Synchronization of Arrays of High Power Lasers

Semiconductor lasers offer significant operational advantages due to their high efficiency, compactness, and flexibility of pulse repetition rates. Their major drawback - which limits quite severely the scope of their applicability - is the relatively low emission power put out by a single semiconductor laser. To overcome this drawback, we propose a compact, high-efficiency, highpower light source based on a synchronized broad-area laser array. A variety of techniques have been proposed to synchronize laser arrays and coherently combine beams from separate lasers [1-10]. They involve primarily optical engineering efforts such as MOPA injection locking, evanescent coupling, the use of Talbot cavities, and spectral beam combining. In some instances, optical engineering techniques have indeed produced phase locking in arrays of lasers (mostly, using low-to-moderate power lasers). However, these techniques are not easily scalable. The fundamental difficulty in realizing a scalable design is the complexity of the underlying dynamics. Indeed, lasers are inherently highly nonlinear systems that are capable of producing varieties of complex behaviors that depend quite sensitively on parameter values and initial conditions. One possible consequence of nonlinearity in lasers is that synchronization techniques that are suitable for low power, single mode lasers may not be applicable to high power, single or multimode lasers, because of the possibility of chaotic behavior that high power lasers usually display. Therefore, thorough understanding of this complex behavior is essential for the design of stable, scalable, and robust high power sources. We designed a novel scalable setup and technique to synchronize high power both CW and pulsed semiconductor laser arrays. Our design combines the major important features necessary to synchronize a nonlinear, possibly chaotic, dynamical system, namely: (a) injection locking and/or reflection from the gratings as a mechanism of mode locking and (b) laser coupling to induce the collective dynamics in the array. We have experimentally demonstrated several designs of synchronization broad-area semiconductor laser arrays using commercially available high-power laser arrays. The key advances of our synchronization experiments include: