Narrow spectral line-width 785 nm DBR tapered lasers with 7 W output power

Lasers in the spectral range around 785 nm are requested as pump lasers for 2 μm eye-safe Tm:YAG lasers and as excitation light sources in Raman spectroscopic experiments with large excitation areas. The output power should be in the range of several watts together with wavelength stabilization and good beam quality. Distributed Bragg Reflector (DBR) tapered diode lasers offer a potential solution. In this contribution 785 nm DBR tapered lasers with a narrow spectral emission width below 1 pm will be presented. The devices are based on GaAsP single quantum wells embedded in a 1 μm thick large optical cavity leading to a vertical far field angle of 29° (FWHM). The 3-inch wafers were grown using metalorganic vapor phase epitaxy. In a full wafer process 4 mm long DBR tapered lasers were manufactured. Two different layouts were processed. One device type (A) consists of a 1.0 mm long 10th order surface DBR grating acting as rear side mirror, a 1.0 mm long ridge waveguide section, and a 2.0 mm long flared section having a full taper angle of 6°, whereas the other one (B) has a 500 μm long DBR grating, a 1.0 mm long RW section and a 2.5 mm long 6° flared section. Both types of devices reach output powers larger than 5 W at 25°C. The device with the shorter tapered section (A) is limited to this output power, whereas the device with longer taper (B) reach up to 7 W within the studied current range up to 8 A. At 3 W output power the latter device has an emission linewidth below 1 pm. Measured at 1/e2 level at this output power the beam waist width of 8.5 μm and the far field angle of 14.4° lead to a beam propagation ratio M2 of 2.1. More than 71% of the emitted power is within the central lobe of the beam waist.