三粒子任意态的量子隐形完全传送

提出一个利用六粒子非贝尔对量子通道对一个任意的三粒子量子态进行隐形传送的方案.发送者Alice对需传送的三粒子量子态与属于自己的纠缠对中的三粒子进行三次Bell基测量,并将测量结果通过经典通道告诉接受者,接受者Bob根据这些信息对自己拥有的粒子进行Toffoli变换,就可使这三粒子处于待发送的原始量子态,从而实现概率为1的量子态隐形传送.利用变换算符的思想,很容易得出塌陷态的表达式以及接受者Bob所做的幺正变换的表达式.     

无序介质中不同模式的激光辐射与散射体密度的关系

以ZnO粉末无序介质激光为例,在介质增益和光场损耗的条件下研究了光子在无序介质中的无规行走行为.在泵浦光强和体积一定的情况下,运用数值模拟研究了不同频率的光受激辐射对散射体密度的要求;得到了不同散射体密度下激光的辐射谱：当散射体密度大于临界密度时才能有激光辐射产生;当散射体密度进一步增大时,辐射谱中出现更高更窄的分离尖锋.     

光子晶体晶粒尺寸和排列结构对随机激光辐射特性的影响

研究了光子晶体对随机激光器的输出特性的调控,并分析了光子晶体的晶粒尺寸和排列结构等对调控作用的影响.对于同一随机介质而言,上下表面用同种材料不同晶粒尺寸的光子晶体覆盖,结果显示:晶粒尺寸合适的光子晶体会使光在系统中来回振荡从而得到很好的放大,使系统中的光与随机增益介质的相互作用加强,激光阈值降低;同时还对激光模式有较强的调制能力,能在一定程度上抑制自发辐射,使之向所需要的频率内辐射.但如果光子晶体的晶粒尺寸与随机增益介质结构匹配不当,则光子晶体对激光模式调制能力较弱,光场能量不能有效地被局域在系统中,系统 关键词： 有限时域差分法 光子晶体 随机激光 辐射特性     

Self-tuned quantum dot gain in photonic crystal lasers

We demonstrate that very few (2-4) quantum dots as a gain medium are sufficient to realize a photonic-crystal laser based on a high-quality nanocavity. Photon correlation measurements show a transition from a thermal to a coherent light state proving that lasing action occurs at ultralow thresholds. Observation of lasing is unexpected since the cavity mode is in general not resonant with the discrete quantum dot states and emission at those frequencies is suppressed. In this situation, the quasicontinuous quantum dot states become crucial since they provide an energy-transfer channel into the lasing mode, effectively leading to a self-tuned resonance for the gain medium.     

Random lasing in ZnO nanocrystals

Nanocrystalline ZnO powders can act as gain and scattering medium in a random laser where the light emission can be strongly amplified. In this work, we compare the luminescence properties of samples with different particle sizes in the regime of linear and nonlinear optics. In the high-excitation regime random lasing is observed in all samples. Here, the lasing threshold depends strongly on the size distribution in the ensemble. Additional characterization of the samples has been done by determining the absolute quantum efficiency of the radiative processes in the powder. The values are in the 10% range and the near-edge luminescence is strongly influenced by the particle sizes. We show that by annealing the nanocrystals coalesce to larger polycrystalline grains, which results in a new emission band at 3.333 eV due to the grain boundaries. Furthermore, it is found that in the annealed samples the threshold for random lasing could be considerably decreased.     

Light transport and correlation length in a random laser

A random laser is a strongly disordered, laser‐active optical medium. The coherent laser feedback, which has been demonstrated experimentally to be present in these systems beyond doubt, requires the existence of spatially localized photonic quasimodes. However, the origin of these quasimodes has remained controversial. We develop an analytical theory for diffusive random lasers by coupling the transport theory of the disordered medium to the semiclassical laser rate equations, accounting for (coherent) stimulated and (incoherent) spontaneous emission. From the causality of wave propagation in an amplifying, diffusive medium we derive a novel length scale which we identify with the average mode radius of the lasing quasi‐modes. We show that truly localized modes do not exist in the system without photon number conservation. However, we find that causality in the amplifying medium implies the existence of a novel, finite intensity correlation length which we identify with the average mode volume of the lasing quasimodes. We show further that the surface of the laser‐active medium is crucial in order to stabilize a stationary lasing state. We solve the laser transport theory with appropriate surface boundary conditions to obtain the spatial distributions of the light intensity and of the occupation inversion. The dependence of the intensity correlation length on the pump rate agrees with experimental findings.     

Lasing spectra of 1.55 μm InAs/InP quantum dot lasers: theoretical analysis and comparison with the experiments

In this paper, a theoretical model is used to investigate the lasing spectrum properties of InAs/InP (113)B quantum dot (QD) lasers emitting at 1.55 μm. The numerical model used is based on a multi-population rate equation (MPRE) analysis. It takes into account the effect of the competition between the inhomogeneous broadening (due to the QD size dispersion) and the homogenous broadening as well as a nonlinear gain variation associated to a multimode laser emission. The double laser emission and the temperature dependence of lasing spectra of self-assembled InAs/InP quantum dot lasers is studied both experimentally and theoretically.     

