Laser Cooling with an Intermediate State and Electronic Structure Studies of the Molecules CaCs and CaNa (original) (raw)
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Computational and Theoretical Chemistry, 2017
The potential energy curves for the molecules MgK, MgRb and MgCs have been computed by using the ab initio CASSCF/ (MRCI+Q) calculation. For the considered electronic states the static and transition dipole moment curves have been calculated along with the Franck-Condon factor (FCF), the spectroscopic constants T e , e , e x e , B e , R e , and the fraction of ionic character. By using the canonical functions approach, the ro-vibrational constants E v , B v , D v and the abscissas of the turning points , and , have been calculated. For these molecules, more than 109 electronic states have been investigated in the present work. These results have great significance to experimentalists as they provide efficient routes to form cold alkali and alkaline earth molecules. Highlights Investigation of 109 electronic states of the Mg, MgRb, MgCs molecules. A ro-vibrational calculation with Einstein coefficients and dipole moments. Franck-Condon calculation and discussion for laser cooling experiments.
Laser cooling of CaF molecules
2014
Cold and ultracold molecules are highly desirable for a diverse range of applications such as precision measurements, tests of fundamental physics, quantum simulation and information processing, controlled chemistry, and the physics of strongly correlated quantum matter. Although laser cooling has been enormously successful in cooling atomic species to extremely low temperatures, this technique has long been thought to be infeasible in molecules because their complex structure makes it difficult to find a closed cycling transition. Recently, however, several diatomic molecules, one of which is CaF, have been shown to possess a convenient electronic structure and highly diagonal Franck-Condon matrix and thus be amenable to laser cooling. This thesis describes experiments on laser cooling of CaF radicals produced in a supersonic source. We first investigate the increased fluorescence when multi-frequency resonant light excites the molecules from the four hyperfine levels of the ground...
Laser cooling and slowing of CaF molecules
We demonstrate slowing and longitudinal cooling of a supersonic beam of CaF molecules using counter-propagating laser light resonant with a closed rotational and almost closed vibrational transition. A group of molecules are decelerated by about 20 m/s by applying light of a fixed frequency for 1.8 ms. Their velocity spread is reduced, corresponding to a final temperature of about 85 mK. The velocity is further reduced by chirping the frequency of the light to keep it in resonance as the molecules slow down.
Laser Cooling of Molecular Anions
Physical review letters, 2015
We propose a scheme for laser cooling of negatively charged molecules. We briefly summarize the requirements for such laser cooling and we identify a number of potential candidates. A detailed computation study with C_{2}^{-}, the most studied molecular anion, is carried out. Simulations of 3D laser cooling in a gas phase show that this molecule could be cooled down to below 1 mK in only a few tens of milliseconds, using standard lasers. Sisyphus cooling, where no photodetachment process is present, as well as Doppler laser cooling of trapped C_{2}^{-}, are also simulated. This cooling scheme has an impact on the study of cold molecules, molecular anions, charged particle sources, and antimatter physics.
Electronic and vibrational radiative cooling of the small carbon clusters C4− and C6−
Physical Review A, 2018
Delayed electron detachment yields of C 4 − and C 6 − induced by photoexcitation in an electrostatic ion storage ring were measured as functions of excitation energies and laser firing times, allowing for a mapping of their radiative cooling in a wide energy range. The energy window concept and discrimination of one-and twophoton absorption are critical in understanding the obtained results. The experimentally obtained electronic and vibrational cooling rates were consistent with a simulation based on detailed-balance theory. The even-odd alternation of vibrational cooling rates, predicted from IR intensities, was also examined. We found that the larger anion cools faster, with no indication of an even-odd alternation.
Laser excitation spectrum of C3 in the region 26000–30700cm−1
Journal of Molecular Spectroscopy, 2010
The vibrational structure of theà 1 P u electronic state of C 3 in the region 26 000-30 775 cm À1 has been reexamined, using laser excitation spectra of jet-cooled molecules. Rotational constants and vibrational energies have been determined for over 60 previously-unreported vibronic levels; a number of other levels have been reassigned. The vibrational structure is complicated by interactions between levels of the upper and lower Born-Oppenheimer components of theà 1 P u state, and by the effects of the double minimum potential in the Q 3 coordinate, recognized by Izuha and Yamanouchi [16]. The present work shows that there is also strong anharmonic resonance between the overtones of the m 1 and m 3 vibrations. For instance, the levels 2 1 + 1 and 0 1 + 3 are nearly degenerate in zero order, but as a result of the resonance they give rise to two levels 139 cm À1 apart, centered about the expected position of the 2 1 + 1 level. With these irregularities recognized, every observed vibrational level up to 30 000 cm À1 (a vibrational energy of over 5000 cm À1) can now be assigned. A R þ u vibronic level at 30181.4 cm À1 , which has a much lower B 0 rotational constant than nearby levels of theà 1 P u state, possibly represents the onset of vibronic perturbations by theB 01 D u electronic state; this state is so far unknown, but is predicted by the ab initio calculations of Ahmed et al. [36].
