  Weak squeezed vacuum light, especially resonant to the atomic transition,
plays an important role in quantum storage and generation of various quantum
sources. However, the general homodyne detection (HD) cannot determine weak
squeezing due to the low signal to noise ratio and the limited resolution of
the HD system. Here we provide an alternative method based on photon statistics
measurement to determine the weak squeezing of the squeezed vacuum light
generated from an optical parametric oscillator working far below the
threshold. The approach is established the relationship between the squeezing
parameter and the second-order degree of coherence. The theoretical analysis
agrees well with the experiment results. The advantage of this method is that
it provides a feasible and reliable experimental measure to determine the weak
squeezing with high precision and the measurement is independent on the
detection efficiency. This method can be used to measure other quantum features
for various quantum states with extremely weak non-classicality.
