Due to the often extreme energies employed, contemporary methods of laser delivery utilized in clinical dermatology allow for a dangerous amount of high-intensity laser light to reflect off a multitude of surfaces, including the patient’s own skin. Such techniques consistently represent a clear and present threat to both patients and practitioners alike. The intention of this work was therefore to develop a technique that mitigates this problem by coupling the light directly into the tissue via physical contact with an optical waveguide. In this manner, planar waveguides cladded in silver with thin-film active areas were used to illuminate agar tissue phantoms with nanosecond-pulsed laser light at 532nm. The light then either refracted or optically tunneled through the active area, photoacoustically generating ultrasonic waves within the phantom, whose peak-to-peak intensity directly correlated to the internal reflection angle of the beam. Consequently, angular spectra for energy delivery were recorded for sub-wavelength silver and titanium films of variable thickness. Optimal energy delivery was achieved for internal reflection angles ranging from 43 to 50 degrees, depending on the active area and thin film geometries, with titanium films consistently delivering more energy across the entire angular spectrum due to their relatively high refractive index. The technique demonstrated herein therefore not only represents a viable method of energy delivery for biological tissue while minimizing the possibility for stray light, but also demonstrates the possibility for utilizing thin films of high refractive index metals to redirect light out of an optical waveguide.

Date Published: 26 February 2015
PDF: 12 pages
Proc. SPIE 9303, Photonic Therapeutics and Diagnostics XI, 93030O (26 February 2015); doi: 10.1117/12.2078994

Published in SPIE Proceedings Vol. 9303:
Photonic Therapeutics and Diagnostics XI
Hyun Wook Kang; Brian J. F. Wong M.D.; Melissa C. Skala; Bernard Choi; Guillermo J. Tearney M.D.; Andreas Mandelis; Nikiforos Kollias; Kenton W. Gregory M.D.; Mark W. Dewhirst D.V.M.; Justus F. Ilgner M.D.; Alfred Nuttal; Haishan Zeng; Laura Marcu; Claus-Peter Richter, Editor(s)