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

pulsing than for

pulsing, in good agreement with a predicted value of 2.18. The harmonic enhancement for

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.