One step beyond the electric dipole approximation: An experiment to observe the 5p → 6p forbidden transition in atomic rubidium

Abstract

An advanced undergraduate experiment to study the 5P3/2→6P3/2 electric quadrupole transition in rubidium atoms is presented. The experiment uses two external cavity diode lasers, one operating at the D2 rubidium resonance line and the other built with commercial parts to emit at 911 nm. The lasers produce the 5s→5p→6p excitation sequence in which the second step is the forbidden transition. Production of atoms in the 6P3/2 state is observed by detection of the 420 nm fluorescence that results from electric dipole decay into the ground state. Lines whose widths are significantly narrower than the Doppler width are used to study the hyperfine structure of the 6P3/2 state in rubidium. The spectra illustrate characteristics unique to electric dipole forbidden transitions, like the electric quadrupole selection rules; they are also used to show general aspects of two-color laser spectroscopy such as velocity selection and hyperfine pumping.

Optical spectroscopy of the 5p3/2→ 6p1/2electric dipole-forbidden transition in atomic rubidium

“…For the two spectra one clearly observes the two expected lines that result from an excitation sequence 5s give place to the dipole-forbidden transitions appearing at a different frequency to those obtained with the maximum F 2 preparation [23]. The strongest of these velocity-selected non-dipole transitions results from the F → F → F excitation chain (2 → 2 → 2 in 87 Rb and 3 → 3 → 3 in 85 Rb).…”

Use of an electric-dipole forbidden transition to optically probe the Autler Townes effect

“…The experimental apparatus has been previously described in detail [31,32]. Figure 7 is presented here to point out its basic features.…”

“…Levels |1 and |2 correspond to the ground state 5S with an appropriate choice of the excitation light polarization. Furthermore, in [32,36] it is demonstrated that the choice of the relative polarization states of the two excitation beams can be utilized to tailor the excitation paths at the level of the magnetic structure of the atoms. Particularly, in the experiments presented on this work a parallel-linear polarization configuration for the preparation and probe beams was employed.…”

“…Velocity-selective spectroscopy with diode lasers is an ideal framework to do this due to its simplicity. Our research group has reported a technique capable of resolving hyperfine levels together with their magnetic spin projection in atomic Rubidium at room temperature [31,32]. Chan et al developed a similar velocity-selective spectroscopic method to resolve E2 Cesium transitions [33].…”

Electric-dipole forbidden transitions for probing atomic state preparation: the case of the Autler–Townes effect

“…Due to its simplicity, velocity-selective spectroscopy with diode lasers is the ideal framework to achieve this. Our research group has reported a technique capable of resolving hyperfine levels together with their magnetic spin projection in atomic rubidium at room temperature [22,23], while Chan et al developed a similar velocity-selective spectroscopic method to resolve E2 transitions in cesium [24]. This work extends the reach of application of E2 transitions providing an ideal probe for performing an in-depth investigation of the dynamics of an atomic system interacting with radiation fields.…”