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

Abstract

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.

Nonperturbative Generation of Harmonics by Nanometer-Scale Localized Electronic States on the Surface of Bulk Materials and Nano-Films

“…Equation (1) means that the harmonic intensity is proportional to the q-th power of the laser intensity: I q ∝ I q 1 . However, when strong laser fields were applied, the experiments observed a different power dependence [4,11,13,[23][24][25][26][27], namely I q ∝ I r 1 with typically r = q. This anomaly can be explained phenomenologically by assuming an intensity dependent susceptibility:…”

“…The experiments [4,11,13,[23][24][25][26][27] show that p can be positive or negative, and r should not be an integer. The form of Equation ( 4) is commonly used to describe non-perturbative harmonic generation in solid, albeit the rank (r) can be different for different intensities; it still can be well applied in limited intensity ranges.…”

van der Waals Decoration of Ultra-High-Q Silica Microcavities for χ(2)–χ(3) Hybrid Nonlinear Photonics

“…An essential requirement for second-order nonlinear processes to occur is inversion symmetry breaking, and typical materials include dielectric crystals (for example, lithium niobate and β-barium borate), III–V semiconductors, and organic crystals . Although second- and third-order nonlinearities can coexist in nanoscale structures such as dielectric nanoparticles, nanocrystals, and layered nanomaterials, , conventional nonlinear optical materials with broken inversion symmetry exhibit strong second-order susceptibility that overwhelms other higher-order nonlinearities. Conversely, second-order nonlinear susceptibility vanishes in centrosymmetric crystals and amorphous materials (e.g., liquids, gases, and amorphous solids), and only third-order processes can be utilized in these χ (3) materials.…”