全光纤超短脉冲掺Yb3+光纤环形激光器

讨论了自启动被动锁模掺Yb³⁺光纤环形激光器产生短脉冲的机理，并研制出全光纤结构超短脉冲掺Yb³⁺光纤环形激光器.采用两个976nm半导体激光器级联抽运作为抽运源，高掺杂浓度掺Yb³⁺光纤作为增益介质，利用光纤的非线性偏振旋转效应，得到自启动、十分稳定的ps量级锁模光脉冲.激光器锁模阈值功率260mW，输出功率25mW，锁模光脉冲中心波长1056nm，3dB带宽11.7nm，重复频率20MHz.与其他结构光纤激光器相比，这种全光纤结构具有更高的效率和更好的稳定性. 关键词： 环形光纤激光器 3+光纤')" href="#">高掺杂浓度掺Yb³⁺光纤 自启动 被动锁模     

Evaluation of quenching effects on silica-based erbium doped fiber micro-ring lasers

While micro-ring lasers is a step forward for the miniaturization of fiber lasers, up-conversion quenching due to ion energy transfer may limit the device size and deteriorate system performance. The effect of Er³⁺ concentration quenching on the characteristics of silica-based Er-doped fiber (EDF) micro-ring laser was investigated. In particular, the dependence on Er³⁺ concentration and laser size of threshold pump power and quantum efficiency is discussed. To achieve high laser efficiency, it was found that ring diameter has to be ∼150 μm with ∼5 wt.% erbium concentration. The threshold value is increased by a factor of 340, for such laser characteristics compared with threshold power when up-conversion is not considered. Moreover, we show that detrimental effect due to up-conversion quenching can be reduced by careful micro-ring laser design.     

40K-87Rb原子冷却的半导体激光系统

对⁴⁰K-⁸⁷Rb原子冷却的半导体激光系统提出了一种实验方案，并进行了初步实验.采用三台外腔光栅反馈半导体激光器(ECDL)、四台注入锁定从激光器和一台半导体激光放大器组成激光系统.三台ECDL通过声光调制器产生四束光，分别作为⁴⁰K和⁸⁷Rb原子的冷却光和再抽运光，四束不同频率成分的激光分别注入锁定四台从激光器，然后Rb 冷却光、K冷却光和K再抽运光再同时注入半导体激光放大器进行放大.该装置可同时产生冷却⁴⁰K和⁸⁷Rb原子的冷却光和再抽运光，结构紧凑、工作稳定. 关键词： 简并费米气体 激光器系统 外腔光栅反馈半导体激光器 半导体激光放大器     

Novel shooting method with simple control strategy for fiber lasers

A novel shooting method with excellent simple control strategy is developed for solving the failure to convergence of the traditional shooting methods themselves in fiber lasers model. Compared with the published literature, the novel shooting method provides a clear physical understanding method for getting the threshold pump power and the exact results with given random functions in Yb³⁺-doped fiber lasers and Er³⁺-doped fiber lasers. Then, the results in Er³⁺-doped fiber lasers and Yb³⁺-doped fiber lasers demonstrate that the solutions using the novel shooting method has high accuracy of 10⁻⁸ W with several iteration steps, which have extended the applicable range of the end-pumped power even lower than 1 mW pump power. Furthermore, compared with 1480 nm pump for the threshold and slope efficiencies of the Er³⁺-doped fiber lasers, 978 nm fiber lasers can extend wider scope of application and be pump source in the coming future. Finally, the lower threshold and higher slope efficiency at 975 nm than those of 910 nm pump in Yb³⁺-doped fiber lasers, 975 nm pump laser provides for broad band excellent cladding pump source.     

Feasibility of a laboratory X-ray laser pumped by ultrashort UV laser pulses

In order to allow widespread application of soft X-ray lasers there is a strong effort worldwide to use as small as possible pump lasers for plasma production. Short pulse lasers ( 1 ps), particularly in the UV, have attracted much interest, since extremely high intensities (up to 10¹⁸ W/cm²) can be achieved with a relatively high repetition rate. In this article we discuss their merit for soft X-ray laser pumping and possible solutions to the specific problems, for instance pulse front distortion, nonlinear absorption in window materials, plasma formation by short laser pulses and the relatively low total pump energy.     

