Increasing bandwidth of Cherenkov-type terahertz emitters by free carrier generation.

We found experimentally that Cherenkov-type terahertz radiation produced by optical rectification of ultrashort laser pulses in LiNbO can experience strong spectral broadening in the regime of multiphoton laser absorption. The broadening is attributed to the terahertz emission from a surge current of the optically generated carriers. The effect can be used to improve the bandwidth of optical-to-terahertz converters based on optical rectification.

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.

Scalable optical-to-terahertz converter with a prism-coupled plane-parallel lithium niobate plate.

A nonlinear optical converter of femtosecond laser pulses to terahertz radiation, which combines the tilted-pulse-front pumping and prism coupling techniques, is proposed and experimentally tested. In contrast to the conventional tilted-pulse-front scheme with a prism-shaped LiNbO crystal, the converter consists of a plane-parallel LiNbO plate sandwiched between two dielectric prisms. One prism is used to couple the pump beam into the LiNbO plate, another prism couples the generated terahertz radiation out of the plate.

Experimental observation of optically generated unipolar electromagnetic precursors.

It was recently predicted [Phys. Rev. A95(6), 063817 (2017) 10.

Noncollinear electro-optic sampling detection of terahertz pulses in a LiNbO crystal while avoiding the effect of intrinsic birefringence.

We propose and experimentally prove efficient high-resolution electro-optic sampling measurement of broadband terahertz waveforms in a LiNbO crystal in the configuration with the probe laser beam propagating along the optical axis of the crystal. This configuration allows one to avoid the detrimental effect of strong intrinsic birefringence of LiNbO without any additional optical elements. To achieve velocity matching of the terahertz wave and the probe beam, the terahertz wave is introduced into the crystal through a Si prism at the Cherenkov angle to the probe beam.