A Q-switched ruby laser was used to irradiate excised biological tissues. An isolated narrow band emission line was observed at 347 nm on irradiation of collagenous tissues. Temporal pulses at 347 nm were narrower than the laser pulses at 694 nm. Reduced crystalline glutathione yielded narrow band emission at 347 nm that was similar to that for the collagenous tissues. The observed narrow band emission at 347 nm is thought to be due to optical second harmonic generation.
S. Fine and W. P. Hansen, "Optical Second Harmonic Generation in Biological Systems," Appl. Opt. 10, 2350-2353 (1971)