Blue upconversion laser operation in Tm:YLiF4 at 450.2 nm on the 1D2→3F4 transition, and at 483.0 nm on the 1G4→3H6 transition has been achieved using cw pumping with Ti Sapphire and DCM dye lasers. The 450.2-nm laser was excited by sequential two-photon absorption with 784.5-nm and 648-nm laser sources and was operated at temperatures up to 70 K. The 483.0-nm laser was pumped with a single red-dye laser using a wavelength resonant only with absorption from a metastable intermediate state but not with absorption from the ground state. With this avalanche absorption pumping scheme, 483.0-nm laser emission was observed up to 160 K.

We report the results of time–resolved optical holeburning of Er3+ ions in YLiF4 (0.02%). In earlier work for H//c we described the time evolution of holes burned at 33kG using laser scanning over a frequency of 40MHz1 and we reported, using larger scans, the occurence of optical side holes. We now describe results for H⊥c with scans > 400 MHz using a new Zeeman technique for frequency scanning the optical transition frequencies which allow one to study the time evolution of the holes and their associated sideholes. The hole lineshapes evolve with time reaching a linewidth of ≃ 10 MHz after 600 μs. We identify the source of the time evolution of the hole shape as spectral diffusion resulting from mutual spin flips of the surrounding fluorine nuclei whose flip rates are strongly modified from the bulk rates by the presence of the large magnetic moment of the Er3+ ion which produces a "frozen core". A computer simulation which takes into account the details of the dynamics of the frozen core successfully describes the time evolution of the holes, confirming the dominant role of F nuclear spin flips.

We report on the phonon-induced optical dephasing processes in the 2E-excited states of Cr3+ in BeAl2O4 (alexandrite). We obtain measurements In the presence of (1) a thermal distribution of phonons in equilibrium conditions and (2) a spectrally narrow distribution of resonant phonons in highly nonequilibrium conditions.