Time-dependent reflection and surface temperatures during CO 2 laser irradiation of dental hard tissues with 100-μs pulses

Abstract

We present time-resolved reflection and surface temperature measurements of dental hard tissue irradiated with 100-microsecond(s) CO 2 laser pluses at two different wavelengths (9.6 and 10.6 micrometers ). The fluences in these single-pulse experiments ranged from 1 to 6 J/cm 2 . Time-resolved temperature measurements indicate enhanced energy coupling (absorption) for the 9.6-micrometers laser light at fluences >= 6 J/cm 2 compared to irradiation at 1 J/cm 2 . At the same time we observe a marked reduction in surface reflection. These results are consistent with a transition from strong, relatively narrow band absorption at low temperatures (low fluences) to weaker and broader band absorption (lower absorption coefficient) at higher temperatures. Near an absorption resonance the decreased absorption coefficient leads directly to reduced reflection losses and thus increased energy coupling to the target.