Highly efficient 1063-nm continuous-wave laser emission in Nd:GdVO4

Highly efficient 1-microm continuous-wave laser emission in 3-mm-thick, 0.5- and 1.0-at. % Nd:GdVO4 crystals longitudinally pumped at 879 nm into the laser emitting level is reported. Under Ti:sapphire pumping, the slope efficiency in absorbed power is approximately 80% for both crystals, while the slope efficiency, the optical-to-optical efficiency (at 1700-mW pump power), and the laser threshold in incident power are 79%, 78%, and 31 mW for 0.5-at. % Nd and 80%, 77%, and 40 mW for 1.0-at. % Nd, respectively. The slope efficiency is close to the quantum defect limit, the difference being fully accounted for by the residual optical losses. Under 879-nm diode laser pumping, the slope efficiency and the optical-to-optical efficiency in absorbed power of the 0.5-at. % Nd:GdVO4 crystal are 60% and 53%, owing to poorer superposition of the pumped and the laser mode volumes.     

不同泵浦光下Nd:GdVO4晶体输出特性

为研究808 nm和879 nm两种泵浦光对Nd:GdVO4晶体激光输出特性的影响,并比较两种不同波长泵浦所得连续输出光的效率高低,分析了Nd:GdVO4晶体的能级结构和两种泵浦光作用下的激光输出特性,发现在879 nm也有较强的吸收峰.用808 nm和879 nm两种不同波长泵浦Nd:GdVO4晶体的过程是不同的,808 nm泵浦是一种间接方式能量转移的过程,在此过程中有明显的热负载产生.而879 nm泵浦是将粒子直接激励到激光辐射上能级,降低无辐射弛豫过程产生的热量.从理论上可知,879 nm的泵浦量子效率要高于808 nm的泵浦量子效率,对减少晶体的热产生有很强的优势.实验中采用激光二极管端面泵浦Nd:GdVO4晶体直腔方案,研究了两种不同泵浦光泵浦Nd:GdVO4晶体以获得1 063 nm的连续光,得到了两种光抽运时的斜效率,发现在同样实验条件下,879 nm泵浦的输出光斜效率在小功率泵浦时略高于808 nm|而在大功率泵浦的情况下明显高于808 nm,最高达到38%.同时,在808 nm抽运时,实验上获得了1 341 nm波长的激光,为光通讯的应用提供了一种光源.     

Efficient pulse operation of Nd:GdVO4 laser with AO Q-switch

We realized an efficient laser diode-pumped Nd:GdVO₄ laser with crystals grown by the floating zone method. In the lasing experiment, a slope efficiency of 78% was achieved with a 1 at.% Nd-doped crystal by pumping at 879 nm. Furthermore, excellent pulsed laser operation was demonstrated with the Nd:GdVO₄ crystal by using an acousto-optical (AO) Q-switch. A pulse width of 7 ns was observed when the pulse-repetition frequency was 40 kHz. It is the shortest pulse width recorded in the case of the AO Q-switched Nd:GdVO₄ laser.     

High-efficiency Nd:YVO4 laser emission under direct pumping at 880 nm

We report a high-efficiency Nd:YVO₄ laser pumped by an all-solid-state Q-switched Ti:Sapphire laser at 880 nm in this paper. Output power at 1064 nm with different-doped Nd:YVO₄ crystals of 0.4-, 1.0- and 3.0-at.% under the 880 nm pumping was measured, respectively. Comparative results obtained by the traditional pumping at 808 nm into the highly absorbing ⁴F_5/2 level were presented, showing that the slope efficiency and the threshold with respect to the absorbed pump power of the 1.0-at.% Nd:YVO₄ laser under the 880 nm pumping was 17.5% higher and 11.5% lower than those of 808 nm pumping. In a 4-mm-thick, 1.0-at.% Nd:YVO₄ crystal, a high slope efficiency of 75% was achieved under the 880 nm pumping, with an optical-to-optical conversion efficiency of 52.4%.     

