Dramatic spectral narrowing of a gain-switched diode laser in a weak nonresonant external cavity

Summary form only given. Narrowing of the spectral bandwidth from a diode laser under RF modulation is of significant interest as it dramatically increases the second harmonic and optical parametric oscillation efficiencies. We have narrowed the spectrum using a simple and compact external cavity scheme with an uncoated glass slide as an external reflector. We used commercial 980 nm InGaAs/GaAs lasers with a single-mode ridge waveguide 3 /spl mu/m wide. Without the external reflector, a typical gain-switched pulse duration was /spl sim/32 ps at a user-defined pulse repetition frequency, in the range of 1.80-2.70 GHz with a spectral bandwidth of /spl sim/11 nm and average powers up to 100 mW.