Proposal for laser-cooling of rare-earth ions

TL;DR

This paper investigates the feasibility of laser-cooling singly-ionized erbium (Er$^+$) by performing detailed electronic-structure calculations, identifying suitable transitions, and discussing repumping schemes, with implications for similar ions.

Contribution

It provides the first detailed theoretical analysis of laser-cooling transitions in Er$^+$, identifying five weak closed transitions and discussing repumping strategies.

Findings

Five weak closed transitions suitable for laser-cooling identified

The broadest transition has a linewidth in the kilohertz range

Repumping schemes are necessary for the strongest transitions

Abstract

The efficiency of laser-cooling relies on the existence of an almost closed optical-transition cycle in the energy spectrum of the considered species. In this respect rare-earth elements exhibit many transitions which are likely to induce noticeable leaks from the cooling cycle. In this work, to determine whether laser-cooling of singly-ionized erbium Er$^+$ is feasible, we have performed accurate electronic-structure calculations of energies and spontaneous-emission Einstein coefficients of Er$^+$, using a combination of \textit{ab initio} and least-square-fitting techniques. We identify five weak closed transitions suitable for laser-cooling, the broadest of which is in the kilohertz range. For the strongest transitions, by simulating the cascade dynamics of spontaneous emission, we show that repumping is necessary, and we discuss possible repumping schemes. We expect our detailed study on Er$^+$ to give a good insight into laser-cooling of neighboring ions like Dy$^+$.