Amplification of femtosecond pulses based on χ⁽³⁾ nonlinear susceptibility in MgO

We experimentally demonstrate large, widely tunable gain using Kerr instability amplification in MgO. By pumping the crystal near optical damage at 1.4×10¹³W/cm² by a femtosecond Ti:sapphire laser, we amplify visible and near-infrared pulses by factors >5000 or a gain g≈17/mm. We temporally characterize the pulses to show that they are 42 fs in duration, much shorter than the pump pulse. In the non-collinear setup, the angle between the pump and seed selects the amplified wavelength, where we find certain angles amplify both the visible and near-infrared simultaneously. We find that near the maximum pumping intensities, higher-order nonlinearities may play a role in the amplification process.