This is the second sentence:

> Nonlinear phenomena become relevant only when the input light is very intense. Typically, in order to observe nonlinear phenomena, an intensity of the electromagnetic field of light larger than 108 V/m (and thus comparable to the atomic electric field of ~1011 V/m) is required.

I don’t know anything about this field. Can you address this point? How close are we to overcoming this in academia?

At milliwatt power, and terahertz frequency?

I mean, researchers have been trying for years, what is different now?