Device and method for diagnosing the compressibility at the centre of an ultra-short pulse based on spatio-spectral data of the pulse having undergone a non-linear effect

An apparatus for measuring of the Strehl ratio of an ultrashort light pulse according to its combined temporal, spatial and spatio-temporal dimensions, comprising:

• a pulse-separating device for decomposing of said ultrashort light pulse into an initial pulse and a secondary initial pulse, which has a different polarization or direction than the initial pulse, wherein phase characteristics of the initial pulse and the secondary initial pulse are essentially identical to said ultrashort light pulse,
• a first imaging spectrometer for measuring of a spatio-spectral intensity of the initial pulse;
• a first memory for storing the spatio-spectral intensity of the initial pulse;
• a nonlinear medium interaction device for allowing interaction of the secondary initial pulse with a nonlinear optical material, said interaction generating, by a nonlinear optical mechanism of order n greater than or equal to 2, a secondary pulse of temporal intensity proportional to the intensity of the secondary initial pulse raised to the power of n, and of which one or both transverse spatial dimensions are focused in the nonlinear optical material;
• a second imaging spectrometer for measuring the spatio-spectral intensity of the secondary pulse obtained by the nonlinear effect;
• second memory for storing the spatio-spectral intensity of the secondary pulse obtained by the nonlinear effect;
• a processor of a calculator configured to perform:
• a first calculation of the spatio-spectral intensity of the initial pulse is obtained from the simulation of the nonlinear effect using the spatio-spectral intensity of the initial pulse without phase distortion,
• a second calculation of the spatio-spectral intensity of the initial pulse is obtained from the simulation of the nonlinear effect using the spatio-spectral intensity of the initial pulse with a very large quadratic phase, stretching the impulse at least by a factor of 3 temporally and spatially compared to the pulse without distortion, and
• an estimate of the distortions of the pulse through comparing the different spectra obtained and translated into the Strehl ratio RI, without estimating the phase of the pulse, by using a formula:
• RI=f(ISS1, ISS2, ISS3, ISS4), where f is a function that provides an estimate of the Strehl ratio through the spatio-spectral intensities, and ISS1 is the spatio-spectral intensity of the initial pulse, ISS2 is spatio-spectral intensity of the second pulse, ISS3 is the spatio-spectral intensity of the initial pulse according to the first calculation, and ISS4 is the spatio-spectral intensity of the initial pulse according to the second calculation.