Slowlight: Publications

Papers

Absolute absorption and dispersion of a rubidium vapour in the hyperfine Paschen-Back regime
Lee Weller, Kathrin S Kleinbach, Mark A Zentile, Svenja Knappe, Charles S Adams and Ifan G Hughes
J. Phys. B: At. Mol. Opt. Phys. 45, 215005 (2012) [arXiv]
Here we report on measurements of the absolute absorption and dispersion properties of an isotopically pure 87Rb vapour for magnetic fields up to and including 0.6 T. We discuss the various regimes that arise when the hyperfine and Zeeman interactions have different magnitudes, and show that we enter the hyperfine Paschen-Back regime for fields greater than 0.33 T on the Rb D2 line. The experiment uses a compact 1 mm3 microfabricated vapour cell that makes it easy to maintain a uniform and large magnetic field with a small and inexpensive magnet. We find excellent agreement between the experimental results and numerical calculations of the weak probe susceptibility where the line positions and strengths are calculated by matrix diagonalization.
Optical isolator using an atomic vapor in the hyperfine Paschen-Back regime
L. Weller, K. S. Kleinbach, M. A. Zentile, S. Knappe, Ifan G. Hughes and Charles S. Adams
Opt. Lett. 37, 3405 (2012) [arXiv]
A light, compact optical isolator using an atomic vapor in the hyperfine Paschen-Back regime is presented. Absolute transmission spectra for experiment and theory through an isotopically pure 87Rb vapor cell show excellent agreement for fields of 0.6 T. We show pi/4 rotation for a linearly polarized beam in the vicinity of the D2 line and achieve an isolation of 30 dB with a transmission >95%.
Optical preparation and measurement of atomic coherence at gigahertz bandwidth
Paul Siddons, Charles S. Adams & Ifan G. Hughes
J. Phys. B: At. Mol. Opt. Phys. 45, 124009 (2012) [arXiv]
We detail a method for the preparation of atomic coherence in a high-density atomic vapour of 87Rb, utilizing a coherent preparation scheme of off-resonant gigahertz bandwidth pulses. The scheme is found to be faster and more effective than techniques based on resonant interaction, such as coherent population trapping and population inversion. A numerical simulation of the preparation scheme is developed, and its efficiency in preparing coherent states is found to be close to unity at the entrance to the medium. The medium is then probed non-invasively with a laser field, the polarization of which is dependent upon the relative phase of the atomic coherence produced by the preparation fields.
Measuring the Stokes parameters for light transmitted by a high-density rubidium vapour in large magnetic fields
Lee Weller, Toryn Dalton, Paul Siddons, Charles S. Adams & Ifan G. Hughes
J. Phys. B: At. Mol. Opt. Phys. 45, 055001 (2012) [arXiv]
Here we report on measurements of the absolute absorption and dispersion of light in a dense rubidium vapour on the D2 line in the weak-probe regime with an applied magnetic field. A model for the electric susceptibility of the vapour is presented which includes both dipole-dipole interactions and the Zeeman effect. The predicted susceptibility is comprehensively tested by comparison to experimental spectra for fields up to 800 G. The dispersive properties of the medium are tested by comparison between experimental measurements and theoretical prediction of the Stokes parameters as a function of the atom-light detuning.
Absolute absorption on the rubidium D1 line including resonant dipole-dipole interactions
Lee Weller, Robert J Bettles, Paul Siddons, Charles S Adams and Ifan G Hughes
J. Phys. B: At. Mol. Opt. Phys. 44, 195006 (2011) [arXiv]
Here we report on measurements of the absolute absorption spectra of dense rubidium vapour on the D1 line in the weak-probe regime for temperatures up to 170oC and number densities up to 3 × 1014 cm-3. In such vapours, modifications to the homogeneous linewidth of optical transitions arise due to dipole-dipole interactions between identical atoms, in superpositions of the ground and excited states. Absolute absorption spectra were recorded with a deviation of 0.1% between experiment and a theory incorporating resonant dipole-dipole interations. The manifestation of dipole-dipole interations is a self-broadening contribution to the homogeneous linewidth, which grows linearly with number density of atoms. Analysis of the absolute absorption spectra allows us to ascertain the value of the self-broadening coefficient for the rubidium D1 line: ϐ/2π = (0.69 ± 0.04) × 10-7 Hz cm3, in excellent agreement with the theoretical prediction.
Optical control of Faraday rotation in hot Rb vapor
Paul Siddons, Charles S. Adams & Ifan G. Hughes
Phys. Rev. A. 81, 043838 (2010) [arXiv]
We demonstrate controlled polarization rotation of an optical field conditional on the presence of a second field. Induced rotations of greater than &pi/2 rad are seen with a transmission of 95%, corresponding to a ratio of phase shift to absorption of 40&pi . This combination of large, controlled rotation and low loss is well suited for the manipulation of light pulses.
Off-resonance absorption and dispersion in vapours of hot alkali-metal atoms
Paul Siddons, Charles S. Adams & Ifan G. Hughes
J. Phys. B: At. Mol. Opt. Phys. 42, 175004 (2009) [arXiv]
We study the absorptive and dispersive properties of Doppler-broadened atomic media as a function of detuning. Beginning from the exact lineshape calculated for a two-level atom, a series of approximations to the electric susceptibility are made. These simplified functions facilitate direct comparison between absorption and dispersion, and show that dispersion dominates the atom-light interaction far from resonance. The calculated absorption and dispersion are compared to experimental data for Rb vapour on the D1 transition, showing the validity of the approximations.
A gigahertz-bandwidth atomic probe based on the slow-light Faraday effect
Paul Siddons, Nia C. Bell, Yifei Cai, Charles S. Adams & Ifan G. Hughes
Nature Photon. 3, 225-229 (2009) [arXiv] See also News & Views
The ability to probe quantum systems on short timescales is central to the advancement of quantum technology. Here we show that this is possible using an off-resonant dispersive probe. By applying a magnetic field to an atomic vapour the spectra of the group index for left and right circularly polarized light become displaced, leading to a slow-light Faraday effect that results in large dispersion and high transmission over tens of gigahertz. This large frequency range opens up the possibility of probing dynamics on a nanosecond timescale. In addition, we show that the group index enhances the spectral sensitivity of the polarization rotation, giving large rotations of up to 15π rad for continuous-wave light. Finally, we demonstrate dynamic broadband pulse switching by rotating a linearly polarized nanosecond pulse by π/2 rad with negligible distortion and transmission close to unity.
Absolute absorption on rubidium D lines: comparison between theory and experiment
Paul Siddons, Charles S. Adams, Chang Ge & Ifan G. Hughes
J. Phys. B 41 155004 (2008) [arXiv]
We study the Doppler-broadened absorption of a weak monochromatic probe beam in a thermal rubidium vapour cell on D lines. A detailed model of the susceptibility is developed which takes into account the absolute linestrengths of the allowed electric dipole transitions and the motion of the atoms parallel to the probe beam. All transitions from both hyperfine levels of the ground term of both isotopes are incorporated. The absorption and refractive index as a function of frequency are expressed in terms of the complementary error function. The absolute absorption profiles are compared with experiment, and are found to be in excellent agreement provided a sufficiently weak probe beam with an intensity under one-thousandth of the saturation intensity is used. The importance of hyperfine pumping for open transitions is discussed in the context of achieving the weak-probe limit. Theory and experiment show excellent agreement, with an rms error better than 0.2% for the D2 line at 16.5°C.
Sagnac interferometry in a slow-light medium
Graham T. Purves, Charles S. Adams & Ifan G. Hughes
Phys. Rev. A 74 023805 (2005)
We use a Sagnac interferometer to measure the dispersive and absorptive properties of room temperature Rubidium vapor on the D2 line at 780.2 nm. We apply a pump beam such that the resulting 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.


