共查询到20条相似文献,搜索用时 31 毫秒
1.
Killian TC Lim MJ Kulin S Dumke R Bergeson SD Rolston SL 《Physical review letters》2001,86(17):3759-3762
We study the formation of Rydberg atoms in expanding plasmas at temperatures of 1-1000 K and densities from 10(5)-10(10) cm(-3). Up to 20% of the initially free charges recombine in about 100 micros, and the binding energy of the Rydberg atoms approximately equals the increase in the kinetic energy of the remaining free electrons. Three-body recombination is expected to dominate in this regime, yet most of our results are inconsistent with this mechanism. 相似文献
2.
In cold dense Rydberg atom samples, the dipole-dipole interaction strength is effectively resonant at the typical interatomic spacing in the sample, and the interaction has a 1/R3 dependence on interatomic spacing R. The dipole-dipole attraction leads to ionizing collisions of initially stationary atoms, which produces hot atoms and ions and initiates the evolution of initially cold samples of neutral Rydberg atoms into plasmas. More generally, the strong dipole-dipole forces lead to motion, which must be considered in proposed applications. 相似文献
3.
We report the creation of an interacting cold Rydberg gas of strontium atoms. We show that the excitation spectrum of the inner valence electron is sensitive to the interactions in the Rydberg gas, even though they are mediated by the outer Rydberg electron. By studying the evolution of this spectrum we observe density-dependent population transfer to a state of higher angular momentum l. We determine the fraction of Rydberg atoms transferred, and identify the dominant transfer mechanism to be l-changing electron-Rydberg collisions associated with the formation of a cold plasma. 相似文献
4.
E. A. Andreev P. V. Kashtanov B. M. Smirnov 《Journal of Experimental and Theoretical Physics》2006,103(4):574-579
The lifetime of a molecule consisting of two Rydberg atoms with respect to electron release is determined from computer simulation
of two classical electrons in the field of Coulomb centers. From this, the cross section of the Penning process of collision
of two Rydberg atoms with electron release is obtained. The rate constant for ionization of Rydberg atoms is evaluated for
the Rydberg plasma within the Thomson model. On the basis of these processes, the kinetics is analyzed for the decay of a
Rydberg plasma. Comparison with experimental data shows that these decay processes are responsible for the first stage of
the decay of a magnetized and nonmagnetized Rydberg plasma located in a magnetic superconducting trap, whereas other processes
become important at a subsequent stage of the plasma evolution.
This article was submitted by the authors in English. 相似文献
5.
6.
We report the results of simulations that explain many properties of ultracold neutral plasmas. We find that three-body recombination is important at very low temperatures since it is a heating mechanism for the electron gas and it preferentially removes the slow ions from the plasma. We also find that collisions between cold electrons and Rydberg atoms are an important source of electron heating and deexcitation of atoms formed in the plasma. Simulations show that the Coulomb coupling constant does not become larger than similar1/5 for the reported experiments. 相似文献
7.
W. Li P. J. Tanner Y. Jamil T. F. Gallagher 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,40(1):27-35
The experiments reported here show that the
dipole-dipole interaction, the fundamental interaction between the
cold Rydberg atoms, is the dominant initial ionization mechanism for
evolution from a frozen Rydberg gas into a plasma. The study also
indicates that plasma formation follows a path of initial
ionization, redistribution of Rydberg population to higher angular
momentum states, and rapid avalanche ionization due to
electron-Rydberg collisions. 相似文献
8.
Andreas Wolf 《Hyperfine Interactions》1993,76(1):189-201
Laser-stimulated radiative transitions from states close to the ionization threshold to low-lying atomic levels are considered
for protons (antiprotons) in a cold electron (positron) plasma and estimates for the resulting formation rate of hydrogen
(antihydrogen) atoms in the ground state are given. The estimates apply to both laser-stimulated recombination and induced
radiative stabilization of high Rydberg levels. First experiments concerning laser-stimulated recombination in merged beams
of electrons and protons are discussed, which have confirmed the rate predictions for this process. In view of antihydrogen
formation in a cold trapped positron plasma, the use of two successive stimulated transitions is considered for obtaining
a high formation rate of ground-state atoms at relatively low radiation intensity. 相似文献
9.
