Petrographic microscope image of a fiber of linen partly colored by excimer laser irradiation.
Ultraviolet excimer laser photons lasting 30 ns cause strain in the cellulose of the linen comparable to as much as 2000 years of natural radiation. This strain changes the birefringence of the crystalline structure of the cellulose, and we observe the effect with a polarizing microscope. For details, see the paper by Baldacchini et al. pp. 1278-1285.