Narrowband high power light from diode lasers

By injecting only 2 mW from a spectrally narrowed diode laser into a 100-mW free-running diode laser array (FRA), the authors have narrowed both its specturm and beam divergence greatly. They collapse the spectrum into a single longitudinal mode <300 kHz wide, 50-100 times stronger, and in a single spatial (transverse) mode whose width is approximately diffraction-limited for the array aperture. The authors have modeled this process and found that its dominant feature is phase matching of the injected wave with the free-running wave in a single strip of the array. This model provides an accurate description of the main output beam features as well as secondary behavior.