Theses

Faraday Rotation of Pulsed and Continuous-wave Light in Atomic Vapour
Paul Siddons
The absorptive and dispersive properties of a Doppler-broadened vapour of rubidium atoms is investigated. A detailed model of the atom-light interation is developed and found to be in excellent agreement with experiment in the regime where the interacting light field is sufficiently weak such that it does not significantly alter the medium through which it propagates. The importance of using a weak beam to probe atomic systems is discussed, and a method of characterising how weak such a beam has to be is provided. The theoretical model is applied to both situations of illumination by continuous-wave and pulsed light, the latter situation providing a demonstration of the slow light effect. This phenomenon is a manifestation of the dispersive properties of the medium and is shown to exist over a particularly large frequency range, compared to the absorption spectrum, in thermal vapours. Off-resonant interactions are studied, in which incident laser-light is detuned from resonance to such a degree that Doppler-broadening can be neglected. We quantify the extent to which the light needs to be detuned to be in this regime, and provide approximations to the line-shape function developed in earlier parts of the thesis. The approximate line-shapes are much easier to manipulate and allow a more intuitive understanding of the atom-light interaction. In the second part of the thesis we study the Faraday effect and related phenomena which are an expression of the birefringent properties of the atom-light system. Beginning with a theoretical and experimental investigation of the Faraday rotation of a weak continuous-wave beam, we move on to the consideration of pulsed light. Optically-induced birefringence via the application of an intense continuous-wave pumping field is demonstrated experimentally, and the theoretical plausibility of controlling the polarisation state of a weak pulsed field mediated via intense pulsed light is shown.
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Posters

Slow-light Faraday Effect
Lee Weller, Paul Siddons, Charles S. Adams & Ifan G. Hughes
This poster was presented at the QuAMP Conference, Oxford University, 19-23 September 2011.
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Slow-light Faraday Effect
Lee Weller, Paul Siddons, Charles S. Adams & Ifan G. Hughes
This poster was presented at the MUARC Summer School, Warwick, 23-27 August 2010 and at QuAMP Summer School, Imperial College London, 30-03 August/September 2010.
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Absolute absorption on the rubidium D lines: comparison between theory and experiment
P. Siddons, C.S. Adams, C. Ge and I.G. Hughes
This poster was presented at ICAP, 2008.
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Content © Lee Weller, Durham University 2008