基于钠硼铝硅酸盐玻璃的PbSe量子点红外单模光纤激光

根据实验制备的钠硼铝硅酸盐PbSe量子点玻璃及其透射电子显微镜(TEM)图、吸收谱和发射谱,计算机数值模拟了以PbSe量子点作为激活增益介质的红外单模光纤激光。应用遗传算法,通过数值求解粒子数速率方程和激光谐振腔振荡方程,优化计算了量子点光纤激光器(QDFL)的最佳抽运波长、光纤长度、掺杂浓度及出射镜反射率。结果表明:饱和抽运功率为2 W,在1676nm激光波长处,QDFL最大输出功率可达1.36 W,抽运效率达68%。与通常的掺稀土离子(Yb3+、Er3+)的光纤激光器相比,QDFL具有抽运效率高、激励阈值低、掺杂密度可调、光纤饱和长度短等特点。由于量子点辐射波长的尺寸依赖特性,容易形成多波长激射或波长可调的新型激光器。     

Giant optical nonlinearity of an atomic Bose-Einstein condensate and low-threshold bistability

The polarization of an atomic Bose-Einstein condensate weakly excited by laser radiation at a nearly resonance frequency is determined. The coefficient of nonlinearity (cubic in field) in the refractive index of the condensate is calculated for the slow decay mode due to the spontaneous emission of excited atoms, as well as for the stationary mode, when the loss of atoms is compensated by the injection of atoms into the trap. In both cases, the cubic nonlinearity coefficients of the condensate are several orders of magnitude larger than the corresponding values for known nonlinear media. The conditions for observing hysteresis in an interferometer containing the condensate in the stationary state in the presence of an incident laser beam are specified.     

ZnO粉末中无序激射现象时间分辨的研究

采用抽运-探测时间分辨方法实验研究了半导体材料ZnO纳米颗粒粉末中的无序激射现象.在2 67nm激光的抽运下，通过精确控制抽运光的能量和样品表面的抽运面积，获得了宽度小于1n m的单模无序激射光谱和多峰的多模无序激射光谱.时间分辨的抽运-探测结果显示，此时样 品的上能级寿命仅为几个皮秒，证明了ZnO粉末的单模无序光谱是受激辐射的结果. 关键词： 高散射介质 多重散射 抽运-探测 无序激射     

Spontaneous-emission spectrum of the nonlasing supermodes in semiconductor laser arrays

It is shown that the interference between amplified spontaneous emission into the nonlasing supermode and the laser field of a semiconductor laser array causes spatial hole burning, which couples the dynamics of the amplified spontaneous emission with the laser field. In particular, phase locking between the amplified spontaneous emission and the lasing mode leads to the formation of a spectral triplet composed of in-phase relaxation oscillation sidebands and an out-of-phase line at the lasing frequency.     

Investigation of cw injection laser with external dispersive cavity

Tunable single-frequency lasing with output power up to 9 mW was achieved in an injection laser with an external dispersive cavity. The bistable lasing mode was investigated theoretically and experimentally. It is shown that its presence is due to the laser-diode active-region optical nonlinearity. Investigation of equal-frequency fluctuation spectra of the output power has shown that only modes with differing transverse structures can be excited simultaneously. Suppression of weak modes by the field of a strong mode was observed. This increases the stability of the single-frequency lasing as the laser output power is increased.Translated from Trudy Ordena Lenina Fizicheskogo Instituta im. P. N. Lebedeva, Vol. 141, pp. 62–88, 1983.     

Stable room-temperature multi-wavelength lasing oscillations in a Brillouin–Raman fiber ring laser

A stable room-temperature multi-wavelength Brillouin–Raman fiber laser with a ring cavity configuration was proposed and experimentally investigated. An obvious suppressant effect for unstable mode hopping of multi-wavelength lasing oscillations induced by deeply saturated effect was observed in the ring cavity configuration. Stable room-temperature multi-wavelength lasing oscillations with more than 30 lasing lines and wavelength spacing of 0.076 nm were obtained with only 250 mW Raman pump power and a section of high nonlinear fiber with a length of 1.5 km. The lasing output is so stable that the maximum power fluctuations for the foremost three Stokes lines over more than 20 min of observation were less than 0.30 dB. The lasing stability of the laser was also compared with a linear cavity configuration with the same gain components and pump conditions. While using the linear laser cavity configuration, obvious mode hopping was observed. The minimum value of the maximum power fluctuations at all lasing lines over more than 10 min of observation was more than 0.90 dB.     

