US Patent 7170909 Low quantum defect holmium fiber laser

A directly pumped, un-sensitized, holmium, quasi-two level fiber laser is disclosed that is doped with Holmium active ions between 0.1 and 2.0 percent by atomic weight. This yields greater energy efficiency from the laser because up-conversion losses are minimized, mismatches created by sensitizer ions are eliminated by having no sensitizer ions, and thermal loading of the fiber medium of the laser is thereby reduced. In addition, the pump ratio of the fiber laser is 0.9 which yields a very low quantum defect. The low doping percentage of holmium active ions also eliminates any absorption of its own energy because the power of the diode pumping source is sufficient to cause the laser to reach transparency.