RESUMO
We demonstrate record â¼0.9% efficiencies for optical conversion to narrowband (<1% relative bandwidth) terahertz (THz) radiation by strongly cascaded difference frequency generation. These results are achieved using a novel, to the best of our knowledge, laser source, customized for high efficiencies, with two narrow spectral lines of variable separation and pulse duration (≥250â ps). THz radiation generation in 5% MgO-doped periodically poled lithium niobate (PPLN) crystals of varying poling period was explored at cryogenic and room temperature operation as well as with different crystal lengths. This work addresses an increasing demand for high-field THz radiation pulses which has, up to now, been largely limited by low optical-to-THz radiation conversion efficiencies.
RESUMO
We generate temporally modulated optical pulses with a beat frequency of 255 GHz, a duration of 360 ps, and a repetition rate of 2 MHz. The temporal envelope, beat frequency, and repetition rate are computer-programmable. A frequency comb serves as a phase and frequency reference for the locking of two laser lines. The system enables beat frequencies that are adjustable in steps of the frequency comb's repetition rate and exhibit Hz-level precision and accuracy. We expect the optical beat pulses to be well suited for versatile multi-cycle terahertz-wave generation with controllable carrier-envelope phase. We demonstrate that the inherent synchronization of the frequency comb's ultra-short pulse train and the synthesized optical beat (or later the multi-cycle terahertz) pulses enables rapid and phase-sensitive sampling of such pulses.