We demonstrate step-tunable single-mode operation of a gain-switched diode
laser by nonresonant self-injection seeding from an uncoated glass slide us
ed as an external cavity reflector. A spectral bandwidth reduction from 11
mn to 0.05 nm and wavelength tunability has been achieved for picosecond (n
ear-transform-limited) pulses with little effect on other laser characteris
tics. Good agreement with numerical simulations based on a compound-cavity
laser model is also reported.