Effect of thermal treatment on chitosan CDs in the solid state causes a redshift of PL emission and changes in surface states.

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We present a nonlinear mixing study of Ince–Gaussian (IG) beams in non-collinear sum-frequency generation, completing the fundamental analysis of all three families of paraxial wave equation solutions under this nonlinear process. Through theoretical and experimental results, we consider the nonlinear mixing of even and odd IG modes, and transition between the paraxial modes by controlling the eccentricity parameter ϵ and helical IG modes possessing arbitrary orbital angular momentum. Additionally, the selection rule of IG modes in the nonlinear mixing processes is determined. This work is important for optical communications and quantum protocols.

We generalize the study of Laguerre–Gaussian beams in nonlinear wave mixing processes, considering optical beams with both integer azimuthal and non-null radial mode index as input modes combined in the nonlinear crystal. Here, we present a deeper discussion of the generation of higher radial orders through a nonlinear wave mixing process leading to a more complete understanding of the nonlinear process considered.