Search

We have observed the conversion of a level perturbing the Yb 6snd 1D2 series into a forced autoionisation resonance by the application of a static field. The perturbing level is barely visible in t...

We report efficient microwave-optical two photon excitation of Rb Rydberg atoms in a magneto optical trap. This approach allows the excitation of normally inaccessible states and provides a path toward excitation of high angular momentum states. The efficiency stems from the elimination of the Doppler width, the use of a narrow band pulsed laser, and the enormous electric dipole matrix element connecting the intermediate and final states of the transition. The excitation is efficient in spite of the low optical and microwave powers, of order 1 kW and 1 mW, respectively. This is an application of the large dipole coupling strengths between Rydberg states to achieve two photon excitation of Rydberg atoms., Comment: 5 pages, 4 figures

One of the most powerful forms of time domain spectroscopy is Fourier transform spectroscopy, pioneered by Pierre Jacquinot. Fourier transform spectroscopy has been widely applied, and it provides the basis of methods used to study Rydberg atoms in the time domain. While results obtained in the time and frequency domains are equivalent, it is often useful to think about a problem in both domains, and the application of time domain spectroscopy to Rydberg atoms has led to many new insights.

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.

By changing an electric field it is possible to effect the same change in configuration as by altering the time delay between two picosecond laser pulses. In particular, we demonstrate that it is possible to change excited Ba atoms from a doubly excited 5d7d state to a singly excited 6snk Rydberg state by changing an electric field by 630 V/cm.

Long-range interactions can substantially modify collision or interaction processes among cold atoms. We are able to monitor their effects on two different systems: Cs atoms which undergo photoassociation and highly excited Cs Rydberg atoms. Although the length and the time scales of the interactions are quite different, their effects can be described with the same resonant dipole picture.

In a room temperature vapor of Rb Rydberg atoms, resonant dipole-dipole energy transfer occurs via binary collisions. In contrast, in the $300\ensuremath{\mu}\mathrm{K}$ vapor produced by a magneto-optical trap, the atoms are nearly frozen in place and many atoms interact simultaneously, as in an amorphous solid. As a result of the simultaneous multiple atom interactions, the energy transfer resonances are broadened substantially in frequency.

Autoionizing Rydberg states in zero field exhibit lifetimes scaling as the cube of the principal quantum number, n3, but in a linearly polarized static or microwave field the lifetimes scale as n4 due to l mixing. To mimic the effects of collisions with charged particles we have examined the effect of a circularly polarized field on the decay rate and find longer lifetimes than in a linearly polarized field, but not an n5 dependence.

We have measured the avoided crossings between the Cs (n+4)s states and the lowest three members of the adjacent n Stark manifold for 20

We have examined the ionization of Na[sub 2] Rydberg states of principal quantum number [ital n]=11--16 converging to rotational-vibrational, [ital v]=3--6 and [ital R][lt]10, states of Na[sub 2][sup +] by 8-GHz microwave fields. Rydberg states lying below the lowest, [ital v]=0, [ital R]=0 ([ital v] and [ital R] are the vibrational and rotational quantum numbers of the molecular ion), ion limit of Na[sub 2][sup +] are observed to ionize at approximately [ital E]=1/3[ital n][sub 0][sup 5], where [ital n][sub 0] is the effective quantum number relative to the [ital v]=[ital R]=0 limit. The agreement with this dependence is not nearly as good as in an atom, and the possible reasons for the deviations are discussed.

Modulateur de phase a des frequences jusqu'a 16,7 GHz applique a un laser dans le domaine visible. Utilisation du cristal LiTaO 3

Dielectronic recombination (DR) of ions and electrons occurs via intermediate doubly excited Rydberg states converging to an excited state of the ion, and the total energy-integrated rate is the sum of the rates through the $n$,$\ensuremath{\ell}$ Rydberg states. To make stringent comparisons between calculated and observed rates, it is useful to resolve the contributions to DR of different $n$ and $\ensuremath{\ell}$ states. It is possible to separate experimentally the $n$ states due to their different energies, but it is not possible to separate the nearly degenerate high-$\ensuremath{\ell}$ states. We propose that it should be possible to measure the contribution to DR of energetically unresolved high-$\ensuremath{\ell}$ states by measuring the recombination rate as a function of electric field. As the field is raised, progressively lower $\ensuremath{\ell}$ states are converted to Stark states. Autoionization rates increase as $\ensuremath{\ell}$ is decreased, and when the field is raised to the point that an $\ensuremath{\ell}$ state with an autoionization rate in excess of the radiative decay rate is added to the manifold of Stark states, the DR rate will exhibit an observable increase. To test this proposal we have made measurements of autoionization yields of the autoionizing Ba $6{p}_{1/2}\mathit{nk}$ and $6{p}_{3/2}\mathit{nk}$ Stark states. The autoionization yield is complementary to DR, and the measurements indicate that the proposed approach should work well. Although it is not surprising that this approach works for excited ion states that are isotropic, such as the Ba${}^{+}$ $6{p}_{1/2}$ state, it is less obvious that it should work for an anisotropic ion state, such as the Ba${}^{+}$ $6{p}_{3/2}$ state. In the latter case there are four quantum defects for each $\ensuremath{\ell}$ state instead of one, and the Stark effect of the Ba $6{p}_{3/2}\mathit{nk}$ Stark states is far more complex than that of the Ba $6{p}_{1/2}\mathit{nk}$ Stark states. Calculations of the Stark effect reveal that, while there are four times as many $6{p}_{3/2}\mathit{nk}$ levels as $6{p}_{1/2}\mathit{nk}$ levels, many of the interactions of the $6{p}_{3/2}\mathit{nk}$ levels are negligible, and in practice the problem is no more complicated than the $6{p}_{1/2}\mathit{nk}$ Stark problem.

