Lasers in Atomic Collisions, Cold Plasma and Cold Atom Physics

W. R. MacGillivray, M. C. Standage

Yang Liu, Zhenjie Shen, X. Wang +1 more

With the continuous advancement and maturation of laser cooling techniques for atoms and molecules and full-dimensional electron and ion imaging technology, using momentum imaging techniques to investigate the characteristic properties of cold atoms and collision dynamics has emerged as a burgeoning research direction. This progress has driven the development of a series of high-resolution electron and ion detection devices, leading to innovative breakthroughs in fields such as cold molecule reactions, Rydberg atoms, nuclear decay, photoionization of Bose-Einstein condensates (BECs) and cold plasmas, collisions between cold atoms and ions/electrons, coherent control of cold atoms, and strong-field ultrafast physics. This article reviews representative instruments and their corresponding seminal achievements in the following domains: In cold molecular/cold chemical reactions, imaging technology has revealed new insights into reaction mechanisms; For cold Rydberg atom interactions, it demonstrates high-precision quantum state manipulation capabilities, advancing quantum information processing; In nuclear decay research, it provides ultra-sensitive detection methods, deepening understanding of decay processes; For BEC photoionization and cold plasma control, it can precisely monitor and manipulate microscopic processes; In cold atomic collision studies, it reveals new details in collision dynamics, refining collision theories; Regarding coherent control of cold atoms, it achieves accurate quantum state manipulation and interference; In strong-field ultrafast processes, it elucidates complex electron dynamics under intense fields, providing innovative methods for ultrafast laser control. Furthermore, this article summarizes the applications of imaging technologies in the aforementioned research areas involving cold atoms, and provides prospects for future developments in this evolving field.

Paul S. Julienne, Andrew M. Smith II, Keith R. Burnett

Edgar J. D. Vredenbregt

Ultracold plasmas (UCPs) represent a marriage between the seemingly distinct fields of cold atom physics and plasma physics. In cold atom physics, dilute clouds of atoms can be trapped with laser radiation and cooled to J.1Ktemperatures. In contrast, in plasma physics the constituents generally have temperatures in the 1,000K-1O,000K range as well as much higher density. In 1999,Rolston and co-workers [1] first converted a cloud of laser-cooled atoms into a plasma by photo-ionizing the atoms just above threshold. This provides very unusual circumstances:the temperature of ions and neutrals is O.OOIK,that of electrons 10K! Such ultra-cold plasmas therefore are interesting subjects for fundamentalplasma physics studies.\nIn a recent paper [2], we argued that ultracold plasmas (UCPs) may in addition provide an entirely new way of generatinghigh-brightnesscharged-particlebeams, such as used in focused-ion beams, laser synchrotrons, and ultra-fast electron microscopy.\nHere, a low temperature T is beneficial for the intrinsic (transverse) brightness B of a\nsource since B = II(A1), where I is the current and A the cross-sectional area. I will discuss an experimental investigation of the properties of ion and electron beams extracted from ultracold plasmas, which shows that such beams indeed have low temperatures, and, as a result, high angular intensity.

Thad G Walker

D. Ciampini, F. Fuso, Jörg Helge Müller +3 more

The recent development of laser cooling and trapping techniques has made possible the controlled realization of dense and cold atomic samples, thus opening the way for spectroscopic investigations in the low and ultra-low temperature regimes not accessible with conventional techniques. In our lab, an apparatus for laser cooling and Bose-Einstein condensation of rubidium atoms is in operation, producing a sample large enough to perform reliable investigations by absorption or emission techniques. Moving from previous photoionization experiments of laser-cooled atoms in a magneto-optical trap irradiated by cw-laser radiation [1] and stimulated by the interest grown recently on ultra-cold plasma [2], we have started a series of experiments aimed at investigating the interaction of intense laser pulses with the ultra-cold neutral sample, boty aboeand below the condensation temperature. Radiation from an excimer-pumped dye laser was used at a wavelength close to 594 nm, corresponding to the ionization threshold of rubidium for two photon non-resonant absorption from the ground state, with intensities in the tens of MW/cm^2 range and a pulse duration of 16 ns. Preliminary results, attained through the dynamical analysis (atom number, temperature) of the cold atom sample after the arrival of the laser pulse, suggest the occurrence of different processes, initiated by multi-photon ionization, involving collisions between cold electrons and ultra-cold neutrals, recombination at low temperatures and collective processes in the weak and cold plasma. Interpretation of those results demonstrates that this class of experiments, based on a variety of topics typical of atomic, plasma and statistical physics, can open the way for novel and intriguing investigations of laser-matter interaction. Further experimental developments will include duplication of the laser pulse frequency and one photon ionization of ground state rubidium laser-cooled atoms. [1] O. Maragò et al., Phys. Rev. A 57 R4110 (1998); E., Arimondo et al., Appl. Surf. Sci. 154-155 527 (2000); F. Fuso et al., Opt. Commun. 173 223 (2000). [2] T.C. Killian et al., Phys. Rev. Lett. 83 4776 (1999); S. Kulin et al., Phys. Rev. Lett. 85 318 (2000).