Rydberg atoms are those which have their valence electron excited to high principal quantum number n. Atoms in the Rydberg state are the research focus of the experiment from which this paper derives. Rydberg atoms are fragile, and thermal collisions are enough to ionize and destroy the Rydberg state. A magneto-optical trap (MOT) serves the purpose of "ultra-cooling" atoms to temperatures around 140 micro-Kelvin and dramatically reduces the impact of thermal collisions. This paper details the theory and equipment necessary to realize a MOT of rubidium-85. It will then discuss the characterization of the MOT we implemented by a technique called low intensity absorption imaging. The result of the measurements by the absorption imaging gave an atom count of N=8.87 +/- (0.45)stat + (0.14)sys X 105 atoms and a peak atomic density of n0=1.57 +/- (0.14)stat + (0.02)sys X 1011 cm-3, where "stat" and "sys" denote statistical and systematic uncertainties. The MOT is of sufficient size and density to continue with the long term goals of the experiment [1][2].
Rydberg atoms are those which have their valence electron excited to high principal quantum number n. Atoms in the Rydberg state are the research focus of the experiment from which this paper derives. Rydberg atoms are fragile, and thermal collisions are enough to ionize and destroy the Rydberg state. A magneto-optical trap (MOT) serves the purpose of "ultra-cooling" atoms to temperatures around 140 micro-Kelvin and dramatically reduces the impact of thermal collisions. This paper details the theory and equipment necessary to realize a MOT of rubidium-85. It will then discuss the characterization of the MOT we implemented by a technique called low intensity absorption imaging. The result of the measurements by the absorption imaging gave an atom count of N=8.87 +/- (0.45)stat + (0.14)sys X 105 atoms and a peak atomic density of n0=1.57 +/- (0.14)stat + (0.02)sys X 1011 cm-3, where "stat" and "sys" denote statistical and systematic uncertainties. The MOT is of sufficient size and density to continue with the long term goals of the experiment [1][2].
Our goal is the preparation and study of ultra- cold plasma and Rydberg matter. We assembled an ex- perimental setup for laser cooling of lithium atoms in a magneto-optical trap (MOT). Trapping of 7 Li atoms in a MOT is demonstrated for a wide range of cooling laser detunings. The number density of 7 Li atoms at different ground-state sublevels is measured by using a probe tun- able laser. The temperature of the trapped atoms is esti- mated. Obtained information is important for the prepara- tion of ultra-cold plasma and highly-excited atoms. duction of recombination in such systems. Our theoreti- cal works show the appearance of short and long-range order (7) and a large reduction of the recombination rate (a few orders of magnitude) in the ultra-cold mixture of Rydberg atoms and plasma in the presence of a strong magnetic field (8-11). The ability to control the decay and crystallization processes in an ensemble of Rydberg atoms could find an application in quantum storage and quan- tum computers. The suggested experiments can model the behavior of the plasma recombination in experiments on creating anti-hydrogen (12-14), and help to increase the number of ground state anti-hydrogen atoms in a strong magnetic field. It is noteworthy that lithium is an element which is very close to hydrogen.
Summary form only given. We report on recent experimental and theoretical investigations of highly excited atoms prepared from a dense atomic sample in a magneto-optical trap (MOT). The goals of the work are two-fold. First, by exciting atoms above the ionization potential (IP) we can study the properties of an ultracold plasma of electrons (T<1 K) and ions (T<1 mK). Second, tuning the excitation below the IP, we can populate high-lying Rydberg states whose atomic radii are comparable to the interparticle spacing, possibly spawning new collective phenomena. In our initial experiments we study Rydberg states. We collect 10/sup 7/ /sup 85/Rb atoms in the MOT at a density of 10/sup 10//cm/sup 3/. Atoms in the 5s ground state are excited into Rydberg states using single photon excitation.
