Fig. 1: Nanocavities enhance sum frequency generation.
From: Tip-enhanced nanocavities amplify the sum frequency generation
a Jablonski energy diagram of sum frequency generation (SFG) and difference frequency generation (DFG). The blue arrow represents the SFG. The green arrow represents the DFG. The red and orange arrows represent the IR and visible lights, respectively. b Two kinds of modified nanoparticle-on-mirror (NPoM) cavity structures12,13. c Tip-enhanced NPoM cavity. When the metal tip is close to the gold nanoparticle, the SFG signal will be enhanced, as illustrated in the right panel. d Schematic of the prospect of Tip-enhanced VSFG. (i) Tip modification effect on the dipole-forbidden vibrational modes. (ii) Super-resolution VSFG image. (iii) Single-molecular VSFG response (iv) Controlling the Strong light-matter coupling
