5.4 - Optical isolators for high-power 1.06-micron glass laser system

Five glasses, four diamagnetic and one paramagnetic, were evaluated as Faraday rotation optical isolator materials. For each glass, absorbance, relative beam-spread degradation, and passive extinction ratio were measured. A number of notched-bore electromagnets and a permanent magnet, which were used in the evaluation of these glasses as isolators, are described. Measurements on a 15-mm-diameter by 55-mm-long rod of terbium-doped alumina silicate at room temperature and in a magnetic field of 6000 gauss, using 1.06-micron amplified spontaneous emission as a source, yielded forward-to-backward ratios of 30 dB over a 1-cm-diameter aperture. Measurements conducted at 0.633 microns on a well-annealed lead-glass sample resulted in forward-to-backward ratios of 45 dB. An analysis is included of the factors limiting high forward-to-backward ratios and experimental details of several completed isolators are given.