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In this study, an optical setup for generating terahertz (THz) pulses through a two-color femtosecond laser filament was carefully designed to achieve a precise overlap of two-color laser pulses in space and time. β-barium borate (BBO), α-BBO, and a dual-wavelength plate were used to compensate the phase delay of the two-color lasers. Tilting of α-BBO could further realize the precise spatial overlap of the two beams by counteracting the walk-off effect. The maximum output THz pulse energy reached 21 μJ in argon gas when using a commercial Ti:sapphire laser with a pulse energy of 6 mJ at a 1 kHz repetition rate. The corresponding conversion efficiency exceeded 0.35%.

A series of new intramolecular charge transfer compounds with absorption bands in shorter wavelengths have been synthesized. Bright visible light emits from the crystals of these new compounds under infrared pulsed laser pumping. The spectral and pump density dependent properties demonstrate that some of the emissions are up-conversion fluorescence due to two photon absorption. The fluorescent yields of one- and two-photon absorption are in the same order at high pump density. This work demonstrates that these new intramolecular charge transfer crystals are good candidates for nonlinear optical materials.

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Field emission from chemical vapor deposited diamond and diamond-like carbon films: Investigations of surface damage and conduction mechanisms