In the proposed research program we plan to develop a series of new tunable solid-state laser materials based on tetravalent chromium (Cr4+) as laser-active ion in various low field dielectric crystal hosts and study their spectroscopic and laser properties. These novel tunable solid state lasers are expected to operate in the technologically important near infrared spectral region between 1 - 2 um. Conventional chromium-doped lasers are based on Cr3+ as an active ion. The spectroscopic and lasing properties of the various new tetravalent chromium-doped laser crystals will be investigated in order to obtain better understanding of lasing mechanisms in these tunable solid-state lasers. One host crystal candidate with suitable tetrahedral sites where Cr4+ ion may substitute for a tetravalent cation will be selected and grown for spectroscopic and laser studies each year. Most promising crystal hosts are various oxide crystals containing the SiO4 or GeO4 tetrahedra in its crystal lattice. Measurements of the absorption spectra, excitation spectra, fluorescence spectra, and fluorescence lifetime as a function of temperature and wavelength will be performed to identify optically active centers. Gain and excited state absorption will be measured to determine possible loss mechanisms in tetravalent chromium-doped crystals. Different modes of laser operation will be investigated. The expected lasing (1-2 um) and forming (500-1000nm) wavelengths by second harmonic generation are important for many possible applications in optical communication, coherent laser radar, night vision technology, remote sensing, range finding, counter measure, infrared semiconductor diagnosis, and medical applications.
