Efficient subnanosecond diode-pumped passively Q-switched Nd:YVO4 self-stimulated Raman laser

Generation of efficient subnanosecond self-stimulated Raman pulses by a diode-pumped passively Q-switched Nd:YVO4/Cr4+:YAG laser is demonstrated. Experimental results reveal that self-frequency Raman conversion can be achieved with a c-cut Nd:YVO4 crystal in a nearly hemispherical cavity. At 2.0 W of incident pump power, the self-stimulated Raman laser produces stable 710-ps pulses at a Stokes wavelength of 1178.6 nm with 7.2 microJ of pulse energy at a 17-kHz repetition rate.     

掺Yb$lt;sup$gt;3+$lt;/sup$gt; 磷硅酸盐微球腔发光特性的探究

本文采用双锥光纤与微球腔耦合系统研究成分为 55.93P₂O₅-3.57Al₂O₃-15Na₂CO₃-20SiO₂的掺Yb³⁺ 磷硅酸盐微球腔的合作上转换发光、下转换激光振荡及其级联拉曼激光振荡等发光特性. 本实验采用中心波长为976 nm、线宽为0.15 nm的单纵模半导体激光作为抽运光源,在掺Yb³⁺磷硅酸盐微球腔中测得中心波长为476.1 nm的蓝色合作上转换荧光,并运用合适的理论模型来解释该合作上转换产生11.9 nm蓝移效应的原因. 同时,在1058.26 nm和1060.02–1126.08 nm处分别测得了由于微球腔谐振产生的下转换单纵模及多纵模激光振荡. 另外,本文首次在同一微球腔中测得了由Yb³⁺下转换激光激发产生的多级级联拉曼激光. 在抽运功率为8.53 mW时,产生的级联拉曼激光可以达到两级,且波长延伸至1300 nm附近. 关键词： 3+磷硅酸盐微球腔')" href="#">掺Yb³⁺磷硅酸盐微球腔 合作上转换 下转换激光 自激发级联拉曼激光     

Compact efficient all-solid-state eye-safe laser with self-frequency Raman conversion in a Nd:YVO4 crystal

An efficient compact eye-safe laser at 1525 nm is presented by use of self-frequency Raman conversion in a diode-pumped actively Q-switched Nd:YVO4 1342-nm laser. At an incident pump power of 13.5 W, the self-stimulated Raman laser produces 1.2 W of 1525-nm average output power at a repetition rate of 20 kHz. The corresponding peak power at 1525 nm is generally greater than 10 kW for repetition rates from 5 to 20 kHz.     

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.     

掺钕微球的受激辐射激光和自受激拉曼散射

采用溶胶-凝胶法在SiO_2微球表面覆盖上一薄层Nd~(3+)掺杂SiO_2,并经电极放电熔融后形成表面光滑的高Q值微球.采用锥光纤将808 nm的抽运激光耦合入钕离子掺杂的高Q值微球形成回廊模,激发产生了1080—1097 nm波段受激辐射激光.由于所产生的激光有足够高的功率密度,在高Q SiO_2微球中激发产生了波长为1120—1143 nm一级自受激拉曼散射激光.推导了锥光纤掺钕微球组合的自受激拉曼散射的输出功率和阈值公式.描述了输出激光的特性:阈值、输出功率、线宽、边模抑制比.     

Nd:YVO4自受激拉曼激光器调Q锁模特性

利用Nd:YVO4激光晶体的自受激拉曼效应,结合Cr:YAG被动锁模技术和倍频技术,实现了结构紧凑的1176 nm和588 nm黄光锁模激光输出。激光器为LD端面泵浦,三镜折叠腔结构,并且采用了透过率为10%的输出镜。Nd:YVO4晶体长度为10 mm,Nd3+离子掺杂质量分数为0.2%,Cr:YAG晶体的初始透过率为67%。10 W激光泵浦时,1176 nm激光平均输出功率为123 mW,调Q包络宽度为6 ns,调Q包络内的锁模脉冲重复频率高达1 GHz。588.2 nm 黄光的平均输出功率为8 mW。     

Spectroscopic characteristics of Pr<Superscript>3+</Superscript> in biaxial La<Subscript>2</Subscript>(WO<Subscript>4</Subscript>)<Subscript>3</Subscript> crystal

A Pr³⁺-doped La₂(WO₄)₃ crystal grown by the Czochralski method has been investigated as a promising laser material. The principal axes of the optical indicatrix and Pr³⁺ concentration of the crystal were determined. The polarized absorption, fluorescence spectra and fluorescence decay curves of the main emission multiplets of the crystal were measured at room temperature. The spectroscopic parameters were obtained by the modified Judd–Ofelt theory combined with the normalized method. The peak stimulated emission cross-sections of the major emission lines were estimated. The good spectroscopic properties imply that the Pr³⁺:La₂(WO₄)₃ crystal is a potential laser gain medium for solid-state laser and self-stimulated Raman laser applications. PACS 78.20.-e; 42.70.Hj     

Coherent decay of positronium bose condensate

The rate of self-stimulated emission of photon pairs by pseudoscalar particles from Bose condensate is calculated. Growing with density, this rate exceeds the density-independent rate of spontaneous two-photon decay at plausible density values of positronium gas, thus opening, in principle, the way to the annihilation gamma ray laser realization.     

