Nonlinear manipulation of orbital angular momentum spectra with second- and third-harmonic generation in a quasi-periodically poled crystal

Optical orbital angular momentum (OAM), as an important degree of freedom of light, has been attracting extensive attention due to its intrinsic feature of the natural discrete infinite dimension. Manipulation of OAM spectra is crucial for many impressive applications from classical to quantum realms, in particular, nonlinear manipulation of OAM spectra. Here, we realized the nonlinear manipulation of OAM spectra by using the simultaneous second- and third-harmonic generation in a single nonlinear crystal of quasi-periodically poled potassium titanyl phosphate, for fundamental waves with a variety of OAM spectra, especially for customized OAM spectra of the second and third harmonics. The experimental results confirmed the theoretical predictions. Our approach not only provides a way to manipulate OAM spectra at shorter wavelengths that are hard to be directly generated but also may find applications toward multiplexing in classical optics and high-dimensional information processing in quantum optics.