Coherent beam combining progress on diode lasers and tapered amplifiers at 808 nm

Abstract

The increase of the optical power levels of diode lasers is a continuous and not trivial challenge. Single frequency diode lasers at 808 nm have maximum powers of the order of a few hundred milliwatts and by using a tapered amplifier can reach a power level of about 2 W. An approach to increase this optical power limit and widen the application fields of direct single frequency diode laser sources is the coherent beam combining (CBC) method. This paper presents the results on a CBC setup by using a purpose-built distributed Bragg reflector ridge waveguide laser (DBR-RWL) at 808 nm as a seed laser and two tapered amplifiers (TPA). The phase control between the two beams has been accomplished through the ridge waveguide current of one of the tapered amplifiers. The phase lock process has been automated with the creation of a reverse hill climbing algorithm and the use of a microcontroller ATmega328P. Remarkable CBC efficiencies over 80 % and an optical power of 3.5 W have been achieved. Full characterization of the DBR-RWL and TPA is presented.