We report the demonstration of FM spectroscopy with a multimode cw laser that in most cases preserves the high sensitivity of FM spectroscopy with a single-mode laser without the stringent alignment requirements. Sensitivity to absorptions as small as 10(-4) can be inferred from our measurements, and the restrictions on modulation frequencies for small sample times are explored.

We report the first known demonstration of frequency-modulation spectroscopy outside the visible spectral region. Specifically, we report the use of second-harmonic generation on a frequency-modulated visible dye-laser beam to produce a frequency-modulated ultraviolet beam that is used to observe the Na 3S ? 4P absorption at 3302 A.

We use delayed field ionization to observe the microwave resonance transitions of Sr from $5snf$ to $5sng$, $5snh$, and $5sni$. The energies of the $5sn\ensuremath{\ell}$, $\ensuremath{\ell}g3$ states are split by the indirect spin-orbit coupling of the Sr core to the Rydberg electron, producing the $K$ splittings. From the $K$ splittings we extract the ionic dipole and quadrupole matrix elements, $⟨5s|r|5p⟩=3.65(25){a}_{0}$ and $⟨5s|{r}^{2}|4d⟩=12(14){a}_{0}^{2}$. From the dipole matrix element we obtain the dipole polarizability of ${\text{Sr}}^{+}$. With the dipole polarizability and the quantum defect differences of adjacent $l$ states, we can determine the ${\text{Sr}}^{+}$ quadrupole polarizability. The dipole and quadrupole polarizabilities of ${\text{Sr}}^{+}$ are ${\ensuremath{\alpha}}_{d}=86(11){a}_{0}^{3}$ and ${\ensuremath{\alpha}}_{q}=1.1\ifmmode\times\else\texttimes\fi{}{10}^{3}(10){a}_{0}^{5}$, respectively.

Collisions with rare-gas atoms are observed to produce a lengthening of the lifetime of the highly excited ($n=5\ensuremath{-}10$) $d$ states of Na. The effect is interpreted as collisional angular momentum mixing of the $d$ state with $lg2$ states; thus the average lifetime of all states for which $lg~2$ is observed. The cross section for the process appears to increase as the geometrical cross section of the excited atom.

When a Rydberg atom is slowly swept through a dipole allowed resonance with an oscillating field adiabatic rapid passage (ARP) from one state to the other can occur. By measuring the time resolved momentum of a Rydberg electron with a half cycle pulse we demonstrate that during ARP the classical oscillating dipole due to the orbital motion of the electron becomes phase locked to the microwave field driving the resonance. Depending on the direction of the sweep through resonance, the atom is in one or the other of the two Floquet eigenstates in which the electron is phase locked in or {pi} out of phase with the driving field. In contrast, in Rabi oscillations the electron motion oscillates between leading and lagging the driving microwave field.

Laser excitation above the limit in the presence of a microwave field can lead to high lying bound states if it occurs at the correct phase of the microwave field, and phase dependent ionization is also observed. The excitation spectra of the high lying states in the presence of the field is a sequence of peaks straddling the limit, spaced by the microwave frequency.

The radial matrix elements connecting the ionic Ba{sup +}6s ground state to low-lying excited 6p and 5d states can be extracted from the K splittings of the bound 6snl states in much the same way that ionic polarizabilities are extracted from the separations between l states. We develop an expression for the K splitting by a pair of expansions which allows us to compare the contributions of different ionic states. This comparison confirms that all but the lowest two may be safely ignored. Finally, we extract the radial Ba{sup +} matrix elements =4.03(12) and =9.76(29) from the experimentally obtained K splittings.

A nondispersing Rydberg wave packet can be made by applying a weak, linearly polarized field at the Kepler frequency of a Rydberg atom. The field phase locks the electron's motion to the microwave field, and the wave packet retains its spatial localization for times in excess of a microsecond. The electron's orbital oscillation leads to an oscillating dipole, which can either oscillate in phase or out of phase with the applied microwave field, creating wave packets analogous to Trojan and anti-Trojan wave packets described theoretically. Our observations can be described in both quantum mechanical and classical terms.

