A self-injection locked DBR laser for laser cooling of beryllium ions

We present a simple, robust, narrow-linewidth, frequency-doubled semiconductor laser source suitable for laser cooling and repumping of 9 Be + ions. A distributed Bragg reflector (DBR) laser diode operating at 626 nm is self-injection-locked to a frequency doubling cavity via phase-stabilised optical feedback when the laser is resonant with the cavity mode. The short-term laser instability is reduced from the MHz level to approximately 20 kHz by the injection process, thus eliminating the need for a high-bandwidth feedback loop to suppress the otherwise troublesome high-frequency laser noise. Long-term stability of the laser frequency is achieved by feeding back to the length of the enhancement cavity utilising an electro-optic frequency comb generator to produce a beatnote with a laser that is detuned by 98 GHz. Long-term injection locking and frequency stabilisation via a wavemeter are ensured using automatic relocking algorithms. This work could find applications throughout the atomic physics community as a cost-effective alternative to expensive, intrinsically narrow-linewidth lasers where cavity-enhanced frequency doubling is required.