Improving molecule trap loading rate from a Cryogenic Buffer Gas Beam

Most experiments that employ direct laser cooling of molecules use cryogenic buffer gas beams (CBGBs) formed by ablating a precursor target in the presence of 4\,K helium. This provides a high flux of slow and rotationally cold molecules. Although CBGBs generate $\sim$ 10$^{12}$ molecules per ablation, only $\sim 10^{4}$ are typically captured in downstream magneto-optical traps (MOTs). Here we report numerical simulations of methods that promise to significantly increase the captured fraction of molecules. Our simulations show that transverse cooling, applied simultaneously with longitudinal slowing, can increase the capture fraction by a factor of 20 by reducing the molecular beam divergence. We also find that the shallow velocity cut-off in `white-light' slowing (a typical slowing scheme in molecule cooling experiments) causes a substantial number of molecules to never reach the MOT on account of being decelerated too quickly. We show that, by adding a 'push' beam co-propagating with the molecules, previously over-slowed molecules can be captured. Simulations indicate that combining these gains with improvements to the white-light slower could increase the capture fraction by a factor of $\gtrsim 100$.