Laser crystals and ceramics: recent advances

After a brief examination of known insulating laser crystals and the stimulated emission channels of their generating activator ions, this article reviews recent advances in the development of novel lasing crystals and ceramics, as well as inorganic and organic nonlinear‐laser crystals for χ⁽³⁾ and cascaded χ⁽³⁾ ↔ χ⁽²⁾ frequency converters. Several new modern attractive technologies in the physics and techniques of crystalline lasers are also discussed.     

Modeling and experimental investigation of short pulse Raman microchip laser

The results of experimental and theoretical investigations of passive Q-switch Raman microchip lasers based on Nd³⁺:LSB active medium and Ba(NO₃)₂ Raman crystal are presented. It has been demonstrated that intracavity Raman conversion in the microchip lasers is a simple and efficient method, capable of delivering high power pulses with sub-100 ps duration. Intracavity generation of the 1st Stokes pulses with duration from 180 down to 48 ps and a peak power of 48 kW has been performed and studied. High peak power and short duration of the 1st Stokes pulses in microchip laser with Ba(NO₃)₂ Raman crystal allows to easily perform extracavity harmonic generation and frequency sum mixing in LBO, BBO, and KTP crystals with discrete-tunable wavelength from ∼1200 down to ∼240 nm. We have developed a generalized model of Q-switched Raman microchip lasers, that takes into account spatial inhomogeneity of pump, laser, and Stokes beams, thermalization within the upper and lower multiplets of activator ions in laser medium, and saturable absorber bleaching and recovery. For the microchip lasers with different saturable absorbers, the model achieves very good agreement with the presented experimental results in a wide range of pump powers.     

Compact Two-Color Pr3+-Doped ZBLAN Fiber Lasers

Two-color laser simultaneous oscillation in compact trivalent praseodymium ion (Pr³⁺)-doped ZrF₄-BaF₂-LaF₃-AlF₃-NaF (ZBLAN) fiber lasers is investigated. Fiber pigtails by coating high-reflective visible dielectric films are utilized as fiber mirrors (FMs) to construct compact all-fiber laser cavity. Reflectance/transmittance of FMs is intentionally designed to balance net gains and reduce gain competition of different lasable wavelengths in the constructed fiber lasers. By using two selected FMs with high reflectivity at green-light and low reflectivity at red-light, simultaneous green and red laser emission in all-fiber Pr³⁺-doped ZBLAN fiber laser is obtained. Moreover, simultaneous orange and red laser emission is also achieved with another selected FM of high reflectivity at orange-light and low reflectivity at red-light. Our work will provide an effective and easy method to construct compact special fiber (e.g.,ZBLAN fiber, chalcogenide fiber) lasers.     

Photo-physical properties and amplified spontaneous emission of a new derivative of fluorescein

The synthesis of new high-performance dyes and the implementation of new ways of incorporating the organic molecules into the solid host matrices have produced a great deal of activity in the field of solid-state dye lasers. In this article, the new laser dye, 2-(6-allyl-3-oxo-3H-xanthen-9-yl)-benzoic acid ethyl ester [AXBE] has been synthesized, and its chemical structure was confirmed by ¹H NMR, ¹³C NMR, IR and elemental analysis. This new dye was covalently bonded with methyl methacrylate (MMA) and 2-hydroxy ethyl methacrylate (HEMA) copolymer backbone and evaluated as the active medium of the solid-state laser dye. Its optical properties were experimentally investigated. Amplified spontaneous emission (ASE) and photostability were studied by pumping the dye sample with 355 nm (8 ns) pulsed Nd-YAG laser.     

