Depends on the wavelength/absorption. The goal was to attack both the root and the leaf. There are more mechanical methods using steam + a spike that work very well too.

Here's a very (terribly) high level technology overview from the company we were working with: https://g-neighbor.com/gni-technology/

> The reason a plant is green is because it reflects green light and for photosynthesis a plant uses blue light. Overloading the blue frequency range disrupts the enzymes in the photosynthetic process, which cuts off the food supply to the plant and it dies. Some herbicides overload the metabolic system of the plant and makes the weed burn from the inside out. I thought that overloading the photosynthetic system would maybe do the same thing.