In a Magneto-Optical Trap (MOT), realized for the first time in 1987, one can trap and cool neutral atoms to temperatures below a mK. The invention of this device caused a revolution in atomic physics. With an MOT collision and spectroscopy experiments could be performed with unprecedented accuracy. The main breakthrough came about 10 years later when the atom from an MOT were used to create a Bose Einstein Condensate (BEC), a source of coherent matter. All this work has been rewarded with no less than two Nobel prizes: in 1997, Chu, Cohen-Tannoudji and Phillips received the Nobel prize for the practical and theoretical development of laser cooling, and in 2001 Cornell, Ketterle and Wieman received the Nobel prize for the realization of a Bose Einstein Condensate in a dilute gas. In 1999 Killian et al. took trapped atoms in an entirely new direction when they succeeded in creating the very first Ultracold Plasma (UCP) from the atoms in an MOT. The temperature of such a plasma is more than 1000 times lower than the temperatures in conventional cold plasmas. As a result, this type of plasmas received a lot of attention, both theoretically and experimentally. So far studies of UCPs have mainly been of a fundamental kind. In this thesis we study both the fundamental aspects of atoms excited from a magneto-optical as well as the feasibility of using the electrons and ions from a UCP as a source for charged particle accelerators. The work in this thesis therefore pioneers the line between atom physics, plasma physics and accelerator physics. The first part of this thesis deals with an experimental study of the effect of an ionizing laser on cold neon atoms. Here we study the loss of atoms from a Magneto-Optical Trap caused by photionization. From these measurements we deduce a new value for the near threshold photoionization cross section 2:05±0:25x10-18 cm2 at ¿ = 351 nm and 2:05±0:25x10-18 cm2 at ¿ = 364 nm, which is a factor of four more accurate than previous measurements. The measured valuesagree with earlier measurements but differ signi¯cantly from theoretical values. The value of this cross section has a practical relevance for the realization of a continuous ion source. The second part of this thesis has been conducted at the University of Virginia. We study the role of dipole-dipole interactions in the formation of a UCP from a gas of cold Rydberg atoms, and the effect of dipole-dipole interactions on the broadening of microwave transitions. We find that the broadening scales linearly with the density en scales with the fourth power of n, the principal quantum number. These results show the great importance of dipole-dipole interactions in gas of cold Rydberg atoms and are also relevant for the possible realization of a quantum computer from Rydberg atoms. In a third part we studied the potential of using a UCP as a source for electron accelerators. This was done based upon elaborate simulations performed with the General Particle Tracer Code. The main result of these simulations is that, based upon realistic parameters, the brightness, i.e., the figure of merit for charged particle sources defined as the current divided by the emittance squared, of such a source can be up to two orders of magnitude larger than the brightness of conventional sources, which is a major advance. The emittance is a measure for the the focusability of the bunch, and scales as p T, with T the electron temperature. The increase in brightness is mainly attributed to the low electron temperatures of approximately 10 K in an UCP, resulting in an initial emittance of 0.01 mm mrad, compared to 1 mm mrad in a conventional source. With experimentally proven techniques it is possible to extract 10 nC/s from the source, which is a competitive repetition rate. In the next part we describe the design, construction and testing of the first setup with which we want to build an electron accelerator based upon cold atoms. For this we first built a vapor-cell magneto-optical trap, in which we can trap over 109 rubidium atoms with a temperature of 200 ¹K, straight from a background vapor, we also designed an atomic beam that will be implemented in the near future and can provide an increased repetition rate. In the last chapter we show how Rydberg atoms excited from an MOT, evolve into an UCP spontaneously. We extracted a minimum of 1 pC from the plasma. As a main result, we were one of the ¯rst to show how the ions and electrons from a UCP can be imaged on a phosphor screen. From these images we can deduct an upper value for the electron and the ion temperature, we extract for both the electrons and the ions an upper temperature of 40 K, when we translate this temperature to an initial emittance, we obtain a value of 0.01 mm mrad, proving the potential of the electrons extracted from atoms excited out of an MOT as a low emittance source. Our measured current of 1 ¹A is not yet competitive and results from the small electric field, but is expected to increase dramatically in the near future. We will implement a 30 kV 10 ns risetime accelerator with which it should be possible to get a current of about 50 mA. Furthermore we will implement the proper diagnostics to measure the proper charge, current and emittance. In the very last chapter we speculate charged particle sources from cold atoms might advance the state of the art in achievable brightness for both electron and ion beams.
