Laser cooling of the AlCl molecule with a three-electronic-level theoretical model

Optimizing pulsed-laser ablation production of AlCl molecules for laser cooling

Aluminum monochloride (AlCl) has been proposed as a promising candidate for laser cooling to ultracold temperatures, and recent spectroscopy results support this prediction. It is challenging to produce large numbers of AlCl molecules because it is a highly reactive open-shell molecule and must be generated in situ. Here we show that pulsed-laser ablation of stable, non-toxic mixtures of Al with alkali or alkaline earth chlorides, denoted XCl_n, can provide a robust and reliable source of cold AlCl molecules. Both the chemical identity of XCl_n and the Al : XCl_n molar ratio are varied, and the yield of AlCl is monitored using absorption spectroscopy in a cryogenic gas. For KCl, the production of Al and K atoms was also monitored. We model the AlCl production in the limits of nonequilibrium recombination dominated by first-encounter events. The non-equilibrium model is in agreement with the data and also reproduces the observed trend with different XCl_n precursors. We find that AlCl production is limited by the solid-state densities of Al and Cl atoms and the recondensation of Al atoms in the ablation plume. We suggest future directions for optimizing the production of cold AlCl molecules using laser ablation.

The study of laser cooling of TeH- anion in theoretical approach

The probabilities of laser cooling of TeH^- anion via a spin-forbidden transition and a three-electronic-level transition are proposed. The potential energy curves of the X¹Σ⁺, a³∏, A¹∏, and b³Σ⁺ electronic states of tellurium monohydride anion (TeH^-) are calculated using multi-reference configuration interaction method. Davidson corrections, core-valence correlations and spin-orbit coupling effects are also considered. The AWCV5Z-PP pseudopotential basis set of Te atom is used. Spectroscopic parameters of the Λ-S and Ω states are obtained by solving radial Schrodinger equation. These results are reported at the first time. Permanent dipole moments of the Ω states and transition dipole moments of the a₂1↔X0⁺ and A1↔X0⁺ transitions are also calculated. Highly diagonally distributed Franck-Condon factors of the a₂1↔X0⁺ and A1↔X0⁺ transitions are obtained, the value of f₀₀ is 0.9970 and 0.9980, respectively. Spontaneous radiative lifetimes of the a₂1 and A1 excited states are predicted. i.e. τ(a₂1) = 200.3 ns and τ(A1) = 84.3 ns. Only the main pump laser is required to driving a₂1↔X0⁺ and A1↔X0⁺ transitions. The laser wavelengths both are in the visible region. Doppler temperatures and recoil temperatures of laser cooling TeH^- anion are also predicted.

In search of molecular ions for optical cycling: a difficult road

Optical cycling, a continuous photon scattering off atoms or molecules, is the key tool in quantum information science.

Laser-cooling with an intermediate electronic state: Theoretical prediction on bismuth hydride

The possibility of laser cooling of bismuth hydride (BiH) molecules has been investigated based on high-level ab initio calculations by considering the core-valence and the spin-orbit coupling (SOC) effects. The potential energy curves of the 12 Λ-S states as well as the 25 Ω states that split from them via SOC are obtained by multireference configuration interaction plus the Davidson correction. The properties of b-X transition are investigated. Based on our calculations, we show that the transition between Ω states b0⁺-X₁0⁺ of BiH is a possible candidate for laser cooling, with consideration of the intermediate Ω state X₂1. An optical cycling scheme is proposed by utilizing four lasers at wavelengths around 471 and 601 nm with 5400 cycles for photon absorption/emission and a sub-microkelvin temperature. Our study should shed some light on searching for possible molecular candidates for laser cooling with the existence of an intermediate electronic state.

Vibrational branching ratios and radiative lifetimes in the laser cooling of AlBr

The feasibility of laser cooling of the AlBr molecule is investigated using ab initio quantum chemistry. Potential energy curves, permanent dipole moments, and transition dipole moments for the ground state X¹Σ⁺ and the first two excited states (a³Π and A¹Π) are calculated using the multi-reference configuration interaction plus Davidson corrections (MRCI+Q) method with the ACVQZ basis set; the spin-orbit coupling effects are also taken into account in electronic structure calculations at the MRCI level. Based on the acquired potential energy curves and transition dipole moments, highly diagonally distributed Franck-Condon factors (f₀₀ = 0.9540, f₁₁ = 0.8172) and vibrational branching ratios (R₀₀ = 0.9708, R₁₁ = 0.8420) for the transition are determined. Radiative lifetime calculations of the A¹Π₁ (ν' = 0-4) state are found to be short (9.16-11.48 ns) enough for rapid laser cooling. The proposed main cycling laser drives the transition at the wavelength λ₀₀ = 279.19 nm. The vibrational branching loss ratios of the A¹Π₁ (ν') state to the intervening states a³Π_0⁺ and a³Π₁ are small (<5.2 × 10^-6) enough to be negligible. The present theoretical results indicate that the AlBr molecule is a promising candidate for laser cooling.

Laser cooling of the OH− molecular anion in a theoretical investigation

The schemes for laser cooling of the OH⁻ anion are proposed using an ab initio method.