arXiv subjects

H. Knöckel

Publications and source records attributed to H. Knöckel.

6 recordsLinked to original sources

arXiv2013

Multi-channel modeling and two photon coherent transfer paths in NaK

We explore possible pathways for the creation of ultracold polar NaK molecules in their absolute electronic and rovibrational ground state starting from ultracold Feshbach molecules. In particular, we present a multi-channel analysis of the electronic ground and K(4p)+Na(3s) excited state manifold of NaK, analyze the spin character of both the Feshbach molecular state and the electronically excited intermediate states and discuss possible coherent two-photon transfer paths from Feshbach molecules to rovibronic ground state molecules. The theoretical study is complemented by the demonstration of STIRAP transfer from the X^1Σ^+ (v=0) state to the a^3Σ^+ manifold on a molecular beam experiment.

physics.atom-ph↗

arXiv2010

The ^1S+^1S asymptote of Sr_2 studied by Fourier-transform spectroscopy

An experimental study of the long range behavior of the ground state X^1Σ^+_g of Sr_2 is performed by high resolution spectroscopy of asymptotic vibrational levels and the use of available photoassociation data. Ground state levels as high as v"=60 (outer turning point at 23 Åand 0.1 cm^-1 below the asymptote) could be observed by Fourier-transform spectroscopy of fluorescence progressions induced by single frequency laser excitation of the v'=4, J'=9 rovibrational level of the state 2^1Σ^+_u. A precise value of the scattering length for the isotopologue ^88Sr_2 is derived and transferred to all other isotopic combinations by mass scaling with the given potential. The derived potential together with already published information about the state 2^1Σ^+_u directs to promising optical paths for producing cold molecules in the electronic ground state from an ultracold ensemble of Sr atoms.

physics.chem-ph↗

arXiv2009

Fourier-transform spectroscopy of Sr2 and revised ground state potential

Precise potentials for the ground state X1Sigma+g and the minimum region of the excited state 2_1Sigma+u of Sr2 are derived by high resolution Fourier-transform spectroscopy of fluorescence progressions from single frequency laser excitation of Sr2 produced in a heat pipe at 950 Celsius. A change of the rotational assignment by four units compared to an earlier work (G. Gerber, R. Möller, and H. Schneider, J. Chem. Phys. 81, 1538 (1984)) is needed for a consistent description leading to a significant shift of the potentials towards longer inter atomic distances. The huge amount of ground state data derived for the three different isotopomers 88Sr2, 86Sr88Sr and 87Sr88Sr (almost 60% of all excisting bound rovibrational ground state levels for the isotopomer 88Sr2) fixes this assignment undoubtedly. The presented ground state potential is derived from the observed transitions for the radial region from 4 to 11 A (9 cm-1 below the asymptote) and is extended to the longe range region by the use of theoretical dispersion coefficients together with already available photoassociation data. New estimations of the scattering lengths for the complete set of isotopic combinations are derived by mass scaling with the derived potential. The data set for the excited state 2_1Sigma+u was sufficient to derive a potential energy curve around the minimum.

physics.chem-ph↗

arXiv2007

Spectroscopy of the a^3Σ_u^+ state and the coupling to the X^1Σ_g^+ state of K_2

We report on high resolution Fourier-transform spectroscopy of fluorescence to the a^3Σ_u^+ state excited by two-photon or two-step excitation from the X^1Σ_g^+ state to the 2^3Π_g state in the molecule K_2. These spectroscopic data are combined with recent results of Feshbach resonances and two-color photoassociation spectra for deriving the potential curves of X^1Σ_g^+ and a^3Σ_u^+ up to the asymptote. The precise relative position of the triplet levels with respect of the singlet levels was achieved by including the excitation energies from the X^1Σ_g^+ state to the 2^3Π_g state and down to the a^3Σ_u^+ state in the simultaneous fit of both potentials. The derived precise potential curves allow for reliable modeling of cold collisions of pairs of potassium atoms in their ^2S ground state.

physics.atom-ph↗

arXiv2005

Study of coupled states for the (4s^{2})^{1}S + (4s4p)^{3}P asymptote of Ca_{2}

The coupled states A^{1}Σ_{u}^{+} (^{1}D +}1}S), c^{3}Π_{u} (^{3}P + ^{1}S) and a^{3}Σ_{u}^{+} (^{3}P +}1}S) of the calcium dimer are investigated in a laser induced fluorescence experiment combined with high-resolution Fourier-transform spectroscopy. A global deperturbation analysis of the observed levels, considering a model, which is complete within the subspace of relevant neighboring states, is performed using the Fourier Grid Hamiltonian method. We determine the potential energy curve of the A^{1}Σ_{u}^{+} and c^{3}Π_{u} states and the strengths of the couplings between them. The c^{3}Π_{u} and \as states are of particular importance for the description of collisional processes between calcium atoms in the ground state ^{1}S_{0} and excited state ^{3}P_{1} applied in studies for establishing an optical frequency standard with Ca.

physics.atm-clus↗

arXiv2003

Optical Manipulation of Long-range Interactions at the 3s+3p Asymptote of Na$_2$

We investigate the influence of a laser field, which is near-resonant to the atomic sodium 3$^2$P$_{1/2}$ $\to$ 3$^2$D$_{3/2}$ transition, on the last bound levels of the A$^1Σ^+_u$ state in Na$_2$. In a molecular beam experiment level shifts up to $\approx$ 100 MHz and light induced line broadenings were observed using an optical double resonance excitation scheme. Moreover, the coupling laser can reduce the number of bound levels of the A state by one or more units, which effectively means that in the picture of a collision of a 3$^2$S$_{1/2}$ and a 3$^2$P$_{1/2}$-atom the scattering phase is altered by more than $π$. The observed effects are interpreted as light induced couplings of the A$^1Σ^+_u$ state, which correlates to the 3s$_{1/2}$+3p$_{1/2}$ asymptote, to the $4^1Σ^+_g$ and $2^1Π_g$ states at the 3s$_{1/2}$+3d$_{3/2}$ asymptote. We performed multi-channel calculations, applying the mapped Fourier grid method, which reproduce our experimentally observed level shifts well.

physics.atm-clus↗