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Physical Review A

Spectroscopy of low-energy atoms released from a solid noble-gas matrix: Proposal for a trap-loading technique

Ricardo Lewis Lambo, C. C. Rodegheri, Daniel Miranda Silveira, Claudio Lenz Cesar

Published Dec 4, 2007• 15 citations
Publisher

Abstract

We have studied the velocity distribution of chromium atoms released from a solid neon matrix at cryogenic temperatures via Doppler spectroscopy. The Ne matrix is grown by directing a small flux of gas onto a cold substrate, while Cr atoms are simultaneously implanted by laser ablation, with the resultant plume directed toward the growing matrix. The atoms are then released by a heat pulse. We have observed neutral Cr atoms at temperatures around $13\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ with densities close to ${10}^{12}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$. The released atoms have a large initial drift velocity, explained by simple kinetic theory arguments, due to the light species' drag force. The scheme could be adapted to produce cryogenic beams of atoms, molecules, and possibly ions, for collisional studies and spectroscopy. However, our main motivation was the construction of a hydrogen trap, and here we discuss the prospects and problems of using this technique for this purpose.

DOI
10.1103/physreva.76.061401

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We have studied the velocity distribution of chromium atoms released from a solid neon matrix at cryogenic temperatures via Doppler spectroscopy. The Ne matrix is grown by directing a small flux of gas onto a cold substrate, while Cr atoms are simultaneously implanted by laser ablation, with the resultant plume directed toward the growing matrix. The atoms are then released by a heat pulse. We have observed neutral Cr atoms at temperatures around 13K13\phantom{\rule{0.3em}{0ex}}\mathrm{K}13K with densities close to 1012cm\ensuremath−3{10}^{12}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}1012cm\ensuremath−3. The released atoms have a large initial drift velocity, explained by simple kinetic theory arguments, due to the light species' drag force. The scheme could be adapted to produce cryogenic beams of atoms, molecules, and possibly ions, for collisional studies and spectroscopy. However, our main motivation was the construction of a hydrogen trap, and here we discuss the prospects and problems of using this technique for this purpose.
In this paper, we report on our recent advances on a new trap loading mechanism for neutral atoms. The idea is based on our recently published results for chromium spectroscopy of atoms released from a solid neon matrix at cryogenic temperatures. The proposed trap loading mechanism consists of magnetically capturing the low-energy fraction of paramagnetic atoms being released from the matrix, while the host Ne atoms stick to the walls. Two different designs are described: one with a superconducting magnet producing a trap depth of 3 T and another with a superconducting dynamically switched magnet that generates a trap depth of about 1 T. Some preliminary results are presented.
Hydrogen is of critical importance in atomic and molecular physics and the development of a simple and efficient technique for trapping cold and ultracold hydrogen atoms would be a significant advance. In this study we simulate a recently proposed trap-loading mechanism for trapping hydrogen atoms released from a neon matrix. Accurate ab initio quantum calculations are reported of the neon-hydrogen interaction potential and the energy- and angular-dependent elastic scattering cross sections that control the energy transfer of initially cold atoms are obtained. They are then used to construct the Boltzmann kinetic equation, describing the energy relaxation process. Numerical solutions of the Boltzmann equation predict the time evolution of the hydrogen energy distribution function. Based on the simulations we discuss the prospects of the technique.
