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Bulletin of the American Physical Society

Comparison of absorption, fluorescence, and polarization spectroscopy of atomic rubidium

Seth Ashman, C. Stifler, Joaquín Romero

Published Jun 11, 2015• 0 citations

Abstract

An ongoing spectroscopic investigation of atomic rubidium utilizes a two-photon, single-laser excitation process. Transitions accessible with our tunable laser include 5P1/2 (F ′ ) ← 5S1/2 (F) and 5P3/2 (F ′ ) ← 5S1/2 (F). The laser is split into a pump and probe beam to allow for Doppler-free measurements of transitions between hyperfine levels. The pump and probe beams are overlapped in a counter-propagating geometry and the laser frequency scans over a transition. Absorption, fluorescence and polarization spectroscopy techniques are applied to this basic experimental setup. The temperature of the vapor cell and the power of the pump and probe beams have been varied to explore line broadening effects and signal-to-noise of each technique. This humble setup will hopefully grow into a more robust experimental arrangement in which double resonance, two-laser excitations are used to explore hyperfine state changing collisions between rubidium atoms and noble gas atoms. Rb-noble gas collisions can transfer population between hyperfine levels, such as 5P3/2 (F ′ = 3) Collision ←− 5P3/2 (F ′ = 2), and the probe beam couples 7S1/2 (F ′′ = 2) ← 5P3/2 (F ′ = 3). Polarization spectroscopy signal depends on the rate of population transfer due to the collision as well as maintaining the orientation created by the pump laser. Fluorescence spectroscopy relies only on transfer of population due to the collision. Comparison of these techniques yields information regarding the change of the magnetic sublevels, mF , during hyperfine state changing collisions.

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Energy-pooling collisions in rubidium:5P_J+5P_J′→5S+5D_J″

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An experimental study of rubidium energy pooling collisions,5P_J+5P_J′→5S+5D_J″,at thermal energies,has been carried out in a cell.Atoms were excited to either the 5P_1/2 or 5P_3/2 state using a single-mode diode laser.The excited-atom density and spatial distribution were mapped by monitoring the absorption of a counterpropagating single-mode diode laser beam,tuned to either 5P_1/2→5D_3/2,5P_3/2→7S_1/2 transition,which could be translated parallel to the pump beam.The excited atom densities are combined with measured fluorescence ratios to determine cross sections for the rubidium energy pooling process 5P_J+5P_J′→5S+5D_J″.Two tunable cw diode lasers were used to excite 5P_1/2 and 5P_3/2 respectively and the 5D_J″→5P_J fluorescence intensities were measured.For 5P_3/2+5P_1/2 collisions the cross sections for 5D_5/2,5D_3/2 are(1.12±0.50)×10~-14 and(1.01±0.45)×10~-14 cm~2,respectively.

Journal of Atomic and Molecular Physics•Jan 1, 2006•0 citations

An ongoing spectroscopic investigation of atomic rubidium utilizes a two-photon, single-laser excitation process. Transitions accessible with our tunable laser include 5P1/2 (F ′ ) ← 5S1/2 (F) and 5P3/2 (F ′ ) ← 5S1/2 (F). The laser is split into a pump and probe beam to allow for Doppler-free measurements of transitions between hyperfine levels. The pump and probe beams are overlapped in a counter-propagating geometry and the laser frequency scans over a transition. Absorption, fluorescence and polarization spectroscopy techniques are applied to this basic experimental setup. The temperature of the vapor cell and the power of the pump and probe beams have been varied to explore line broadening effects and signal-to-noise of each technique. This humble setup will hopefully grow into a more robust experimental arrangement in which double resonance, two-laser excitations are used to explore hyperfine state changing collisions between rubidium atoms and noble gas atoms. Rb-noble gas collisions can transfer population between hyperfine levels, such as 5P3/2 (F ′ = 3) Collision ←− 5P3/2 (F ′ = 2), and the probe beam couples 7S1/2 (F ′′ = 2) ← 5P3/2 (F ′ = 3). Polarization spectroscopy signal depends on the rate of population transfer due to the collision as well as maintaining the orientation created by the pump laser. Fluorescence spectroscopy relies only on transfer of population due to the collision. Comparison of these techniques yields information regarding the change of the magnetic sublevels, mF , during hyperfine state changing collisions.

The goal of this experiment was to measure the hyperfine energy splittings of the ground to first excited state transitions in rubidium using saturated absorption spectroscopy. Using this technique, we measured these transition energy spectra by taking the difference of two photodiode outputs due to multiple beams of a single laser scanned over a range of frequencies and shone through a cell of Rb vapor. When the laser frequency was resonant with an atomic transition, photons of those frequencies were absorbed, leaving a dip in intensity of the beam measured at the photodiode. One of the two laser beams had its excitations saturated by a more intense, counter-propagating pump beam from the same laser. The pump beam saturated the absorption of the velocity equal zero atoms that the counter-propagating probe beam could have also interacted with due to no Doppler shift. At these frequencies the probe beam experienced less absorption that was measured by a photodiode. The photodiode output was calibrated to the change in frequency of the scanned laser using a Fabry-Pérot interferometer. The output of this interferometer served as a reference for how the laser frequency changed. Final results for the 87Rb F=1 spectrum accounted for the largest error with a maximum of 12.2% deviation from accepted energy spacing values due in part to systematic error. Other spectra measurements were in better agreement, possessing error ranging from 2.1% to 10.1% and some agreeing with accepted values to within our uncertainty.

