Laser cooling and photoionization of alkali atoms (original) (raw)

Ion processes in the photoionization of laser cooled alkali atoms

Optics Communications, 2000

The results of recent photoionization experiments performed on laser cooled cesium and rubidium atoms are critically examined. The role of processes, as ion diffusion and recombination, determining the time evolution and the rate of the produced atomic ions is discussed. A more precise model of the ion evolution is presented, numerically solved and compared to the experimental data. q 2000 Elsevier Science B.V. All rights reserved. PACS: 32.80.Pj; 67.65.q z; 51.10.q y 0030-4018r00r$ -see front matter q 2000 Elsevier Science B.V. All rights reserved.

Photoionization Cross-Section Measurements of the 5P3/2 Excited State of Laser-Cooled Rubidium

2010

Photoionization cross-section measurements are relevant for fundamental tests of the atomic theory, as well as state-selective detection of trapped atomic and molecular species and plasma research, including ultracold plasma formation. We have extended the current photoionization cross-section measurements of the 5P3/2 exited state of rubidium by including three additional wavelengths close to the ionization threshold of 479.1 nm. The measurements were performed in a rubidium magneto-optical trap using several lines from a mixed argon-krypton ion laser ranging from 457.9 nm to 476.5 nm. The photoionization rate for each wavelength was determined from the loss rate of atoms in the trap during exposure to the ionizing laser radiation. Our results are in good agreement with other experimental results and allow for comparison with theoretical predictions of the photoionization cross section versus the ionizing photon energy.

New Results in Photoionization of Laser-Excited Atoms

2003

The use of high-spectral resolution VUV-photon beams in atomic photoionization experiments has significantly increased over the past few years, owing to the number of operating third generation synchrotron radiation sources and associated high-resolution beam lines. For laser-excited atoms, however, the number of experiments is still low, because of the difficulties in combining the use of these two widely-different photon sources.

Ultraviolet light-induced atom desorption for large rubidium and potassium magneto-optical traps

Physical Review A, 2006

We show that light-induced atom desorption ͑LIAD͒ can be used as a flexible atomic source for large 87 Rb and 40 K magneto-optical traps. The use of LIAD at short wavelengths allows for fast switching of the desired vapor pressure and permits experiments with long trapping and coherence times. The wavelength dependence of the LIAD effect for both species was explored in a range from 630 to 253 nm in an uncoated quartz cell and a stainless steel chamber. Only a few mW/ cm 2 of near-UV light produce partial pressures that are high enough to saturate a magneto-optical trap at 3.5ϫ 10 9 87 Rb atoms or 7 ϫ 10 7 40 K atoms. Loading rates as high as 1.2ϫ 10 9 87 Rb atoms/s and 8 ϫ 10 7 40 K atoms/s were achieved without the use of a secondary atom source. After the desorption light is turned off, the pressure quickly decays back to equilibrium with a time constant as short as 200 s, allowing for long trapping lifetimes after the MOT loading phase.

Laser Cooling of Transition Metal Atoms

We propose the application of laser cooling to a number of transition-metal atoms, allowing numerous bosonic and fermionic atomic gases to be cooled to ultra-low temperatures. The non-zero electron orbital angular momentum of these atoms implies that strongly atom-state-dependent light-atom interactions occur even for light that is far-detuned from atomic transitions. At the same time, many transition-metal atoms have small magnetic dipole moments in their low-energy states, reducing the rate of dipolar-relaxation collisions. Altogether, these features provide compelling opportunities for future ultracold-atom research. Focusing on the case of atomic titanium, we identify the metastable a 5 F5 state as supporting a J → J +1 optical transition with properties similar to the D2 transition of alkali atoms, and suited for laser cooling. The high total angular momentum and electron spin of this state suppresses leakage out of the nearly closed optical transition to a branching ratio estimated below ∼ 10 −5. Following the pattern exemplified by titanium, we identify optical transitions that are suited for laser cooling of elements in the scandium group (Sc, Y, La), the titanium group (Ti, Zr), the vanadium group (V, Nb), the manganese group (Mn, Tc), and the iron group (Fe, Ru). Laser cooling and the achievement of quantum degen-eracy of atomic gases has led to an ever broadening range of scientific investigations and applications. This growing impact on science and technology has been fueled by the availability of quantum gases produced from an increasing number of elements, each of which has a new set of properties that can enable a new family of experiments. For example, the fortuitous collisional properties of ru-bidium and sodium enabled the first realizations of scalar [1, 2] and spinor [3-5] atomic Bose-Einstein condensation. The accessible Feshbach resonances of lithium allowed studies of Efimov states [6]. Isotopes of potassium and lithium allowed the study of resonantly interacting Fermi gases [7-10]. The detectability of single metastable helium atoms on micro-channel plate detectors allowed for studies of quantum atom optics [11]. The narrow lines of alkali-earth atoms and ytterbium enabled the realization of optical lattice clocks [12, 13]. The magnetism of chromium allowed for studies of quantum ferrofluids [14], accentuated by the even stronger magnetic dipole interactions of dysprosium [15] and erbium [16]. Gaining access to a greater variety of ultracold atomic gases can, therefore, be expected to broaden the impact of ultracold atomic physics even further. Conversely, the limitations of present-day ultracold atom systems pose limitations on the range of scientific topics that they can be used to study. As an example, we consider the prospect of studying gases in a stable mixture of internal spin states while subject also to coherent spin-state dependent optical potentials. Each of these two conditions can be achieved separately in extant quantum gases: Stable spinor gases are realized with alkali atoms, whose small magnetic moments forestalls inelastic dipolar relaxation collisions [17]. Highly coherent spin-dependent optical potentials are realized for lanthanide atoms, owing to their complex atomic structures [18]. However, in neither case are both conditions simultaneously achieved: Spin-dependent optical potentials for alkali atoms have low coherence (as we explain in Sec. I). Spinor gases of lanthanide atoms decay generally through strong magnetic dipolar relaxation, although the specific relaxation via collision channels with indistinguishable initial or final spin states can be suppressed by Fermi statistics [19]. Here, we open a door to new studies of quantum atomic gases by describing pathways for laser-cooling a number of transition-metal elements, including those in the scandium group (Sc, Y, La), the titanium group (Ti, Zr, and possibly Hf), the vanadium group (V, Nb), the manganese group (Mn, Tc), and the iron group (Fe, Ru, and possibly Os). Specifically, we find for all these elements that there is a strong, electric-dipole allowed, optical transition (see Tab. I), with linewidth on the order of 10 MHz, which resembles the D2 line of alkali atoms in that an electron is driven from ns 1/2 to the np 3/2 state. The lower level on this transition, which we call the laser-cooling state, is either the atomic ground state (in Ru and Mn) or a metastable excited state (in the other cases). In all cases, these transitions are cycling, or at least very nearly so, and connect states with total angular momentum J → J +1. As such, these transitions are suitable for standard laser cooling techniques such as Zeeman slowing [21], magneto-optical trapping [22], and polarization-gradient cooling [23, 24]. These elements have atomic properties that differ from those of existing ultracold atomic gases. Present-day arXiv:2008.06147v4 [physics.atom-ph] 2 Dec 2020

