  Laser intensity noise suppression has essential effects on preparation and
characterization of the audio-frequency squeezed vacuum state of light based on
a sub-threshold optical parametric oscillator (OPO).We have implemented two
feedback loops by using relevant acousto-optical modulators (AOM) to stabilize
the intensity of 795-nm near infrared (NIR) fundamental laser and 397.5-nm
ultraviolet (UV) laser generated by cavity-enhanced frequency doubling.Typical
peak-to-peak laser intensity fluctuation with a bandwidth of $\sim10$ kHz in a
half hour has been improved from $\pm7.45$$\%$ to $\pm0.06$$\%$ for 795-nm NIR
laser beam, and from $\pm9.04$$\%$ to $\pm0.05$$\%$ for 397.5-nm UV laser beam,
respectively. The squeezing level of the squeezed vacuum state at 795 nm
prepared by the sub-threshold OPO with a PPKTP crystal has been improved from
-3.3 to -4.0 dB around 3$\sim$9 kHz of audio analysis frequency range.
