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arXiv:1810.01135 · Journal of Physics B Atomic Molecular and Optical Physics

Quantitative optical spectroscopy of 87Rb vapour in the Voigt geometry in DC magnetic fields up to 0.4 T

James Keaveney, Francisco S Ponciano-Ojeda, Stefan M Rieche, Mark J. Raine, Damian P. Hampshire, Ifan G. Hughes

Published Jan 24, 2019• 20 citations
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Abstract

We present a detailed spectroscopic investigation of a thermal 87 Rb atomic vapour in magnetic fields up to 0.4 T in the Voigt geometry. We fit experimental spectra with our theoretical model ElecSus and find excellent quantitative agreement, with RMS errors of ∼0.3%. We extract the magnetic field strength and the angle between the polarisation of the light and the magnetic field from the atomic signal and find excellent agreement to within ∼1% with a commercial Hall probe. Finally, we present an investigation of the relative sensitivity of this technique to variations in the field strength and angle with a view to enabling atom-based high-field vector magnetometry.

DOI
10.1088/1361-6455/ab0186

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Abstract This paper provides details of a spectroscopic investigation of a thermal 87Rb atomic vapour. The experiment was conducted with an external magnetic field of 1.5 T in the Voigt geometry. Very good quantitative agreement between experimental data and theory is found for all four Stokes parameters—with RMS errors of ∼1.5% in all cases. From the fits to our experimental data a value for the magnetic field strength is extracted, along with the angle between the magnetic field and the polarisation of the light. The effects of the cell window birefringence on the optical rotation signals are characterised. This allows us to carry out precise measurements at a high field strength and arbitrary geometries, allowing further development of possible areas of application for atomic magnetometers.

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We present experimental and theoretical work on atomic bandpass filters and spectroscopic characterisations of alkali vapour systems for magneto-optical applications. We demonstrate a new method for generating arbitrary angle magnetic fields in atomic filters using Rb vapour. This involves a fixed of permanent magnets in a Voigt geometry combined with a solenoid. We compare this method with the previously used method of rotating the permanent magnet pair. This setup offers more precise and flexible angle control. While both methods generate similar transmission profiles, the new setup allows larger angles and supports longer vapour cells, enhancing magneto-optical filters. Next, we investigate K D1 transition in the presence of neon buffer gas, in particular the pressure induced broadening and frequency shift, and the Zeeman splitting in the hyperfine Paschen-Back (HPB) regime. We use dual-control temperature systems to independently adjust Doppler and collisional effects, and we achieve excellent agreement with literature values for potassium-neon collisions. For the first time, buffer gas effects integrate into our theoretical model ElecSus, producing accurate prediction of modified Voigt profiles. We conduct a comprehensive experimental and theoretical study into the Stokes polarimetry of potassium atomic vapour with neon buffer gas, focusing on the temperature and magnetic field effects. This work represents the first application of ElecSus to model the buffer gas polarimetry of K D1 transitions. This study provides new insights into the effects of buffer gases on Stokes parameters, and indicates advances in a theoretical framework for understanding atom-light interactions in buffer gas environments.

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An investigation into the temperature evolution of transmission and absorption coefficient spectra of Rubidium atoms in the hyperfine Paschen-Back regime was successfully undertaken for a continuous laser detuning of approximately 150 GHz. All experiments were undertaken using a 1 mm long cell of isotopically enhanced 87Rb. The magnet used had a peak field of 1.54 T. The forms of both the S0 and S1 Stokes Parameters showed excellent agreement with the theory from ElecSus at temperatures ranging from 56◦C to 160◦C, with the S0 parameter also agreeing in narrow-band spectra of up to 20 GHz.The absorption coefficient ratio of strong transitions, expected to be equal to 3.00, was measured to be within their uncertainty of this value when a possible temperature fluctuation of <1 K was taken into account. Both the strong and weak transitions were measured and compared to the theory from ElecSus, which was found to successfully predict the behaviour of 87Rb atoms in the hyperfine Paschen-Back regime. Areas of expansion and improvement of the ElecSus program were identified.The power evolution of the D2 line of Rubidium was also investigated for a narrow beam of w < 0.4 mm in both no external magnetic field and the hyperfine Paschen-Back regime. The inhomogeneous shape of the power evolution was found to not fit the data, while the χ2 analysis showed that the homogeneous shape was better. The Weak Probe regime was found to be reached at values of I/Isat up to 2 orders of magnitude higher than the 1e−3 found previously. This provides possibilities for applications such that the SNR can be increased when measuring transmission or absorption coefficients. It is unclear whether the use of a magnetic field significantly changes the intensity required to reach the Weak Probe regime. This should be investigated using a wider beam, with a different experimental cell.