Compact efficient self-frequency Raman conversion in diode-pumped passively Q-switched Nd:GdVO<Subscript>4</Subscript> laser

I report the first demonstration of the generation of efficient sub-nanosecond self-stimulated Raman pulses by a diode-pumped passively Q-switched Nd:GdVO₄/Cr⁴⁺:YAG laser. The conversion efficiency for the average power is 7% from pump diode input to self-Raman output and the slope efficiency is up to 14%. At an incident pump power of 2.0 W, the pulse duration, pulse energy, and peak power for the Stokes wavelength of 1175.6 nm were found to be 750 ps, 6.3 J, and 8.4 kW, respectively, with a pulse-repetition rate of 22 kHz. PACS 42.55.Ye; 42.55.Xi; 42.60.Gd     

Spectroscopic properties of Pr 3+ in anisotropic PbWO4 crystal

The polarized absorption spectra, polarized fluorescence spectra, and fluorescence decay curves of Pr³⁺ ions in anisotropic PbWO₄ single crystal, which was grown by the modified Bridgman method, were measured at room temperature. The standard and modified Judd–Ofelt theories, extended to anisotropic crystal, have been applied to analyze the spectra. The spectroscopic parameters, including the Judd–Ofelt intensity parameters _t(t=2,4,6), spontaneous emission probabilities, fluorescence branching ratios, radiative lifetimes, stimulated emission cross sections, and fluorescence quantum efficiencies, were estimated. The good spectroscopic properties show the possible application of the Pr³⁺-doped PbWO₄ crystal as solid-state and self-stimulated Raman laser materials. PACS 78.20.-e; 42.70.Hj     

波长锁定878.9nm激光二极管抽运内腔式YVO_4/BaWO_4连续波拉曼激光器

采用波长锁定878.9 nm激光二极管共振抽运复合Nd:YV04激光晶体,改善热效应的同时提高抽运吸收率,分别以YVO_4和BaWO_4晶体作为拉曼介质,实验和理论研究了晶体性能、谐振腔结构和稳定性对内腔分体式连续波拉曼激光器性能的影响.结果表明:由于内腔分体式拉曼激光器腔长较长,谐振腔稳定性对激光器性能影响较大,选择高增益的拉曼晶体,不仅可获得高拉曼转换效率,还能一定程度上减轻热效应.而平凹腔结构中输出镜的曲率半径越小,拉曼晶体中基频光的功率密度越大,腔的动态稳定区越宽,获得的拉曼激光输出功率更高.最终以30 mm的BaWO_4晶体作为拉曼介质,在抽运功率25.1 W时,获得了3.02 W的连续拉曼激光输出,光-光转换效率达到12%.     

Continuous-wave Raman generation in a diode-pumped Nd3+:KGd(WO4)2 laser

Continuous-wave Raman generation in a compact solid-state laser system pumped by a multimode diode laser is demonstrated. The Stokes radiation of stimulated Raman scattering at 1.181 microm is generated as a result of self-frequency conversion of the 1.067 microm laser radiation in Nd3+:KGd(WO4)2 crystal placed in the cavity. The Raman threshold was measured at 1.15 W of laser diode power. The highest output power obtained at the Stokes wavelength was 54 mW. The anomalous delay of Raman generation relative to the start of laser generation (the oscillation buildup) due to slow accumulation of Stokes photons in the cavity at low Raman gain and Raman threshold dependence not only on the laser intensity but also on the time of laser action are observed.     

Second Stokes 1129 nm generation in gray-trace resistance KTP intracavity driven by a diode-pumped Q-switched Nd:YVO4 laser

A gray-trace resistance KTP (GTR-KTP) second Stokes Raman laser intracavity driven by a diode-pumped acousto-optic Q-switched Nd:YVO₄ laser was first demonstrated in this paper. With an incident pump power of 9.5 W, the intracavity GTR-KTP Raman laser, operating at the repetition rate of 20 kHz, produced the maximum average output power of 860 mW at 1129 nm. The minimum pulse width obtained in this GTR-KTP Raman laser was 10.8 ns. When the GTR-KTP was substituted with a common KTP, a lower average output power of 720 mW and longer pulse width of 15.9 ns were obtained in the common KTP Raman laser under the same pump condition and cavity setup as the GTR-KTP Raman laser. Experimental results indicated that the decreased absorption at the fundamental and Stokes wave in GTR-KTP was beneficial to improve the stimulated Raman scattering performance.     

