Enhancement of laser radiation coupled into turbid media by using a unidirectional mirror

This article analyzes a simple method for the enhancement of laser radiation coupled into deep layers of turbid samples. This is accomplished by using a multilayer dielectric bandpass filter that acts as a unidirectional mirror and reflects photons re-emerging from the sample back into it. The research establishes a theoretical framework, and a very basic feasibility study is performed. In this study, laser intensity, delivered through a 14 mm slab of tissue, and a 3.9 mm pharmaceutical tablet were enhanced by factors of 1.6 and 3.8, respectively. Potential applications include photothermal and photodynamic cancer therapies of subsurface tissue, deep optical spectroscopy and imaging of biological tissue and powders, as well as thermal and optical subsurface treatment of powder materials, colloids, and catalysts. (c) 2008 Optical Society of America.