Cavity-enhanced nonlinear frequency conversion and manipulation of vector fields

Frequency conversion via nonlinear optical processes is crucial for applications in both quantum and classical optics. As is well known, the optical nonlinear process in a laser cavity can greatly enhance the conversion efficiency and has been widely used for second harmonic generation (SHG) of the Gaussian mode. However, generally the laser cavity can only support a limited number of resonant modes, and the direct application of arbitrary vector fields within a laser cavity is impractical due to this constraint. Here, based on a nested-ring digital laser cavity, we use two orthogonally placed nonlinear crystals in the cavity and then successfully achieve the cavity-enhanced frequency conversion and manipulation of vector fields. Compared to the extra-cavity method, our configuration enhances the SHG by over 80 times. This method extends the cavity-enhanced nonlinear process from the Gaussian mode to the vector fields. Our method enriches the available toolkit for nonlinear manipulation of vector fields and opens up new possibilities in related areas.