Enhanced Atomic Desorption of 209 and 210 Francium from Organic Coating

Abstract

Controlled atomic desorption from organic Poly-DiMethylSiloxane coating is demonstrated for improving the loading efficiency of ^209,210Fr magneto-optical traps. A three times increase in the cold atoms population is obtained with contact-less pulsed light-induced desorption, applied to different isotopes, either bosonic or fermionic, of Francium. A six times increase of ²¹⁰Fr population is obtained with a desorption mechanism based on direct charge transfer from a triboelectric probe to the adatom-organic coating complex. Our findings provide new insight on the microscopic mechanisms of atomic desorption from organic coatings. Our results, obtained at room temperature so as to preserve ideal vacuum conditions, represent concrete alternatives, independent from the atomic species in use, for high-efficiency laser cooling in critical conditions.

Figure 1

Atomic desorption processes for laser cooling of Francium isotopes. (a) Interplay between the source of Fr, the vapour phase, the MOT population and the main sources of loss of atomic population. Adsorption can be effectively contrasted by controlled desorption mechanisms, as discussed in the main text. (b) Normal operation loading of the Fr MOT. (c) Loading of the Fr MOT with pulsed photodesorption of atoms embedded in the PDMS coating. (d) Loading of the Fr MOT with charge transfer-induced atomic desorption. Sketches are not to scale and are shown for illustrative purposes only.

Figure 2

Pulsed LIAD of ²¹⁰Fr from PDMS. Left: ²¹⁰Fr MOT population time evolution after a broadband light pulse at t = 0 s. Right: Subsequent desorption events produced by repeated flashes exhibit similar characteristics. Arrows mark the timestamp of the flash. Horizontal dashed lines indicate the equilibrium population.

Figure 3

Pulsed LIAD of ²⁰⁹Fr from PDMS. ²⁰⁹Fr MOT population time evolution after a broadband light pulse at t = 0 s. The vertical arrow marks the beginning of LIAD. The horizontal dashed line indicates the equilibrium MOT population.

Figure 4

Charge transfer-induced desorption of ²¹⁰Fr from PDMS. ²¹⁰Fr MOT population after local charge transfer from a dielectric probe at t = 0. The horizontal dashed line indicates the MOT equilibrium population. Inset: Relative variation of the ²¹⁰Fr MOT population Δ (Equation 1) in the same experiment, with a second application at t = 161 s of the charge transfer from the dielectric probe. Continuous and dashed curves correspond to the best exponential fits of experimental data.