Challenges of laser-cooling molecular ions
New Journal of Physics, 2011
The direct laser cooling of neutral diatomic molecules in molecular beams suggests that trapped molecular ions can also be laser cooled. The long storage time and spatial localization of trapped molecular ions provides the opportunity for multi-step cooling strategies, but also requires a careful consideration of rare molecular transitions. We briefly summarize the requirements that a diatomic molecule must meet for laser cooling, and we identify a few potential molecular ion candidates. We then perform a detailed computational study of the candidates BH + and AlH + , including improved ab initio calculations of the electronic state potential energy surfaces and transition rates for rare dissociation events. Based on an analysis of population dynamics, we determine which transitions must be addressed for laser cooling and compare experimental schemes using continuous-wave and pulsed lasers.
2015
In the paper, several theoretical approaches to the determination of the reduced absorption and emission coefficients under local thermodynamic equilibrium conditions were exposed and discussed. The full quantum-mechanical procedure based on the Fourier grid Hamiltonian method was numerically robust but time consuming. In that method, all transitions between the bound, free, and quasi-bound states were treated as bound-bound transitions. The semi-classical method assumed continuous energies of ro-vibrational states, so it did not give the ro-vibrational structure of the molecular bands. That approach neglected the effects of turning points but agreed with the averaged-out quantum-mechanical spectra and it was computer time efficient. In the semi-quantum approximation, summing over the rotational quantum number J was done analytically using the classical Franck-Condon principle and the stationary-phase approximation and its consumption of computer time was lower by a few orders of magnitude than the case of the full quantum-mechanical approach. The approximation described well the vibrational but not the rotational structure of the molecular bands. All the above methods were compared and discussed in the case of a visible and near infrared spectrum of LiHe, Li 2 , and Cs 2 molecules in the high temperature range.
XXVI ENFMC - Annals of Optics Volume5- 2003 Two-Photon Doppler Cooling of Calcium Atoms
2015
A new possibility of laser cooling of Calcium atoms using a two-photon transition is analyzed We investigate the possibility of Doppler cooling of Calcium using its two-photon (4s2) 1S0- (4s5s) 1S0 transition, with excitation in near resonance with the (4s4p) 1P1 level. The two-photon absorption of laser beams at 423 and 1034 nm greatly increases the two-photon rate, allowing an effective transfer of momentum. The experimental implementation of this technique is discussed and we show that two-photon cooling can be used to achieve a temperature limit of about 1/7 of the one-photon Doppler limit reached in a conventional MOT.
Laser cooling of molecular internal degrees of freedom by a series of shaped pulses
The Journal of Chemical Physics, 1993
Laser cooling of the vibrational motion of a molecule is investigated. The scheme is demonstrated for cooling the vibrational motion on the ground electronic surface of HBr. The radiation drives the excess energy into the excited electronic surface serving as a heat sink. Thermodynamic analysis shows that this cooling mechanism is analogous to a synchronous heat pump where the radiation supplies the power required to extract the heat out of the system. In the demonstration the flow of energy and population from one surface to the other is analyzed and compared to the power consumption from the radiation field. The analysis of the flows shows that the phase of the radiation becomes the active control parameter which promotes the transfer of one quantity and stops the transfer of another. In the cooling process the transfer of energy is promoted simultaneously with the stopping population transfer. The cooling process is defined by the entropy reduction of the ensemble. An analysis based on the second law of thermodynamics shows that the entropy reduction on the ground surface is more than compensated for by the increase in the entropy in the excited surface. It is found that the rate of cooling reduces to zero when the state of the system approaches an energy eigenstate and is therefore a generalization of the third law of thermodynamics. The cooling process is modeled numerically for the HBr molecule by a direct solution of the Liouville von Neuman equation. The density operator is expanded using a Fourier basis. The propagation is done by a polynomial approximation of the evolution operator. A study of the influence of dissipation on the cooling process concludes that the loss of phase coherence between the ground and excited surface will stop the process.