Analysis of thermal therapy using infrared diode lasers operated in continuous wave and pulsed mode

The design (software control) guidelines are presented for medical laser systems based on the analysis of the tissue temperature response to various lasers at both cw and pulsed modes. By solving the laser volume-heating diffusion equation, we analyze the roles of various laser and tissue (or water) parameters on the laser-heated solution temperature profiles, including laser intensity, pulse-width, on-off ratio, absorption and thermal constants of the solution or tissues. Two experimental setups are designed to measure the real-time temperature profiles change under laser interactions with results compared to the computer simulations. One experiment uses nano-gold solution which is heated by a diode laser at 808 nm and temperature increases on the surface and inside the solution are monitored for feedback controlled laser on-off time. The other experiment uses water as the solution and heated by a diode laser at 1450 nm. Our new finding includes the optimal control of the laser on-off time and the adjustment of absorption coefficient by off-resonance excitation. The finding and novel features are analyzed theoretically. Correspondence to: Jui-Teng Lin, New Vision Inc., 5F, No. 27, Lane 10, Jiuquan St. Da-tung Dist. Taipei, Taiwan, Tel: 886-961-306-877; E-mail: [email protected]