High power linearly polarized Raman fiber laser at 1120 nm

An all-fiber linearly polarized Raman fiber laser at 1120 nm is demonstrated. With a 1 070-nm linearly polarized Yb-doped fiber laser as pump source, an output of up to 7.7 W at 1120 nm is obtained with an optical efficiency of 55%. The polarization extinction ratio of the linearly polarized Raman fiber is higher than 18 dB. A numerical simulation model is developed to determine the Raman coefficient of the gain fiber and to evaluate the laser performance. The spectral isolation between the Raman fiber laser and the pump fiber laser is determined to be necessary for further improvements of performance.     

Continuous-wave intracavity Raman laser at 1179.5 nm with SrWO<Subscript>4</Subscript> Raman crystal in diode-end-pumped Nd:YVO<Subscript>4</Subscript> laser

We report a continuous-wave intracavity Raman laser at 1179.5 nm with a SrWO₄ Raman crystal in a diode-end-pumped Nd:YVO₄ laser. The highest output power of 2.23 W is obtained at the laser diode power of 21.2 W corresponding to the slope efficiency of 17.3% and a diode-to-stokes optical conversion efficiency of 10.5%. The dependence of the Raman laser performance on the pump polarization is also studied. The measured Raman thresholds are about 9.3 and 8.3 W in the diode pump laser power for the a- and b-polarized configurations, respectively. The Raman gain coefficients of the c-cut SrWO₄ crystal for a- and b-polarized pumps are estimated to be about 4.9 and 4.7 cm/GW, respectively.     

A compact efficient continuous-wave self-frequency Raman laser with a composite YVO4/Nd:YVO4/YVO4 crystal

We report a low-threshold continuous-wave self-Raman laser with a composite YVO₄/Nd:YVO₄/YVO₄ crystal. The use of the composite crystal can reduce the thermal effects and achieve the low-threshold and high Raman output operation. The Raman threshold is as low as 2.2 W for the 808-nm diode pump. Under the pump of a diode power of 25.5 W, the highest Raman output of 2.8 W is obtained at 1175 nm, corresponding to a slope efficiency of 12% and a diode-to-Stokes optical conversion efficiency of 11%. The power fluctuation is less than 1.1% under the highest Raman output.     

High-power linearly-polarized tunable Raman fiber laser

In this study, we demonstrate an all-fiber high-power linearly-polarized tunable Raman fiber laser system. An inhouse high-power tunable fiber laser was employed as the pump source. A fiber loop mirror(FLM) serving as a high reflectivity mirror and a flat-cut endface serving as an output coupler were adopted to provide broadband feedback. A piece of 59-m commercial passive fiber was used as the Raman gain medium. The Raman laser had a 27.6 nm tuning range from1112 nm to 1139.6 nm and a maximum output power of 125.3 W, which corresponds to a conversion efficiency of 79.4%.The polarization extinction ratio(PER) at all operational wavelengths was measured to be over 21 d B. To the best of our knowledge, this is the first report on a hundred-watt level linearly-polarized tunable Raman fiber laser.     

Continuous-wave Raman laser pumped within a semiconductor disk laser cavity

A KGd(WO?)? Raman laser was pumped within the cavity of a cw diode-pumped InGaAs semiconductor disk laser (SDL). The Raman laser threshold was reached for 5.6 W of absorbed diode pump power, and output power up to 0.8 W at 1143 nm, with optical conversion efficiency of 7.5% with respect to the absorbed diode pump power, was demonstrated. Tuning the SDL resulted in tuning of the Raman laser output between 1133 and 1157 nm.     

Raman fiber laser improvement by using Yb3+-doped fiber

We report here the efficiency improvement in a fiber Raman laser by splicing to it short pieces of 10000-ppm Yb³⁺-doped fibers. The amplified spontaneous emission produced by the doped fiber started the stimulated Raman scattering earlier than the spontaneous scattering in the 350-m silica-fiber cavity. In the best case, when splicing to the cavity 127 cm of doped fiber, the pump threshold decreased from 2.9 down to 1.27 W, representing a 56% improvement. This power was close to the theoretical minimum of 1.25 W for very long fibers. The second stokes signal (1175 nm) was only present when the doped fibers were inserted. At 4-W pump, the non-doped cavity delivered 2 W of first stokes signal (1117 nm) that represent a 50% efficiency compared to ～3 W delivered (～75%) when a 34-cm doped fiber was inserted. This improvement is intended to reduce the cost of fiber Raman lasers because less powerful sources or shorter fibers are necessary to produce more stokes components.     

Efficient continuous-wave and Q-switched operation of a diode-pumped Yb:KLu(WO4)2 laser with self-Raman conversion

Efficient cw and passively Q-switched operation with self-stimulated Raman scattering conversion was demonstrated in a compact diode-pumped Yb:KLu(WO4)2 laser. A cw output power of 3.28 W was obtained with an optical efficiency of 48.2% and a slope efficiency of 78.2% with respect to the incident pump power. Stable Q-switched operation was achieved with a Cr4+:YAG saturable absorber, generating 32.4 microJ fundamental pulses with a duration of 1.41 ns at 1030.6 nm and 14.4 microJ Raman pulses with a duration of 0.71 ns at 1137.6 nm. At an incident pump power of 7.0 W, the average output power reached 0.9 and 0.4 W for fundamental and Raman radiation, with slope efficiencies of 32.1% and 14.1%, respectively.     

