High-order sum and difference frequency generation using tunable two- and three-color commensurate and incommensurate mid-infrared pumps of graphite plasma

We demonstrate high-order sum and difference harmonic generation using the mixing of tunable (1200–2600 nm) pulses from optical parametric amplifier and 810-nm ultrashort pulses in the extended laser-produced graphite plasma. Optimization of high-order harmonic generation using various parameters (delay between two-color incommensurate and commensurate waves, ratio between pulse intensities, use of parallel and orthogonal polarizations of interacting pulses, etc.) and comparison with a two-color pump using mid-infrared and second-harmonic pulses are presented. We show that, despite the nonoptimal spatiotemporal overlap of two or three sources of radiation in plasma, the application of the proposed technique allows generation of significantly denser combinations of interacting waves, leading to sum and difference frequency generation in the extreme ultraviolet region.

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