Cold Rydberg atoms exposed to strong magnetic fields possess unique properties which open the pathway for an intriguing many-body dynamics taking place in Rydberg gases, consisting of either matter or anti-matter systems. We review both the foundations and recent developments of the field in the cold and ultracold regime where trapping and cooling of Rydberg atoms have become possible. Exotic states of moving Rydberg atoms, such as giant dipole states, are discussed in detail, including their formation mechanisms in a strongly magnetized cold plasma. Inhomogeneous field configurations influence the electronic structure of Rydberg atoms, and we describe the utility of corresponding effects for achieving tightly trapped ultracold Rydberg atoms. We review recent work on large, extended cold Rydberg gases in magnetic fields and their formation in strongly magnetized ultracold plasmas through collisional recombination. Implications of these results for current antihydrogen production experiments are pointed out, and techniques for the trapping and cooling of such atoms are investigated. 相似文献
10.
Signals of ultracold plasma are observed by two-photon
ionization of laser-cooled caesium atoms in a magneto-optical trap.
Recombination of ions and electrons into Rydberg atoms during the
expansion of ultracold plasma is investigated by using
state-selective field ionization spectroscopy. The dependences of
recombination on initial electron temperature (1--70 K) and initial
ion density ($ \sim $10$^{10}$ cm$^{ - 3})$ are investigated. The
measured dependence on initial ion density is $N^{1.547\pm 0.004}$
at a delay time of 5 $\mu $s. The recombination rate rapidly
declines as initial electron temperature increases when delay time
is increased. The distributions of Rydberg atoms on different values
of principal quantum number $n$, i.e. $n=30$--60, at an initial
electron temperature of 3.3 K are also investigated. The main
experimental results are approximately explained by the three-body
recombination theory. 相似文献
11.
Experimental Research of Spontaneous Evolution from Ultracold Rydberg Atoms to Plasma 总被引:1,自引:0,他引:1
下载免费PDF全文
![点击此处可从《中国物理快报》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The spontaneous evolution from ultracold Rydberg atoms to plasma is investigated in a caesium MOT by using the method of field ionization. The plasma transferred from atoms in different Rydberg states (n = 22-32) are obtained experimentally. Dependence of the threshold time of evolving to plasma and the threshold number of initial Rydberg atoms on the principal quantum number of initial Rydberg states is studied. The experimental results are in agreement with hot-cold Rydberg-Rydberg atom collision ionization theory. 相似文献
12.
We present a technique for state-selective position
detection of cold Rydberg atoms. Ground state Rb atoms in a
magneto-optical trap are excited to a Rydberg state and are
subsequently ionized with a tailored electric field pulse. This
pulse selectively ionizes only atoms in e.g. the 54d state and not
in the 53d state. The released electrons are detected after a slow
flight towards a micro channel plate. From the time of flight of
the electrons the position of the atoms is deduced. The state
selectivity is about 20:1 when comparing 54d with 53d and the
one-dimensional position resolution ranges from 6 to 40 μm
over a range of 300 μm. This state selectivity and position
resolution are sufficient to allow for the observation of coherent
quantum excitation transport. 相似文献
13.
C. S. Hofmann G. Günter H. Schempp N. L. M. Müller A. Faber H. Busche M. Robert-de-Saint-Vincent S. Whitlock M. Weidemüller 《Frontiers of Physics》2014,9(5):571-586
Recent developments in the study of ultracold Rydberg gases demand an adwanced level of experimental sophistication, in which high atomic and optical densities must be combined with excellent control of external fields and sensitive Rydberg atom detection. We describe a tailored experimental system used to produce and study Rydberg-interacting atoms excited from dense ultracold atomic gases. The experiment has been optimized for fast duty cycles using a high flux cold atom source and a three beam optical dipole trap. The latter enables tuning of the atomic density and temperature over several orders of magnitude, all the way to the Bose--Einstein condensation transition. An elec- trode structure surrounding the atoms allows for precise control over electric fields and single-particle sensitive field ionization detection of Rydberg atoms. We review two experiments which highlight the influence of strong Rydberg---Rydberg interactions on different many-body systems. First, the Rydberg blockade effect is used to pre-structure an atomic gas prior to its spontaneous evolution into an ultracold plasma. Second, hybrid states of photons and atoms called dark-state polaritons are studied. By looking at the statistical distribution of Rydberg excited atoms we reveal correlations between dark-state polaritons. These experiments will ultimately provide a deeper understanding of many-body phenomena in strongly-interacting regimes, including the study of strongly-coupled plasmas and interfaces between atoms and light at the quantum level. 相似文献
14.
