New Oxide Crystals for Solid State Lasers

Selective Laser Spectroscopy of the Bixbyite-Type Yttrium Scandate Doped by Rare-Earth Ions

Yttrium scandate crystals doped by Nd3+ and Tm3+ ions have been successfully grown in the form of fibers using the laser-heated pedestal growth (LHPG) technique. The selective laser spectroscopy methods have identified and distinguished three distinct types of optically active centers associated with Nd3+ and Tm3+ ions. The substitution of Y3+ and Sc3+ for rare-earth ions in the C2 structural site leads to the formation of two distinct basic long-time centers. In Nd3+:YScO3, another type of center (a short-lifetime one) is formed known as the Nd3+-Nd3+ aggregate pair. This center arises from the substitution of Y3+ or Sc3+ for Nd3+ cation in the adjacent MO6 polyhedra that share an edge. In Tm3+:YScO3, the third optical center is formed as a result of the substitution of Y3+ or Sc3+ for Tm3+ in the MO6 octahedra with the C3i site symmetry. The fluorescence decay lifetimes of Nd3+ and Tm3+ ions in the YScO3 crystal structure have been accurately measured and estimated. A Stark level diagram illustrating the splitting of 4F3/2, 4I11/2, and 4I9/2 multiplets of Nd3+ ions has been constructed to show features of the active optical centers with the C2 site symmetry.

Pressure driven polymorphic transitions in nanocrystalline Lu2O3, Tm2O3 and Eu2O3

The crystallite size of the materials considerably influences the material properties, including their compressibility and resistance to external forces and the stability of the crystalline structure; a corresponding study for which, so far, has been limited for the important class of nanocrystalline Rare Earth Sesquioxides (REOs). In the present study, we report the crystallographic structural transitions in nanocrystalline Rare Earth Oxides (REOs) under the influence of pressure, investigated via high-energy X-Ray Diffraction (XRD) measurements. The study has been carried out on three of the REOs, namely Lutetium oxide (Lu2O3), Thulium oxide (Tm2O3) and Europium oxide (Eu2O3) up to the pressures of 33, 22 and 11 GPa, respectively. The diffraction data of Lu2O3 and Tm2O3 suggests the occurrence of irreversible structural transitions from cubic to monoclinic phase, while Eu2O3 showed a transition from the cubic to hexagonal phase. The transitions were found to be accompanied by a collapse in the volume and the resulting Pressure-Volume (P-V) graphs are fitted with the 3rd order Birch-Murnaghan (BM) equation of state (EOS) to estimate the bulk moduli and their pressure derivatives. Our study establishes a qualitative relationship between the crystallite size and various material properties such as the lattice parameters, transition pressure, bulk modulus etc., and strengthens the knowledge regarding the behaviour of this technologically important class of materials.

High-resolution laser induced excitation spectroscopy and decay dynamics of YNbO4:Er3

The rare earth materials have attracted intensive attention due to their strong luminescent characteristic. However, the split fine Stark levels are difficult to be determined. Here we report a room-temperature detection for Stark levels of YNbO₄: Er³⁺ using established laser-induced spectroscopy system with dye laser of superhigh resolution of wavelength at 0.005 nm. From excitation spectra, six split Stark levels of ⁴G_11/2 (Er³⁺) were directly detected. Moreover, nonradiative relaxations of ⁴G_9/2→⁴G_11/2 and ⁴G_11/2→²H_11/2/ ⁴S_3/2 have been observed with weighed lifetimes of 0.70 μs and 6.15 μs, and characteristic green emission of Er³⁺ (@555 nm) yields lifetime of 31.78 μs.

