We show that an Optical Parametric Oscillator which is simultaneously resonant for several modes, either spatial or temporal, generates both below and above threshold a multimode non-classical state of light consisting of squeezed vacuum states in all the non-oscillating modes. We confirm this prediction by an experiment dealing with the degenerate TEM01 and TEM10 modes. We show the conservation of non-classical properties when the threshold is crossed. The experiment is made possible by the implementation of a new method to lock the relative phase of the pump and the injected beam.
@article{arxiv.0912.4212,
title = {Multimode non-classical light generation through the OPO threshold},
author = {Benoît Chalopin and Francesco Scazza and Claude Fabre and Nicolas Treps},
journal= {arXiv preprint arXiv:0912.4212},
year = {2015}
}