Saturable second harmonic generation in 2D polar metal heterostructures

In this presentation, I will describe recent advances in using ultrafast coherent multi-dimensional nonlinear optical microscopy to identify resonant electronic excitations in 2D metals. I will demonstrate that resonance matching at harmonic wavelengths results in a population inversion, which in turn saturates SHG transduction. Numerical modeling shows that internal energy transfer on sub-cycle timescales (< 2fs) mediates the population inversion. These effects are determined by atomic-level structure of the 2D metal.