Photoionisation of rubidium in strong laser fields

European Physical Journal D, 2019

The photoionisation of rubidium in strong infra-red laser fields based on ab initio calculations was investigated. The bound and the continuum states are described with Slater orbitals and Coulomb wave packets, respectively. The bound state spectra were calculated with the variational method and we found it reproduced the experimental data within a few percent accuracy. Using the similar approach, ionisation of Rb was also successfully investigated. The effects of the shape and the parameters of the pulse to the photoionisation probabilities and the energy spectrum of the ionised electron are shown. These calculations may provide a valuable contribution at the design of laser and plasma based novel accelerators, the CERN AWAKE experiment.

Laser spectroscopy of alkali atoms

Hyperfine Interactions, 1981

Isotope shifts, spins and hyperfine structure measurements have been performed on 20-31Na, 38-47K, 76-98Rb, 118-145Cs, 208-213Fr and some of their isomers, including far from stability nuclei. The method consists of high resolution laser spectroscopy using thermal atomic beam and rests upon the detection of optical resonances through a magnetic deflection of atoms. Francium measurements correspond to the first observation of one of its optical lines(D2). The variation of the mean square charge radii deduced from the isotope shift exhibit many interesting features such as neutron-shell effects, oddeven staggering, deformations and shape isomerism.

Low-Energy Ions from Laser-Cooled Atoms

Physical Review Applied, 2016

We report the features of an ion source based on two-color photoionization of a laser-cooled cesium beam outsourced from a pyramidal magneto-optical trap. The ion source operates in continuous or pulsed mode. At acceleration voltages below 300 V, it delivers some ten ions per bunch with a relative energy spread ΔU rms =U ≃ 0.032, as measured through the retarding field-energy-analyzer approach. Spacecharge effects are negligible thanks to the low ion density attained in the interaction volume. The performances of the ion beam in a configuration using focused laser beams are extrapolated on the basis of the experimental results. Calculations demonstrate that our low-energy and low-current ion beam can be attractive for the development of emerging technologies requiring the delivery of a small amount of charge, down to the single-ion level and its eventual focusing in the 10-nm range.

Cooling and trapping of radioactive atoms: the Legnaro francium magneto-optical trap

Journal of the Optical Society of America B, 2003

A magneto-optical trap for francium radioactive atoms has been set up at the Istituto Nazionale di Fisica Nucleare, Legnaro laboratories, and its characterization and optimization are under way. The main features of the Fr ϩ beam line, of the target, and of the magneto-optical trap are described in detail. Measurements of the Fr-ion production rate as a function of the target temperature, the primary beam intensity, and energy have been made. Preliminary tests with other stable alkali atoms aimed at an improvement of the magnetooptical trap collection efficiency are reported. Fast and efficient trap loading of rubidium has been obtained through the light-induced atomic desorption from an organic coating. A larger number of sodium atoms, as compared with a monochromatic trapping laser, has been trapped by use of a broadband laser.

Ionization spectroscopy in cold rubidium atoms

We demonstrate photoionization spectroscopy in cold rubidium atoms trapped in a working magneto-optical trap. Three-photon ionization with two-photon resonance proceeds along various channels, with the step-by-step 5S-5P-5D transition and with the two-photon excitation of the 5D or 7S state. The processes are monitored by measuring ion signals which allow sensitive spectroscopy of weak transitions in a cold-atom sample.