Heuristic model for sum frequency generation in chirped quasi-phase-matching gratings with application to selective, cascaded harmonic generation.

The use of chirped quasi-phase-matching (CQPM) for cascaded harmonic generation (CHG) in a single crystal has gained attraction in recent years. CHG involves multiple stages of second harmonic and sum frequency generation processes, of which their complex dynamics in CQPM structures are not well understood when far from the adiabatic limit. This subsequently poses a challenge to design CQPM structures for the optimization of higher order harmonic generation via cascaded processes. In this paper, we derive a heuristic model with analytical expressions for the approximation of the efficiency, location and length of second harmonic and sum frequency generation processes in CQPM structures in the non-adiabatic, fully nonlinear regime (i.e. with pump depletion). With the developed model, we present a design framework to create cascaded CQPM structures for the generation of any arbitrary harmonic with efficiency close to 100%.

Plasmon-Polaron Coupling in Conjugated Polymer on Infrared Nanoantennas.

We propose and demonstrate a novel type of coupling between polarons in a conjugated polymer and localized surface plasmons in infrared (IR) nanoantennas. The near-field interaction between plasmons and polarons is revealed by polarized photoinduced absorption measurements, probing mid-IR polaron transitions, and infrared-active vibrational modes of the polymer, which directly gauge the density of photogenerated charge carriers. This work proves the possibility of tuning the polaronic properties of organic semiconductors with plasmonic nanostructures.