High-energy LDA switched side-pumped electro-optical Q-switched Nd : YAG ceramic laser

By employing a uniformly compact side-pumping system, a high-energy electro-optical Q-switched Nd:YAG ceramic laser has been demonstrated. With 420 W quasi-cw laser-diode-array pumping at 808 ran and a 100 Hz modulating repetition rate, 50 mJ output energy at 1064 nm was obtained with 10 ns pulse width, 5 W average output power, and 5 MW peak power. Its corresponding slope efficiency was 29.8%. The laser system operated quite stably and no saturation phenomena have been observed, which means higher output energy could be expected. Laser parameters between ceramic and single-crystal Nd:YAG lasers have been compared, and pulse characteristics of Nd:YAG ceramic with different repetition rate have been investigated in detail. The still-evolving Nd:YAG ceramics are potential super excellent media for high-energy laser applications. (C) 2007 Optical Society of America.

Highly efficient diode side-pumped Nd : YAG ceramic laser with 210W output power

We developed a highly efficient diode side-pumped Nd:YAG ceramic laser with a diffusive reflector as an optical pump cavity. A maximum output power of 211.6W was obtained with an optical -to- optical conversion efficiency of 48.7%. This corresponds to the highest conversion efficiency in the side-pumped ceramic rod. Thermal effects of the Nd:YAG ceramic rod were analyzed in detail through the measurements of laser output powers and beam profiles near the critically unstable region. A M-2 beam quality factor of 18.7 was obtained at the maximum laser output power. (c) 2006 Elsevier Ltd. All rights reserved.

Radially polarized and pulsed output from passively Q-switched Nd:YAG ceramic microchip laser

For the first time, to the best of our knowledge, a radially polarized laser pulse was produced from a passively Q-switched Nd:YAG ceramic microchip laser with a piece of Cr4+:YAG crystal as the saturable absorber and multilayer concentric subwavelength grating as the polarization-selective output coupler. The averaged laser power reached 450 mW with a slope efficiency of 30.2%. The laser pulse had a maximum peak power of 759 W, a minimum pulse duration of 86 ns, and a 6.7 kHz repetition rate at 3.7 W absorbed pump power. The polarization degree of the radially polarized pulse was measured to be as high as 97.4%. Such a radially polarized laser pulse with a high peak power and a short width is important to numerous applications such as metal cutting. (C) 2008 Optical Society of America

High-power Nd:YAG planar waveguide laser with YAG and Al2O3 claddings

Thermal effects in Nd:YAG planar waveguide lasers with non-symmetrical claddings are discussed. The heat generated in the active core can be removed more efficiently by directly contacting the active core to the heat sink. Several cladding materials are compared to optimize the heat removal. Furthermore, uniform pumping is achieved with oblique edge-pumping technique. Using quasi-CW pumping at 1 KHz repetition rate, an average output power of 280 W with a slope efficiency of 38% is obtained with a positive unstable resonator. (C) 2008 Elsevier B.V. All rights reserved.

Efficient excitations of radially and azimuthally polarized Nd 3+:YAG ceramic microchip laser by use of subwavelength multilayer concentric gratings composed of Nb2O5/SiO2

Cylindrical vector beams were produced from laser diode end-pumped Nd:YAG ceramic microchip laser by use of two types of subwavelength multilayer gratings as the axisymmetric-polarization output couplers respectively. The grating mirrors are composed of high- and low-refractive-index (Nb2O5/SiO2) layers alternately while each layer is shaped into triangle and concentric corrugations. For radially polarized laser output, the beam power reached 610mW with a polarization extinction ratio ( PER) of 61: 1 and a slope efficiency of 68.2%; for azimuthally polarized laser output, the beam power reached 626mW with a PER of 58: 1 and a slope efficiency of 47.6%. In both cases, the laser beams had near-diffraction limited quality. Small differences of beam power, PER and slope efficiency between radially and azimuthally polarized laser outputs were not critical, and could be minimized by further optimized adjustment to laser cavity and the reflectances of respective grating mirrors. The results manifested, by use of the photonic crystal gratings mirrors and end-pumped microchip laser configuration, CVBs can be generated efficiently with high modal symmetry and polarization purity. (C) 2008 Optical Society of America.

