Development of High Brightness Blue Laser source for additive manufacturing

Recent applications of Additive Manufacturing (AM) pose new challenges that are difficult to meet with the commonly used Infrared (IR) laser, but instead could be well addressed by blue lasers. Indeed, while high-power IR lasers have found extensive usage in materials processing, switching to blue lasers would improve the processing quality and efficiency of some materials that are finding increasing importance in industrial applications, such as copper, gold and aluminum, because of their higher absorption in the blue wavelengths than in the IR region. This also improves the energy consumption since blue laser diodes show an higher Wall Plug Efficiency (WPE) than IR fiber lasers. Advances in both laser technology and additive manufacturing processes are expected to drive further expansion and enable the implementation of innovative applications. In particular, efficient processing of high reflective metals and high-tech polymers require a blue laser source capable of emitting some hundreds of watts. Today, state of the art in high power blue laser sources are multi-emitter diode modules that deliver some tens of watts; therefore, to meet the application requirements a plurality of these modules must be multiplexed. The aim of the thesis is to design a blue laser source for a system prototype of a new concept of low-cost Additive Manufacturing (AM) machine specific for the manufacturing of small-volume parts using high-performance semi-crystalline engineering thermoplastic or difficult to laser process metals. The use of high brightness Blue Laser (BL) source enables the development of a flexible laser based system, composed of lower power multi emitter which eases the replacement in case of failures (graceful degradation), lowering the ownership costs, increasing the energy efficiency, and improving the product quality. Among the various beam multiplexing approaches, wavelength (or spectral) combination of multi- emitter modules has been studied and implemented. Efficient wavelength multiplexing requires beams with stable spectral emission but the emission of laser diodes is heavily influenced by temperature and driving current. This problem can be solved by wavelength stabilization. This can be obtained by building an external cavity using diffraction gratings. As a preliminary step an experimental setup has been built to prove the feasibility of stabilization at different wavelength and in different conditions, like continuous or pulsed emission. The measurement has been complemented with simulations conducted using a finite element analysis-based software. Then, the spectral combination of the multi-emitter module was analyzed using OpticStudio, an optical design software capable of analyzing complex sources in optical systems. The obtained experimental results that followed are consistent with predictions, validating the adoption of spectral multiplexing to combine modules without deterioration of beam quality. The compactness and interchangeability of such approach opens the way to a modular configuration scalable both in power and brightness.