In this letter, we report tunable operation of a gain-switched diode laser
by nonresonant self-injection seeding from an uncoated glass slide used as
an external cavity reflector. A spectral linewidth reduction from 11 to 0.0
5 nm has been achieved for picosecond pulses with little effect on other la
ser characteristics. Good agreement with numerical simulations based on a c
ompound-cavity laser model is also reported.