Pulsed photothermal radiometry in turbid media: internal reflection of backscattered radiation strongly influences optical dosimetry

• DOI: 10.1364/ao.28.002256
• Publication Date: 2009-03-18T17:09:02Z
• Authors: R. Rox Anderson; Heather Beck; Ulrich Bruggemann; William Farinelli; Steven L. Jacques; John A. Parrish
• Keywords: Collimated light; Diffuse reflection

The integrated irradiance (energy fluence rate) within tissue can exceed the incident due to backscattered and multiply reflected light near sample surface. This was studied quantitatively using pulsed photothermal radiometry, which measures blackbody radiation emitted by a during after absorption of an optical pulse. Aqueous gels containing absorbing dye with or without various scattering materials were fast sensitive IR detector system 1-μs tunable laser. For nonscattering samples, temperature transient (T-jump) laser pulse consistent Beer's law for homogeneous media. When present, increases up almost order magnitude in T-jump observed. given coefficient, there proportional relationship between increase sample's diffuse reflectance. A model describing reflectance at boundary derived explain this result. To test model, refractive index varied air as external medium also matched that BaF2 externalmedium. subsurface is, reasonable approximation, E ≅ E0(1 + 2bR), where E0 is infinitely wide collimated beam, b coefficient strongly dependent on only index, R measured sample. study shows tissues greatly light, effect should be accounted photomedical dosimetry research.