27 Mar 2007
Stefano Bonora from the University of Padova, Italy, exploits compact reflective optics in a new design for a beam transformation system (J. Opt. A: Pure Appl. Opt. 9 380-386.)
The strong asymmetry in the emission of the fast and slow axes of semiconductor power lasers means that a significant optical beam transformation system is needed to achieve the parameters needed for micromachining, laser end-pumping and advanced applications. Bonora proposes a simple solution to this problem based on an array of cylindrical mirrors.
The system minimizes the number of optical elements involved in brightness equalization, while at the same time achieving both a compact design and a high brightness beam. This optical scheme can also be effectively exploited in combination with polarization coupling of diode bar stacks as well as with beam coupling by beam compression.
The beam parameter product for one quasi-continuous-wave bar is about 26 and 40 mm mrad for the slow and fast axes, respectively, with spot size radii of 0.10 mm × 0.15 mm. This result is comparable to the state-of-the-art.
The configuration proposed by Bonara has several advantages: it permits the use of tilted arrays of optical elements as a non-imaging class, extending their use to more powerful diode laser bar geometries; the linear symmetry allows the use of short focal length lenses for focusing, creating a very compact device; and compressed diode-laser bar stacks and polarization combiners can be used to strongly increase the output power because it is a non-imaging system.