Why are KLASTECH DPSS lasers inherently single frequency?
The second cavity that contains a frequency doubling crystal is seen from the first cavity that holds an active laser crystal as a resonant reflector. This arrangement is known, when without a non-linear crystal, as a Fox-Smith interferometer. Hence, locking the two above cavities at one of the resonances of the Fox-Smith interferometer for optimal intra-cavity coupling and highest second harmonic generation efficiency, inherently leads to the lasing at only that resonant frequency. This single frequency (single longitudinal mode SLM) lasing remains as long as the two above cavities remain locked, hence, no mode hopes occur during the stable operation of the laser.
