Efficient Cherenkov-Type Optical-to-Terahertz Conversion of Femtosecond Oscillator Pulses

We demonstrate experimentally that a recently proposed structure comprising a tens of microns thick layer of LiNbO3 sandwiched between two totally reflecting Si prisms can serve as an efficient Cherenkov-type optical-to-terahertz converter of femtosecond laser pulses from an optical oscillator. Using Ti:sapphire laser pulses of 3.75 nJ energy as a pump, we achieved a conversion efficiency of 2.3 x10-5, which exceeds the efficiency of the conventional collinear scheme with a ZnTe crystal by an order of magnitude. The converter can be used as a reliable radiation source for performing terahertz time-domain spectroscopy.