Cooling atoms to the ultracold regime has allowed for studies of physics, ranging from many-body physics of quantum degenerate gases, quantum computing, precision measurements and tests of fundamental symmetries. Extending these experiments to polar molecules has the prospect of enhancing the sensitivity of such tests and of enabling novel studies, such as cold controlled chemistry. However, applying traditional laser cooling techniques to molecules is rendered difficult due their additional degrees of freedom which result in a limited photon scattering budget. Here we study aluminum monochloride (AlCl) as a promising candidate for laser cooling and trapping. The cooling transition at 261 nm ( $A^{1} \Pi - X^{1} \Sigma^{+}$ ) has a theoretical Franck-Condon factor of 99.88\% which allows for scattering ~800 photons with a single laser before the molecule enters an excited vibrational state. We use a frequency-tripled (SHG + SFG) Titanium-Sapphire laser and generate AlCl via laser ablation in a cryogenic helium buffer gas beam source. We will present our spectroscopy results on AlCl and the measured molecular constants of the $A^{1}\Pi$ state and compare them with ab-initio calculations. We will also discuss our estimates on the Franck-Condon factors.Cooling atoms to the ultracold regime has allowed for studies of physics, ranging from many-body physics of quantum degenerate gases, quantum computing, precision measurements and tests of fundamental symmetries. Extending these experiments to polar molecules has the prospect of enhancing the sensitivity of such tests and of enabling novel studies, such as cold controlled chemistry. However, applying traditional laser cooling techniques to molecules is rendered difficult due their additional degrees of freedom which result in a limited photon scattering budget. Here we study aluminum monochloride (AlCl) as a promising candidate for laser cooling and trapping. The cooling transition at 261 nm ($A^{1} \Pi - X^{1} \Sigma^{+}$) has a theoretical Franck-Condon factor of 99.88\% which allows for scattering ~800 photons with a single laser before the molecule enters an excited vibrational state. We use a frequency-tripled (SHG + SFG) Titanium-Sapphire laser and generate AlCl via laser ablation in a cryogenic helium buffer gas beam source. We will present our spectroscopy results on AlCl and the measured molecular constants of the $A^{1}\Pi$ state and compare them with ab-initio calculations. We will also discuss our estimates on the Franck-Condon factors.

International Symposium on Molecular Spectroscopy (ISMS)Jun 24, 20211 citation

Hyperfine structure of the A1Π state of AlCl and its relevance to laser cooling and trapping