Indium Tin Oxide Nanowire Arrays as a Saturable Absorber for Mid-Infrared Er:Ca0.8Sr0.2F2 Laser

We demonstrated a passively Q-switched Er:Ca_0.8Sr_0.2F₂ laser with indium tin oxide nanowire arrays as an optical modulator in the mid-infrared region. In the Q-switched regime, the maximum output power of 58 mW with a slope efficiency of 18.3% was acquired. Meanwhile, the minimum pulse duration and highest repetition rate of the stable pulse trains were 490 ns and 17.09 kHz, corresponding to single pulse energy of 3.4 μJ and peak power of 6.93 W, respectively. To the best of our knowledge it was the first time that indium tin oxide nanowire arrays were employed as a saturable absorber to make pulse lasers carried out at 2.8 μm. The experimental data show that indium tin oxide nanowire arrays can be employed as a competitive candidate for saturable absorber in the field of mid-infrared solid-state lasers.

Optimized growth of high length-to-diameter ratio Lu2O3 single crystal fibers by the LHPG method

Lu₂O₃ crystals have attracted intense attention due to their great potential in the field of high power solid-state lasers.

Controllable and directional growth of Er:Lu2O3 single crystals by the edge-defined film-fed technique

The sesquioxide Lu₂O₃ single crystal, with high quality and optical homogeneity, has been grown controllably with an oriented seed by EFG method for the first time. The EFG method is promoted to an extremely high temperature of 2450 °C.

Highly efficient dual-wavelength mid-infrared CW Laser in diode end-pumped Er:SrF2 single crystals

The spectral properties and laser performance of Er:SrF₂ single crystals were investigated and compared with Er:CaF₂. Er:SrF₂ crystals have larger absorption cross-sections at the pumping wavelength, larger mid-infrared stimulated emission cross-sections and much longer fluorescence lifetimes of the upper laser level (Er³⁺:⁴I_11/2 level) than those of Er:CaF₂ crystals. Dual-wavelength continuous-wave (CW) lasers around 2.8 μm were demonstrated in both 4at.% and 10at.% Er:SrF₂ single crystals under 972 nm laser diode (LD) end pumping. The laser wavelengths are 2789.3 nm and 2791.8 nm in the former, and 2786.4 nm and 2790.7 nm in the latter, respectively. The best laser performance has been demonstrated in lightly doped 4at.% Er:SrF₂ with a low threshold of 0.100 W, a high slope efficiency of 22.0%, an maximum output power of 0.483 W.

Mid-infrared self-Q-switched Er, Pr:CaF2 diode-pumped laser

A diode-end-pumped self-Q-switched mid-infrared laser was demonstrated with Er³⁺, Pr³⁺ co-doped CaF₂ crystal for, to the best of our knowledge, the first time. Maximum average output power of 262 mW was achieved and the corresponding slope efficiency was 14.9%. Stable self-Q-switched laser pulses as short as 718 ns were obtained with a repetition rate of 52.63 kHz at the center wavelength of 2803.7 nm. This highly compact nanosecond laser using a 3 at. % Er³⁺ and 0.03 at. % Pr³⁺ co-doped CaF₂ crystal is free from any active or passive modulators in cavity, potentially promising for a micro and integrated diode-pumped mid-infrared laser system.

Efficient laser operation based on transparent Nd:Lu2O3 ceramic fabricated by Spark Plasma Sintering

Efficient laser operation of Nd:Lu₂O₃ ceramic fabricated by Spark Plasma Sintering (SPS) was demonstrated. Transparent Nd:Lu₂O₃ ceramic was successfully fabricated by Spark Plasma Sintering and its laser experiment was done. On the ⁴F_3/2 to ⁴I_11/2 transition, the obtained maximum output is 1.25W at the absorbed pump power of 4.15W with a slope efficiency of 38% and two spectral lines at 1076.7nm and 1080.8nm oscillated simultaneously. The slope efficiency of 38% is near two times higher than the previously demonstrated SPSed Nd:Lu₂O₃ ceramic lasers. On the ⁴F_3/2 to ⁴I_13/2 transition, the laser operated at the wavelength of 1359.7nm and the maximum output of 200mW was obtained at the absorbed pump power of 2.7W.

