An all-silicon Raman laser

The possibility of light generation and/or amplification in silicon has attracted a great deal of attention for silicon-based optoelectronic applications owing to the potential for forming inexpensive, monolithic integrated optical components. Because of its indirect bandgap, bulk silicon shows very inefficient band-to-band radiative electron-hole recombination. Light emission in silicon has thus focused on the use of silicon engineered materials such as nanocrystals, Si/SiO2 superlattices, erbium-doped silicon-rich oxides, surface-textured bulk silicon and Si/SiGe quantum cascade structures. Stimulated Raman scattering (SRS) has recently been demonstrated as a mechanism to generate optical gain in planar silicon waveguide structures. In fact, net optical gain in the range 2-11 dB due to SRS has been reported in centimetre-sized silicon waveguides using pulsed pumping. Recently, a lasing experiment involving silicon as the gain medium by way of SRS was reported, where the ring laser cavity was formed by an 8-m-long optical fibre. Here we report the experimental demonstration of Raman lasing in a compact, all-silicon, waveguide cavity on a single silicon chip. This demonstration represents an important step towards producing practical continuous-wave optical amplifiers and lasers that could be integrated with other optoelectronic components onto CMOS-compatible silicon chips.     

A continuous-wave Raman silicon laser

Achieving optical gain and/or lasing in silicon has been one of the most challenging goals in silicon-based photonics because bulk silicon is an indirect bandgap semiconductor and therefore has a very low light emission efficiency. Recently, stimulated Raman scattering has been used to demonstrate light amplification and lasing in silicon. However, because of the nonlinear optical loss associated with two-photon absorption (TPA)-induced free carrier absorption (FCA), until now lasing has been limited to pulsed operation. Here we demonstrate a continuous-wave silicon Raman laser. Specifically, we show that TPA-induced FCA in silicon can be significantly reduced by introducing a reverse-biased p-i-n diode embedded in a silicon waveguide. The laser cavity is formed by coating the facets of the silicon waveguide with multilayer dielectric films. We have demonstrated stable single mode laser output with side-mode suppression of over 55 dB and linewidth of less than 80 MHz. The lasing threshold depends on the p-i-n reverse bias voltage and the laser wavelength can be tuned by adjusting the wavelength of the pump laser. The demonstration of a continuous-wave silicon laser represents a significant milestone for silicon-based optoelectronic devices.     

Ultralow-threshold Raman laser using a spherical dielectric microcavity

The ability to confine and store optical energy in small volumes has implications in fields ranging from cavity quantum electrodynamics to photonics. Of all cavity geometries, micrometre-sized dielectric spherical resonators are the best in terms of their ability to store energy for long periods of time within small volumes. In the sphere, light orbits near the surface, where long confinement times (high Q) effectively wrap a large interaction distance into a tiny volume. This characteristic makes such resonators uniquely suited for studies of nonlinear coupling of light with matter. Early work recognized these attributes through Raman excitation in microdroplets-but microdroplets have not been used in practical applications. Here we demonstrate a micrometre-scale, nonlinear Raman source that has a highly efficient pump-signal conversion (higher than 35%) and pump thresholds nearly 1,000 times lower than shown before. This represents a route to compact, ultralow-threshold sources for numerous wavelength bands that are usually difficult to access. Equally important, this system can provide a compact and simple building block for studying nonlinear optical effects and the quantum aspects of light.     

强激光受激转动喇曼散射的瞬态阈值理论计算

由半经典耦合方程出发,本文完整建立了均匀大气中准直激光传输时瞬态受激转动喇曼散射的阈值理论,讨论了激光脉冲波形、激光波长、气压等对瞬态阈值的影响。     

Controlled injection and acceleration of electrons in plasma wakefields by colliding laser pulses