An efficient continuous-wave YVO_4/Nd:YVO_4/YVO_4 self-Raman laser pumped by a wavelength-locked 878.9 nm laser diode

We report an efficient continuous-wave self-Raman laser at 1176 nm based on a 20-mm-long composite YVO_4/Nd:YVO_4/YVO_4 crystal and pumped by a wavelength-locked 878.9 nm diode laser.A maximum output power of 5.3 W is achieved at a pump power of 26 W,corresponding to an optical conversion efficiency of 20%and a slope efficiency of 21%.The Raman threshold for the diode pump power was only 0.92 W.The results reveal that in-band pumping by a wavelength-locked diode laser significantly enhances output power and efficiency of self-Raman lasers by virtue of improved pump absorption and relieved thermal loading.     

高效率,窄脉冲1 198.5 nm Ba(NO3)2喇曼激光器

利用1064nm的Nd∶YAG激光抽运振荡腔内的硝酸钡晶体,获得高效率、窄脉冲的喇曼激光输出.硝酸钡晶体由水溶液降温法生长,长度为48 mm.喇曼振荡腔由对抽运光、一阶、二阶斯托克斯光有不同反射率的双色平面镜构成.当抽运光功率达到4.5 W时,获得最高的一阶斯托克斯喇曼激光功率为1.48 W,相应的转换效率为32.9%,并测得斜率效率为40%.由于受激喇曼散射的作用,喇曼脉冲光由抽运脉冲光的19.8 ns压缩为2.4 ns,获得的喇曼激光脉冲波形具有的“上升沿陡峭、下降沿缓慢”的特性,对其形成过程作了定性分析.测得喇曼激光的波长为1 198.5 nm,半峰全宽（FWHM）为1.2 nm.     

Broadband tunable Raman soliton self-frequency shift to mid-infrared band in a highly birefringent microstructure fiber

Raman soliton self-frequency shifted to mid-infrared band(λ 2 μm) has been achieved in an air-silica microstructure fiber(MF). The MF used in our experiment has an elliptical core with diameters of 1.08 and 2.48 μm for fast and slow axis. Numerical simulation shows that each fundamental orthogonal polarization mode has two wide-spaced λZDW and theλZDW pairs located at 701/2110 nm and 755/2498 nm along the fast and slow axis, respectively. Using 810-nm Ti:sapphire femtosecond laser as pump, when the output power varies from 0.3 to 0.5 W, the furthest red-shift Raman solitons in both fast and slow axis shift from near-infrared band to mid-infrared band, reaching as far as 2030 and 2261 nm. Also, midinfrared Raman solitons can always be generated for pump wavelength longer than 790 nm if output pump power reaches0.5 W. Specifically, with pump power at 0.5 W, the mid-infrared soliton in slow axis shifts from 2001 to 2261 nm when the pump changes from 790 nm to 810 nm. This means only a 20 nm change of pump results in 260 nm tunability of a mid-infrared soliton.     

High Power Photonic Crystal Fibre Raman Laser

A cw Raman laser based on a 100-m photonic crystal fibre is demonstrated with up to 3.8 W output power at the incident pump power of 12 W, corresponding to an optical-to-optical efficiency of about 31.6%.. The second order Stokes light, which is firstly reported in a cw photonic crystal fibre Raman laser, is obtained at 1183nm with an output power of 1.6 W and a slope efficiency of about 45.7%.     

Highly efficient cascaded P-doped Raman fiber laser pumped by Nd:YVO4 solid-state laser

A highly efficient cascaded P-doped Raman fiber laser （RFL） pumped by a 1064-nm continuous wave （CW） Nd：YVO4 solid-state laser is reported. 1.15-W CW output power at 1484 nm is obtained while the input pump power is 4 W, corresponding to the power conversion efficiency of 28.8%. The threshold pump power for the second-order Stokes radiation is 1.13 W. The slope efficiency is as high as 42.6%. The experimental results are in good agreement with theoretical ones. Furthermore, the power instability of the P-doped RFL at 1484 nm in an hour is observed to be less than 5%.     

Eye-safe Raman laser at 1532 nm with BaWO<Subscript>4</Subscript> crystal

A diode-end-pumped actively Q-switched eye-safe intracavity Raman laser at 1532 nm is demonstrated, with Nd:YVO₄ as the laser crystal and BaWO₄ as the Raman crystal. The highest average power of 1.5 W is obtained, with an incident pump of 12 W and a pulse repetition rate of 35 kHz, corresponding to a diode-to-Stokes conversion efficiency of 12.5%.     

