“But this process has a penalty,” Baker said. “It’s never 100 percent efficient. What you’re putting in is pump energy, not the high quality light at the wavelength you want. What’s coming out is a much higher quality of light at the specific wavelength that you want, but the remaining energy that isn’t converted into laser light is wasted and converted into heat.”
That loss of energy, Baker said, ultimately limits power scaling and the quality of the laser light, which makes efficiency especially important.
With the aid of a nano-particle ‘dopant,’ they’re able to achieve the 85 percent level of efficiency with a laser that operates at a 2 microns wavelength, which is considered an “eye-safer” wavelength, rather than the traditional 1 micron. Of course, Baker pointed out, no laser can be said to be safe when it comes to the human eye.
The danger arises from the potential of scattered light to be reflected into the eye during a laser’s operation. Scattered light from the path of a 100-kilowatt laser operating at 1 micron can cause significant damage to the retina, leading to blindness. With an eye-safer laser, operated at wavelengths beyond 1.4 micron, however, the danger from scattered light is considerably lessened.
According to Baker, the nano-particle doping also solves several other problems, such as that it shields the rare earth ions from the silica. At 2 microns, the silica’s glassy structure can reduce the light output from the rare earth ions. The nanoparticle doping also separates the rare earth ions from each other, which is helpful since packing them closely together can also reduce the light output.
(Traditional lasers that operate at 1 micron, using an ytterbium dopant, aren’t nearly as affected by these factors, Baker said.)