Squeezing Intensity Noise on Laser-like Beams

Abstract

Parametric down-conversion generates beams having strong quantum correlations. This property can be easily understood by reasoning in terms of photons : let us consider a non-linear crystal irradiated by light at frequency ω₀. For each pump photon absorbed at frequency ω₀, it simultaneously emits two “twin” signal photons with frequencies ω₁ and ω₂ (such that ω₀ = ω₁ + ω₂). Such non-classical correlations have been observed by photon coincidence techniques |1|. However, with the available cw lasers and non-linear crystals, the parametric process generates only very weak correlated beams (typically a few photons/second), because the pump power is spread into an infinity of twin modes. To concentrate the output energy into a few pair of modes only, the non-linear crystal can be inserted in an optical cavity having mirrors with a high reflectivity for the signal frequencies ω₁ and ω₂. Above some pump power threshold, the system can oscillate and yields a pair of intense, laser-like, “twin” beams.