Bright, continuous beams of cold free radicals
Jamie Shaw, Daniel McCarron
Abstract
We demonstrate a cryogenic buffer gas-cooled molecular beam source capable of producing bright, continuous beams of cold and slow free radicals via laser ablation over durations of up to 60 seconds. The source design uses a closed liquid helium reservoir as a large thermal mass to minimize heating and ensure reproducible beam properties during operation. Under typical conditions, the source produces beams of our test species SrF, containing $5\ifmmode\times\else\texttimes\fi{}{10}^{12}$ molecules per steradian per second in the $X{\phantom{\rule{0.16em}{0ex}}}^{2}\mathrm{\ensuremath{\Sigma}}(v=0,N=1)$ state with a rotational temperature of 1.0(2) K and a forward velocity of $140\phantom{\rule{0.28em}{0ex}}\mathrm{m}/\mathrm{s}$. The beam properties are robust and unchanged for multiple cell exit geometries, but depend critically on the helium buffer gas flow rate, which must be $\ensuremath{\ge}10$ standard cubic centimeters per minute to produce bright, continuous beams of molecules for an ablation repetition rate of 55 Hz.