Lasing without inversion in a four-level diamond system

<正>We study the lasing without inversion in a four-level diamond configuration in the case of incoherent pumping field within the framework of the bare-state basis.With the strong fields limit,we obtain the approximate steady-state solution,and discuss the dependence of population distribution and system gain on probe detuning and auxiliary field Rabi frequency.     

Detection of a new SRS‐promoting phonon mode and cross‐cascaded χ(3)‐nonlinear lasing in single crystals of calcite (trigonal CaCO3)

For calcite (CaCO₃), one of the pioneer crystals in nonlinear optics, new results of stimulated Raman scattering (SRS) spectroscopy are presented. Among them are the discovery of a new SRS‐promoting vibration mode with ω_SRS2 ≈︁ 282 cm^‐1 and its participation, together with the main SRS mode ω_SRS1 ≈︁ 1086.5 cm^‐1, in cross‐cascaded (χ⁽³⁾ ↔ χ⁽³⁾) nonlinear‐lasing generation, as well as the observation of efficient self‐upconversion via cascaded parametric four‐wave processes of one‐micron Stokes and anti‐Stokes χ⁽³⁾‐lasing into the UV‐region of third harmonic generation. The investigations show that calcite is able to generate a χ⁽³⁾‐lasing comb of more than two octaves bandwidth. The article also gives a brief review on the discovery and study of the SRS‐effect in natural crystals (minerals), which have expanded our ability to study the photon‐phonon nonlinear‐laser interactions in crystalline materials. A short summary of information about χ⁽³⁾‐lasing properties of the triangular planar structure units in SRS‐active crystals is included.     

回音壁模式光纤激光器的阈值特性研究

研究了一种新型光纤激光器——消逝波激励的回音壁模式光纤激光器的阈值特性.将不同直径的石英光纤分别浸入低折射率的罗丹明6G乙醇和乙二醇混合溶液中,采用沿光纤轴向光抽运消逝波激励染料增益的方式,发现回音壁模式光纤激光辐射的阈值能量和混合溶液的折射率存在不同的依赖关系.随折射率的增加,对小直径光纤,阈值能量随之增加;对大直径光纤,阈值能量单调缓慢递减;对直径适中的光纤,阈值能量先减后增,存在一个和最小阈值能量对应的最佳折射率.用消逝波激励的回音壁模式激光理论,导出了回音壁模式光纤激光的阈值能量公式.理论计算曲线 关键词： 光纤激光器 回音壁模式 激光阈值 消逝波     

ZnO薄膜的光抽运紫外激射

采用等离子体增强MOCVD方法生长出高质量的ZnO薄膜,并观察到了ZnO薄膜的光抽运紫外激射现象。在不同激发强度下进行了光荧光谱测量,发现紫外发光强度随着激发光强度的增加呈直线增强,证明此紫外发光峰来源于带边自由激子辐射复合。激发的激光器为3倍频YAG激光器,脉宽15ps,每秒10个脉冲。抽运光达到样品的光斑直径约为25μm,激射阈值为0．28μJ,利用光纤连接到CCD来探测接收激射光。在385～390nm之间的激射峰,其半峰全宽为0．03nm。所观察到的激射没有固定的方向,也就是说是往各个方向发射的。对于ZnO薄膜,由于我们并没有制作通常激光器的谐振腔,激射是通过晶粒强烈的散射导致的自形成谐振腔所产生的。     

Bichromatic coherent random lasing from dye-doped polymer stabilized blue phase liquid crystals controlled by pump light polarization

In this paper, we investigate the bichromatic coherent random lasing actions from the dye-doped polymer stabilized blue phase liquid crystals. Two groups of lasing peaks, of which the full widith at half maximum is about 0.3 nm, are clearly observed. The shorter- and longer-wavelength modes are associated with the excitation of the single laser dye (DCM) monomers and dimers respectively. The experimental results show that the competition between the two groups of the lasing peaks can be controlled by varying the polarization of the pump light. When the polarization of the pump light is rotated from 0° to 90°, the intensity of the shorter-wavelength lasing peak group reduces while the intensity of the longer-wavelength lasing peak group increases. In addition, a red shift of the longer-wavelength modes is also observed and the physical mechanisms behind the red-shift phenomenon are discussed.     

Amplified Emissions Spectroscopy for Sensing Applications

Amplified emission spectroscopy is promising for applications of qualitative and quantitative sensing of elements and their states. This technique has the characteristics of a narrow spectral line, high spectral resolution, and high signal‐to‐noise ratio. Recently, this technology has advanced tremendously with progress in excitation methods, that is, resonance multiphoton absorption and filamentation with ultrafast lasers. The mechanism, conditions, excitation, signal processing, and applications of amplified emission spectroscopy are reviewed herein. In particular, the different formation patterns of the amplified emission spectra produced by an ultrafast laser are analyzed in detail. In addition, a brief introduction is given to the existing applications of amplified emission. Finally, both a conclusion and a perspective of the future for amplified emission are presented.     

稳态V型和Λ型无粒子数反转激光增益的比较研究

在相应参量取值相同的情况下,利用数值模拟的方法对比研究了封闭的V型和Λ型原子系统稳态增益随相干光场失谐量的变化规律.研究发现,这两种系统的稳态探测激光增益随探测激光场失谐量的变化曲线具有相似的形状,但数值上存在差异.这一现象与两种系统的原子相干性与粒子数分布的特点直接相关.另外,还发现驱动激光失谐及由于自发辐射诱导相干导致的原子相干性的增强能显著影响探测激光增益. 关键词： 无粒子数反转激光 失谐 原子相干性 粒子数分布     

增益导波垂直腔激光器注入电流空间分布及其对激光近场模式影响的理论分析和表征

依据导电介质的稳态电场理论建立了一种对增益导波型垂直腔半导体激光器注入电流矢量分析的三维解析模型. 计算研究了电流密度空间分布及其与顶面电注入环参量之间的相互关联性. 结果显示在两极之间存在一个载流子径向分布中心极大的区域. 由于激光功率与注入电流之间存在线性关系,因此,要使器件能够获得基模或中心均匀的光强输出以及尽可能低的阈值,应使激光有源层与载流子均匀分布的临界层重合. 计算结果对顶发射与底发射结构以及不同环参数下的载流子分布情况及对近场模式形成的影响进行了分析和讨论. 关键词： 垂直谐振腔激光器 注入电流 激光模式     

用染料激光增益降低二元混合物中少量化合物的受激拉曼散射可探测浓度

在二元混合物构成的圆形谐振腔中,用染料的激光增益增强了少量化合物(乙醇溶液中的甲醇、水溶液中的乙醇)的受激拉曼散射（SRS）光谱,将少量化合物在悬垂液滴中的瞬态SRS探测极限提高了近一个数量级. 用受激拉曼散射理论,解释了增强少量化合物SRS的机理. 关键词： 受激拉曼散射 染料激光增益 二元混合物 最小可探测浓度