Highly efficient Cherenkov-type terahertz generation by 2-μm wavelength ultrashort laser pulses in a prism-coupled...

Terahertz generation by optical rectification of femtosecond laser pulses propagating in a 40-μm thick LiNbO ₃ layer attached to an output Si prism has been experimentally investigated for different laser wavelengths from 800 to 2100 nm. For longer wavelengths, the saturation of the optical-to-terahertz conversion efficiency has been observed at higher laser pulse energies, thus enabling higher efficiencies. In particular, record high conversion efficiency of 1.3% has been achieved with 30-μJ laser pulse energy at 2100 nm.