Polarization Enhanced Deep Optical Dipole Trapping of $\mathrm{\Lambda }$-cooled Polar Molecules

We demonstrate loading of SrF molecules into an optical dipole trap (ODT) via in-trap $\mathrm{\Lambda }$-cooling. We find that this cooling can be optimized by a proper choice of relative ODT and $\mathrm{\Lambda }$ beam polarizations. In this optimized configuration, we observe molecules with temperatures as low as 14(1) $\mu$K in traps with depths up to 570 $\mu$K. With optimized parameters, we transfer $\text{\hspace{0.17em}⁣}\sim \text{\hspace{0.17em}⁣}5$% of molecules from our radio-frequency magneto-optical trap into the ODT, at a density of $\sim \text{\hspace{0.17em}⁣}2\times {10}^9$ cm${}^{-3}$, a phase space density of $\sim \text{\hspace{0.17em}⁣}2\times {10}^{-7}$, and with a trap lifetime of $\text{\hspace{0.17em}⁣}\sim \text{\hspace{0.17em}⁣}1$ s.