Method and device for controlling the amplitude of the wavelength spectrum of ultra-short light pulses emitted by multiple passage laser amplifiers

A method for controlling the amplitude of the wavelength spectrum of ultra-short light pulse having a duration between a few femtoseconds and a few pictoseconds in a laser amplification chain using a laser cavity comprising an amplifier with multiple passages of light in an amplifier crystal, said method comprising filtering of the amplitude of the spectrum of said light pulse at each of said passages by collinear or quasi-linear interaction between said light pulse and transverse shear acoustic wave generated by a transducer in birefringent acousto-optic crystal having an optical axis and an input face onto which an incident optical wave is applied and is divided into said acousto-optic crystal in a diffracted optical wave which is not used and a non diffracted direct optical wave which travels along an internal optical path and which emerges from an output face of said acousto-optic crystal to be used in said laser amplification chain, said incident optical wave being aligned with the Poynting vector of the acoustic wave, said acoustic wave having a vector forming an angle θa comprised between 0° and 15° with said optical axis, said non diffracted direct optical wave having a polarization identical with one of said incident optical waves, said shear acoustic wave being polarized perpendicular to the plane including said internal optical path, said vector of the acoustic wave being located in said plane and said transducer being driven by a generator controlled by a computer to have an amplitude modulation of the spectrum of the non diffracted direct optical wave and to obtain a desired shape of the optical pulse spectrum at the output of the amplification chain.