Laser performance of highly neodymium-doped yttrium aluminum garnet crystals

The laser performance of highly neodymium-doped yttrium aluminum garnet (YAG) crystals is reported. In cw laser-diode pumping, a slope efficiency of 54% was achieved for a 2-at. %-doped sample, which was comparable with the slope efficiency of 55% of YVO(4) . The crystal also exhibited a slope efficiency of 64% under pulsed Ti:sapphire pumping. Such a high efficiency suggests a total cavity loss of ~1% , which is as low as that of commercially available 1-at. % YAG crystal. The excellent performance of the neodymium-doped YAG crystals indicates their high optical quality.     

Efficient, resonantly pumped, room-temperature Er3+:GdVO4 laser

We report an efficient room-temperature operation of a resonantly pumped Er3+:GdVO4 laser at 1598.5 nm. The maximum continuous wave (CW) output power of 3.5 W with slope efficiency of 56% was achieved with resonant pumping by an Er-fiber laser at 1538.6 nm. With pumping by a commercial laser diode bar stack, a quasi-CW (QCW) output of 7.7 W and maximum slope efficiency of ~53% versus absorbed pump power were obtained. This is believed to be the first resonantly (in-band) pumped, room-temperature Er3+:GdVO4 laser.     

Laser emission in highly doped Nd:YAG crystals under (4)F(5/2) and (4)F(3/2) pumping

A comparison of laser emission in highly doped (2.4-and 3.5-at. %) Nd:YAG crystals is made for conventional 808-nm pumping in F(5/2)(4) and resonant pumping at 885 nm in the band that collects the hot transitions Z(2)?R(1) and Z(3)?R(2) of I(9/2)(4)?F(3/2)(4) absorption. A systematic improvement of the laser parameters (slope efficiency and emission threshold) in absorbed power under hot-band pumping is observed, as expected from the reduction of the pump's quantum defect. Together with the expected reduction of heat generation, resonant hot-band pumping in concentrated components shows prospect for greatly increasing the emission capabilities of the Nd:YAG lasers.     

Neodymium concentration dependence of 0.94-, 1.06- and 1.34-μm laser emission and of heating effects under 809- and 885-nm diode laser pumping of Nd:YAG

Laser emission in the 0.94-, 1.06- and 1.34-micron ranges in diluted and concentrated Nd:YAG crystals longitudinally pumped by a 885-nm diode laser on the ⁴ I _9/2→⁴ F _3/2 transition is investigated. Continuous-wave operation at watt level in all these wavelength ranges is demonstrated with a 1.0-at. % Nd:YAG crystal; however, the laser performance is impeded by the low pump absorption efficiency. Improved output power and overall efficiency were obtained with a highly doped 2.5-at. % Nd:YAG crystal: 5.5 W at 1.06 μm and 3.8 W at 1.34 μm with 0.38 and 0.26 efficiencies, respectively. Comparative results with traditional pumping at 809 nm into the highly absorbing ⁴ F _5/2 level are presented, showing the advantage of the direct ⁴ F _3/2 pumping. The influence of the lasing wavelength and of the Nd concentration on the thermal effects induced by the optical pumping in the laser material is discussed. A clear relation between the heat generated in the Nd:YAG crystals in lasing and non-lasing regimes, a function of the Nd doping, is demonstrated. PACS 42.55.Rz; 42.60.By; 42.60.Da     

Lasing characteristics and optimizations of a diode-side-pumped Tm, Ho:GdVO4 laser

A diode-pumped Tm, Ho:GdVO4 laser with a side-pumping configuration is demonstrated for the first time to our knowledge. Optimum Tm and Ho dopant concentrations for GdVO4 are somewhat lower than those for garnet and fluoride crystals. With a 3% Tm, 0.3% Ho:GdVO4 crystal an output energy of 31.2 mJ and a slope efficiency of 14.5% were obtained in normal-mode operation at room temperature.     

Thermally-boosted pumping of Nd:LiYF<Subscript>4</Subscript> using Ti:Sapphire laser

We report for the first time (to our knowledge) a 1053 nm Nd:LiYF₄ (Nd:YLF) laser by directly pumping into the upper lasing level with a tunable Ti:sapphire laser. The results obtained for direct upper laser level pumping at 872 and 880 nm of Nd:YLF were compared with traditional 806 nm pump band excitation. Highly efficient 1053 nm continuous-wave (CW) laser emission under direct pumping at 880 nm in an 8 mm thick, 1.0 at % Nd:YLF crystal is obtained. The slope efficiency is improved from 39.1% for traditional pumping at 806 nm to 63.9% for direct pumping at 880 nm.     

