Development of high-brightness diode lasers: the z-laser

During recent years the performance of high power diode lasers in terms of output power and lifetime has increased significantly. However, for many applications not only a high output power but also a good beam quality is necessary - in other terms, high brightness is required. While the beam quality of classical broad area-type high power diode lasers is poor, special laser structures have been developed to achieve an improved beam quality. Examples are the tapered laser, the alpha-DFB-laser and - the latest development - the so-called "z-laser". The z-laser uses internal total reflection for the suppression of higher-order modes. The effectiveness of this working principle was first demonstrated by performing extensive numerical simulations. During the last year the first z-laser structures have been processed and characterized. The experimental results of these first test lasers are compared with the predictions from the numerical simulations and show a very good agreement. With these first lasers, approximately 500 mW output power at 6-times diffraction limited beam quality have been demonstrated. Nevertheless, there are also some not well understood features of the z-laser to be investigated, like a reduced conversion efficiency and untypical characteristic curves showing kinks. Understanding these features, demonstrating the reproducibility of the structure and further performance improvements are the goals of current research.