International Cooperative Study of Multiphonon Relaxation of Mid IR Transitions in Laser Crystals with Short Phonon Spectra

University Of Alabama At Birmingham, Birmingham AL

Investigators

Abstract

0140484 Mirov It is proposed to extend a collaborative research effort between the University of Alabama at Birmingham (UAB) and Laser Materials and Technology Research Center of General Physics Institute RAS (LMT RC GPI). The current cooperation in laser spectroscopy, investigations of the fundamental optical properties and optical relaxation processes of the energy of electronic excitation in laser crystals would be continued and broadened to include a comprehensive study of the relaxation processes which affect the optically excited state of promising rare-earth and transitional metal doped laser materials. The proposed research would combine the expertise of the Russian investigators in lasers and fundamental physical processes with the expertise in lasers and laser spectroscopy and state-of-the-art facilities at the University of Alabama at Birmingham. Investigation of the multiphonon relaxation (MR) at the potential mid- IR laser transitions (4- 7 um) in the fluoride, chalcogenide, chloride and bromide crystals with short phonon spectra doped with trivalent rare- earth ions like Pr 3+ , Nd 3+ , Dy 3+ , Ho 3+ , Er 3+ and Tm 3+ and divalent transient metals ions like Ti 2+ , V 2+ , Cr 2+ , Mn 2+ , Fe 2+ , Co 2+ and Ni 2+ will be done. A search of doped crystal matrixes with highly efficient radiative transitions in the mid IR spectral region minimally by-passed by multiphonon relaxation will be provided. In doing so the normal modes of vibrational spectra of crystal matrixes and electronic transitions selections rules for possible types of optical centers of different rare- earth dopants will be considered theoretically. Their influence on both radiative and nonradiative transition rates will be analyzed. After theoretical study the crystal matrixes having the electronic transitions in the mid- IR spectral region with large radiative and low multiphonon relaxation rates will be grown. Site- selective spectroscopic studies and temperature dependent fluorescence kinetics measurements using highly sensitive correlated photon counting technique and highly sensitive in the mid- IR spectral region fast photodetectors will be provided at the potential mid IR laser transitions. The temperature dependencies of multiphonon relaxation rates of practically all optical RE transitions perspective for mid IR lasing will be measured and analyzed. Spontaneous (without temperature simulation) multiphonon relaxation rates will be measured at helium temperatures and calculated theoretically. The calculations will be provided considering nonlinear mechanisms of multiphonon relaxation taking into account the real phonon spectra of crystal matrix and partial level- to level inter- multiplet spontaneous multiphonon relaxation rates. These results will be compared with the simple single frequency approximation of lattice vibrations. Comparison of the theory and experiment will be provided. The quantum yield of fluorescence and absorption and emission cross- sections of corresponding optical transitions will be determined and compared with the predicted ones. The general regularities of the radiative and the multiphonon relaxation rates on the anion and cation masses and unit dimensions of crystal lattice and on the rare- earth ion and optical transition types will be determined. The anticipated result of this research effort is a better understanding of relaxation processes which effect the optically excited states of promising RE and TM doped mid-IR laser materials. The perspectives of obtaining mid-IR lasing including broadly tunable for divalent transient metal ions will be analyzed in different types of above-mentioned crystals.