Nd∶YVO4/Nd∶GdVO4双波长激光器的功率均衡实验研究

实验研究了Nd∶YVO4/Nd∶GdVO4双波长激光器在不同抽运功率条件下,通过调节热沉温度达到功率均衡时的输出特性.实验结果表明:对于Nd∶YVO4/Nd∶GdVO4双波长激光器,当提高抽运功率,需要重新降低热沉温度达到功率均衡输出,降温幅度与抽运功率增加之比为11.23℃/W.与此同时,随着抽运功率和热沉温度的变化,双波长激光器的中心波长会出现小幅度的漂移,左峰波长随抽运功率增加的蓝移速率为0.056 nm/W,右峰波长随抽运功率增加的蓝移速率为0.054 nm/W.实验还发现功率均衡条件下激光器的输出总功率随抽运功率的增加而增加,拟合斜效率为8.7%,当抽运功率为5.58 W时,输出最大总功率达到115.7 mW.     

Intracavity optical parametric oscillator at 1.5-7-μm wavelength pumped by passive Q-switched Nd:GdVO4 laser

A high-repetition-rate eye-safe optical parametric oscillator(OPO),using a non-critically phase-matched KTP crystal intracavity pumped by a passively Q-switched Nd:GdVO4/Cr4 :YAG laser,is experimentally demonstrated.The conversion efficiency for the average power is 7% from pump diode input to OPO signal output and the slope efficiency is up to 10.3%.With an incident pump power of 7.3 W.the compact intracavity OPO(IOPO)cavity,operating at 15 kHz,produces an average power of 0.57 W at 1570 nm with a pulse width as short as 6 ns.The peak power at 1570 nm is higher than 6.3 kW.     

Continuous-wave high-power multi-pass pumped thin-disc Nd:GdVO4 laser

A thin-disc Nd:GdVO₄ laser in multi-pass pumping scheme was developed. Continuous-wave output power of 13.9 W at 1.06 μm for an absorbed power at 808 nm of 22 W was demonstrated from a 250-μm thick, 0.5-at.% Nd:GdVO₄ in a 4-pass pumping; the slope efficiency in absorbed power was 0.65, or 0.47 in input power. Output performances were also investigated under diode laser pumping at 879 nm, directly into the emitting ⁴F_3/2 level: maximum power of 3.6 W was obtained at 6.2 W of absorbed power with 0.69 slope efficiency. Compared with pumping at 808 nm, into the highly absorbing ⁴F_5/2 level, improvements of laser parameter in absorbed power (increase of slope efficiency, decrease of threshold) were obtained, showing the advantages of the pumping into the emitting level. However, the laser performances expressed vs. the incident power were modest owing to the low absorption efficiency at 879 nm. Thus, increased number of passes of the medium would be necessary in order to match the performances in input power obtained under 808-nm pumping.     

Comparison of 885 nm pumping and 808 nm pumping in Nd:CNGG laser operating at 1061 nm and 935 nm

A Nd:CNGG laser operated at 935 nm and 1061 nm pumped at 885 nm and 808 nm, respectively, is demonstrated. The 885 nm direct pumping scheme shows some advantages over the 808 nm traditional pumping scheme. It includes higher slope efficiency, lower threshold, and better beam quality at high output power. With the direct pumping, the slope efficiency increases by 43% and the threshold decreases by 10% compared with traditional pumping in the Nd:CNGG laser operated at 935 nm. When the Nd:CNGG laser operates at 1061 nm, the direct pumping increases the slope efficiency by 14% with a 20% reduction in the oscillation threshold.     

