Low-Phase-Noise High-Power Diode Laser Systems for the STIRAP transfer of Ultracold ⁶Li⁴⁰K Molecules

⁶Li⁴⁰K molecules in their rovibrational ground state possess a relatively large permanent electric dipole moment of 3.6 Debye, which makes them good candidates for studying quantum many-body physics and quantum chemistry. Two sub-kHz linewidth external cavity diode laser (ECDL) systems have been built to transfer weakly-bound ⁶Li⁴⁰K molecules to their ground state using Stimulated Raman Adiabatic Passage (STIRAP). Excessive residual laser phase-noise and scattering from unwanted intermediate levels have been identified as the two major contributions for the low transfer efficiency in our experiment. The cavity length of the ECDLs are extended from 3 cm to 20 cm to narrow the free-running laser linewidth. This leads to a reduction of integrated phase-noise from 200 mrad to 48 mrad in 10 MHz bandwidth. To suppress the scattering from unwanted states, a large single-photon detuning should be used in upcoming experiments. Tapered amplifiers have been integrated in the ECDL systems for achieving higher Rabi frequencies while preserving the low phase-noise of the long-cavity ECDLs.