Abstract : Femtosecond lasers are an incredible precision resource for metrology. The ability to produce squeezed states in this regime could then improve even more physical measurements. In a first part, I will present a precision limit for the estimation of parameters carried by the electromagnetic field, using general gaussian resources. It can be proven that a single-mode squeezer, on a well defined mode, is optimal from an experimental point of view. I will then exhibit a simple general scheme, based on homodyne detection, which allows to optimally measure parameters carried by the EM field. In the second part, I will present the experimental results we obtained using a femtosecond synchronously pumped optical parametric oscillator. I will demonstrate the production of intensity squeezing in that regime and the proof of the multimode aspect of the light produced. This is a crucial step in the production of tailored multimode squeezed states in the femtosecond regime.