Several hard host materials are investigated as roomtemperature continuous-wave laser possibilities. These include yttrium aluminum garnet, lanthanum aluminate, and calcium molybdate. Stable divalent dysprosium in CaF2 is obtained by either of two techniques a chemica reduction or solid-state electrolysis. The first crystal obtained using the electrolytic technique gave laser performance as good as the best crystal reduced by gammairradiation. Laser beam patterns were measured, and cw lasers operated using external reflectors. The effects of static, homogeneous magnetic fields on cw CaF2 Dy2 lasers were observed, and two interesting anamolies were found in certain laser crystals. Pumping lamp efficiencies were studied experimentally, and the results were found to be in good agreement with previously described calculations. The electro-optic coefficients, loss tangents, and dielectric constants of GaAs and CuC1 were measured. A microwave-frequency cavity modulator was operated with hexamine.