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Journal of the Optical Society of America B

Two-photon excitation of launched cold atoms in flight

Rene C. Gonzalez, Eduardo Alejandro, Emma Erwin, Anne L. Goodsell

Published May 4, 2017• 1 citation
Publisher

Abstract

We demonstrate two-photon bi-chromatic excitation of cold rubidium atoms in flight, using the pathway 5S1/2→5P3/2→5D5/2 with two resonant photons. In our experiment, Rb85 atoms are laser-cooled in a magneto-optical trap and launched upward in discrete clouds with a controllable vertical speed of 7.1±0.6 m/s and a velocity spread that is less than 10% of the launch speed. Outside the cooling beams, as high as 14 mm above the original center of the trap, the launched cold atoms are illuminated simultaneously by spatially localized horizontal excitation beams at 780 nm (5S1/2→5P3/2) and 776 nm (5P3/2→5D5/2). We monitor transmission of the 780-nm beam over a range of intensities of 780-nm and 776-nm light. As the center of the moving cloud passes the excitation beams, we observe as much as 97.9±1.2% transmission when the rate of two-photon absorption is high and the 5S1/2 and 5P3/2 states are depopulated, compared to 87.6±0.9% transmission if only the 780-nm beam is present. This demonstrates two-photon excitation of a launched cold-atom source with controllable launch velocity and narrow velocity spread, as a foundation for three-photon excitation to Rydberg states.