Power scaling of a continuous-wave and passively Q-switched Yb:KLu(WO<Subscript>4</Subscript>)<Subscript>2</Subscript> laser end-pumped by a high-power diode

The power scaling capacity of a diode end-pumped Yb:KLu(WO₄)₂ laser, operating in the continuous-wave (cw) and passively Q-switched regimes, has been investigated. A cw output power of 11.5 W was achieved with an optical-to-optical efficiency of 41% with respect to the incident pump power, while the slope efficiency amounts to 60%. The passively Q-switchedoperation yielded an average output power of 4.3 W at the fundamental wavelength of 1031.7 nm, and 1.15 W of Raman radiation at 1139.3 nm. The total slope efficiency for Q-switched operation was 40%. The highest pulse energy, duration, and peak power were 170 μJ, 2.2 ns, and 77.3 kW for the fundamental radiation, and 51 μJ, 2.3 ns, and 22.2 kW for the Raman radiation. PACS 42.55.Rz; 42.55.Xi; 42.55.Ye     

高效率599 nm Ba(NO3)2外腔喇曼激光器

橘黄色波段固体激光器在基于荧光探测的生物医学诊断和显示等众多方面有着广泛的实际应用. 报道了利用532 nm的Nd∶YAG倍频激光抽运外置喇曼腔内的硝酸钡晶体,获得高效率的599 nm橘黄色喇曼激光的实验结果.对外置喇曼腔实验装置和运转参量进行了优化,喇曼振荡腔由对二阶斯托克斯光有最优化反射率的腔镜构成,对实验中所得到的二阶斯托克斯喇曼激光脉宽压缩及出现双尖峰的现象进行了分析.当抽运光功率达到4.1 W时,获得二阶斯托克斯喇曼激光功率为710 mW,输出光中心波长为599.38 nm,半峰全宽（FWHM）为1.1 nm,激光器最大光光转换效率为17.5%,斜率效率为24.8%.     

Output Characteristics of High-Power Continuous Wave Raman Fiber Laser at 1239 nm Using Phosphosilicate Fiber

A high-power singlemode Raman fiber laser (RFL) with maximum output power of 4.11 W and maximum power conversion efficiency of 47.40% at 1239 nm is realized using continuous wave 8.4 W Yb-doped double-clad fiber laser as a pump, 700 m phosphosilicate fiber, and a Raman cavity formed by a pair of fiber Bragg grating mirrors at 1239 nm. The output characteristics of the RFL at 1239 nm for different fiber lengths and output mirror reflectance are reported. Theoretical simulation is done to numerically optimize for fiber length and output coupler reflectivity to obtain maximum first Stokes power.     

Eye-safe Raman laser at 1532 nm with BaWO<Subscript>4</Subscript> crystal under direct 880 nm pumping

A highly efficient 880 nm laser diode pumped actively Q-switched Nd:YVO₄/BaWO₄ eye-safe Raman laser is demonstrated. With an absorbed pump power of 10.9 W, 1.7 W of average output power at the Stokes wave-length is generated at a PRF of 40 kHz, corresponding to a diode-to-Stokes conversion efficiency of 15.6%.     

800 mW/1484 nm highly efficient two-cascaded phosphosilicate Raman fiber laser pumped by Nd:YVO4 solid-state laser

Using 1064 nm CW Nd:YVO₄ solid-state laser as a pump, 1-km phosphosilicate fiber and cascaded cavities with two pairs of fiber Bragg grating mirrors for 1239 and 1484 nm, we obtained a CW 800 mW/1484 nm Raman fiber laser (RFL) for an actual incident pump power of about 2 W (Nd:YVO₄ power of 6.90 W). The conversion efficiency is as high as 40%. To the best of our knowledge, this is the highest conversion efficiency of RFL pumped by solid-state laser. The output power instability at 1484 nm in half an hour is less than 3%. In addition, the numerical simulations are also performed. Good agreement between the results of numerical simulation and the results of the experiment has been demonstrated.     

Continuous-wave wavelength conversion for high-power applications using an external cavity diamond Raman laser

We demonstrate continuous-wave (cw) operation of a diamond Raman laser at 1240 nm in an external cavity configuration. The output power increased linearly with pump power with a 49.7% slope efficiency and reached 10.1 W at the maximum available pump power of 31 W. The combination of resonator design with diamond provides a novel approach to power-scalable cw wavelength and beam conversion.     

Passively Q-switched <Emphasis Type="Italic">a</Emphasis>-cut Nd:YVO<Subscript>4</Subscript> self-Raman laser

A passively Q-switched a-cut Nd:YVO₄ self-stimulating Raman laser using a Cr:YAG saturable absorber has been demonstrated for the first time. The maximum average output power of the self-Raman laser at 1176 nm is 347 mW at the incident pump power of 10 W with a pulse repetition frequency (PRF) of 66 kHz. The pulse width, pulse energy of the 1176 nm are found to be 10 ns and 5.6 μJ. The conversion efficiency from diode laser input power to Raman output power is 3.47%.