Yonggui Yu

High-power dual-wavelength laser with disordered Nd:CNGG crystals

We demonstrate the high-power dual-wavelength laser output with disordered Nd:CNGG laser crystals. Continuous-wave output power of 4.03 W was obtained under the incident pump power of 15.62 W. In the passively Q-switched operation, the shortest pulse width, largest pulse energy, and highest peak power were achieved to be 12.9 ns, 173.16 microJ, and 12.3 kW, respectively, with Cr(4+):YAG crystals as the saturable absorbers. By spectral analysis, the output lasers were found to have dual wavelengths. We believed that the passively Q-switched dual-wavelength laser should be possible to be used as a source for the generation of terahertz radiation.

Enhancement of passive Q-switching performance with mixed Nd:Lu x Gd 1−x VO 4 laser crystals

Passive Q-switching operation has been demonstrated with a class of mixed Nd:Lu(x)Gd(1-x)VO(4) laser crystals. With respect to that obtained with Nd:GdVO(4), the passive Q-switching performance, including threshold, pulse energy, and peak power, was found to be greatly enhanced with the mixed vanadate crystals. The shortest pulse width of 6.2 ns, largest pulse energy of 192.5 microJ, and highest peak power of 31.1 kW were obtained at the incident pump power of 13.75 W with the mixed crystal for x=0.5.

Growth and characterization of Nd:Y x Gd 1−x VO 4 series laser crystals

A series of Nd:YxGd1−xVO4 (x=0.17, 0.37, 0.53, 0.63, 0.70, 0.81) mixed laser crystals with doping concentration of 0.5 at.% Nd were successfully grown by the Czochralski method. Thermal properties including the specific heat, thermal diffusion coefficient, and the thermal conductivity were systematically studied. The material constants Ms were calculated and show that the thermal fracture limit of the mixed crystals should be comparable with that of Nd:YVO4. Diode-pumped continuous-wave (CW) laser performance at 1.34 μm and 1.06 μm with a- and c-cut crystals was demonstrated. The influence of different x values on laser performance and emission cross sections was also discussed. All the results show that Nd:YxGd1−xVO4 represents a new series of crystals suitable for application as high-power diode-pumped lasers.

Continuous wave and passively Q-switched laser performance of a Nd-doped mixed crystal Nd:Lu0.5Gd0.5VO4

The authors reported continuous wave (cw) and passively Q-switched laser performances of Nd:Lu0.5Gd0.5VO4 crystal at 1.06μm. cw output power of 6.65W was obtained under the incident pump power of 13.75W with slop efficiency of 51%. In the passively Q-switched operation, the shortest pulse width, largest pulse energy, and highest peak power were achieved to be 6.2ns, 192.5μJ, and 31.06kW, respectively, with Cr4+ doped yttrium aluminum garnet crystals as the saturable absorbers.

Growth, structure and thermal properties of Yb3+-doped NaGd(WO4)2 crystal

Yb3+ : NaGd(WO4)2 single crystal with dimensions O30 × 60 mm2 has been grown by the Czochralski method. XRPD experimental results show that the as-grown Yb3+ : NaGd(WO4)2 crystal belongs to the tetragonal system and the I41/a space group. The high crystalline quality of the as-grown Yb3+ : NaGd(WO4)2 crystals was confirmed by HRXRD. The effective segregation coefficient of the Yb element in Yb3+ : NaGd(WO4)2 crystal growth was measured to be 0.812 using the x-ray fluorescence method. Subsequently, the thermal properties were systematically studied by measuring the thermal expansion, specific heat and thermal diffusion coefficients. The density of the as-grown Yb3+ : NaGd(WO4)2 crystal at 22 °C was measured by using the buoyancy method with a resulting value of 7.143 g cm−3 and almost linearly decreases as the temperature increases due to the thermal expansion. Comparing the thermal properties of several tungstate crystals, we find that the Yb3+ : NaGd(WO4)2 crystal possesses relatively larger anisotropic thermal expansion and specific heat but smaller thermal conductivity than those of other tungstate crystals.

