Parametric amplification and squeezing of a mode-locked pulse train:: A comparison of MgO:LiNbO3 with bulk periodically poled LiNbO3 -: art. no. 043807

We report on an initial squeezing of 3.3 dB below the shot noise level, generated in bulk, quasi-phase-matched lithium niobate. This squeezing was generated by degenerate parametric amplification. at 1047 nm, of a mode-locked pulse train. We present a detailed comparison of the process performed in both the quasi-phase-matched material and in MgO:LiNbO3, which was phase marched using conventional birefringent methods. The single-pass gain measured was 2.5 from MgO:LiNbO3 and 3.9 from periodically Doled lithium niobate (PPLN), although the former was affected by photorefractive damage. We directly recorded 11% of noise reduction in the vacuum using the PPLN parametric amplifier, purely because the detection efficiency was so low in our experiment. The experimental data was fitted to a model which includes the initial squeezing level and the homodyne detector efficiency as free parameters. The observed squeezing agrees well with the a total detection efficiency of just 16% and an initial squeezing level of 3.3 dB (53%) in PPLN.