Fig.7

Mode or phase matching at the SH frequency. SEM images (a) and optical images at SH wavelength (b) of three gap antennnas with the gap values of 0, 15 nm and 70 nm from the bottom to top. c, d show the electric field distributions of the gap antennas with the gap value of 15 nm at the fundamental and SH wavelengths, respectively. Reprinted with permission from Optics Express 2012, 20, 10,498–10508. Copyright 2012 Optical Society of American. e Remote excitation of SHG and TPL of Au gapped nanorods through excitation of surface plasmons. Reprinted with permission from Physical Review Letters 2015, 115, 19,740. Copyright 2015 American Physical Society. f, g An SH photon was created by annihilating two copropagating surface plasmons. Reprinted with permission from Physical Review Letters 2012, 108, 136,802. Copyright 2012 American Physical Society. h An SH photon was created by annihilating two counterpropagating surface plasmons. Reprinted with permission from Nano Letters 2017, 17(12), 7803–7808. Copyright 2017 American Chemical Society