Contents I. Introduction
High power lasers are universally employed for many applications, from materials processing [1], [2] to optical communications [3], [4] and 3D sensing [5], [6]. Semiconductor diode lasers often play a role in high power laser systems, as they can deliver high power with good electrical-to-optical efficiency. However, traditional high power diode lasers are edge-emitting broad area lasers, which suffer from low brightness (power per unit area per unit angle), meaning that the energy from the laser output cannot be effectively focused to a high intensity spot at a distant target. Therefore, diode lasers are often used indirectly as pumps [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17] for other optically active gain media, such as fiber lasers or solid-state lasers. These lasers operate in a single spatial mode, thus providing the high brightness output needed. In such systems, the fiber laser or solid-state laser may be called a “brightness converter”, as it converts the high efficiency beam from the diode laser pump into a high brightness beam. This conversion process does degrade the overall system efficiency, which must consider the electrical-to-optical efficiency of the diode laser and the optical-to-optical conversion efficiency of the gain media being pumped by the diode laser. In addition to the reduced efficiency, these cascaded laser systems are inherently more bulky, more expensive, and have more potential failure points due to the added components as well as their associated thermal management systems. As technology advances and systems miniaturize, there is a continual drive to push systems to lower cost, size, weight, and power consumption (c-SWAP), provided this system optimization does not come at the expense of reduced performance.
