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Conference on Lasers and Electro-Optics

Photoionization for Na and Li cold atoms in a MOT

Volker Wippel, C. Binder, W. Huber, Laurentius Windholz, F. Fuso, M. Allegrini, E. Arimondo

Published Aug 29, 2005• 0 citations
Publisher

Abstract

Summary form only given. Photoionization of cold atoms in their first excited state has been applied to measure the photoionization cross section in rubidium magneto-optical trap (MOT), and cesium MOT. The modifications of the MOT loading rate and of the steady state number of trapped atoms allow one to measure the dependence of the cold atom photoionization cross section on the laser wavelength for absorption from the excited atomic state. We report here on measurements of photoionization cross-sections of both laser-cooled sodium and lithium atoms at various photoionization wavelengths.

DOI
10.1109/iqec.2000.907934

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Bulletin of the American Physical Society•May 1, 1996•0 citations
Summary form only given. Photoionization of cold atoms in their first excited state has been applied to measure the photoionization cross section in rubidium magneto-optical trap (MOT), and cesium MOT. The modifications of the MOT loading rate and of the steady state number of trapped atoms allow one to measure the dependence of the cold atom photoionization cross section on the laser wavelength for absorption from the excited atomic state. We report here on measurements of photoionization cross-sections of both laser-cooled sodium and lithium atoms at various photoionization wavelengths.
A two element magneto-optical trap (MOT) in standard configuration for Na and 7Li or 6Li is used to cool and trap Na and one Li isotope simultaneously or separately. The metal background vapor out of which the atoms are trapped comes from dispensers. The two atom clouds can be slightly shifted what makes it easy to overlap them. The number and density of the clouds were determined and the temperature measured roughly. The mutual influence of the clouds was investigated and turned out to be smaller than the noise. Preliminary experiments working towards the production of heteronuclear cold molecules by photoassociation were performed, showing the well known production of Na2 long- range molecules. Additionally, the photoionization cross- section was determined by ionizing cold atoms in the excited state by UV-laser light. The results are in reasonable agreement with data obtained elsewhere using synchrotron radiation.
Photoionization of a cold atomic sample offers intriguing possibilities for observing collective effects at extremely low temperatures. Irradiation of a rubidium condensate and of cold rubidium atoms within a magneto-optical trap (MOT) with laser pulses ionizing through one-photon and two-photon absorption processes was performed. Losses and modifications in the density profile of the remaining trapped cold cloud or the remaining condensate sample were examined as functions of the ionizing laser parameters. Ionization cross sections were measured for atoms in a MOT, while in magnetic traps losses larger than those expected for ionization process were measured.
A two element magneto-optical trap (MOT) in standard configuration for Na and 7Li or 6Li is used to cool and trap Na and one Li isotope simultaneously or separately. The metal background vapor out of which the atoms are trapped comes from dispensers. The two atom clouds can be slightly shifted what makes it easy to overlap them. The number and density of the clouds were determined and the temperature measured roughly. The mutual influence of the clouds was investigated and turned out to be smaller than the noise. Preliminary experiments working towards the production of heteronuclear cold molecules by photoassociation were performed, showing the well known production of Na2 long- range molecules. Additionally, the photoionization cross- section was determined by ionizing cold atoms in the excited state by UV-laser light. The results are in reasonable agreement with data obtained elsewhere using synchrotron radiation.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
Losses from a cesium magneto-optical trap induced by an additional laser ionizing the atoms in the 6P3/2{6P}_{3/2}6P3/2​ state have been measured as a function of the intensity and frequency of the ionizing laser. The absolute cross section for ionization of the 6P3/2{6P}_{3/2}6P3/2​ state has been derived as a function of the wavelength of the ionizing laser. Our values are compared with previous ones and available theoretical predictions. A simple model describing the photoionization processes has been developed.
ABSTRACTCandidate?s Names: John AgomuoDegree Title: PhDThesis Title: Excitation And Photoionization Of Laser-Cooled Atoms In The AC Driven Magneto-Optical Trap (AC-MOT), Using Resonant And Non-Resonant Radiation.Date: 19/12/2014Results of experiments involving the manipulation of atoms using laser radiation are presented. A high-density trap of potassium atoms was created using an AC-driven magneto-optical trap (AC-MOT), loaded from a Zeeman-slowed atomic beam. The AC-MOT was operated in a pulsed mode, with a trapping laser that was detuned by -4?, where ? is the natural line-width of the trapping transition. Under these conditions, the AC-MOT trapped an average of 3.63�0.02�?10?^8 atoms, which were cooled to a mean temperature of 275?K�33?K.Using the AC-MOT, the absolute photoionization cross-section of cold potassium atoms was determined using ionizing laser radiation at 450.4 nm obtained from a high-power diode laser. The measured photoionization cross-section from the 42P3/2 excited state was obtained by measuring the loss rate and the lifetime of the AC-MOT during the loading and decay processes. Using these methods, the cross section was determined to be 1.49�0.13 Mb, and 2.38�0.18 Mb respectively. Precise energy levels of high-n Rydberg states of potassium have also been measured using stepwise-excitation of the trapped atoms, with the intermediate state being the 42P1/2 state that was excited by resonant laser radiation at 389,286,368.12 MHz. Excitation from the 42P1/2 state to the n^2 S_(1/2) states was carried out using blue radiation from a dye laser, for transitions to Rydberg states with principal quantum numbers ranging from n = 18 to ~200. For excitation to the n^2 D_(3/2) states, transitions up to Rydberg states with n ranging from 18 to 167 were studied. Due to the strong interaction between Rydberg atoms, the measured energy levels deviated from their predicted theoretical values at high principal quantum numbers (n?130 for the S-states, and n?100 for the D-states). For principal quantum numbers greater than these values, the spectral lines were found to both broaden and shift in energy, and new features in the Rydberg spectra were observed. These new features have been attributed to the dipole-forbidden n2P1/2 and n2P3/2 states, which cannot be excited directly by the laser. These states must hence be excited due to interplay between the highly excited Rydberg atoms that is occurring due to their large effective size and close proximity in the AC-MOT.
The authors have used laser cooling and trapping techniques to investigate photoionization and cold collisions. With laser-trapped Rb, they have measured the photoionization cross section from the first excited (5P) level by observing the photoionization-induced loss rate of neutral atoms from the trap. This technique has the advantage that it directly measures the photoionization rate per atom. Knowing the ionizing laser intensity and the excited-state fraction, the measured loss rate gives the absolute cross section. Using this technique, the Rb 5P photoionization cross section at {approximately}400 nm has been determined with an uncertainty of 9%. The authors are currently attempting to extend this method to the 5D level. Using time-ordered pulses of diode-laser light (similar to the STIRAP technique), they have performed very efficient two-photon excitation of trapped Rb atoms to 5D. Finally, they will present results from a recent collaboration which combines measurements form conventional molecular spectroscopy (single photon and double resonance) with photoassociation collisions of ultracold Na atoms to yield a precise ({le}1 ppm) value for the dissociation energy of the X {Sigma}{sub g}{sub +} ground state of the Na{sub 2} molecule.