Mid-infrared femtosecond pulses obtained by optical rectification of 10-fs optical pulses

We generate quasi single-cycle femtosecond pulses in the mid-infrared spectral domain by performing the optical rectification of 10-fs visible pulses. This represents a tenfold increase in the frequencies achieved through optical rectification, previously generated in the far-infrared domain only. The 10-fs pulses produced by a 100-MHz Ti:sapphire oscillator are first sent through a modified Michelson interferometer, allowing to focus a sequence of two pulses on a nonlinear material such as GaAs or GaSe. Due to the second-order nonlinear response of these materials, the incident pulses are optically rectified. This results in a transient polarization of duration 10 fs, which in turn radiates an electromagnetic wave with frequency components ranging from 0 to 50 THz