed to exhibit electromagnetically induced transparency together with a rapidly varying refractive index. A reduction in group velocity for the probe beam (${v}_{g}=\frac{c}{13.2}$) is inferred from the measured dispersion curve with 52.5% suppressed absorption on resonance.

Physical Review Letters•Jan 30, 1995•731 citations
Continuous wave extended cavity diode lasers are used to measure the absorptive and dispersive properties of the 5 2S1/2 → 5 (^2)Рз/2 resonance, at 780 nm, in Rubidium (Rb) vapour. The Doppler-broadened hyperfine transitions are studied both with and without a pump beam. The investigation concentrates on three-level Л-systems, realized in the presence of a pump beam, exhibiting Electromagnetically Induced Transparency (EIT). Electromagnetically Induced Absorption (EIA) IS also seen. The EIT and EIA resonances can be several orders of magnitude narrower than the natural line width of the atomic transitions in the absence of the pump beam. Further, the EIT resonances are sensitive to applied magnetic fields. The narrowest resonances measured in this work have a full-width at half- maximum of 〜 80 kHz. This is limited by the transit time of the atoms through the probe and pump beams. Predictions of theoretical calculations and models are compared to experimental results. The theory of beam splitters and interferometers is developed to enable the implementation of a Sagnac interferometer in a novel "biased" alignment. This allows the dispersion of atomic resonances to be measured directly. The direct measurement of the dispersion of the narrow EIT features in a "biased" Sagnac interferometer is presented. Such a signal is ideally suited to precision measurement applications such 88 inertial sensing and magnetometry.
The dispersive and absorptive features of a closed transition in atomic cesium are investigated by means of a heterodyne interferometer as a function of the powers of probe and pump laser. Coherent population trapping (CPT) phenomena have raised the interest of the community in recent years. Possible applications of such effects are in the field of slow light propagation and, on the other side, superluminal effects. In particular, special interest has been devoted to the investigation of the refractive index of coherently prepared atoms. The goal of this investigation is the design of new optical media which show either negative or positive dispersion without absorption or with increased anomalous absorption. Such media could be useful ui building white light cavities, opto-optical modulators, and in quantum non-demolition (QND) measurements which are crucial to the development of the future generations gravitational wave detectors. Among these coherency processes we have been studying the phenomenon of electromagnetically induced absorption (EIA) (2) in a closed transition in cesiumatoms. The transition under analysis was the 'CS DZ line at 852 nm, in particular the hyperfine transition 6s zS~/2 F=4 + 6p 2P~/2 F'=5. The system was analyzed by means of a three beam heterodyne interferometer (l). This experimental setup shows high sensitivity to phase measurements and strongly reduced sensitivity to acoustical or vibrational noise. Using a third reference laser which does not interact with the mediumone can perform simultaneous measurements of the phase shift and the absorption of either the probe or the pump laser. The dispersion and the absorption of probe and coupling lasers have been measured as a funcion of the power of the coupling and probe lasers themselves. The power of the lasers are changed in the range of several decades. The halfwidth of the EL4 signal shows an increase with respect to the power of the probe laser while the phase shift of the probe laser decreases. The possibility to extend EIA measurements to a closed four level system in cesium is under analysis and is discussed here. Such possible developments of the experimental setup using a fourth laser or modulating the present reference laser enhance the capability to exploit simultaneous measurements of dispersion and absorption even in the four level system. This work was supported by SFB 407 of the Deutsche Forschungsgemeinschaft (German Research Society).
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.
We use a Sagnac interferometer to measure the dispersive and absorptive properties of room temperature Rubidium vapor on the D2{D}_{2}D2​ line at 780.2nm780.2\phantom{\rule{0.3em}{0ex}}\mathrm{nm}780.2nm. We apply a pump beam such that the resulting $\ensuremath{\Lambda}$ system exhibits electromagnetically induced transparency. Using a ``biased alignment'' technique we demonstrate a direct and robust method of measuring the rapid variation in the refractive index. Such a ``slow-light'' Sagnac interferometer is ideally suited to precision measurement applications such as magnetometry and inertial sensing.
