Second to fifth harmonic generation in individual β-barium borate nanocrystals

We have studied the nonlinear optical properties of single β-barium borate nanocrystals, with potential applications as probes in nonlinear sensing and imaging schemes. Our work demonstrates their ability to generate second, third, fourth, and fifth harmonics. The particles' polarization response is studied and compared with simulations based on the bulk nonlinear tensors, with good agreement. Furthermore, the nonlinear susceptibilities of different orders are estimated.