Diffractive optics are used to create low-and high-order Laguerre-Gaussian ͑LG͒ beams from the output of a diode laser. We examine the mode purities, conversion efficiencies, extinction ratios, and propagation characteristics. We present detailed analyses of the beam profiles for one low-order (LG 0 1) and one high-order (LG 1 2) Laguerre-Gaussian mode. Modeling the LG 1 2 beam as a superposition of LG modes, we find (99.3 Ϯ0.9%) of the laser intensity in the LG 1 2 mode, a mode purity greater than for LG beams created by other methods external to the laser cavity. The high mode purity may be useful in making atom traps for precision measurements and for Bose-Einstein condensation.
We measure and simulate numerically the Hanle effect and non-zero field level crossing signals in 85 Rb and 87 Rb atoms in a magnetic field at room temperature. Diode laser radiation from 4 mW cm −2 to 3.3 W cm −2 tuned to the D 2 absorption line of each isotope excites atoms into all the excited-state hyperfine levels simultaneously inside the unresolved Doppler profile. Polarization fluorescence detection is used to observe dark and bright resonances, as well as non-zero field level crossing resonances, for several excitation lines. A broad spectral line excitation model is applied to analyse the measured signals. The non-linear Zeeman effect is included in the model for both ground and excited states. Although the applied magnetic field does not exceed 80 G, several hyperfine levels of the excited state show a substantial deviation from the linear Zeeman effect.
We report 2D confinement of 87 Rb atoms in a Laguerre-Gaussian laser beam. Changing of the sign of the detuning from the atomic resonance dramatically alters the geometry of the confinement. With the laser detuned to the blue, the atoms are confined to the dark, central node of the Laguerre-Gaussian laser mode. This trapping method leads to low ac Stark shifts to the atomic levels. Alternatively, by detuning the laser to the red of the resonance, we confine atoms to the high intensity outer ring in a multiply-connected, toroidal configuration. We model the confined atoms to determine azimuthal intensity variations of the trapping laser, caused by slight misalignments of the Laguerre-Gaussian mode generating optics.
Multiply-connected traps for cold, neutral atoms fix vortex cores of quantum gases. Laguerre-Gaussian laser modes are ideal for such traps due to their phase stability. We report theoretical calculations of the Bose-Einstein condensation transition properties and thermal characteristics of neutral atoms trapped in multiply connected geometries formed by Laguerre-Gaussian (LG l p ) beams. Specifically, we consider atoms confined to the anti-node of a LG 1 0 laser mode detuned to the red of an atomic resonance frequency, and those confined in the node of a blue-detuned LG 1 1 beam. We compare the results of using the full potential to those approximating the potential minimum with a simple harmonic oscillator potential. We find that deviations between calculations of the full potential and the simple harmonic oscillator can be up to 3% − 8% for trap parameters consistent with typical experiments.
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