Efficient optical-to-terahertz conversion of femtosecond laser pulses propagating along a sandwich structure with thin LiNbO3 core

A new scheme for efficient optical-to-terahertz conversion of femtosecond laser pulses is experimentally demonstrated. In this scheme the laser pulse is cylindrically focused into thin LiNbO₃ layer placed between the BK7 glass substrate and silicon prism. The pulse excites a moving nonlinear polarization in LiNbO₃ that emits the Cherenkov cone of terahertz waves in the silicon prism. We measured the terahertz waveform and terahertz energy as a function of the optical pump energy. Up to 10^-3 conversion efficiency has been observed for 50 mum thick LiNbO₃ layer pumped with 100 muJ, 200 fs Ti:sapphire laser pulse.