  Electron shelving gives rise to bright and dark periods in the resonance
fluorescence of a three-level atom. The corresponding incoherent spectrum
contains a very narrow inelastic peak on top of a two-level-like spectrum.
Using the theories of balanced and conditional homodyne detection we study
ensemble averaged phase-dependent fluctuations of intermittent resonance
fluorescence. The sharp peak is found only in the spectra of the squeezed
quadrature. In balanced homodyne detection that peak is positive, which greatly
reduces the squeezing, also seen in its variance. In conditional homodyne
detectionCHD, for weak to moderate laser intensity, the peak is negative,
enhancing the squeezing, and for strong fields the sidebands become dispersive
which, together with the positive sharp peak dominate the spectrum. The latter
effect is due to non-negligible third order fluctuations produced by the
atom-laser nonlinearity and the increased steady state population of the
shelving state. A simple mathematical approach allows us to obtain accurate
analytical results.