We describe the generation and properties of a cryogenic beam of 7^77Li2_22​ dimers from sublimation of a neon matrix where lithium atoms have been implanted via laser ablation of solid precursors of metallic lithium or lithium hydride (LiH). Different sublimation regimes lead to pulsed molecular beams with different temperatures, densities and forward velocities. With laser absorption spectroscopy these parameters were measured using the molecular 7^77Li2_22​ (R) transitions A$^1Σ_u^+(v'=4,J'=J''+1)\leftarrow XXX^1Σ_g^+ (v''=0,J''=0,1,3).Inatypicalregime,sublimatingamatrixat16K,translationaltemperaturesof6−−8Kwithadriftvelocityof130m. In a typical regime, sublimating a matrix at 16 K, translational temperatures of 6--8 K with a drift velocity of 130 m.Inatypicalregime,sublimatingamatrixat16K,translationaltemperaturesof6−−8Kwithadriftvelocityof130m\,sss^{-1}$ in a free expanding pulsed beam with molecular density of 109^99 cm−3^{-3}−3, averaged along the laser axis, were observed. Rotational temperatures around 5--7 K were obtained. In recent experiments we were able to monitor the atomic Li signal -- in the D2 line -- concomitantly with the molecular signal in order to compare them as a function of the number of ablation pulses. Based on the data and a simple model, we discuss the possibility that a fraction of these molecules are being formed in the matrix, by mating atoms from different ablation pulses, which would open up the way to formation of other more interesting and difficult molecules to be studied at low temperatures. Such a source of cryogenic molecules have possible applications encompassing fundamental physics tests, quantum information studies, cold collisions, chemistry, and trapping.
Ground-state 52Cr{}^{52}\mathrm{Cr}52Cr atoms have been magnetically trapped using buffer-gas loading. The atoms are produced by laser ablation of solid 52Cr,{}^{52}\mathrm{Cr},52Cr, thermalized by collisions with a cryogenically cooled helium buffer gas, and trapped by an anti-Helmholtz quadrupole magnetic field. The atoms are detected by absorption spectroscopy on the ${a}^{7}{S}_{3}\ensuremath{\leftrightarrow}{z}^{7}{P}_{3}$ transition at 427.6 nm. Using this technique, approximately 1011{10}^{11}1011 atoms are loaded into the trap in a single ablation pulse. Loading has been demonstrated at temperatures from 0.3 to 1.4 K.
We report the magnetic trapping and evaporative cooling of bosonic and fermionic isotopes of atomic chromium. Using a cryogenic helium buffer gas, 10 1 2 chromium atoms are trapped at an initial temperature of ∼ 1 K. The chromium atoms are then cooled adiabatically and evaporatively to temperatures as low as ∼10 mK. Elastic and inelastic 5 2 Cr collisional cross sections are measured over this temperature range. Prospects for simultaneously creating a 5 2 Cr Bose-Einstein condensate and 5 3 Cr Fermi degenerate gas will he discussed.
A range of experimental techniques for application in reaction studies between ionic and neutral atoms/molecules and high resolution spectroscopy experiments with sympathetically cooled molecular ions are presented. A novel ion trap loading scheme using the photo-ionisation of atoms generated by the pulsed laser ablation of a solid calcium target has been characterised. We have identified the range of ablation laser fluences that must be used in order to produce a flux of neutral calcium atoms, which is a prerequisite for isotope selective ion trap loading. Calcium ions are trapped and laser cooled in a linear radio-frequency ion trap. We have developed a spectroscopy scheme that allows the entire fluorescence spectrum of trapped ions to be rapidly collected with high precision while maintaining a low ion temperature and good ion localisation throughout interrogation. The scheme has been demonstrated by measuring the saturation intensity of the calcium ion 4S1/2?4P1/2 transition. We have developed a novel scheme to measure the secular motion of trapped ions and demonstrated the application of the technique to ion-neutral collision reaction experiments. Employing pulsed excitation and Doppler velocimetry, we have measured the centre-of-mass mode frequency of single ions as well as large ion crystals with a frequency precision better than 2x10-3 within an interrogation time on the order of seconds. This method has been used to measure the mass of ions and observe charge exchange collisions between trapped calcium isotopes. In particular, we have measured the 44Ca++40Ca!40Ca++44Ca reaction cross section and demonstrated the single-event resolution of the technique. Finally, we have developed a novel all-optical broadband scheme for exciting, amplifying and measuring the secular motion of ions in the trap. Oscillation induced by optical excitation has been coherently amplified to control and measure the ion's secular motion. Requiring only a single interrogation laser, the ion's oscillation amplitude can be precisely controlled. The application of this technique to non-destructive spectroscopy of trapped molecular ions is discussed.