Characterization of mixed Nd:LuxGd1−xVO4 laser crystals

A series of laser crystals Nd:LuxGd1−xVO4 (x=0.14,0.32,0.50,0.61,0.70,0.80) was grown by the Czochralski method. The thermal properties, including the average linear thermal expansion coefficients, thermal diffusion coefficients, specific heats, and thermal conductivities, of the mixed crystals were obtained. The material constants Ms for the thermal stress resistance figure were calculated and showed that the thermal fracture limits of the mixed crystals should be comparable with that of Nd:YVO4. The polarization absorption spectra from 240to1000nm were measured at room temperature and the absorption cross sections at 809nm were calculated. Using the Judd-Ofelt theory, the theoretical radiative lifetimes were calculated and compared with the experimental results. Continuous wave laser performances were achieved with the mixed crystals at the wavelength of 1.06μm when they were pumped by a laser diode. Thermal, optical, and laser properties have shown variation as a function of x and proved that the mixed...

Passive mode-locking performance with a mixed Nd:Lu 0.5 Gd 0.5 VO 4 crystal

Continuous-wave (cw) mode-locking of a diode-pumped Nd:Lu(0.5)Gd(0.5)VO(4) mixed crystal laser is reported for the first time to our knowledge with a simply compact three-mirror cavity. Stable pulses as short as 5.5 ps were generated at a repetition rate of 147 MHz. At the absorbed pump power of 16 W, a mode-locked laser with average output power of 5.31 W was obtained, giving an optical conversion efficiency of 33.2%, and a slope efficiency of 46.7%.

Continuous-wave and passively Q-switched laser performance with a disordered Nd:CLNGG crystal

We demonstrated efficient high-power continuous-wave (cw) and passively Q-switched disordered Nd:CLNGG laser performance. In cw operations, the output power was obtained to be 3.81 W with a slope efficiency of 30.3%. To our knowledge, they are the highest cw power and efficiency with Nd:CLNGG as the gain medium and a laser-diode (LD) as the pump source. Recorded with a spectrum analyzer, no splitting was found in the Nd:CLNGG laser, which is different with that of its isomorph Nd:CNGG. The LD pumped passively Q-switched Nd:CLNGG laser was obtained for the first time to our knowledge. The shortest pulse width, largest pulse energy and highest peak power were achieved to be 12.3 ns, 199.1 microJ and 16 kW, respectively, with Cr(4+):YAG crystals as the saturable absorbers.

Thermal properties of cubic KTa1−xNbxO3 crystals

Cubic potassium tantalite niobate [KTa1−xNbxO3 (KTN)] crystals of large size, good quality, and varying Nb concentration have been grown by the Czochralski method and their thermal properties have been systematically studied. The melting point, molar enthalpy of fusion, and molar entropy of fusion of the crystals were determined to be: 1536.9 K, 12 068.521 J mol−1, and 7.85 J K−1 mol−1 for KTa0.67Nb0.33O3; and 1520.61 K, 15 352.511 J mol−1, and 10.098 J K−1 mol−1 for KTa0.67Nb0.33O3, respectively. Based on the data, the Jackson factor was calculated to be 0.994f and 1.214f for KTa0.67Nb0.33O3 and KTa0.63Nb0.37O3, respectively. The thermal expansion coefficients over the temperature range of 298.15−773.15 K are: α=4.0268×10−6/K, 6.4428×10−6/K, 6.5853×10−6/K for KTaO3, KTa0.67Nb0.33O3, and KTa0.63Nb0.37O3, respectively. The density follows an almost linear decrease when the temperature increases=from 298.15 to 773.15 K. The measured specific heats at 303.15 K are: 0.375 J g−1 K−1 for KTaO3; 0.421 J g−1 K−1 ...

Dual-wavelength neodymium-doped yttrium aluminum garnet laser with chromium-doped yttrium aluminum garnet as frequency selector

We report on a potential source for the generation of terahertz radiation using the well-known neodymium-doped yttrium aluminum garnet as the laser material, and chromium-doped yttrium aluminum garnet (Cr:YAG) as the frequency selector and saturable absorber. Continuous-wave output power as high as 5.28 W at 1052 nm was achieved. With Cr:YAG, the laser has a dual-wavelength output at 1052 and 1064 nm. The maximum average output power, pulse repetition rate, and pulse energy are 3.75 W, 41.2 kHz, and 90.1 μJ, respectively. We also found that the intensity ratio of the two oscillating modes can be tuned by adjusting the pump power.