Atomic coherence resonances such as electromagnetically induced transparency (EIT) and electromagnetically induced absorption (EIA) signals are observed in a Doppler broadened multi-level system for the D 2 line of 85 Rb atoms in a vapour cell considering different types of atom–laser coupling schemes. Besides the coherence resonances, the nonlinear resonances like velocity selective optical pumping (VSOP) dips and velocity selective resonances (VSR) are also observed for the non-zero velocity selective groups of atoms. In the presence of pump, control and probe laser fields, we observe two EIT signals in a double Λ-type system and two EIA signals in a double V -type system. We are able to see the EIA signal for the non-zero velocity group of atoms when the pump laser is locked with an open transition by a small red detuning. We also report the experimental observation of simultaneous EIT and EIA signals in a (Λ+ V )-type system. The effect of frequency tuning of the control laser is also studied in the presence of the frequency locked pump laser. A simple theoretical analysis explains the experimental results.
The subject of this thesis is the study of coherent interaction of light with matter (atoms) to improve the precision measurements and techniques. Special attention is drawn to get the narrow subnatural electromagnetically induced transmission (EIT), electromagnetically induced absorption (EIA) and nonlinear magneto-optic rotation (NMOR) caused by alkali atoms contained in a vapor cell. Subnatural polarization rotation introduces by a strong circularly polarized light in the absence of any external magnetic field was also studied. A detailed theoretical treatment, given in this dissertation, allows to associate each of the features of the spectra with a special physical mechanism. Many quantum phenomena related to interferences, coherences, optical pumping etc. experiments are studied using home-built diode lasers. This thesis also describes laser cooling and trapping of rubidium atoms using two techniques. Deflection of cold atoms horizontally from MOT using pushing beams are discussed in close consideration for the improvements in the precision measurements. This thesis is organized as follows. In Chapter 1, an introduction to the importance of sub-natural narrow resonance and simplified technique in the precision measurement will be discussed. In Chapter 2, an introduction to EIT, EIA and NMOR resonance are discussed. This chapter will provide a basic theoretical background of atom-field interactions, especially for Λ-type and N -type systems and its steady state solution using density matrix analysis and experimental tools. The most important notion of laser cooling of atoms, ions or molecule i.e., exchange of momentum between light and atoms combining with the Doppler effect will be discussed. In Chapter 3, the observation of subnatural EIT and subnatural EIA in closed and open degenerate two-level system using room temperature vapor cell filled with Rb will be presented. Physical mechanisms that contribute to EIT and EIA, and the contrast of our results from the coherent population trapping (CPT)–type resonances are discussed in detail in appendix A.2 according to our experimental results. In Chapter 4, the narrowing of subnatural EIT and subnatural EIA linewidth in closed and open systems again in degenerate two level transition, using the “Laguerre-Gaussian” control beam instead of generally studied Gaussian beam, will be discussed in detail. In Chapter 5, the conversion between subnatural EIT to subnatural EIA in a degenerate Λ system will be discussed. The physical mechanism created by the introduction of a coherent counter propagating control laser to the co-propagating probe and the control laser are studied. The effect of polarization and axial velocity Doppler averaging will also be studied. In Chapter 6, we will discuss the sensitive technique for precise measurement of small magnetic fields using the NMOR, by chopping the resonant laser beam. We will study the sensitivity and the potential application of this technique in the measurement of an atomic electric-dipole moment. In Chapter 7, we will…
The dispersive properties of the atomic transition in the rubidium D2{D}_{2}D2​ line ($5{S}_{\frac{1}{2}}\ensuremath{-}5{P}_{\frac{3}{2}}$) at 780.0 nm are measured with a Mach-Zehnder interferometer when an additional coupling field at 775.8 nm is applied to an upper transition ($5{P}_{\frac{3}{2}}\ensuremath{-}5{D}_{\frac{5}{2}}$). This ladder-type system is observed to exhibit electromagnetically induced transparency together with a rapidly varying refractive index. A reduction in group velocity for the probe beam (vg=c13.2{v}_{g}=\frac{c}{13.2}vg​=13.2c​) is inferred from the measured dispersion curve with 52.5% suppressed absorption on resonance.