Experiments on Indium Tin Oxide (ITO) have revealed that a relatively broad 200THz pump pulse, roughly 30 cycles in width, can switch ITO from a transparent to a reflecting state within one or two optical cycles, a few Femtoseconds. So far the rapid switching has remained unexplained by theory. Here a very simple bare bones theory explains the key experimental features in terms of an avalanche model suggested by avalanche diodes.
Cite
@article{arxiv.2407.08391,
title = {An avalanche model for femtosecond optical response},
author = {J. B. Pendry},
journal= {arXiv preprint arXiv:2407.08391},
year = {2024}
}