From ScOOH to Sc2 O3 : Phase Control, Luminescent Properties, and Applications

In the controlled synthesis of ScOOH nanomaterials, the surfactant molecule Na3 Cit not only helps to manipulate the crystallographic structures, but also to initiate the transfer from α-ScOOH to γ-ScOOH. Further annealing of ScOOH generates cubic Sc2 O3 with morphologies inherited from respective origins. When doped with lanthanide ions, both ScOOH and Sc2 O3 can be utilized for high-temperature probing and light-emitting-diode lighting.

Efficient high-power continuous wave Er:Lu2O3 laser at 2.85 μm

We report on crystal growth, spectroscopy, thermal conductivity and (4)I(11/2)→(4)I(13/2)-laser performance of Er:Lu(2)O(3). Pumping with an optically pumped semiconductor laser at 971 nm, 1.4 W of cw output power with a slope efficiency of ∼36% at 2.85 µm was obtained at room temperature. This exceeds the Stokes efficiency due to an upconversion process recycling population of the lower laser level back into the upper laser level, yielding the highest efficiency of any Er-sesquioxide laser around 3 µm. Under diode pumping, 5.9 W of output power with 27% of slope efficiency was achieved with an M(2) of 1.2 to 1.4.

Frontiers in passively mode-locked high-power thin disk laser oscillators

Semiconductor saturable absorber mirror (SESAM) mode-locked thin disk lasers define the state-of-the-art performance for high average power and high pulse energy femtosecond laser oscillators. To date pulse energies above 30 µJ and average powers above 140 W have been demonstrated. In this paper we review the achievements of mode-locked thin disk lasers in terms of average power and pulse energy. Stable mode locking requires single transverse mode operation even at the highest average power, which is challenging and therefore addressed in more detail. We then summarize our expectations on the main challenges and limitiations for the next generation of mode-locked thin disk laser oscillators with an average power above 500 W and pulse energies in excess of 100 µJ.

Ceramic Laser Materials

Ceramic laser materials have come a long way since the first demonstration of lasing in 1964. Improvements in powder synthesis and ceramic sintering as well as novel ideas have led to notable achievements. These include the first Nd:yttrium aluminum garnet (YAG) ceramic laser in 1995, breaking the 1 KW mark in 2002 and then the remarkable demonstration of more than 100 KW output power from a YAG ceramic laser system in 2009. Additional developments have included highly doped microchip lasers, ultrashort pulse lasers, novel materials such as sesquioxides, fluoride ceramic lasers, selenide ceramic lasers in the 2 to 3 μm region, composite ceramic lasers for better thermal management, and single crystal lasers derived from polycrystalline ceramics. This paper highlights some of these notable achievements.

Spectroscopy and laser performance of Nd:Lu2O3 crystal

The spectra of Nd(3+):Lu(2)O(3) crystal have been examined at room temperature. Judd-Ofelt theory was applied to calculate the spectral parameters of the crystal. With a laser diode as pump source, a continuous-wave laser output power of 2.81 W is achieved, which is the highest value ever reported in this crystals to our knowledge, and its wavelength is also found to be dual-wavelength. Because of the emission cross-section at 1076 nm and 1080 nm are almost identical, laser oscillation for such two wavelengths can be obtained simultaneously. All the properties show that Nd:Lu2O3 is an excellent crystal for laser applications.

The Structure of C-type Gd2O3. A Powder Neutron Diffraction Study using Enriched 160Gd

The structure of the cubic C-type phase of Gd2O3 has been refined using high-resolution powder neutron diffraction data. The sample was enriched in 160Gd to avoid the high neutron absorption of naturally occurring Gd. The refined structure is in excellent agreement with that estimated using perturbed angular correlation spectroscopy.

Diode-pumped mode-locked Yb:LuScO(3) single crystal laser with 74 fs pulse duration

The mode locking of the mixed sesquioxide single crystal Yb:LuScO(3) is demonstrated. This crystal is locally disordered and has the broadest emission spectrum of all sesquioxides known so far. Pulse durations as short as 111 and 74 fs were obtained using the semiconductor saturable absorber mirror and Kerr-lens mode locking, respectively. The latter regime was reached using a two-section distributed Bragg-reflector tapered diode laser as a pump source.