Linear birefringence, an optical property that results from a material's st
ructure and composition, can be used to study dynamic changes in tissue str
ucture, Single, 200 ps-long pulses from a Ho:YAG laser emitting 2.1 pm radi
ation were used to induce changes in the linear birefringence of rat tail t
endon. Such changes were measured on a millisecond timescale, The measured
rate coefficients describing the denaturation are not predicted by previous
studies of collagen denaturation induced by slower, lower-temperature heat
ing. Two types of laser-induced collagen denaturation can be differentiated
: thermal denaturation, which appears rate-limited, and thermomechanical de
naturation, which is observed at higher laser radiant exposures, Neither pr
ocess is described by standard Arrhenius-type kinetic models.