Efficient Upconversion Blue Laser Source

An efficient blue laser concept is proposed based on two-photon upconversion of diode laser near-IR radiation into the blue in a doped-crystal fiber. The upconversion process offers certain performance advantages not readily realized from a system containing nonlinear elements, such as resistance to damage and more relaxed requirements on the laser medium. With thulmium as the doping ion, wavelenghts in the 450-560 nm range are readily realized as was already demonstrated, mostly in fluoride crystals and glasses. We propose alternative host crystals which, based on calculations by Dr. Gruber, our collaborator on this project, have more optimal conditions for upconversion when doped with Tm, due to favorable branching ratios and cross sections. Another key element in our approach is the use of crystal fibers which are known to possess low thresholds and are therefore highly advantageous for the transitions considered, some of which are quasi-three-level by nature. While the proposed project targets the 450-460 nm spectral range, extention to other wavelengths in the blue, blue-green and red region are possible using alternative active ions (such as erbium and praesidymium) based on the same general concept of upconversion in crystal fiber lasers.