In laser-plasma-based accelerators, an intense laser pulse drives a large electric field (the wakefield) which accelerates particles to high energies in distances much shorter than in conventional accelerators. These high acceleration gradients, of a few hundreds of gigavolts per metre, hold the promise of compact high-energy particle accelerators. Recently, several experiments have shown that laser-plasma accelerators can produce high-quality electron beams, with quasi-monoenergetic energy distributions at the 100 MeV level. However, these beams do not have the stability and reproducibility that are required for applications. This is because the mechanism responsible for injecting electrons into the wakefield is based on highly nonlinear phenomena, and is therefore hard to control. Here we demonstrate that the injection and subsequent acceleration of electrons can be controlled by using a second laser pulse. The collision of the two laser pulses provides a pre-acceleration stage which provokes the injection of electrons into the wakefield. The experimental results show that the electron beams obtained in this manner are collimated (5 mrad divergence), monoenergetic (with energy spread <10 per cent), tuneable (between 15 and 250 MeV) and, most importantly, stable. In addition, the experimental observations are compatible with electron bunch durations shorter than 10 fs. We anticipate that this stable and compact electron source will have a strong impact on applications requiring short bunches, such as the femtolysis of water, or high stability, such as radiotherapy with high-energy electrons or radiography for materials science.     

光纤拉曼放大器中拉曼阈值的理论分析

为探讨光纤拉曼放大器中的阈值条件，基于抽运光和信号光耦合方程组，推导了考虑抽运光能量转移给信号光能量时的阈值功率公式，并对满足阈值条件时光纤的最大损耗和最短长度进行了计算．将所得结果与文献中已有的阈值功率公式和近期实验结果作了比较，发现文中推导的阈值功率公式比原有的公式更严密，与实验结果更吻合．文中最后得出了设计光纤拉曼放大器时的最优抽运功率和光纤长度．     

ZnO纳米晶的拉曼光谱

通过溶胶-凝胶法制备了5~31 nm氧化锌纳米晶,测量了它们的拉曼光谱,结果表明二级拉曼模随粒径减小相对强度增大,归因于尺寸效应.新出现的938 cm-1模指认为来自表面氧空位.     

GaN受激喇曼散射谱研究

对ＧａＮ样品薄膜进行了喇曼背散射几何配置下的喇曼散射测试与分析,其样品分别是在不同衬底上以金属有机物气相沉积（ＭＯＣＶＤ）法和分子束外延（ＭＢＥ）法生长的,观测到了纤锌矿结构ＧａＮ的允许模式Ａ１（ＬＯ）模和Ｅ２（高）模,同时也观测到了一些禁戒模式,结果表明：受激喇曼散射是研究ＧａＮ结构的一种有效手段。     

消逝波增益耦合球形微腔中的受激拉曼散射

针对球形微腔能否将腔外介质的拉曼增益耦合到腔内,并在微腔回音壁模式的支持下形成腔外介质的受激拉曼辐射的问题,通过石英球腔在纯水中的受激拉曼散射实验,首次观察到水的拉曼增益确实可以通过消逝场耦合进入球腔,并在腔内形成拉曼光的受激辐射放大.     

激光家族中的一氧化碳激光器(英)

描述了作为激光光谱分析仪中光源的纵向直流激励自持放电小功率宽频带可调谐一氧化碳激光器,并给出了有关高功率一氧化碳激光器的发展概况．在所描述的一氧化碳激光器中,有相当一部分是由作者在近20年中研制成功的．最后给出了5μm波段一氧化碳激光器和10．6μm波段二氧化碳激光器在金属切割方面的比较实例,并指出了在一氧化碳激光器研究领域尚需解决的问题．     

单个红细胞的拉曼光谱研究

研究了不同物种的血红细胞的拉曼光谱,采用一个波长为785nm的半导体激光束来囚禁血红细胞和激发血红细胞的拉曼光谱。结果显示不同物种血红细胞的拉曼光谱在1603cm^-1苯丙氨酸和色氨酸的C=C平行振动模及1616cm^-1酪氨酸和色氨酸的C=C拉伸模有明显的差异,这可以用来作为不同种血红细胞鉴定的特征标记。表明激光镊子拉曼光谱技术可以成为血红细胞分析的有效手段。     

