Comparison of electro-optical, spectral, and spatial beam parameters of 785 nm DBR tapered lasers with different grating lengths

In this contribution, the properties of 4 mm long DBR-tapered lasers with different DBR grating lengths and different ridge waveguide lengths will be investigated. For the different device designs, the influence of the ridge waveguide current on the spectral and spatial parameters will be presented. The vertical layer structure of the devices is based on a GaAsP single quantum well in a large optical cavity. Three different grating lengths, i.e., 500 μm, 750 μm, and 1 mm, were manufactured using e-beam lithography. For the first two gratings, the tapered section has a length of 2.5 mm, for the latter 2.0 mm. All devices have a full tapered angle of 6°. The devices having the longer tapered sections reach output powers up to 7 W with a narrow spectral width. Increasing the ridge waveguide current increases the optical output power up to a saturation level. At saturation level, although the output remains approximately stable, differences in the spectral behavior and the beam quality occur. The dependence of spectral properties and beam parameters on the ridge waveguide current will be discussed. A correlation between spectral properties and lateral beam profile measured at beam waist position can be supposed. The measured emission width amounts to 19 pm, which is limited by the resolution of the used spectrometer. In best cases, at an output power of 5 W the lateral beam propagation ratio is below 3.5 (1/e²) and 8.4 (2^nd moments). These lasers are well-suited as pump lasers for Tm:YAG lasers and as excitation light sources in Raman spectroscopic experiments with large excitation areas.