It has been more than 30 years since the first demonstration of a magneto-optical trap (MOT) using sodium atoms. Since then the MOT has revolutionised the field of atomic physics by facilitating the emergence of a broad range of productive avenues of research using atoms prepared at low temperatures and high densities. This thesis describes the development of a novel kind of magneto-optical trap: the blue-detuned MOT. Unlike in all previous MOTs the light is blue detuned from atomic resonances and drives "type-II" transitions that have dark ground-state sub-levels. A discussion of the position-dependent and velocity-dependent forces experienced by an atom or molecule in a MOT is first used to consolidate recent theoretical work and, in particular, to introduce the concept of a blue-detuned MOT. The design and construction of an experiment that has been built to demonstrate a blue-detuned MOT using \Rb{87} is described. A thorough characterisation of this novel MOT has been performed. At high magnetic field gradients, radiation-pressure-limited densities exceeding 1011~cm−3 have been reached whilst temperatures are cooled below 30~\si{\micro K} by the efficient and robust sub-Doppler cooling mechanisms. The maximum phase-space density measured is 6×10−6, which is higher than in most normal atomic MOTs, comparable to the best dark SPOTs, and a million times higher than that reported for red-detuned type-II MOTs. This makes the blue-detuned MOT particularly attractive for molecules where laser cooling and trapping always uses type-II transitions. For the first time, a study of trap loss due to ultra-cold collisions between atoms occurring in the presence of near-resonant blue-detuned light is undertaken. Finally, the experiment is used to demonstrate many new and unreported configurations of MOT for \Rb{87}, showing that a comprehensive understanding of complicated MOTs is now possible, and presenting a clear direction for further research.
A detailed experimental and theoretical investigation of a magneto-optical trap for caesium atoms is presented. Particular emphasis has been placed on achieving high spatial number densities and low temperatures. Optimizing both of these together enables efficient evaporative cooling from a conservative trap, a procedure which has recently led to the first observations of Bose-Einstein condensation in a dilute atomic vapour. The behaviour of a magneto-optical trap is nominally determined by four independent parameters: the detuning and intensity of the light field, the magnetic field gradient and the number of trapped atoms. A model is presented which incorporates previous treatments into a single description of the trap that encompasses a wide range of its behaviour. This model was tested quantitatively by measuring the temperature of the cloud and its spatial distribution as a function of the four parameters. The maximum density was found to be limited both by the reabsorption of photons scattered within the cloud and by a reduction of the confining force at small light shifts. The nonlinear variation with position of the restoring force was found to be significant in limiting the number of atoms confined to a high density. A maximum density in phase space (defined as the number of atoms in a box with sides of dimension one thermal de Broglie wavelength) of (1.5 ± 0.5) x 10-5 was observed, with a spatial density of 1.5 x 1011 atoms per cm3. Cold collision losses from a caesium magneto-optical trap have been studied with the purpose of assessing their influence on spatial densities. In contrast to previous measurements of similar quantities, these measurements did not require the use of an ultra-low (< 10-10 Torr) background vapour pressure. The dependence of the cold collision loss coefficient β on the trapping intensity was measured to permit identification of the different cold collision processes. The largest loss rates observed were those due to hyperfine structure-changing collisions, with a coefficient β = (2±1) x 10-10cm3s-1. A study is presented of a modified magneto-optical trap in which a fraction of the population is shelved into a hyperfine level that does not interact with the trapping light. In this so-called "dark" magneto-optical trap, improved densities of nearly 1012cm-3 have been previously reported for sodium. The application of the technique to caesium is not straightforward due to the larger excited state hyperfine splittings. A simple theory for caesium is presented and its main predictions verified by measurements of density, number and temperature. A density of nearly 1012cm,-3 was indeed obtained but at a temperature substantially higher than in the conventional magneto-optical trap.
This project was to measure the atomic density of (85)Rb atoms in a magneto optical trap using a low-intensity probe laser. Additionally, a dark spontaneous force optical trap was constructed in an attempt to boost the trap density. The dark spot failed to appreciably increase the overall trap density (which remained steady at - N = 10^10 atoms/cm^3) but it did increase the density of dark-state atoms in the trap by an order of magnitude. This is a useful result since many experiments on cold Rydberg atoms involve exciting atoms starting in the ground state rather than the first excited state, which is occupied by a large number of atoms in a traditional magneto optical trap. The dark spot trap shows promise for boosting both the density of dark state atoms in the trap as well as the overall trap density. However, the latter goal will require further adjustment to the trap.