Fiber-coupled diode laser modules with wavelengths around 2 &mgr;m

The common wavelength regime for high-power diode laser modules is the range between 800 nm and 1000 nm. However, there are also many applications that demand for a wavelength of around 2 &mgr;m. This wavelength range is extremely interesting for applications such as the processing of plastics, medical applications as well as environmental analytics. The interest in lasers with this wavelength is based on the special absorption characteristics of different types of material: Numerous plastics possess an intrinsic absorption around 2 &mgr;m, so that the use of additives is no longer necessary. This is of great value especially for medical-technical products, where additives require a separate approval. Furthermore the longer wavelength allows the processing of plastics which are clear and transparent at the visible. In addition, water, which is an essential element of biologic soft tissue, absorbs radiation at the wavelength about 2 &mgr;m very efficiently. As radiation of this wavelength can be guided by glass fibers, this wavelength may be very helpful for laser surgery. Currently available lasers at the spectral range about 2 &mgr;m are solid-state lasers based on Ho- and Tmdoped crystals. These systems suffer from high purchase costs as well as size and weight. In contrast to this, diode lasers can be built more compact, are much cheaper and more efficient. For this background, GaSb based high-power laser diodes for the wavelength regime of 1.9 - 2.3 &mgr;m are developed at the Fraunhofer Institute for Solid State Physics (IAF). At the Fraunhofer Institute for Laser Technology (ILT), fiber-coupled laser diode modules based on these laser bars are designed and realized. A first module prototype uses two laser bars with a wavelength of 1.9 &mgr;m to provide an output power of approx. 15 W from a 600 &mgr;m, NA 0.22 fiber. The module setup as well as the characteristics of the laser bars at 1.9 &mgr;m wavelength are described in this paper.