Five conical harmonic beams are generated from the interaction of femtosecond mid-infrared （mid-IR） pulses at a nominal input wavelength of 1997 nm with a 2D LiNbO3 nonlinear photonic crystal with Sierpinski fractal...Five conical harmonic beams are generated from the interaction of femtosecond mid-infrared （mid-IR） pulses at a nominal input wavelength of 1997 nm with a 2D LiNbO3 nonlinear photonic crystal with Sierpinski fractal superlattices. The main diffraction orders and the corresponding reciprocal vectors involved in the interaction are ascertained. Second and third harmonics emerging at external angles of 23.82° and 36.75° result from non-linear Cerenkov and Bragg diffractions, respectively. Three pathways of fourth-harmonic generation are observed at external angles of 14.21°, 36.5°, and 53.48°, with the first one resulting from nonlinear Cerenkov diffraction, and the other two harmonics are generated via different cascaded processes.展开更多
基金supported by the National Natural Science Foundation of China(No.11004175)the Communication University of China(Nos.3132016XNG1616and YXJS201306)support of the Air Force Office of Scientific Research(AFOSR),USA Grant nos.FA9550-12-1-0454 and FA9550-16-1-0069
文摘Five conical harmonic beams are generated from the interaction of femtosecond mid-infrared （mid-IR） pulses at a nominal input wavelength of 1997 nm with a 2D LiNbO3 nonlinear photonic crystal with Sierpinski fractal superlattices. The main diffraction orders and the corresponding reciprocal vectors involved in the interaction are ascertained. Second and third harmonics emerging at external angles of 23.82° and 36.75° result from non-linear Cerenkov and Bragg diffractions, respectively. Three pathways of fourth-harmonic generation are observed at external angles of 14.21°, 36.5°, and 53.48°, with the first one resulting from nonlinear Cerenkov diffraction, and the other two harmonics are generated via different cascaded processes.
