High-power laser bars with emission in the red spectral range for medical applications

摘要

High-power laser bars with emission in the red spectral range (635 - 660 nm) are of great interest for several applications such as display and projection solutions or pumping of Cr:LiSAF solid state lasers. Another field of application is a medical use of red lasers. The German funded project ROLAS combines medical and technical aspects of photodynamic therapy (PDT). One special approach under investigation is a laser bar based multi-port PDT system: To allow the optimum treatment of widespread, complex-shaped tumors a PDT laser system with 8 independently operable fiber outputs is designed, based on two laser bars with 652 nm emission and independently addressable emitters. The necessity of individually addressable emitters leads to a more complex and allows a thermally less optimized package design. In combination with conductive cooling - which is a must for most medical applications - the possibilities for low-temperature operation of the laser bars are severely constricted. Especially for high-power laser bars in the 635-660 nm range operation under the expected unfavourable thermal conditions constitutes an additional challenge: These devices by principle exhibit a strong temperature dependence of their performance due to the comparably weak carrier confinement in the InGaAlP material system.In this paper, based on detailed measurements, an analysis of the temperature dependence of the laser bar performance is carried out and the consequences for mounting and application of the laser bars are shown. The measurements illustrate the significant progress that has been achieved during the last two years in terms of temperature stability by applying specific design measures.