Generation of sub-MV/cm terahertz fields with large-size Cherenkov-type optical-to-terahertz converters.

It is known that a structure comprising a tens of microns thick, and ∼1 × 1 cm in size, layer of LiNbO attached to a Si prism can serve as an efficient Cherenkov-type converter of tens of microjoules-energy femtosecond laser pulses to broadband terahertz radiation. Here we experimentally demonstrate scaling up the terahertz energy and field strength by extending the width of the converter to several centimeters, expanding appropriately the pump laser beam, and increasing the pump pulse energy to hundreds of microjoules. In particular, chirped Ti:sapphire laser pulses of 450 fs duration and 600 µJ energy were converted to 1.2 µJ terahertz pulses, and 0.5 MV/cm peak terahertz field was obtained when pumping by unchirped laser pulses of 60 fs duration and 200 µJ energy.