Second-harmonic enhancement using a self-locked 0.63-µ He-Ne laser

Relative second-harmonic power generated in a non-linear crystal has been measured for a multimode He-Ne 0.63-μ laser source operating unlocked and in two different types of spontaneous locking. For the same average laser power the harmonic power was 2.15 times larger for
c/2L
pulsing than for
c/L
pulsing, in good agreement with a predicted value of 2.18. The harmonic enhancement for
c/2L
pulsing compared with unlocked operation was 3.31, considerably lower than the analytic estimate of 4.2, indicating that significant interaction was present between the modes of the unlocked laser.