DOI
10.1364/josab.34.001090

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Journal of the Physical Society of Japan•Jul 18, 2018•7 citations
We demonstrate two-photon bi-chromatic excitation of cold rubidium atoms in flight, using the pathway 5S1/2→5P3/2→5D5/2 with two resonant photons. In our experiment, Rb85 atoms are laser-cooled in a magneto-optical trap and launched upward in discrete clouds with a controllable vertical speed of 7.1±0.6 m/s and a velocity spread that is less than 10% of the launch speed. Outside the cooling beams, as high as 14 mm above the original center of the trap, the launched cold atoms are illuminated simultaneously by spatially localized horizontal excitation beams at 780 nm (5S1/2→5P3/2) and 776 nm (5P3/2→5D5/2). We monitor transmission of the 780-nm beam over a range of intensities of 780-nm and 776-nm light. As the center of the moving cloud passes the excitation beams, we observe as much as 97.9±1.2% transmission when the rate of two-photon absorption is high and the 5S1/2 and 5P3/2 states are depopulated, compared to 87.6±0.9% transmission if only the 780-nm beam is present. This demonstrates two-photon excitation of a launched cold-atom source with controllable launch velocity and narrow velocity spread, as a foundation for three-photon excitation to Rydberg states.
The interaction of light with atoms and molecules is of fundamental interest in many branches of science. In atomic physics, this interaction can be used to cool and spatially confine (trap) atoms. These traps can be used as the starting point for other experiments, but the dynamics of the cooling and trapping processes is itself of interest. In order to better understand the physics of trapping atoms in an optical dipole force trap, we have conducted a series of spectroscopic measurements of ultracold rubidium atoms in such a trap. The trap was created at the focus of a Nd:YAG laser beam with wavelength 1064nm and nearly Gaussian spatial mode. For rubidium, the trap light is red-detuned and the atoms are confined to the highest intensity in the beam. In order to probe the atoms confined in the trap, we have performed spectroscopy on the 5S1/2 → 5P3/2 transition. Because the polarizability of the ground and excited states is not the same at the trap wavelength, the spectra exhibit both a shift and inhomogeneous broadening. We have investigated the spectra for both linear and circular polarized traps. We also studied the application of a second laser to couple the excited state (5P3/2) to another higher excited state (5D5/2) to reduce the inhomogeneous broadening of the 5S1/2 → 5P 3/2 transition. Finally, two-photon spectroscopy was performed on atoms in the dipole force trap and compared to spectra taken in a magneto optical trap (MOT). Autler-Townes splitting was clearly observed in the MOT and appears to have been observed in the dipole force trap also.
Utilizing two-photon excitation in hot Rb vapor we demonstrate the generation of collimated optical fields at 420 and 1324 nm. Input laser beams at 780 and 776 nm enter a heated Rb vapor cell collinear and circularly polarized, driving Rb atoms to the 5D5/2 state. Under phase-matching conditions coherence among the 5S1/2 → 5P3/2 → 5D5/2 → 6P3/2 transitions produces a blue (420 nm) beam by four-wave mixing. We also observe a forward and backward propagating IR (1324 nm) beam, due to cascading decays through the 6S1/2 → 5P1/2 states. Power saturation of the generated beams is investigated by scaling the input powers to greater than 200 mW, resulting in a coherent blue beam of 9.1 mWpower, almost an order of magnitude larger than previously achieved. We measure the dependences of both beams in relation to the Rb density, the frequency detuning between Rb ground-state hyperfine levels, and the input laser intensities. (C) 2014 Optical Society of America
We present our experimental results of two-photon laser excitation 5S1/2→5P3/2→nS1/2 of Rb atoms to Rydberg nS1/2 states with a homemade 480 nm laser in the second excitation step. In an experiment with cold Rb atoms, we excited the 42S1/2 state and detected Rydberg atoms with a selective-field-ionization (SFI) detector that provides single-atom resolution. The resonance line shapes well agreed with numerical simulations in a three-level theoretical model. We also studied the multiatom spectra of Rydberg excitation of mesoscopic atom ensembles which are of interest to quantum information processing. In the experiment with hot Rb atoms, we first excited the 30S1/2 state and observed a narrow Rydberg EIT resonance. Its line shape also agreed well with theory. Then, we performed a similar experiment with the higher 41S1/2 state and observed the Autler–Townes splitting of the EIT resonance in the presence of a microwave field, which was in resonance with the microwave transition 41S→41P3/2. This allowed us to measure the average strength of the microwave field and, thus, demonstrate the operation of a Rydberg microwave sensor. We may conclude that the developed homemade laser at 480 nm substantially extends our capabilities for further experiments on quantum information and quantum sensing with Rydberg atoms.
Three-photon laser excitation of single rubidium atoms in an optical dipole trap (ODT) into the37P Rydberg state by laser radiation with wavelengths of 780, 1367, and 743 nm has been experimentally demonstrated. The excitation to Rydberg states is detected by an optical method using the losses of atoms in the ODT. The laser excitation spectra of single Rydberg atoms in the ODT are recorded, and the dependence of the excitation probability on the laser pulse duration is measured. The measured spectrum width was 2MHz. Experiments on fluorescence quenching spectroscopy of a cloud of cold atoms in a magneto-optical trap during the three-photon laser excitation of atoms to Rydberg states are also carried out. The experimental results are compared with a numerical calculation. Methods for increasing the accuracy of the coherent three-photon laser excitation of Rydberg atoms in the ODT are considered.
Abstract The temporal dynamics of three-photon 5S1/2 → 5P3/2 → 6S1/2 → 39P3/2 laser excitation of mesoscopic ensembles of cold Rb atoms to Rydberg states in a magneto-optical trap is studied using cw single-frequency lasers at each stage. The ensembles comprise N = 1 – 5 atoms and are detected by the method of selective field ionisation with postselection with respect to the number of atoms. The dependence of the excitation probability on the duration of the exciting laser pulses and the number of detected Rydberg atoms is investigated. At short interaction times, a linear increase in probabilities is observed, and at large times, the probabilities reach saturation, while each number of atoms has its own characteristic features. The experimental dependences are compared with the results of numerical calculations in the framework of a four-level model, and their good agreement is obtained. The conditions necessary for observing Rabi population oscillations are determined. The obtained results are important for the application of Rydberg atoms in quantum information.
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.