Retrieving Squeezing From Classically Noisy Light in 2nd-Harmonic Generation

We report the results of a study of the quantum noise properties of a squeezing system involving a three-level laser pumping tare similar second-harmonic-generating crystals. We show that squeezing that has been obscured by intensity and phase noise from the pump laser may be retrieved by difference detection of both second-harmonic outputs. Similarly, the squeezed vacuum formed by combining the two outputs on a 50/50 beam splitter will be squeezed at frequencies that are classically noisy in the individual beams