Impact of size upon lasing in ZnO microtetrapods

High optical quality, well end leg faceted ZnO microtetrapods with leg length between 1 and 12 μm have been grown by carbothermal chemical vapor deposition. Lasing with mode quality factors of 2500–3000 is demonstrated. The origin of laser resonator cavity is discussed as a function of the tetrapod size. It is shown that in big tetrapods with legs of 12 μm in length the laser emission lines are well explained by longitudinal Fabry–Pérot modes generated in cavities formed by individual tetrapod legs. The dispersion of the ZnO refractive index is experimentally determined from the position of lasing modes in the temperature interval from 10 to 300 K. It is shown that the lasing mode structure is seriously affected by the decrease of the tetrapod size. For a small tetrapod with a leg length of 1 μm, the lasing modes cannot be explained anymore by the formation of longitudinal Fabry–Pérot modes in separate tetrapod legs, and the generation of guided modes by multiple total internal reflections in single tetrapod legs or in pairs of legs should be taken into account. The correlations between the lasing threshold and the tetrapod size are discussed.     

Mode competition of bichromatic laser emission in two-dimensional strong scattering random medium

The mode competition of the bichromatic laser emission in two-dimensional (2D) random medium was studied. Based on the time-dependent theory, a model for dual-wavelength random laser was established. The Maxwell equations and rate equations were combined and solved by using the finite different time domain (FDTD) method. Results show that the emission intensity of both wavelength ranges increases simultaneously with the increasing of the surface-filling fraction. The mode dominance of the bichromatic emission can be switched by changing the scatterer radius. The emission intensity of the longer wavelength increases when enlarging the excitation area. The controllability of these lasing modes may provide a potential application of optical switches.     

轴向隐失波激励的回音壁模式光纤激光器

采用轴向隐失波激励增益的方式,使激光增益区域局限在光纤回音壁模式的模场区域内,显著地降低了回音壁模式光纤激光辐射的抽运阈值,由此形成一种低阈值的回音壁模式光纤激光器.在微焦耳量级的低抽运能量条件下,用回音壁模式光纤激光器研究了激光染料的浓度效应.实验结果表明,随着激光染料浓度的增加,回音壁模式激光辐射的波长向长波方向移动,激光波长范围变宽.用回音壁模式染料激光的四能级模型得到激光上能级和所有能级上的分子数比值γ(λ)曲线后,很好地解释了实验结果.低抽运阈值的回音壁模式光纤激光器,为研究液体激光现象提供了极为便利的手段.     

New biochemical material laser emission in microdroplets using ribo-flavin and its enhancement by mixing highly scattering intralipid medium

New laser emission from a biochemical material, ribo-flavin (vitamin B₂), at 570 nm was observed for the first time in liquid microdroplets pumped at 475 nm using a pulsed optical parametric oscillator. Laser emission spectra from microdroplets containing ribo-flavin in water and glycerol solution exhibit periodic mode structures depending on the microdroplet diameter demonstrating the morphology-dependent resonances. Magnitude enhancement of lasing emission is confirmed experimentally from liquid microdroplets of ribo-flavin solution with appropriate mixture of the fat emulsion Intralipid-10% suspension as highly scattering medium. We believe that such biochemical-soft multiple light scatterer systems may allow a wide range lasing of other bio-materials and even lead to the discovery of some novel species as well as highly sensitive analysis and diagnosis for future applications.     

无序介质激光的方向效应

无序介质激光是由该介质的非周期-类结构与相匹配的泵浦光场相互作用时其整体多重散射的干涉效应产生的.因此其局域模不仅与无序介质被泵浦的功率、面积有关,而且与方向有关.本文以ZnO粉末激光为例,运用传输矩阵的方法计算模拟了其局域模谱的方向效应.     

掺杂硅石纳米粉末的染料随机激光发射

针对染料随机激光器特性与应用研究,讨论了无序介质中荧光粒子和额外散射粒子的发光性质、浓度变化以及颗粒尺寸与随机激光发射阈值之间的关系。采用时域有限差分法直接求解Maxwell方程组及速率方程组的方法,模拟仿真出了相应的发射谱线及浓度变化与激光发射阈值的关系曲线。所设计的样品中Rh6G-SiO2的质量分数为4%,其阈值大小为8.5 J/pulse时,额外微小散射体TiO2的加入对该介质随机激光发射产生的影响很小,可忽略不计。在此基础上,通过进一步模拟分析了处于不同条件和背景下随机激光的阈值特性。     

Splitting of oscillation frequencies of a ring gas laser caused by the diffraction lens effect: II. Nonlinear theory

An analysis is made of the problem of generating the fundamental mode in a laser cavity containing a weakly nonlinear active medium and an aperture. Frequency-dependent nonlinear loss of counterpropagating waves is calculated. The loss was found to have a jumpwise decrease at the boundary of the lasing region. An explanation is given regarding the mechanism responsible for the asymmetry of loss about the central frequency of the transition. It is shown that counterpropagating waves differ in loss, as well as in the phase velocity, which is one of the reasons of that the counterpropagating waves of a ring laser, without special nonreciprocal devices, have different frequencies and intensities.