Mode shaping in semiconductor broad area lasers by monolithically integrated phase structures.

By broadening the stripe width of the active waveguide region, it is possible to extract high optical powers from semiconductor broad area lasers. However, a weak output beam quality, optical filamentation, and high peak power densities will result, which are invoked by the amplification of higher order modes. We show an approach to influence the optical field inside the resonator by integrating optical phase structures directly into the waveguide. Those elements offer the possibility to enlarge the active gain area for the desired fundamental laser mode, while additional diffraction losses for higher order modes are generated, thus achieving an improved beam quality. We report on considerations in designing those elements and demonstrate a first experimental realization.

Modeling electro-optical characteristics of broad area semiconductor lasers based on a quasi-stationary multimode analysis.

To increase the brightness of broad area laser diodes, it is necessary to tailor the optical properties of their waveguide region. For this purpose, there is the need for simulation tools which can predict the optical properties of the complete device and thus of the outcoupled light. In the present publication, we show a numerical method to calculate typical intensity distributions of the multimode beam inside a high-power semiconductor laser. The model considers effects of mode competition and the influence of the gain medium on the optical field. Simulation results show a good agreement with near and far field measurements of the analyzed broad area laser diodes.

Improving the brightness of a multi-kilowatt single thin-disk laser by an aspherical phase front correction.

We report on results obtained with an aspherical mirror to compensate for the phase front aberrations of a cw thin-disk laser with a single disk in the resonator. A record output power of 5 kW with a beam quality suitable for laser cutting (beam propagation factor M2=9.2) has been achieved.

Experimental realization of a diffractive unstable resonator with Gaussian amplitude of the outcoupled beam using a VECSEL amplifier.

Unstable resonators show an intense discrimination of undesired higher order modes but a high beam quality cannot be obtained with conventional resonators composed of spherical mirrors. In the present paper we demonstrate the possibility to tailor the fundamental mode by inserting diffractive elements into the resonator to generate a desirable output beam profile even for unstable resonators. We show a concept to design such surface structured elements for customizing the amplitude shape of the outcoupled beam. Further we demonstrate the first experimental realization of an unstable diffractive resonator with a Gaussian shaped amplitude profile of the laser beam for a vertical external cavity surface emitting laser (VECSEL).