Investigation on the hydrodynamics of slab x-ray laser plasma by nonuiform line focused laser irradiation

Based on the two-dimensional model,this paper compares the hydrodynamics of slab x-ray laser plasma produced by different nonuniform line focused irradiations.It finds that the average intensity and the duration of laser pulse and the overall shape of the intensity distribution in the focal line have different influences on the plasma.Calculations show that the evolution of temperature variation is more sensitive to the pulse duration and the electron density variation is more sensitive to the pulse intensity.Pulses with duration of 200 ps to 500 ps and with intensity of 0.2 TW/cm 2 to 1.0 TW/cm 2 are proved acceptable in slab x-ray lasers.     

Cr,Nd:YAG self-Q-switched laser with high efficiency output

The high efficient laser performance of self-Q-switched laser in the co-doped Cr⁴⁺,Nd³⁺:YAG microchip with 1.8 mm thickness was demonstrated. The slope efficiency is varied with the reflectivity of output coupler at 1064 nm, and the highest slope efficiency of 26% was obtained for 95% reflectivity of output coupler at 1064 nm. The pulse width, the single pulse energy and the pulse repetition rate for different reflectivity of the output couplers were measured, and the experimental results agree with the numerical calculations of the passively Q-switched rate equations. This can lead to develop the diode laser pumped monolithic self-Q-switched solid-state microchip lasers, especially for the intracavity frequency-doubled solid-state microchip lasers.     

基于公共环形腔耦合的光纤激光器相干合成技术

 为提高光纤激光器无源自调整相干合成阵列的效率、稳定性和可扩展性,提出了基于公共光纤环形腔耦合与单模光纤滤波的光纤激光器相干合成方案。将多个2×2的光纤耦合器分别插入各单元激光器的谐振腔,利用耦合器余下的端口,两两相连构成公共环形耦合腔。采用单模光纤滤波技术,提高了各输出激光束之间相位锁定的稳定性。利用该方案在实验上实现了三路光纤激光器的被动锁相输出,实验测得的远场干涉光斑、输出功率及光谱均表明该方案适于构建性能较好的光纤激光器相干合成阵列。     

Investigation of warm dense matter using time-resolved X-ray absorption spectroscopy with third- and fourth- generation light sources

The advent of high-power lasers has provided insights into laboratory high energy density (>10¹¹ J/m³) physics. In particular, the properties of warm dense matter (WDM) with temperatures of 10⁴–10⁶ K and near-solid densities is a research area that has garnered significant interest recently. However, owing to the high temperatures and pressures associated with WDM, the measurement of fundamental properties is difficult, and insufficient data has been a significant setback in WDM research. Herein, we review recent developments in time-resolved X-ray absorption spectroscopy with synchrotron and X-ray free electron lasers for WDM research. Various physical properties, such as atomic bonding, electronic structures, electron–phonon coupling, and thermal conductivity of various elements in WDM conditions are investigated via this noble X-ray technique at various time scales from 100 ps to 100 fs.     

超强激光-等离子体相互作用过程中的辐射阻尼效应

基于包含辐射阻尼效应的电子运动方程,通过坐标变换,分析了圆极化和线极化超强激光在等离子体中传播时,辐射阻尼效应对电子运动的影响。结果表明:两种极化情况下,辐射阻尼效应都随等离子体密度的增大而增强;在圆极化激光中,激光强度在1023~1026 W/cm2范围(对应于不同的等离子体密度)时,辐射阻尼效应将对电子的运动产生显著的反作用,而对于线极化激光,只有当激光强度远大于极限光强时,辐射阻尼效应才对电子的运动有明显的作用。     

Design considerations and scaling laws for high power convective cooled CW CO2 lasers

Various criteria for designing high power convective cooled CO₂ lasers have been discussed. Considering the saturation intensity, optical damage threshold of the optical resonator components and the small-signal gain, the scaling laws for designing high power CW CO₂ lasers have been established. In transverse flow CO₂ lasers having discharge of square cross-section, the discharge lengthL and its widthW for a specific laser powerP (Watt) and gas flow velocityV (cm/s) can be given byL = 1.4 x 10⁴ p ^1/2 V ^-1 cms andW = 0.04P ^1/2 cms. The optimum transmitivity of the output coupler is found to be almost constant (about 60%), independent of the small signal gain and laser power. In fast axial flow CO₂ lasers the gas flow should be divided into several discharge tubes to maintain the flow velocity within sonic limit. The discharge length in this type of laser does not depend explicitly on the laser power, instead it depends on the input power density in the discharge and the gas flow velocity. Various considerations for ensuring better laser beam quality are also discussed.     

