Laser collimation of an atomic gallium beam

We have laser collimated a gallium atomic beam in one dimension using the linear-perpendicular-linear polarization gradient technique. Operating on the cycling $4p^2{P}_{3∕2}(F=3)\to 4d^2{D}_{5∕2}(F=4)$ transition at $294.45\text{nm}$, the full angular divergence of the atomic beam was reduced to $0.3\text{mrad}$, corresponding to a transverse velocity of $\pm 11\text{cm}∕\mathrm{s}$, about one-half the Doppler cooling limit. The dependence of the cooling efficiency on the laser detuning and power was investigated. Optical pumping of the atoms out of the $4p^2{P}_{3∕2}(F=3)$ state by the cooling laser was observed. Repumping schemes were investigated and found to successfully repopulate the cooled $F=3$ hyperfine state.

Figure 1

(a) Energy-level diagram of Ga. (b) Schematic of the laser collimation experiment. (c) Laser-induced fluorescence spectrum of the $4p^2{P}_{3∕2}\to 4d^2{D}_{5∕2}$ transition together with the calculated peak locations for Ga (from Ref. [14]). The zero of the frequency scale is set at the $F=3\to 4$ cooling transition of ${}^{69}\mathrm{Ga}$. The other labels indicate relevant ${}^{69}\mathrm{Ga}$ transitions.

Figure 2

(Color online) CCD images of laser-induced fluorescence from an atomic gallium beam: (a) no laser cooling, $\text{FWHM}=3.72\text{mm}$, (b) cooling with Doppler molasses only, $\text{FWHM}=2.30\text{mm}$, and (c) cooling with lin $\perp$ lin polarization gradient, $\text{FWHM}=1.94\text{mm}$. Cooling laser $52\text{mW}$ power, $\Delta =-12\text{MHz}$.

Figure 3

Collimation of the Ga beam as a function of the cooling laser detuning below resonance.

Figure 4

Collimation of the Ga atomic beam for two different detunings as a function of the total power in the cooling laser.

Figure 5

(a) The laser-induced fluorescence spectrum obtained by $417\text{nm}$ excitation with the cooling laser on (dark line) and off (light line). (b) The calculated line spectrum for both isotopes of Ga.

Figure 6

Laser arrangement for cooling and repumping of a Ga beam.

Figure 7

$417\text{nm}$ laser-induced fluorescence spectra taken with (a) only a cooling laser on and (b) both a cooling and repump laser on. The repump laser detuned $+334\text{MHz}$ from the cooling laser and power $=4.5\text{mW}$.