Doppler-free optical double-resonance spectroscopy is used to study the   s p p 5 5 6 1 2 3 2 3 2 excitation sequence in room-temperature rubidium atoms. This involves a  s p 5 5 F or ±2 electric quadrupole transitions.

Direct evidence of excitation of the 5p 3/2 → 6p 3/2 electric dipole forbidden transition in atomic rubidium is presented. The experiments were performed in a room temperature rubidium cell with continuous wave extended cavity diode lasers. Optical-optical double resonance spectroscopy with counterpropagating beams allows the detection of the non-dipole transition free of Doppler broadening. The 5p 3/2 state is prepared by excitation with a laser locked to the maximum F cyclic transition of the D2 line, and the forbidden transition is produced by excitation with a 911 nm laser. Production of the forbidden transition is monitored by detection of the 420 nm fluorescence that results from decay of the 6p 3/2 state. Spectra with three narrow lines (≈ 13 MHz FWHM) with the characteristic F − 1, F and F + 1 splitting of the 6p 3/2 hyperfine structure in both rubidium isotopes were obtained. The results are in very good agreement with a direct calculation that takes into account the 5s → 5p 3/2 preparation dynamics, the 5p 3/2 → 6p 3/2 non-dipole excitation geometry and the 6p 3/2 → 5s 1/2 decay. The comparison also shows that the electric dipole forbidden transition is a very sensitive probe of the preparation dynamics.PACS numbers: 32.70. Cs,32.70.Fw While the electric dipole approximation is a cornerstone in the study of the interaction between optical radiation fields and atoms, transitions induced by optical fields beyond this approximation have also become important tools in basic and applied studies of atoms. These so called "forbidden transitions" have been traditionally used in astrophysical and plasma studies [1]. They now play a fundamental role in metrology [2] and have also been used in experiments testing parity nonconserving interactions in atoms [3].In early studies of forbidden transitions, Sayer et al. [4] determined transition probabilities of electric quadrupole (E2) transitions using a tungsten lamp. The first direct observation of electric quadrupole effects in multiphoton ionization dates back to the work of Lambropoulos et al.[5]. Electric-dipole-forbidden transitions were exploited in three-wave-mixing experiments for optical sum and difference frequency generation in [6].The use of intense continuous-wave or pulsed laser sources has facilitated the observation of weak absorption lines. For instance, Tojo et al.[7] reported a determination of the oscillator strength of a E2 transition with a temperature-controlled cell and an extended cavity diode laser. Also, the study of strongly forbidden J = 0 → J = 0 transitions via single-photon excitation is presented in [8]. Excitation of forbidden transitions involving states with nonzero angular momentum in alkali atoms have also been studied over the last few years [9][10][11][12][13]. The coherent mixing of waves is theoretically studied in [9] for n 1 2 P − n 2 2 P transitions. The excitation of the 5p → 8p forbidden transition in thermal rubidium atoms was produced with a pulsed laser in [10] and using cold atoms in [12]. The experiment with co...

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 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.

We present the first evidence of excitation of the 5p 3/2 → 6p 1/2 electric dipole-forbidden transition in atomic rubidium. The experiments were carried out in a rubidium vapor cell using Doppler-free optical-optical double-resonance spectroscopy with counter-propagating beams. A 5s 1/2 → 5p 3/2 electric dipole preparation step using a diode laser locked to the F = 3 → 4 cyclic transition of the D2 line in 85 Rb is used to prepare the atoms in the first excited state. This is then followed by the 5p 3/2 F 2 = 4 → 6p 1/2 F 3 dipole-forbidden excitation (λ ≈ 917.5 nm) to establish a two-photon ladder (Ξ) excitation scheme. Production of atoms in the 6p 1/2 excited state is verified by detection of the 421 nm fluorescence that results from direct decay into the 5s 1/2 ground state.The polarization dependence of the relative intensities of the lines of the decay fluorescence is also investigated. Experimental data for different polarization configurations of the light beams used in this two-photon spectroscopy are compared with the results of calculations that consider a strong atom-field coupling in the preparation step, followed by a weak electric quadrupole excitation and the blue fluorescence decay emission. Good agreement between experiment and this three-step model is found in the case of linear-linear polarizations.