Investigation of Limits on Peak Powers and Conversion Efficiencies for Quasi-Single-Cycle THz Pulses Based on Phase-Matched Difference-Frequency Generation: Review

摘要

We have reviewed our most recent results. Let us consider a second-order nonlinear medium in whichperfect phase-matching can be achieved at one particular output wavelength for the process of the THzgeneration from a train of ultrafast laser pulses based on difference-frequency generation. We assume thatthe coherence lengths for the THz generation are sufficiently long within a wide bandwidth around thisperfect phase-matching wavelength due to a slight dispersion in the THz region (i.e. broadband phasematching).In this theoretical work, we show that quasi-single-cycle THz pulses can be efficiently generated.An efficient conversion for the THz generation is made possible not only by utilizing the broadband phasematchingbut also by optimizing the pulse width for each peak THz frequency. We have investigated theregime of the strong pump depletion and found the limits to the conversion efficiencies. We have ruled outthe significant contributions due to the effects of multiphoton absorption, free-carrier absorption, andnonlinear refractive indices.