Active mode locking of the far-infrared p-Ge laser giving a train of 200 ps
pulses is achieved via gain modulation by applying an rf electric field to
gether with an additional bias at one end of the crystal parallel to the Vo
igt-configured magnetic field. Harmonic mode locking yields a train of puls
e pairs with variable time separation from zero to half the roundtrip perio
d, where pulse separation is electrically controlled by the external bias t
o the rf field. (C) 1999 American Institute of Physics. [S0003-6951(99)0200
2-1].