Short and long term stability of the Diomed 630PDT laser evaluated with integrating sphere, power meter, and calorimeter

Abstract

The short and long term stability of the Diomed 630 PDT laser with attached fiberoptic microlens was evaluated by means of integrating sphere, power meter and a calorimetric system. The calorimeter system was designed as a thermal mug with absorbing media (dye and water). Both the tip of the irradiation fiber and the detection probe of a thermocouple thermometer were positioned inside the dye solution and stirred during the measurements. The calorimetric system yielded measurement results consistent with the other two methods, and similar long term variations were observed by all methods. With an indicated laser power of 1 W, the detectors' readings ranged from 0.66 to 1.29 W. For short term stability study, the deviation of laser output assessed by integrating sphere, power meter and calorimetric system were 0.3%, 0.1% and 2.8% with long term deviations of 13%, 7% and 9% respectively. This wide variation in the laser output implies the needs to establish quality control procedures involving measurements pre and post PDT procedures. The calorimetric system has been demonstrated to be a powerful tool for clinical laser QA and maintenance of the calibration factor of the detectors used in this work.