We present the first large-scale simulations of an ultracold neutral plasma, produced by photoionization of laser-cooled xenon atoms, from creation to initial expansion, using classical molecular-dynamics methods with open boundary conditions. We reproduce many of the experimental findings such as the trapping efficiency of electrons with increased ion number, a minimum electron temperature achieved on approach to the photoionization threshold, and recombination into Rydberg states of an anomalously low principal quantum number. In addition, many of these effects establish themselves very early in the plasma evolution ( similar ns) before the present experimental observations begin. 相似文献
15.
P. V. Kashtanov M. I. Myasnikov B. M. Smirnov 《Journal of Experimental and Theoretical Physics》2009,108(1):18-26
The standard classical method of computer simulation is used for evaluation of the inelastic cross section in electron collisions
with a highly excited (Rydberg) atom. In the course of collision, the incident and bound electrons move along classical trajectories
in the Coulomb field of the nucleus, and the scattering parameters are averaged over many initial conditions. The reduced
ionization cross section of a Rydberg atom by electron impact approximately corresponds to that of atoms in the ground states
with valence s-electrons and coincides with the results of the previous Monte Carlo calculations. The cross section of an atom transition
between Rydberg atom states as a result of electron impact is used for finding the stepwise ionization rate constant of atoms
in collisions with electrons or the rate constant of three-body electron-ion recombination in a dense ionized gas because
these processes are determined by kinetics of highly excited atom states. Surprisingly, the low-temperature limit of electron
temperatures is realized when the electron thermal energy is lower than the atom ionization potential by about three orders
of magnitude, as follows from the kinetics of excited atom states.
The article is published in the original. 相似文献
16.
17.
18.
Branching ratio and angular distribution of ejected electrons from Eu 4f~76p_(1/2)nd auto-ionizing states
下载免费PDF全文
![点击此处可从《中国物理 B》网站下载免费的PDF全文](/ch/ext_images/free.gif)
The branching ratios of ions and the angular distributions of electrons ejected from the Eu 4f~76p_(1/2)nd auto-ionizing states are investigated with the velocity-map-imaging technique.To populate the above auto-ionizing states,the relevant bound Rydberg states have to be detected first.Two new bound Rydberg states are identified in the region between41150 cm~(-1)and 44580 cm~(-1),from which auto-ionization spectra of the Eu 4f~76p_(1/2)nd states are observed with isolated core excitation method.With all preparations above,the branching ratios from the above auto-ionizing states to different final ionic states and the angular distributions of electrons ejected from these processes are measured systematically.Energy dependence of branching ratios and anisotropy parameters within the auto-ionization spectra are carefully analyzed,followed by a qualitative interpretation. 相似文献
19.
Dutta SK Feldbaum D Walz-Flannigan A Guest JR Raithel G 《Physical review letters》2001,86(18):3993-3996
Cold, dense Rydberg gases produced in a cold-atom trap are investigated using spectroscopic methods and time-resolved electron counting. Optical excitation on the discrete Rydberg resonances reveals long-lasting electron emission from the Rydberg gas ( >20 ms). Our observations are explained by lm-mixing collisions between Rydberg atoms and slow electrons that lead to the population of long-lived high-angular-momentum Rydberg states. These atoms thermally ionize slowly and with large probabilities. 相似文献
20.
A. V. Bogatskaya E. A. Volkova A. M. Popov 《Journal of Experimental and Theoretical Physics》2016,123(3):382-390
The interference stabilization of Rydberg atoms in strong laser fields is proposed for producing a plasma channel with the inverse population. Inversion between a group of Rydberg levels and low-lying excited levels and the ground state permits amplification and lasing in the IR, visible, and VUV frequency ranges. The lasing and light amplification processes in the plasma channel are analyzed using rate equations and the efficiency of this method is compared with that in the usual method for high harmonic generation during rescattering of electrons by a parent ion. 相似文献