Generation of femtosecond diffraction-compensated beam through an opaque disk.

The generation of a femtosecond diffraction-compensated beam through an opaque disk is presented: 100 fs pulses are focused in the vicinity of an opaque disk. A bright beam surrounded by concentric rings is generated. The beam can be collimated by a lens. A non-diffracting femtosecond beam which conserves a 500microm large central spot over more than 1.7m is then observed, without any nonlinear mechanism. Our theoretical analysis predicts well the results.