  We report on an attempt to generate highly stable continuous terahertz (THz)
wave by using optical frequency comb (OFC). About 10-nm wide OFC has been
generated through a deep phase modulation of a 852 nm laser line in lithium
niobate crystal cavity. The multiple optical modes (side bands) of the OFC,
which are equally separated from each other by the modulation frequency (=6
GHz) are taken as the frequency reference. When another semiconductor laser is
frequency locked, the stability of the difference frequency between the master
laser and the second laser is improved on the same order of the RF modulator.
An ultra-narrow line and tunable THz radiation source can be achieved by
photomixing of this stable difference-frequency optical beat in a
photoconductive antenna.
