Estimation of Spectral and Thermal Effects on the Optical Beam for the Choice of a Lens for Photothermal Therapy

摘要

Photothermal therapy requires focusing of a beam on a tissue for the therapy. One such development work involves use of a halogen lamp and planoconvex lens to focus a broadband beam to achieve certain beam diameter depending on the tissue surface to be treated. For the system development, it is observed that the lens operating temperature reaches to ～130 °C in steady state condition. So, there is need to estimate the effect of variation in the wavelength of light, as well effect of thermal operating conditions for a suitable lens material. So, the variation in focal length as well spot diameter of fused silica and borosilicate crown (BK-7) plano-convex lenses is analyzed by using ZEMAX software considering the change in incident wavelength and operating temperature of the lens. It is observed that the effective focal length of the fused silica lens varies considerably as compared to that of BK-7 lens due to change in temperature and incident wavelength.