•Jan 1, 2017•1 citation
We present a detailed spectroscopic investigation of a thermal 87 Rb atomic vapour in magnetic fields up to 0.4 T in the Voigt geometry. We fit experimental spectra with our theoretical model ElecSus and find excellent quantitative agreement, with RMS errors of ∼0.3%. We extract the magnetic field strength and the angle between the polarisation of the light and the magnetic field from the atomic signal and find excellent agreement to within ∼1% with a commercial Hall probe. Finally, we present an investigation of the relative sensitivity of this technique to variations in the field strength and angle with a view to enabling atom-based high-field vector magnetometry.
Abstract This paper provides details of a spectroscopic investigation of a thermal 87Rb atomic vapour. The experiment was conducted with an external magnetic field of 1.5 T in the Voigt geometry. Very good quantitative agreement between experimental data and theory is found for all four Stokes parameters—with RMS errors of ∼1.5% in all cases. From the fits to our experimental data a value for the magnetic field strength is extracted, along with the angle between the magnetic field and the polarisation of the light. The effects of the cell window birefringence on the optical rotation signals are characterised. This allows us to carry out precise measurements at a high field strength and arbitrary geometries, allowing further development of possible areas of application for atomic magnetometers.
We present investigations of magneto-optical phenomena using a 87^{87}87Rb thermal vapour in large magnetic fields. At this point, in the hyperfine Paschen-Back regime, optical transitions can be separated by more than their Doppler-broadened linewidth, providing a high level of control over the atomic system and a simpler theoretical model for studying atom-light-magnetic field interactions. In this context, we study the spectra of 87^{87}87Rb at magnetic fields of 0.4 0.4~0.4 T and 1.5 1.5~1.5 T in the Voigt geometry. In both cases we find excellent agreement between experimental and theoretical absorption spectra. With the 1.5 1.5~1.5 T field we also study polarisation changes induced in the light by the atoms subject to a large magnetic field. Using this approach, we consider the practical applications of our system as a vector magnetometer. We present a scheme that eliminates most sources of systematic errors in the measurement of the field strength by using pairs of transitions that cancel excited-state terms in the energy shifts. Finally, we extend the concepts and ideas investigated to an application in precision thermometry. We discuss how good understanding of the spectra and the magnetic field strength potentially allow detection of small differences in different spectral features, which could then be traced to the effect of the Boltzmann factor, krmBTk_{\\rm{B}}TkrmB​T, on the atomic populations.
We present investigations of nonlinear optical phenomena using a 87^{87}87Rb thermal vapour in a high magnetic field. The magnetic field (of strength 0.6~T) separates the optical transitions by more than their Doppler-broadened linewidths. This technique provides a high level of control over thermal-vapour systems, which can be used as a simpler alternative to conventional state-preparation methods such as optical pumping. Using this approach, we study electromagnetically induced transparency in a non-degenerate 3-level ladder system. Finding excellent agreement with the numerically modelled transmission spectra, we are able to directly infer the dipole moment of the 5P$_{3/2}\to5D5D5D_{5/2}$ transition ∣⟨5P3/2∣∣er∣∣5D5/2⟩∣=(2.27±0.002stat±0.04syst) ea0|\langle5P_{3/2}||er||5D_{5/2}\rangle|= (2.27\pm0.002_{\rm stat}\pm0.04_{\rm syst})~ea_{0}∣⟨5P3/2​∣∣er∣∣5D5/2​⟩∣=(2.27±0.002stat​±0.04syst​) ea0​. Changing the coupling field to a standing-wave geometry, we observe resonant enhanced absorption: an effect that previously had only been observed in systems involving 4 or more atomic states. We also consider four-wave mixing (FWM) in a diamond level-scheme. Compared to the zero magnetic field case, we find good agreement with the FWM spectra using a simple model, even in the regime of strong laser dressing. Finally, we investigate heralded single-photon generation by spontaneous FWM. With strong laser dressing we observe the appearance of collective quantum beats, a single-photon interference effect due to the relative motion of atoms in a collective spin excitation. A violation of the Cauchy-Schwarz inequality by 6.7 standard deviations is reported.