John R. Daniel, Jamie Shaw, Chen Wang +4 more

The majority of molecules proposed for laser cooling and trapping experiments have $\mathrm{\ensuremath{\Sigma}}$-type ground states. Specifically, ${}^{2}\mathrm{\ensuremath{\Sigma}}$ states have cycling transitions analogous to ${D}_{1}$ lines in alkali-metal atoms while ${}^{1}\mathrm{\ensuremath{\Sigma}}$ states offer both strong and weak cycling transitions analogous to those in alkaline-earth atoms. Despite this proposed variety, to date, only molecules with ${}^{2}\mathrm{\ensuremath{\Sigma}}$-type ground states have successfully been confined and cooled in magneto-optical traps. While none of the proposed ${}^{1}\mathrm{\ensuremath{\Sigma}}$-type molecules have been successfully laser cooled and trapped, they are expected to have various advantages in terms of exhibiting a lower chemical reactivity and an internal structure that benefits the cooling schemes. Here, we present the prospects and strategies for optical cycling in AlCl---a ${}^{1}\mathrm{\ensuremath{\Sigma}}$ molecule---and report on the characterization of the ${A}^{1}\mathrm{\ensuremath{\Pi}}$ state hyperfine structure. Based on these results, we carry out detailed simulations on the expected capture velocity of a magneto-optical trap for AlCl. Finally, using ab initio calculations, we identify the photodissociation via a ${3}^{1}\mathrm{\ensuremath{\Pi}}$ state and photoionization process via the ${3}^{1}{\mathrm{\ensuremath{\Sigma}}}^{+}$ state as possible loss mechanisms for a magneto-optical trap of AlCl.The majority of molecules proposed for laser cooling and trapping experiments have $\mathrm{\ensuremath{\Sigma}}$-type ground states. Specifically, ${}^{2}\mathrm{\ensuremath{\Sigma}}$ states have cycling transitions analogous to ${D}_{1}$ lines in alkali-metal atoms while ${}^{1}\mathrm{\ensuremath{\Sigma}}$ states offer both strong and weak cycling transitions analogous to those in alkaline-earth atoms. Despite this proposed variety, to date, only molecules with ${}^{2}\mathrm{\ensuremath{\Sigma}}$-type ground states have successfully been confined and cooled in magneto-optical traps. While none of the proposed ${}^{1}\mathrm{\ensuremath{\Sigma}}$-type molecules have been successfully laser cooled and trapped, they are expected to have various advantages in terms of exhibiting a lower chemical reactivity and an internal structure that benefits the cooling schemes. Here, we present the prospects and strategies for optical cycling in AlCl---a ${}^{1}\mathrm{\ensuremath{\Sigma}}$ molecule---and report on the characterization of the ${A}^{1}\mathrm{\ensuremath{\Pi}}$ state hyperfine structure. Based on these results, we carry out detailed simulations on the expected capture velocity of a magneto-optical trap for AlCl. Finally, using ab initio calculations, we identify the photodissociation via a ${3}^{1}\mathrm{\ensuremath{\Pi}}$ state and photoionization process via the ${3}^{1}{\mathrm{\ensuremath{\Sigma}}}^{+}$ state as possible loss mechanisms for a magneto-optical trap of AlCl.

arXiv:2309.16835Physical Review ADec 26, 20236 citations

Laser cooling and trapping of atoms

Philip H. Jones, Onofrio M. Maragò, Giovanni Volpe

Cambridge University Press eBooksDec 3, 20153 citations

A^{1} \Pi - X^{1} \Sigma^{+}

) has a theoretical Franck-Condon factor of 99.88\% which allows for scattering ~800 photons with a single laser before the molecule enters an excited vibrational state. We use a frequency-tripled (SHG + SFG) Titanium-Sapphire laser and generate AlCl via laser ablation in a cryogenic helium buffer gas beam source. We will present our spectroscopy results on AlCl and the measured molecular constants of the

A^{1}\Pi

state and compare them with ab-initio calculations. We will also discuss our estimates on the Franck-Condon factors.

{D}_{1}

lines in alkali-metal atoms while ${}^{1}\mathrm{\ensuremath{\Sigma}}$ states offer both strong and weak cycling transitions analogous to those in alkaline-earth atoms. Despite this proposed variety, to date, only molecules with ${}^{2}\mathrm{\ensuremath{\Sigma}}$-type ground states have successfully been confined and cooled in magneto-optical traps. While none of the proposed ${}^{1}\mathrm{\ensuremath{\Sigma}}$-type molecules have been successfully laser cooled and trapped, they are expected to have various advantages in terms of exhibiting a lower chemical reactivity and an internal structure that benefits the cooling schemes. Here, we present the prospects and strategies for optical cycling in AlCl---a ${}^{1}\mathrm{\ensuremath{\Sigma}}$ molecule---and report on the characterization of the ${A}^{1}\mathrm{\ensuremath{\Pi}}$ state hyperfine structure. Based on these results, we carry out detailed simulations on the expected capture velocity of a magneto-optical trap for AlCl. Finally, using ab initio calculations, we identify the photodissociation via a ${3}^{1}\mathrm{\ensuremath{\Pi}}$ state and photoionization process via the ${3}^{1}{\mathrm{\ensuremath{\Sigma}}}^{+}$ state as possible loss mechanisms for a magneto-optical trap of AlCl.