Optothermal skin pigment spectral depth profiling using an OPO laser

Abstract

This paper presents the results of a research programme to quantify the factors that determine the visual appearance of human skin. We use in-vivo opto-thermal transient emission radiometry (OTTER) with a tunable OPO laser (400-590nm) to measure spectrally resolved pigment depth profiles. Radiation in this wavelength range is only weakly absorbed by stratum corneum and epidermis, but strongly absorbed by sub-surface pigments, mainly melanin and haemoglobin. These produce characteristic delayed thermal wave (DTW) signals, detected using a high speed Mercury Cadmium Telluride detector sensitive in the wavelength range 6-13 microns. The measured intensity-time profiles yield the desired concentration depth profiles through either model-based non-linear least-squares analysis or model-independent inverse analysis. Results on melanin and haemoglobin distributions within normal, tape stripped and wash-damaged skin are presented.