We propose and demonstrate pump-probe spectroscopy of rubidium absorption that reveals the sub-Doppler hyperfine structure of the ${}^{5}{\mathrm{S}}_{1/2}\ensuremath{\leftrightarrow}{}^{5}{\mathrm{P}}_{3/2}$ (

{\mathrm{D}}_{2}

) transitions. The counterpropagating pump and probe lasers are independently tunable in frequency, with the probe operating at the single-photon level. The two-dimensional spectrum measured as the laser frequencies are scanned shows fluorescence, Doppler-broadened absorption dips, and sub-Doppler features. The detuning between the pump and probe lasers allows compensation of the Doppler shift for all atomic velocities in the room-temperature vapor, meaning we observe sub-Doppler features for all atoms in the beam. We detail a theoretical model of the system that incorporates fluorescence, saturation effects, and optical pumping and compare this with the measured spectrum, finding a mean absolute percentage error of 3.11%. This high level of agreement allows us to extract the number density and temperature of the

\mathrm{Rb}

vapor from the two-dimensional spectrum. In the future this technique could be used as an atomic frequency standard for calibrating and characterising a single-photon or low-light-level source.

We experimentally study the high-resolution two-photon spectroscopy of rubidium using a single laser. The 5S1/2 − 5P3/2 − 5D5/2 transition is realized via 778.1 nm laser beams acting on the vapor with a counter-propagating configuration. The intensity modulation method is employed to improve the signal-to-noise ratio of the spectrum by two orders of magnitude compared with that for direct measurement. The effects of the vapor temperature, the frequency-scanning speed of the laser, the polarization combination of the laser beams, and the laser power on the spectra are investigated to obtain the optimal experimental parameters. This research is expected to be beneficial for potential applications since it can be used to realize a compact and high-precision frequency standard for optical communication.

We describe an experiment for investigating the 5S1∕2→5D5∕2 two-photon transition in rubidium using a single grating-feedback diode laser operating at 778.1nm (385THz). Continuous tuning of the laser frequency over 4GHz allows for the clear resolution of the Doppler-free spectral features and allows accurate measurement of the hyperfine ground-state splitting. A direct comparison between Doppler-broadened and Doppler-free spectral features is possible because both are distinctly evident in the two-photon spectra. By independently modifying the polarization state of the two laser fields, the impact of electric dipole selection rules on the two-photon transition spectra is investigated. This experiment is a valuable addition to the advanced undergraduate laboratory because it uses much of the same equipment as the single-photon saturated absorption spectroscopy experiment performed on the 5S1∕2→5P3∕2 transition in rubidium (λ=780.24nm) and provides students with an opportunity to investigate characteristics of atomic spectra not evident in the single-photon experiment.

We present a method to precisely determine the hyperfine structure constants of the rubidium 5D5/2 and 7S1/2 states in a cascade atomic system. The probe laser is coupled to the 5S1/2→5P3/2 hyperfine transition, while the coupling laser is scanned over the 5P3/2→5D5/2(7S1/2) transition. The high-resolution double-resonance optical pumping spectra are obtained with two counter-propagating laser beams acting on rubidium vapor. The hyperfine splitting structures are accurately measured by an optical frequency ruler based on the acousto-optic modulator, thus, the magnetic dipole hyperfine coupling constant A and quadrupole coupling constant B are determined. It is of great significance for the atomic hyperfine structure and fundamental physics research.

An experimental study of rubidium energy pooling collisions,5P_J+5P_J′→5S+5D_J″,at thermal energies,has been carried out in a cell.Atoms were excited to either the 5P_1/2 or 5P_3/2 state using a single-mode diode laser.The excited-atom density and spatial distribution were mapped by monitoring the absorption of a counterpropagating single-mode diode laser beam,tuned to either 5P_1/2→5D_3/2,5P_3/2→7S_1/2 transition,which could be translated parallel to the pump beam.The excited atom densities are combined with measured fluorescence ratios to determine cross sections for the rubidium energy pooling process 5P_J+5P_J′→5S+5D_J″.Two tunable cw diode lasers were used to excite 5P_1/2 and 5P_3/2 respectively and the 5D_J″→5P_J fluorescence intensities were measured.For 5P_3/2+5P_1/2 collisions the cross sections for 5D_5/2,5D_3/2 are(1.12±0.50)×10~-14 and(1.01±0.45)×10~-14 cm~2,respectively.