Diode pumped solid state mid-IR lasers for medical applications

The spectral region between 2 and 3 microns is of particular interest for medical applications because of the water absorption bands near 2 and 3 microns which lead to strong laser-tissue interactions. Recently we have tuned the tripositive thulium rare earth ion so that it can generate laser wavelengths over the spectral regions between 1.85 to 2.15 microns and between 2.20 to 2.37 microns continuously. Both laser systems, which operate CW, can be resonantly pumped with AlGaAs laser diodes operating at 785 nm. There has also been some interest in employing the 2 micron laser in a Q-switched mode. The thulium ion, however, has a low cross-section for the 2 micron transition so that efficient Q-switched operation has not been achieved in this ion. The traditional approach to the diode-pumped 2 micron laser has been to utilize crystals doped with both thulium and holmium ions. The thulium ion absorbs the pump radiation from AlGaAs diode lasers, while the laser transition takes place on the holmium transition at 2.1 microns which has a higher stimulated emission cross-section