We present experimental and theoretical work on atomic bandpass filters and spectroscopic characterisations of alkali vapour systems for magneto-optical applications. We demonstrate a new method for generating arbitrary angle magnetic fields in atomic filters using Rb vapour. This involves a fixed of permanent magnets in a Voigt geometry combined with a solenoid. We compare this method with the previously used method of rotating the permanent magnet pair. This setup offers more precise and flexible angle control. While both methods generate similar transmission profiles, the new setup allows larger angles and supports longer vapour cells, enhancing magneto-optical filters. Next, we investigate K D1 transition in the presence of neon buffer gas, in particular the pressure induced broadening and frequency shift, and the Zeeman splitting in the hyperfine Paschen-Back (HPB) regime. We use dual-control temperature systems to independently adjust Doppler and collisional effects, and we achieve excellent agreement with literature values for potassium-neon collisions. For the first time, buffer gas effects integrate into our theoretical model ElecSus, producing accurate prediction of modified Voigt profiles. We conduct a comprehensive experimental and theoretical study into the Stokes polarimetry of potassium atomic vapour with neon buffer gas, focusing on the temperature and magnetic field effects. This work represents the first application of ElecSus to model the buffer gas polarimetry of K D1 transitions. This study provides new insights into the effects of buffer gases on Stokes parameters, and indicates advances in a theoretical framework for understanding atom-light interactions in buffer gas environments.
This thesis presents a comparative study of the measured and calculated absolute absorption and dispersion properties of the Rb D lines through a dense thermal vapour in the absence and presence of an applied magnetic field. A detailed theoretical model valid in the weak-probe regime is calculated. The model uses a matrix representation of the atomic Hamiltonian including the magnetic field interaction for Rb in the completely uncoupled basis. Numerical diagonalisation allows the frequency detunings and transition strengths to be calculated. The lineshape of each transition is modelled as a Voigt profile, a convolution of the inhomogeneous and homogeneous profiles. The medium’s susceptibility is found by summing over all the electric-dipole-allowed transitions. For dense thermal vapours a modification to the homogeneous linewidth of each transition, which grows linearly with the number density of atoms, arises due to resonant dipole-dipole interactions between identical atoms in superpositions of the ground and excited terms. In the presence of an applied magnetic field we investigate the Stokes parameters of light propagating through a dense thermal vapour. For fields larger than 0.33 T we enter the hyperfine Paschen-Back regime on the Rb D lines. We present a compact optical isolator based on an atomic vapour, exploiting the spectral region of high transmission and large dispersion where we would normally expect absorption on the Rb D lines. Frequency up-conversion is shown in the fluorescence measurements over the visible and near infra-red regions for strong excitation. Low density transfer arises due to the energy-pooling effect between two identical atoms in their first excited terms. At high densities resonant dipole-dipole interactions give rise to a threshold for the energy transfer. We characterise the threshold behaviour with increasing number density.
An investigation into the temperature evolution of transmission and absorption coefficient spectra of Rubidium atoms in the hyperfine Paschen-Back regime was successfully undertaken for a continuous laser detuning of approximately 150 GHz. All experiments were undertaken using a 1 mm long cell of isotopically enhanced 87Rb. The magnet used had a peak field of 1.54 T. The forms of both the S0 and S1 Stokes Parameters showed excellent agreement with the theory from ElecSus at temperatures ranging from 56◦C to 160◦C, with the S0 parameter also agreeing in narrow-band spectra of up to 20 GHz.The absorption coefficient ratio of strong transitions, expected to be equal to 3.00, was measured to be within their uncertainty of this value when a possible temperature fluctuation of <1 K was taken into account. Both the strong and weak transitions were measured and compared to the theory from ElecSus, which was found to successfully predict the behaviour of 87Rb atoms in the hyperfine Paschen-Back regime. Areas of expansion and improvement of the ElecSus program were identified.The power evolution of the D2 line of Rubidium was also investigated for a narrow beam of w < 0.4 mm in both no external magnetic field and the hyperfine Paschen-Back regime. The inhomogeneous shape of the power evolution was found to not fit the data, while the χ2 analysis showed that the homogeneous shape was better. The Weak Probe regime was found to be reached at values of I/Isat up to 2 orders of magnitude higher than the 1e−3 found previously. This provides possibilities for applications such that the SNR can be increased when measuring transmission or absorption coefficients. It is unclear whether the use of a magnetic field significantly changes the intensity required to reach the Weak Probe regime. This should be investigated using a wider beam, with a different experimental cell.