Wavelength Beam Combining for Power and Brightness Scaling of Laser Systems

The ideal electric laser efficiently converts electrical power into optical power in the form of a beam that can propagate a long distance with minimal diffraction-limited spreading. Various laser applications require scaling to high power (kWs to MWs) while maintaining a diffrac-tion-limited beam; thus, many efforts have been directed toward that goal. The main impediment to this high-power scaling has been associated with thermo-optical distortions in the laser gain media that occur as a result of heat generated in the less-than-perfect electrical-to-optical power-conversion process. For any class of laser, there is a power level that is difficult to exceed without degrading beam quality; however, technological advances have mitigated some thermo-optical effects. For example, diode lasers and fiber lasers are two attractive classes of electric lasers developed to efficiently generate diffraction-limited beams in the W-class and kW-class, respectively. Beam combining offers a modular approach to power scaling while preserving beam quality. The concept of beam combining laser arrays to scale up in power with a diffraction-limited beam is an old one, with some pioneering work done at Lincoln Laboratory in the 1980s [1, 2]. Subsequent laser technology advances have allowed for practical implementations of those beam-combining concepts, and beam combining today is a well-accepted avenue for laser power scaling. Wavelength beam combining allows for scaling the power of a laser system in a modular approach while preserving the quality of the combined beam. Lincoln Laboratory has demonstrated a wavelength-beam-combining technique that significantly improves the brightness and intensity achieved by diode laser systems. This technology could lead to diode lasers' replacing other types of lasers in industrial applications such as metal cutting and welding.