Based on the different noise machanisms of the intracavity-doubling quasi-three-level and four-level lasers

the blue(473 nm) and green (532 nm)lasers are made to study their noise characteristics using the same laser crystal (Nd∶YAG) and the same doubling crystal(LiB

3

O

5

). The magnitude of the noise is

>

120% at output power of 50 mW in a intracavity-doubling quasi-three-level laser

but in a similar intracavity-doubling four-level laser

it is

<

5% at output power of 60 mW. It is shown that the noise in intracavity-doubling quasi-three-level laser is larger than that in four-level laser system. These properties of high-frequency noise in intracavity-doubling laser have been analysed through coupled-differential equation models and analysis results point out that these properties are caused by the reabsorption losses in quasi-three-level intracavity-doubling laser system.The noise in tracavity-doubling quasi-three-level laser will be decreased if reabsorption losses are controlled.