Source of slow lithium atoms from Ne or H2 matrix isolation sublimation

Abstract

We have studied, via laser absorption spectroscopy, the velocity distribution of (7)Li atoms released from cryogenic matrices of solid neon or molecular hydrogen. The Li atoms are implanted into the Ne or H(2) matrices--grown onto a sapphire substrate--by laser ablation of a solid Li or LiH precursor. A heat pulse is then applied to the sapphire substrate sublimating the matrix together with the isolated atoms. With a NiCr film resistor deposited directly onto the sapphire substrate we are able to transfer high instantaneous power to the matrix, thus reaching a fast sublimation regime. In this regime the Li atoms can get entrained in the released matrix gas, and we were also able to achieve matrix sublimation times down to 10 μs for both H(2) or Ne matrix, enabling us to proceed with the trapping of the species of our interest such as atomic hydrogen, lithium, and molecules. The sublimation of the H(2) matrix, with its large center-of-mass velocity, provides evidence for a new regime of one-dimensional thermalization. The laser ablated Li seems to penetrate the H(2) matrix deeper than it does in Ne.

Slow ground state molecules from matrix isolation sublimation

“…This allows for a direct measure of the sample's forward velocity. The Doppler profile enables the measurement of the sample's longitudinal temperature (in other studies we have investigated the transverse temperature as well [14,15]). The lasers frequency scans are monitored using two 1 GHz free spectral range Fabry-Perot interferometers.…”

“…The experimental setup has been described in detail elsewhere [14,15] and a diagram is shown in figure 1. The system consists of a closed-cycle cryostat, with optical access, that reaches 3 K at its cold plate with 1 W cooling power at 4 K. A sapphire substrate, with a deposited resistive film of NiCr, is thermally connected, through a chosen thermal link, to the cold plate.…”

“…Then, we can subtract the lasers amplitude modulation, by fitting it at longer times, in absence of atomic or molecular absorption, and extending to the earlier times. The interference fringe from the Ne matrix sublimation at early times can also be subtracted by a complex thermal model [14] or by a simple linearization near the absorption peaks. Finally, the spectrum is adjusted by a double gaussian yielding several parameters, such as: peak optical density, forward velocity and temperature of the molecular and the atomic beams.…”

“…With a forward velocity of ∼130 m s −1 , the sample's center-of-mass would reach the window at 500 µs (longer than the typical time at which we get our signals). Moreover, as the atoms or showing visual fits and their parameters [14]. Taking into account a similar set of data and using mainly the information on the strongest signal we find the parameters to be compatible with the following values: forward velocity vCM ≈ 130 -140 m s −1 and longitudinal translational temperature T long ≈ 6 − 8 K. From the sublimation time we infer a sapphire temperature TS ≈ 16 K. From the optical densities one can obtain the molecular density along the laser path.…”

“…In the present work we expand our research program on Matrix Isolation Sublimation (MISu) -where intense cryogenic atomic beams of Cr and Li originating from Ne or H 2 matrices have been studied [14][15][16][17] -to demonstrate a cryogenic beam of 7 Li 2 dimers sublimated from a Ne matrix. The transitions in 7 Li 2 dimers are accessible by the experimental setup and diode lasers built in the laboratory and also allow for a simultaneous comparison of the molecular signal to the atomic signal which has been extensively studied.…”