Stabilization of solid state laser oscillation by coexistence of rare earth ions and color centers

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In addition to the optical study to achieve room-temperature stable color centers lasers using F_3^+, F_2, F_2^+ and F_2^- color centers in LiF crystal, the spectroscopic investigation of optical materials used for rare-earth-ion solid state lasers has been undertaken. The main results are as follows. (1) Laser oscillation experiment was done for the F_3^+, F_2, F_2^+ and F_2^- color centers in LiF crystal, which were created by irradiation with γ-rays, using two-mirror cavity. Laser oscillations by F_3^+, F_2, F_2^+ and F_2^- color centers were achieved. (2) Stable laser oscillation by F_2^+ color centers, however, was not achieved because they are decayed at room temperature immediately after creation. We achieved stable F_2^+ color center laser oscillation at room temperature using the F_2^+ color centers created by photochemical reaction from the stable F_2 color centers. (3) It was confirmed that the LiF color center lasers except the LiF: F_2^- color center laser are not stable and show weak laser output power. (4) We revealed the presence of the higher excited states for the F_2^- and F_3^- color centers, and evaluated the values of absorption and emission cross-sections, oscillator strength, emission efficiency, emission polarization, emission decay time, etc. for these color centers. (5) We observed the energy transfer among the F_3^-, F_4 and F_2^- color centers, and clarified its process. (6) We measured the absorption, emission, two-photon excited emission, and emission decay time of the rare-earth ions in ionic crystals, and we clarified the electron-lattice interaction and relaxation process of Er^<3+>, Yb^<3+>, Tm^<3+>, Ce^<3+>, Tb^<3+>, Eu^<3+>, Eu^<2+> ions and energy transfer between Er^<3+> and Yb^<3+> and between Ce^<3+> and Tb^<3+>. (7) We created the F_2^<+*> and F_2 centers in Eu^<2+>-doped CsI and Eu^<3+>- and OH^--doped LiF crystals by irradiation with γ-rays, from which we clarified the effect of rare-earth ions on the color centers.