980 nm 抽运下Yb-Tm-Ho 三掺氟磷酸盐玻璃的2 μm 荧光性质

The thermal stability, 2 μm fluorescence properties and energy transfer mechanism in Ho³⁺ doped fluorophosphate glass sensitized by Yb³⁺ and Tm³⁺ were investigated. The characteristic temperatures, absorption spectrum and fluorescence spectrum of the glass sample were measured. ΔT calculated from the characteristic temperatures shows that the thermal stability of fluorophosphate glass is better than fluoride glass. According to the absorption spectrum, several spectroscopic parameters of the glass sample, such as Judd-Ofelt parameters and spontaneous transition probability were calculated and compared with other glass hosts. The largest spontaneous transition probability for Ho³⁺:⁵ I7&rarr⁵I8 transition in fluorophosphate glass which is 78.48 s^-1 indicates that fluorophosphate glass is an appropriate base glass to achieve 2 m fluorescence. From the fluorescence spectrum of the glass sample, the extremely strong 2.0 μm fluorescence intensity is observed, which is higher than the intensity of 1.8 μm fluorescence, showing that Ho³⁺ ions sensitized by Yb³⁺ and Tm³⁺ is efficient. Meanwhile, the absorption sections and emission sections of Yb³⁺, Tm³⁺ and Ho³⁺ were calculated and the pumping scheme and energy transfer mechanism among Yb³⁺, Tm³⁺ and Ho³⁺ are discussed. The study indicates that Yb-Tm-Ho tri-doped fluorophosphate glass is a significant sensitization glass system under 980 nm excitation for 2 μm applications.

热处理对共沉淀法制备YAG纳米粉体性能的影响

以Al（NO3）3和Y（NO3）3为原料，采用共沉淀法制备出粒度大小为60-100nm，颗粒呈球形的纯相YAG纳米粉。研究了前驱物在不同条件下热处理对YAG纳米粉体性能的影响，并对前驱物在焙烧过程中的物相变化进行了观察。发现延长前驱物在低温下的干燥时间会导致晶粒尺寸增大，而采用在晶化温度前后分别进行保温的方法可在较低的温度获得纯相的YAG粉体。对比了焙烧温度和保温时间对产物粒度的影响，结果表明：在保证粉体晶化完全的前提下，升高焙烧温度比延长保温时间对晶粒尺寸有更显著的影响。

Passively Q-switched Nd:YVO4 laser with a Cr4+:YAG crystal saturable absorber

We demonstrate, for the first time as far as Re known, a passively Q-switched operation of a Nd:YVO4 laser in which a Cr4+:YAG crystal and a laser-diode bar are used as the saturable absorber and the pump source, respectively. Stable laser pulses as short as 28 ns with 20-mu J energy can be generated with this laser, which has the advantages of simplicity, high efficiency, and good long-term stability. (C) 1997 Optical Society of America.

Passively Q-switched Yb : YAG laser with Cr4+: YAG as the saturable absorber

By using a continuous-wave Ti:sapphire laser as a pumping source, we demonstrated a passively Q-switched Yb:YAG laser at room temperature with Cr4+:YAG as the saturable absorber. We achieved an average output power of as much as 55 mW at 1.03 mum with a pulse width (FWHM) as short as 350 ns. The initial transmission of the Cr4+:YAG has an effect on the pulse duration (FWHM) and the repetition rate of the Yb:YAG passively Q-switched laser. The Yb:YAG crystal can be a most promising passively Q-switched laser crystal for compact, efficient, solid-state lasers. (C) 2001 Optical Society of America.