Narrow-linewidth and stable-frequency light source for laser cooling of magnesium fluoride molecules

We demonstrate the frequency doubling, linewidth narrowing, and frequency stabilization of two cw Ti:sapphire lasers for the laser cooling of magnesium fluoride (MgF) molecules. From the energy-level structure of MgF, both lasers are frequency-doubled to ultraviolet to serve as cooling and repumping lasers. By constructively establishing a frequency stabilization system that firstly stabilizes both lasers via a "side-of-fringe scheme to their reference resonators, which are then length-locked to a helium-neon (HeNe) laser through a transfer cavity, we obtain two lasers with a narrow linewidth of ∼6 kHz and an extraordinary long-term frequency stability of ±2.8 MHz.