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Laser-induced plasma generation of terahertz radiation using three incommensurate wavelengths

We present the generation of THz radiation by focusing ultrafast laser pulses with three incommensurate wavelengths to form a plasma. The three colors include 800 nm and the variable IR signal and idler outputs from an optical parametric amplifier. We observe that stable THz is generated when all three colors are present, with a peak-to-peak field strength of ∼200 kV cm−1 and a relatively broad, smooth spectrum extending out to 6 THz, without any strong dependence on the selection of signal and idler IR wavelengths (in the range from 1300 to 2000 nm). We confirm that three colors are indeed needed, and we present plasma current modeling that corroborates our observations.