1.3-Octave Nonlinear Cherenkov Radiation Triggered by Intense 2.2-Octave Femtosecond White Laser

Nonlinear Cherenkov radiation (NCR), an intriguing noncollinear second harmonic generation process satisfying versatile longitudinal phase matching and its diffraction in space, has been realized in periodically poled lithium niobate (PPLN) nonlinear grating and other engineered nonlinear photonic structures. Here, we report on the observation of unprecedented ultrabroadband NCR (with a 1.3-octave bandwidth ranging from 363 to 900 nm) from a single PPLN nonlinear grating plate driven by a high-peak-power ultrashort femtosecond pump white laser that covers 2.2-octave bandwidth ranging from 400 to 1,850 nm and possesses a maximum pulse energy of 1.7 mJ. Multiple colored NCR patterns along the direction of Cherenkov conical angles simultaneously appear and superimpose in space, leading to a beautifully colorful red-violet rainbow picture dispersed in space clearly observable by the naked eye that has never been reported before. The experiments would enrich the basic physical and optical understanding of nonlinear optical interaction and diffraction characteristics of ultrabroadband high-peak-power white laser sources with engineered nonlinear microstructures.