用预泵浦技术实现Cr4+、Nd3+双掺YAG激光器自调Q可控输出

对LD泵浦Cr⁴⁺、Nd³⁺双掺YAG自调Q激光器进行了研究,在连续泵浦和脉冲泵浦下获得了1.064μm调Q偏振激光脉冲输出,脉冲宽度(FWHM)为30ns,单脉冲能量为0.5μJ.采用直流预泵浦技术使Q开关时间的不确定度从×10ms减小到5μs左右,并使激光Q脉冲重复率从1kHz提高到近17kHz,该方法也同样适用于其它被动调Q激光器.     

Nanoimprinted distributed feedback lasers comprising TiO2 thin films: Design guidelines for high performance sensing

Design guidelines for optimizing the sensing performance of nanoimprinted second order distributed feedback dye lasers are presented. The guidelines are verified by experiments and simulations. The lasers, fabricated by UV‐nanoimprint lithography into Pyrromethene doped Ormocomp thin films on glass, have their sensor sensitivity enhanced by a factor of up to five via the evaporation of a titanium dioxide (TiO₂) waveguiding layer. The influence of the TiO₂ layer thickness on the device sensitivity is analyzed with a simple model that accurately predicts experimentally measured wavelength shifts induced by varied superstrate refractive indices. The superstrate refractive index is additionally shown to determine which of the possible waveguiding modes dominates for lasing, indicating a method to flexibly select the polarization of the laser. The detection limit of the sensor system is further discussed, finding an optimum at 7.5· 10⁻⁶ RIU. Wavelength changes caused by dye bleaching must be taken into account for long‐term measurements.     

Tunable erbium-doped fiber ring laser for applications of infrared absorption spectroscopy

We fabricate a low noise erbium-doped fiber ring laser that can be continuously tuned over 102 nm by insertion of the fiber Fabry-Perot tunable filter (FFP-TF) in the ring cavity with a novel cavity structure and the optimal gain medium length. As an application of this fiber ring laser, we performed the absorption spectroscopy of acetylene (¹³C₂H₂) and hydrogen cyanide (H¹³C¹⁴N) and measure the absorption spectra of more than 50 transition lines of these gases with an excellent signal to noise ratio (SNR). The pressure broadening coefficients of four acetylene transition lines are obtained using this fiber ring laser and an external cavity laser diode.     

Advances in vanadate laser crystals at a lasing wavelength of 1 micrometer

Sapphire, garnet and vanadate crystals are the most prominent optical materials, and vanadates play important roles in optics, especially in lasers and nonlinear optics. Neodymium‐doped yttrium vanadate (Nd:YVO₄) is representative and available commercially. Based on Nd:YVO₄, several vanadate crystals are being developed with the goal of fulfilling the need for differential applications and improvement of certain operational aspects, such as with pulsed lasers or high‐power continuous‐wave lasers. In recent years, some important effects, including energy enhancement, bistability of output performance, self‐Raman frequency shifting, etc., and some novel applications, such as quantum optics, pulsed lasers modulated by the two‐dimensional crystals, etc., have been discovered with vanadates as gain materials. In this paper, the preparation, characterization and laser applications of vanadate laser crystals at the lasing wavelength of 1 micrometer, including YVO₄, GdVO₄, LuVO₄, Gd_xY_1–xVO₄ and Lu_xGd_1–xVO₄ (0 < x < 1) doped with Nd³⁺ and ytterbium (Yb³⁺) are systematically reviewed by highlighting the most recent research progress. Their specific properties are presented, generation mechanisms of novel physical effects are discussed, new applications are given and possible future applications proposed by focusing on some potential strengths.