Search results for "EXCITATION"
showing 10 items of 1290 documents
Thermal Excitation of Fourth Sound in Liquid Helium II
1974
In narrow channels filled with helium II two wave modes propagate, fourth sound1–3 and the fifth wave mode.4–6 According to new results of theoretical studies,7–8 it has been predicted that it should be possible to excite both wave modes mechanically by vibrating the diaphragm of a condenser microphone as well as thermally by periodically heating the surface of a solid body (e.g., a resistance layer). Shapiro and Rudnick3 have produced and detected fourth-sound signals mechanically. In the present contribution it will be experimentally verified that it is also possible to excite fourth sound thermally. Since the theory7,8 gives the result that fourth sound can be generated thermally only if…
Two-photon spectroscopy of mercury and velocity-selective double resonances
2009
Two-photon laser spectroscopy of the $6\text{ }{^{1}S}_{0}\ensuremath{-}7\text{ }{^{1}S}_{0}$ transition in mercury has been performed using two copropagating continuous-wave laser beams. One laser beam is at 254 nm wavelength and can be tuned to the $6\text{ }{^{1}S}_{0}\ensuremath{-}6\text{ }{^{3}P}_{1}$ resonance. The other laser beam is at 408 nm. Two very different regimes can be distinguished, one far off resonance and one near resonance with the one-photon resonance. A resonance which is not Doppler broadened has been observed for low Rabi frequencies. This velocity-selective double resonance in a three-level ladder system is analogous to the dark resonance in three-level $\ensuremat…
Direct detection of the elusive 229thorium isomer: Milestone towards a nuclear clock
2017
Recently, the first direct detection of the long-searched low-lying isomeric first excited state of 229Th could be realized via its internal conversion decay branch, which confirms the isomer's existence and lays the foundation for precise studies of its decay parameters, in particular its half-life and excitation energy. Follow-up studies confirmed the theoretically expected lifetime reduction by about 109 of neutral 229mTh compared to charged isomers with τ∼10 μS thus emphasizing the need to efficiently suppress internal conversion when aiming for the detection of a potential photonic decay branch of 229mTh. Work towards precisely determining the excitation energy of the thorium isomer is…
Validity of rate equations for Zeeman coherences for analysis of nonlinear interaction of atoms with broadband laser radiation
2004
In this paper we, to our knowledge, for the first time obtain the rate equations for Zeeman coherences in the broad line approximation and steady-state balance equations directly from optical Bloch equations without the use of the perturbation theory. The broad line approximation allows us to use the adiabatic elimination procedure in order to eliminate the optical coherences from the optical Bloch equations, but the steady-state condition allows us to derive the balance equations straightforward. We compare our approach with the perturbation theory approach as given previously and show that our approach is more flexible in analyzing various experiments. Meanwhile we also show the validity …
Electric field induced hyperfine level-crossings in (nD)Cs at two-step laser excitation: experiment and theory
2005
The pure electric field level-crossing of m_F Zeeman sublevels of hyperfine F levels at two-step laser excitation was described theoretically and studied experimentally for the nD_3/2 states in Cs with n = 7,9, and 10, by applying a diode laser in the first 6S_1/2 to 6P_3/2 step and a diode or dye laser for the second 6P_3/2 to nD_3/2 step. Level-crossing resonance signals were observed in the nD_3/2 to 6P_1/2 fluorescence. A theoretical model was developed to describe quantitatively the resonance signals by correlation analysis of the optical Bloch equations in the case when an atom simultaneously interacts with two laser fields in the presence of an external dc electric field. The simulat…
Broadening and intensity redistribution in theNa(3p)hyperfine excitation spectra due to optical pumping in the weak excitation limit
2008
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 3p1/2 and 3p3/2 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 …
Landé factor and lifetime measurements in even-parity Rydberg series of PbIusing time-resolved laser spectroscopy
2001
Lande gJ factors and lifetimes for the levels in the even-parity Rydberg series 6pnp (n = 9-16) and 6pnf (n = 6-12) as well as for the levels from perturbing configurations of neutral lead have been measured using laser-induced fluorescence and Zeeman quantum-beat techniques. Two-step excitation was performed in a thermal atomic lead beam. Strong perturbations in the Rydberg series are manifested both in the gJ factor and lifetime data.
Fluorescence of rubidium in a submicrometer vapor cell: spectral resolution of atomic transitions between Zeeman sublevels in a moderate magnetic fie…
2005
It is experimentally demonstrated that use of an extremely thin cell (ETC) with the thickness of a Rb atomic vapor column of ∼400 nm allows one to resolve a large number of individual transitions between Zeeman sublevels of the D1 line of 87Rb and 85Rb in the sub-Doppler fluorescence excitation spectra in an external magnetic field of ∼200 G. It is revealed that due to the peculiarities of the Zeeman effect for different hyperfine levels of Rb, all allowed transitions between magnetic sublevels can be clearly resolved for 87RbF_g = 1 --> F_e = 1, 2 and F_g = 2 --> F_e = 1, 2 fluorescence excitation. Also, relatively good spectral resolution can be achieved for 85RbF_g = 2 --> F_e = 2, 3 flu…
STABILITY AND SPECTRA OF SMALL 3He-4He CLUSTERS
2005
Diffusion Monte Carlo calculations have been systematically performed to analyze the stability of small mixed 3 He -4 He clusters, as well as their excitation spectra. The picture that emerges is that of systems with strong shell effects whose binding and excitation energies are essentially determined by the monopole properties of an effective Hamiltonian.
Cluster-transfer reactions with radioactive beams: A spectroscopic tool for neutron-rich nuclei
2015
An exploratory experiment performed at REX-ISOLDE to investigate cluster-transfer reactions with radioactive beams in inverse kinematics is presented. The aim of the experiment was to test the potential of cluster-transfer reactions at the Coulomb barrier as a mechanism to explore the structure of exotic neutron-rich nuclei. The reactions Li7(Rb98,αxn) and Li7(Rb98,txn) were studied through particle-γ coincidence measurements, and the results are presented in terms of the observed excitation energies and spins. Moreover, the reaction mechanism is qualitatively discussed as a transfer of a clusterlike particle within a distorted-wave Born approximation framework. The results indicate that cl…