976 nm激光抽运二氧化硅微球级联拉曼散射激光的研究

利用电极放电产生的电弧高温熔融二氧化硅单锥细纤, 熔融的二氧化硅在表面张力作用下形成表面光滑的微球, 完成高品质因子微球腔的制备. 将976 nm激光通过锥光纤以倏逝场方式高效耦合入微球, 研究具有高能量密度回廊模的微球腔中的三阶非线性现象——受激拉曼散射现象. 在实验中测得了六级级联的拉曼散射激光, 各级拉曼散射激光分别测得单纵模或多纵模; 在抽运光功率不少于582.6 μW时, 测得位于1200 nm附近的拉曼散射激光; 当抽运光功率为3.014 mW时, 测得位于1287.04 nm附近的第六级拉曼散射激光. 关键词： 微球腔 锥光纤 高品质因子 拉曼散射激光     

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.     

Multimode pumped continuous-wave solid-state Raman laser

We demonstrate the continuous-wave operation of a solid-state Raman laser containing a barium nitrate crystal as the Raman medium. The Raman laser, which has a singly resonant cavity, is pumped by multimode radiation. The Raman oscillation threshold is reached at approximately 2 W of pump power. As much as 500 kW/cm2 of Stokes power density at 60-kW/cm2 pump power density is obtained in the cavity.     

Temperature dependence of the raman spectra of carbon nanotubes with 1064 nm excitation

In this report, the near infrared 1064 nm line of an Nd:YAG laser, which has strong thermal effect, was used as the excitation. A temperature dependence of the Raman spectra of carbon nanotubes was observed at different temperatures by varying the incident laser power. The results show that the relative Raman intensities to the tangential stretching mode (G mode) of the higher-order Raman modes within 2500–3500 cm⁻¹ increase with increasing excitation laser power at the sample and the changes in the relative Raman intensities are linear in the excitation laser power. This has not been reported elsewhere. Thorough analysis shows that this is a temperature dependence of double-phonon Raman scattering and maybe provide important information for the studying of CNTs and double-phonon Raman scattering.     

Generation of an ultrashort optical pulse by four-wave Raman mixing in deuterium cooled at 77 K

When a 100-fs Ti:sapphire laser is focused into molecular deuterium cooled at 77 K, rotational stimulated Raman emission is generated based on four-wave Raman mixing. By phase locking the emission lines, the laser pulsewidth was reduced to 40 fs, when a nearly transform-limited pulse was utilized as a fundamental laser. The pulsewidth was further reduced to 20 fs, when a positively chirped pulse was employed. Computer simulation suggests that the Raman emission is strongly chirped and a train of pulses with lower intensities are formed when a chirp pulse is used as a fundamental laser. PACS 42.65.Dr; 42.55.Ye; 42.50-p     

First-Stokes Wavelengths at 1175.8 and 1177.1 nm Generated in a Diode End-Pumped Nd:YVO_4/LuVO_4 Raman Laser

A diode end-pumped acousto-optic Q-switched Nd:YVO_4/LuVO_4 Raman laser is demonstrated. Both YVO_4 and LuVO_4 can work as Raman gain, and slightly different active vibration modes of both crystals can result in different first-Stokes wavelengths. The output characteristic as the Raman competition between YVO_4 and LuVO_4 crystals for the laser systems with both shared cavity and coupled cavity is experimentally investigated.For the shared cavity, simultaneous Raman conversion in both YVO_4 and LuVO_4 crystals is achieved with dualwavelength emission at 1175.8 and 1177.1 nm. The maximum output power of 1.03 W and the conversion efficiency of 10.3% are obtained. The 0.84 W single first Stokes wavelength at 1177.1 nm with LuVO_4 Raman conversion is achieved with the coupled cavity. The results show that the coupled cavity with short Raman cavity can obtain a narrow pulse width. The separated laser crystal and Raman gain media with different vanadates in shared cavity have advantages in achieving dual-wavelength lasers with small frequency intervals.     

Multi-wavelength hybrid gain fiber ring laser based on Raman and erbium-doped fiber

A stable and uniform multi-wavelength fiber laser based on the hybrid gain of a dispersion compensating fiber as the Raman gain medium and an erbium-doped fiber (EDF) is introduced. The gain competition effects in the fiber Raman amplification (FRA) and EDF amplification are analyzed and compared experimentaUy. The FRA gain mechanism can suppress the gain competition effectively and make the present multi-wavelength laser stable at room temperature. The hybrid gain medium can also increase the lasing bandwidth compared with a pure EDF laser, and improve the power conversion efficiency compared with a pure fiber Raman laser.