Simple Yet Effective Method to Determine Multiphoton Absorption Cross Section of Colloidal Semiconductor Nanocrystals

Colloidal semiconductor nanocrystals (NCs) are on the vanguard of nonlinear optical materials due to their superb optical properties including tunable multiphoton absorption (MPA) with large absorption cross sections. So far, investigating MPA of NCs has been regarded as a difficult task, mostly constrained by the lack of measurement techniques with high precision and consistency. Here, an alternative method to measure the MPA cross section of luminescent NCs is presented. The new method, referred to as multiphoton absorption photoluminescence saturation (MPAPS), does not depend on any specific property of an NC sample, allowing for a precise comparative study of NC samples either holding different structures (e.g., core-only or core–shell heterostructure) or exhibiting slow multicarrier dynamics (e.g., engineered NCs for reduced Auger rates).