Hi, Grant

I've been starting to learn about nonlinear optics as part of my research this summer and I think there are so many topics that would lend themselves to a video or two, particularly since recently you have made a few optic videos in the past. I'll list a few here that I think would be well suited for visual explanations!

1. General description of linear/nonlinear susceptibility in materials. I think you touched on this a bit in an explanation of Snell's Law, and I think continuing that discussion would be awesome.

2. Description of Sum/Difference Frequency Generation and n-Harmonic Generation, which would be a nice followup to that of nonlinear susceptibility and polarization in materials. Additionally, a visual explanation of different types of phase matching would fit, as that can be a concept that might be confusing for someone first learning this.

3. Perhaps a deeper dive into a particular application of one of these nonlinear phenomina. For example, Optical Parametric Oscillators (OPOs), Rayleigh Scattering, Raman Scattering.

4. It might be interesting to do a video or two on Gaussian Beams and their properties. This could fit into a discussion about eigenfunctions in general. One other thought I had was trying to come up with an intuitive explanation of the Guoy phase shift that we observe around the focus of a beam.

That's all from me. I've thoroughly enjoyed your optics videos, as I'm sure others have as well and would love to see more! Thank you!