Spectral properties of second, third and fourth harmonics generation from broadband multimode bright squeezed vacuum

We study theoretically the spectra of second, third and fourth harmonics from multimode bright squeezed vacuum obtained by type-I broadband high-gain parametric down conversion. The different contributions to the spectra of harmonics are analyzed. A new method for the measurement of second-order correlation function g((2))(0) of parametric down conversion radiation is suggested.