Crystal growth and spectroscopic characterization of Ni-doped MgGa2O4 belonging to inverse-spinel structure crystal
family are described. Single crystals of this material were grown by floating zone method for the first time. Oxygen gas
flow was essential to minimize evaporation of Ga2O3 during the floating zone crystal growth process. Bubble and
inclusion-free crystals were obtained for the growth rate less than 5 mm/hour. Ni:MgGa2O4 single crystal was
characterized by broadband fluorescence in 1100-1600 nm wavelength range and 1.6 msec room-temperature lifetime. It
could be attributed to the transition of 3T2(3F)→3A(2F) transition of the octahedrally coordinated Ni2+. The internal
quantum efficiency of the near-infrared fluorescence was about 82 % for 1 mol% Ni-doped MgGa2O4 single crystal at
room temperature. The new material is to be very promising for tunable laser applications covering the important optical
communication, eye safe, 1100-1600 nm wavelength.
Raman spectral bandwidths of tellurite glasses are widened by using Raman active components of suitable
concentration in appropriate base glasses. The MoO6 octahedra were found to have high octahedral distortion; therefore,
have high Raman polarizability compared to WO6, NbO6, and TaO6 octahedra and PO4 tetrahedra. This high Raman
polarizability enabled broadening of the spectral width up to ~350 cm-1 while maintaining high Raman scattering
intensities. Although similar bandwidths could be achieved using combined generation of WO6 octahedra and PO4
tetrahedra, the resultant Raman scattering intensity of such glasses is only half of that could be achievable using MoO6.
It is shown that the simplest tellurite glass showing wide spectral broadening is a quaternary system comprising a
network modifier (BaO or Bi2O3) and two Raman oscillators (NbO6 and MoO6 octahedra). Using the newly developed
gain medium gain flattened S+ C+ L ultrabroadband fiber Raman amplifier are designed by solving the inverse
amplifier design problem. The relative gain flatness and the effective bandwidth of new gain medium are better and
larger than those of conventional tellurite fibers.
We demonstrate a 22 dB all-fiber amplifier at 546 nm using Er3+-doped fluoride fiber by forward upconversion pumping
of a 974 nm laser diode. The gain saturation effects and the power conversion efficiency of this amplifier are investigated
in detail based on gain characteristics and numerical simulations.
Visible lasers and amplifiers have potential applications in the fields of optical data storage, spectroscopy, biomedical and
optical local area networks. In this study, Tb3+-Yb3+ co-doped fluorophosphate glasses were synthesized and properties
of the visible emission at 0.54 µm were investigated. A upconversion excitation efficiency from Yb3+ to Tb3+ was studied
by evaluations of a cooperative energy transfer efficiency from Yb3+ to Tb3+ (ηCET) and a back-transfer efficiency from
Tb3+ to Yb3+ (ηBT ) which give positive and negative contribution to upconversion excitation, respectively. The ηCET was
as high as 25 %, and the ηBT was less than 1 % in the fluorophosphate glass. This indicates that Tb3+-Yb3+ co-doped
fluorophosphate glass is promising as new laser and gain media in the 0.54 μm band.
Tellurite glass micro-superspheres (Te-μSSs) were prepared by the surface-tension mold (StM) technique, and their whispering
gallery mode (WGM) resonances have been investigated as the first trial to realize an ultra-broadband Raman
resonator. Micrometer-sized tellurite glass particles were melted on an optical grade glassy-carbon substrate then cooled to
room temperature (StM technique). Resultant Te-μSS possesses a super-spherical shape with high optical transparency. The
size of the partly truncated area, resulting from the contact surface with the substrate, can be controlled by the composition
of the glass and a microsphere with no truncated area was achieved for a glass with 56TeO2-3.5BaO-10.5SrO-8Nb2O5-4WO3-16P2O5 (TBSN-4W-16P) composition. The TBSN-4W-16P μSS was excited at 532 nm, and the WGM resonance
emission attributed to broad Raman scattering of the glass itself was observed. The Q value of the μSS was ≈ 5 × 103.
It was confirmed that the prepared μSSs possess a sufficiently spherical shape and acted as an efficient WGM resonator.
These results predict that the Te-μSS has potential for a novel broadband Raman laser.
KEYWORDS: Terbium, Ytterbium, Energy transfer, Ions, Glasses, Upconversion, Absorption, Energy efficiency, Acquisition tracking and pointing, Temperature metrology
Spectroscopic analyses have been performed on Tb3+ and Yb3+ co-doped in borosilicate glass, to assess their potential as green laser and amplifier gain media. The energy transfer efficiencies between Tb3+ and Yb3+ are clarified based on experimental observations and numerical analyses on the emission decay dynamics.
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