35 research outputs found
Ionization of Sodium and Rubidium nS, nP and nD Rydberg atoms by blackbody radiation
Results of theoretical calculations of ionization rates of Rb and Na Rydberg
atoms by blackbody radiation (BBR) are presented. Calculations have been
performed for nS, nP and nD states of Na and Rb, which are commonly used in a
variety of experiments, at principal quantum numbers n=8-65 and at three
ambient temperatures of 77, 300 and 600 K. A peculiarity of our calculations is
that we take into account the contributions of BBR-induced redistribution of
population between Rydberg states prior to photoionization and field ionization
by extraction electric field pulses. The obtained results show that these
phenomena affect both the magnitude of measured ionization rates and shapes of
their dependencies on n. The calculated ionization rates are compared with the
results of our earlier measurements of BBR-induced ionization rates of Na nS
and nD Rydberg states with n=8-20 at 300 K. A good agreement for all states
except nS with n>15 is observed. We also present the useful analytical formulae
for quick estimation of BBR ionization rates of Rydberg atoms.Comment: 14 pages, 6 figures, 6 tables in Appendi
Collisional and thermal ionization of sodium Rydberg atoms I. Experiment for nS and nD atoms with n=8-20
Collisional and thermal ionization of sodium nS and nD Rydberg atoms with
n=8-20 has been studied. The experiments were performed using a two-step pulsed
laser excitation in an effusive atomic beam at atom density of about 2 10^{10}
cm^{-3}. Molecular and atomic ions from associative, Penning, and thermal
ionization processes were detected. It has been found that the atomic ions were
created mainly due to photoionization of Rydberg atoms by photons of blackbody
radiation at the ambient temperature of 300K. Blackbody ionization rates and
effective lifetimes of Rydberg states of interest were determined. The
molecular ions were found to be from associative ionization in Na(nL)+Na(3S)
collisions. Rate constants of associative ionization have been measured using
an original method based on relative measurements of Na_{2}^{+} and Na^{+} ion
signals.Comment: 23 pages, 10 figure
Broadening and intensity redistribution in the Na() hyperfine excitation spectra due to optical pumping in the weak excitation limit
Detailed analysis of spectral line broadening and variations in relative
intensities of hyperfine spectral components due to optical pumping is
presented. Hyperfine levels of sodium and levels are
selectively excited in a supersonic beam at various laser intensities under the
conditions when optical pumping time is shorter than transit time of atoms
through the laser beam. The excitation spectra exhibit significant line
broadening at laser intensities well below the saturation intensity, and
redistribution of intensities of hyperfine spectral components is observed,
which in some cases is contradicting with intuitive expectations. Theoretical
analysis of the dynamics of optical pumping shows that spectral line broadening
depends sensitively on branching coefficient of the laser-driven transition.
Analytical expressions for branching ratio dependent critical Rabi frequency
and critical laser intensity are derived, which give the threshold for onset of
noticeable line broadening by optical pumping. Transitions with larger and
smaller branching coefficients are relatively less affected. The theoretical
excitation spectra were calculated numerically by solving density matrix
equations of motion using the split propagation technique, and they well
reproduce the observed effects of line broadening and peak intensity
variations. The calculations also show that presence of dark (i.e., not laser-
coupled) Zeeeman sublevels in the lower state results in effective branching
coefficients which vary with laser intensity and differ from those implied by
the sum rules, and this can lead to peculiar changes in peak ratios of
hyperfine components of the spectra.Comment: 12 pages, 10 figure
Effect of photoions on the line shapes of the F\"orster resonance and microwave transitions in cold rubidium Rydberg atoms
Experiments on the spectroscopy of the F\"orster resonance Rb(37P)+Rb(37P) ->
Rb(37S)+Rb(38S) and microwave transitions nP -> n'S, n'D between Rydberg states
of cold Rb atoms in a magneto-optical trap have been performed. Under ordinary
conditions, all spectra exhibited a 2-3 MHz line width independently of the
interaction time of atoms with each other or with microwave radiation, although
the ultimate resonance width should be defined by the inverse interaction time.
Analysis of the experimental conditions has shown that the main source of the
line broadening was the inhomogeneous electric field of cold photoions appeared
at the excitation of initial Rydberg nP states by broadband pulsed laser
radiation. Using an additional pulse of the electric field, which rapidly
removed the photoions after the laser pulse, lead to a substantial narrowing of
the microwave and F\"orster resonances. An analysis of various sources of the
line broadening in cold Rydberg atoms has been conducted.Comment: 10 pages, 6 figure
Ionization of Rydberg atoms by blackbody radiation
We have studied an ionization of alkali-metal Rydberg atoms by blackbody
radiation (BBR). The results of the theoretical calculations of ionization
rates of Li, Na, K, Rb and Cs Rydberg atoms are presented. Calculations have
been performed for nS, nP and nD states which are commonly used in a variety of
experiments, at principal quantum numbers n=8-65 and at the three ambient
temperatures of 77, 300 and 600 K. A peculiarity of our calculations is that we
take into account the contributions of BBR-induced redistribution of population
between Rydberg states prior to photoionization and field ionization by
extraction electric field pulses. The obtained results show that these
phenomena affect both the magnitude of measured ionization rates and shapes of
their dependences on n. A Cooper minimum for BBR-induced transitions between
bound Rydberg states of Li has been found. The calculated ionization rates are
compared with our earlier measurements of BBR-induced ionization rates of Na nS
and nD Rydberg states with n=8-20 at 300 K. A good agreement for all states
except nS with n>15 is observed. Useful analytical formulas for quick
estimation of BBR ionization rates of Rydberg atoms are presented. Application
of BBR-induced ionization signal to measurements of collisional ionization
rates is demonstrated.Comment: 36 pages, 16 figures. Paper is revised following NJP referees'
comments and suggestion
The Human Serum Metabolome
Continuing improvements in analytical technology along with an increased interest in performing comprehensive, quantitative metabolic profiling, is leading to increased interest pressures within the metabolomics community to develop centralized metabolite reference resources for certain clinically important biofluids, such as cerebrospinal fluid, urine and blood. As part of an ongoing effort to systematically characterize the human metabolome through the Human Metabolome Project, we have undertaken the task of characterizing the human serum metabolome. In doing so, we have combined targeted and non-targeted NMR, GC-MS and LC-MS methods with computer-aided literature mining to identify and quantify a comprehensive, if not absolutely complete, set of metabolites commonly detected and quantified (with today's technology) in the human serum metabolome. Our use of multiple metabolomics platforms and technologies allowed us to substantially enhance the level of metabolome coverage while critically assessing the relative strengths and weaknesses of these platforms or technologies. Tables containing the complete set of 4229 confirmed and highly probable human serum compounds, their concentrations, related literature references and links to their known disease associations are freely available at http://www.serummetabolome.ca