Crystal growth,spectroscopic and CW laser properties of Nd<Subscript>0.03</Subscript>Lu<Subscript>2.871</Subscript>Gd<Subscript>0.099</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript> crystal

Nd_0.03Lu_2.871Gd_0.099Al₅O₁₂ (Nd:LuGdAG) crystal was grown by the Czochralski method. The absorption, fluorescence spectra and fluorescence lifetime of Nd:LuGdAG crystal at room temperature were investigated for the first time. We reported the continuous-wave (CW) Nd:LuGdAG laser operation under diode pumping. Output power of 1.43 W at 1064 nm was achieved with a slope efficiency of 34.1%. All the results show that Nd:LuGdAG crystal is a promising laser material.     

Growth and laser properties of Nd:Ca4YO(BO3)3 crystal

Nd:Ca₄YO(BO₃)₃ (Nd:YCOB) crystal was grown by the Czochralski method, and its structure was measured by using a four circle X-ray diffractometer. The transparent spectrum from 200 to 2600 nm was measured at room temperature. The fluorescence spectrum near 1.06 μm showed that the main emission wavelength of Nd:YCOB crystal was centered at 1060.8 nm. Laser output at 1.06 μm has been demonstrated when it was pumped by a Ti:sapphire laser at the wavelength of 794 nm, the highest output power was 68 mW under pumping power of 311 mW, the pumping threshold was 163 mW and slope efficiency was 46.9%. The self-frequency doubled green light has been observed when it was pumped by a Ti:sapphire or a laser diode (LD). A 14.5 mm Nd:YCOB crystal sample cut at (θ, φ)=(90°, 33°) was used for type I second-frequency generation (SHG) of the 1.06 μm laser pulse. The SHG conversion efficiency was 22%.     

Efficient 1047 nm CW laser emission of Nd:YLF under direct pumping into the emitting level

We demonstrate a 1047 nm Nd:LiYF₄ (Nd:YLF) laser by directly pumping into the upper lasing level with a tunable Ti:Sapphire laser. The results obtained for direct upper laser level pumping at 863, 872 and 880 nm of Nd:YLF were compared with traditional 806 nm pump band excitation. Highly efficient 1047 nm continuous-wave (CW) laser emission under direct pumping at 880 nm in an 8 mm thick, 1.0 at.% Nd:YLF crystal is obtained. The slope efficiency is improved from 55.6% for traditional pumping at 806 nm to 76.3% for direct pumping at 880 nm.     

Crystal growth,spectral and laser properties of Nd:LSAT single crystal

Nd:(La, Sr)(Al, Ta)O₃ (Nd:LSAT) crystal was grown by the Czochralski method. The absorption and fluorescence spectra of Nd:LSAT crystal at room temperature were investigated. With a fiber-coupled diode laser as pump source, the continuous-wave (CW) laser action of Nd:LSAT crystal was demonstrated. The result of diode-pumped laser operation of Nd:LSAT crystal single crystal is reported for what is to our knowledge the first time. The maximum output power at 1064 nm was obtained to be 165 mW under the incident pump power of 3 W, with the slope efficiency 10.9%.     

CW laser properties of Nd:GdYAG,Nd:LuYAG,and Nd:GdLuAG mixed crystals

Three mixed crystals, Nd:GdYAG, Nd:LuYAG, and Nd:GdLuAG, were grown by Czochralski method. We report the continuous-wave (CW) Nd:GdYAG, Nd:LuYAG, and Nd:GdLuAG laser operation under laser diode pumping. The maximum output powers are 4.11, 5.31, and 7.47 W, with slope efficiency of 73.0, 55.3, and 57.1%, respectively. With replacing Lu³⁺ or Y³⁺ ions with large Gd³⁺ ions, the pump efficiency increases.     

High-efficiency Nd:GdVO4 laser at 1341 nm under 880 nm diode laser pumping into the emitting level

Highly efficient 1341 nm continuous-wave laser under 880 nm diode laser pumping in Nd:GdVO₄ crystal is reported. Comparative results obtained by the traditional pumping at 808 nm were presented, showing that the slope efficiency and the threshold with respect to the absorbed pump power under 880 nm pumping was 34.9% higher and 12.6% lower than those of 808 nm pumping. A high slope efficiency of 49.1% was achieved under 880 nm pumping, with an optical-to-optical conversion efficiency of 41.7%.