核酸的激光喇曼光谱

本文研究了核酸的激光喇曼光谱与它的结构及生化功能的关系。确认应用激光喇曼光谱研究核酸是具有信息量大、高灵敏度及高分辨本领的。     

反铁磁拉曼散射的压缩态

在量子力学研究领域中,人们发现了许多的非经典态,压缩态是其中的一类非经典态,由不确定性关系,处于压缩态的量子涨落小于相干态的量子涨落．人们期望利用这一性质去减少量子噪声,进行高精度信号的测量．所以玻色子的压缩态研究成为物理学研究领域很重要的研究课题．该文分析了二阶拉曼散射中温度因素对量子涨落的作用,讨论了温度对磁振子压缩态的影响,确定了压缩态存在的温度范围。     

含喇曼效应的暗孤子解

应用变分法,讨论喇曼效应对光纤中暗孤子传输特性的影响,导出了暗孤子参数演化的方程组,并得出了存在喇曼效应时暗孤子的孤波解.     

纳米硅薄膜的拉曼谱研究

通过等离子增强化学汽相沉积法,制备了本征和掺磷的氢化纳米硅薄膜（ｎｃ－Ｓｉ：Ｈ）研究了晶粒尺寸和掺杂浓度对纳米硅薄膜拉曼谱的影响。结果表明晶粒变小和掺杂浓度增加都使纳米晶粒的ＴＯ模峰位逐渐偏离声子限制模型的计算值。Ｘ－射线衍射和透射电镜像的结果表明晶粒变小导致硅晶粒应力增加,而掺杂使晶粒内部杂质和缺陷增多,这些因素破坏了晶粒内晶格的平移对称性,进一步减小声子的平均自由程,导致实验值偏离理论计算值,     

甲醇和乙醇的激光喇曼光谱

采用激光喇曼方法,对甲醇和乙醇液体样品进行了喇曼光谱研究,得到了上述样品的喇曼光谱,并对其进行了归属.经过分析比较,给出了检测甲醇的特征谱线,为假酒鉴别、深入研究甲醇和乙醇的能级结构等提供了可供借鉴的参考.     

木质素焦炭导电特性的拉曼分析

研究了炭化工况对木质素焦炭电阻率的影响,并结合拉曼光谱和XRD分析研究了温度和催化剂对焦炭结构和导电性能的影响.结果表明:炭化温度的提高和催化剂的添加有利于焦炭石墨化,即提高焦炭导电性能.添加催化剂需要采用两段炭化法以避免焦油对催化剂的中毒作用.随着温度的升高,拉曼光谱中D峰强度不断增加,产生的活性炭原子与焦炭中的灰分结合形成的离子络合物导致了电阻率的降低.添加催化剂使得D峰和G峰强度均有增加,说明催化剂可以促进焦炭的炭化和石墨化.镍基催化剂较容易使焦炭获得石墨化结构,在低温阶段催化效果明显.而铁基催化剂在高温下也可以体现出较强的催化能力.     

ZnTe纳米粉的共振Raman散射研究

用Zn粉和Te粉为源材料,利用水热法在不同条件下制备了ZnTe纳米粉.用X射线衍射仪、透射电子显微镜和显微Raman光谱仪对ZnTe纳米粉进行了表征.X射线衍射谱表明制备的纳米ZnTe具有闪锌矿结构.透射电子显微镜给出在100℃,120℃和160℃时生长2h的ZnTe颗粒的平均大小分别为67 nm,89 nm和120 ...     

污水回注井最大注水量预测模型

探讨污水回注井最大注水量的预测方法,为安全高效的污水回注决策提供理论依据.在常规稳定渗流理论的基础上,利用实际的注水动态资料,考虑了回注污水对地层渗透率的损害,采用累加的思想来消除单次注水参数的偶然误差,推导建立了预测污水回注井最大注水量模型.在川中地区污水回注井中的运用表明,该模型能准确预测单井的最大注水量.     

碳纳米管的拉曼光谱定量分析研究

拉曼光谱分析技术具有对样品无破坏、用量少等独特优点．本文用拉曼光谱技术对碳纳米管进行研究，获得了高质量的单壁碳纳米管拉曼谱．并通过单壁碳纳米管的“G”峰和聚苯乙烯拉曼特征峰的积分强度的变化，对不同组分的单壁碳纳米管／聚苯乙烯复合物进行了定量成分分析．实验结果表明，拉曼光谱技术的分析结果同该复合物的原始配比一致．