When the dipole-dipole energy transfer, $\mathrm{Rb} {25s}_{1/2}+\mathrm{Rb} {33s}_{1/2}\ensuremath{\rightarrow}\mathrm{Rb} {24p}_{1/2}+\mathrm{Rb} {34p}_{3/2},$ resonant at fields of 3.0 and 3.4 V/cm, is observed in a cold Rydberg gas, the resonances are broader than expected for this dipole-dipole interaction alone. Using a variant of the Ramsey interference method, in which the system is detuned from the resonance, we observe a density-dependent dephasing which we attribute to the inhomogeneities in the always resonant dipole-dipole excitation exchange interactions $\mathrm{Rb} {25s}_{1/2}+\mathrm{Rb} {24p}_{1/2}\ensuremath{\rightarrow}\mathrm{Rb} {24p}_{1/2}+\mathrm{Rb} {25s}_{1/2}$ and $\mathrm{Rb} {33s}_{1/2}+\mathrm{Rb} {34p}_{3/2}\ensuremath{\rightarrow}\mathrm{Rb} {34p}_{3/2}+\mathrm{Rb} {33s}_{1/2}.$ Since the dephasing rate is comparable to the observed widths, it appears that all of these interactions contribute to the observed linewidths.

We have measured the probability of inner-electron ionization (IEI) of Sr 5s 16l atoms when exposed to intense 230-fs laser pulses. We find that the probability of IEI rises sharply at l = 5 and is approximately equal to one for l>5. For l=5 the classical inner-turning point is at 15a 0 , far greater than the size of the Sr + ionic core, ruling out core penetration as the factor governing inner-electron ionization. For the Sr 5 p 1 / 2 16l states of l>5 the autoionization lifetime, which is due to the electrostatic interaction between two-valence electrons, is greater than the Kepler orbit time. These comparisons suggest that both inner-electron ionization and autoionization are governed by long-range electrostatic interactions.

As a continuation of our work with 1,4,5 substituted imidazole inhibitors of p38alpha, we report a series of 1-(4-piperidinyl)-4-(4-fluorophenyl)-5-(2-phenoxy-4-pyrimidinyl) imidazoles related to 7. The compounds have IC50's for inhibition of p38alpha ranging from 6.0 to 650nM. Statistical analysis of the p38beta inhibitor potencies shows a correlation of IC50's with the electron donating strength of low molecular weight substituents.

A model system for adventitious root formation in woody plants was used to identify transcripts that are up-regulated during this process. 1 mm stem-disks from micropropagated shoots of the apple cultivar Jork 9 can be induced to form roots by treatment with the auxin indole butyric acid (IBA). Stem discs are placed on medium containing IBA for 24 hours and then transferred to IBA-free medium. Root initials become visible after 5-6 days and root elongation occurs within 7-9 days. The first visible cell divisions, which will give rise to the adventitious roots, are detectable 48 hours following IBA treatment. We have used this system to identify transcripts that are induced during adventitious root formation. Two techniques were employed in this analysis: differential messenger RNA display (DDRT) and mRNA representational difference analysis (RDA), a technique that couples PCR and subtractive hybridisation. Using both of these techniques a number of clones have been isolated that exhibit differential expression during auxin induced root formation. Both up-regulated and down-regulated transcripts have been identified. Expression of these genes has initially been verified by reverse northern blot analysis. Northern blot analysis with individual clones has confirmed the expression pattern observed in the reverse northern analysis. Tentative identities of some of the clones have been established by sequencing the partial cDNAs. Among the up-regulated transcripts are clones that share sequence homology with polygalacturonase and MAP kinases. A full-length cDNA for the most abundant up-regulated mRNA, a 2-oxoacid dependent dioxygenase, was characterised. This mRNA is expressed between 24 and 72 hours following IBA treatment of apple stem disks.

To investigate glyburide pharmacokinetics in patients with well-controlled noninsulin-dependent diabetes mellitus (NIDDM), and test the hypothesis that intersubject variability in the glyburide dose is due to patient differences in the drug's pharmacokinetics.Prospective, open-label study.University-affiliated, internal medicine outpatient clinic.Fifty-one patients with NIDDM (11 women, 40 men, mean age 56.7 +/- 15.3 yrs) receiving oral glyburide and with well-controlled glycohemoglobin levels 10.0% or below.After fasting overnight, patients ingested their regular morning dose of glyburide and then ate breakfast. Blood samples were drawn before dosing and between 0.5-2 hours, 2-5 hours, and 5-10 hours after dosing.Serum glyburide was assayed by high-performance liquid chromatography and pharmacokinetics by NONMEM. Glyburide clearance was proportional to weight and greater in older patients (60 yrs).Variability in the glyburide dose was not primarily due to intersubject differences in the drug's pharmacokinetics.