Emission induced by collision of two plumes during pulsed laser ablation

We observed plume expansion dynamics during pulsed laser ablation when two plumes collided head-on. Si and Ge targets were placed parallel each other, and they were irradiated simultaneously by two pulsed lasers. A new emission appeared near the center of the targets from 250 ns after the irradiation. However, the predominant ejected species is neutral SiI or GeI at this time region when an individual single target is irradiated, and the new emission emerged by collision is a mixture of ionized SiII and GeII. This indicates that the kinetic energy of the collision excites the species to an ionized state. The intensity of this new emission decreased by increasing the background gas pressure. This suggests that collision between two plumes induces a higher-temperature plasma. Since the new emission is composed of ionized Si and Ge species and remains a relatively long period after the collision, this technique will provide a new reactive field to prepare a new kind of alloy nanomaterials.     

粉末随机激光辐射

粉末随机激光辐射是一种刚刚被人们发现的激光过程,这种激光由粉末状介质的多次散射来提供光学反馈,不需要外加谐振腔。随机激光辐射过程除了对激光物理有很大意义之外,还有巨大的应用前景,例如,有可能在平板场发射显示器中得到广泛应用,文章介绍了粉末激光的原理及其实现过程。     

Episodic synchronization via dynamic injection

We report the occurrence of spontaneous synchronizing events between two semiconductor lasers, when the emission of a frequency- and intensity-chaotic driving laser is unidirectionally coupled into a second stable response laser. The driving laser is driven chaotic by delayed optical feedback, the response laser is a device-identical solitary laser. We demonstrate the onset of an episodic synchronization regime when the two lasers are spectrally detuned with respect to each other. By a joint experimental and modeling analysis we can attribute the onset and the duration of the episodes to properties of spectral overlap of both lasers. This effect can even give rise to seemingly anticorrelated intensity behavior. We expect episodic synchronization to be a generic scenario for the loss of synchronization of chaotic oscillators exhibiting frequency cycles.     

脉冲放电金属蒸气激光

评述了脉冲放电激励的金属蒸气激光的发展历程和现状，根据激光发射过程，分别阐述了自终止跃迁激光和碰撞辐射复合激光的机理，报道了作者课题组最近在相关领域研究取得的新进展：包括共振－亚稳跃迁激光和复合激光的交替振荡现象，不同介质多谱线激光同时振荡现象以及碱土金属卤化物多谱线激光的实现和新发现的M－M跃迁激光。     

Spectral characteristics of a Yb-doped Y<Subscript>2</Subscript>O<Subscript>3</Subscript> ceramic laser

We report the experimental observation of random wavelength emission and intensity-dependent central-wavelength shift in a diode-pumped Yb³⁺-doped Y₂O₃ ceramic laser. We show experimentally that, like conventional lasers, the emission of the laser has fixed well-defined transverse modes; however, its instantaneous emission wavelengths change randomly with time. The central wavelength of the laser emission also shifts with the intracavity light intensity. A model was developed to describe the spectral behavior of Yb³⁺-doped lasers. We show that the observed random wavelength emission and central lasing wavelength shift of the laser could be well explained based on the strong reabsorption of light in the gain medium. PACS 42.55.Rz; 42.60.Mi; 42.55.Xi     

Laser intracavity absorption spectroscopy

Emission spectra of multimode lasers are very sensitive to spectrally selective extinction in their cavity. This phenomenon allows the quantitative measurement of absorption. The sensitivity of measurements of intracavity absorption grows with the laser pulse duration. The ultimate sensitivity obtained with a cw laser is set by various perturbations of the light coherence, such as quantum noise, Rayleigh scattering, four-wave mixing by population pulsations, and stimulated Brillouin scattering. It depends on the particular laser type used, and on its operative parameters, for example pump power, cavity loss, cavity length, and length of the gain medium. Nonlinear mode-coupling dominates the dynamics of lasers that feature a thin gain medium, such as dye lasers, whereas Rayleigh scattering is more important in lasers with a long gain medium, such as doped fibre lasers, or the Ti:sapphire laser. The highest sensitivity so far has been obtained with a cw dye laser. It corresponds to 70000 km effective length of the absorption path. The ultimate spectral resolution is determined by the spectral width of mode emission, which is 0.7 Hz in this dye laser. High sensitivity and high temporal and spectral resolution allow various practical applications of laser intracavity spectroscopy, such as measurements and simulations of atmospheric absorption, molecular and atomic spectroscopy, process control, isotope separation, study of free radicals and chemical reactions, combustion diagnostics, spectroscopy of excited states and nonlinear processes, measurements of gain and of spectrally narrow light emission. Intracavity absorption in single-mode lasers shows enhanced sensitivity as well, although not as high as in multimode lasers. Received: 10 May 1999 / Published online: 29 July 1999     

硅基III-V族量子点激光器的发展现状和前景

本文简要综述了硅基III-V族量子点激光器的研究进展. 在介绍了量子点激光器的优势和发展后, 重点介绍了近年来硅基、锗基III-V族量子点材料生长上的突破性进展及所带来的器件性能的大幅提高, 如实现了锗基和硅基1.3 μm InAs/GaAs量子点激光器的室温激射, 锗基量子点激光器的阈值电流低至55.2 A/cm²并可达60 ℃以上的连续激射, 通过锗硅虚拟衬底, 在硅基上实现了30 ℃下以16.6 mW的输出功率达到4600 h的激光寿命, 这些突破性的进展为硅基光电子集成打开了新的大门.     

Laser stabilization to an atomic transition using an optically generated dispersive line shape

We report a simple and robust technique to generate a dispersive signal which serves as an error signal to electronically stabilize a monomode continuous-wave laser emitting around an atomic resonance. We explore nonlinear effects in the laser beam propagation through a resonant vapor by way of spatial filtering. The performance of this technique is validated by locking semiconductor lasers to the cesium and rubidium D₂ lines and observing long-term reduction of the emission frequency drifts, making the lasers well adapted for many atomic physics applications.     

Role of pulse shaping in control of focus and intensity of terahertz radiation

In this work, we uncover the role of lasers pulse shaping for controlling the terahertz peaks with their separation in addition to their intensities. We have developed a mathematical model for obtaining the amplitude, frequency, and power of the emitted Terahertz radiation for the lasers whose shape is tailored based on the index and skew parameter. Then the results are compared with the case of Gaussian laser pulse in collisional plasma. We optimize the process by applying magnetic field and by varying the index of the lasers for compensating the negative influence of collisions on the THz emission. Specifically the effect of laser beam width, magnetic field and collision frequency is investigated on the electric field of the terahertz radiation and the efficiency of the mechanism.     

Functional organic single crystals for solid‐state laser applications

Because of long‐range order and high chemical purity, organic crystals have exhibit unique properties and attracted a lot of interest for application in solid‐state lasers. As optical gain materials, they exhibit high stimulated emission cross section and broad tunable wavelength emission as similar to their amorphous counterpart; moreover, high purity and high order give them superior properties such as low scattering trap densities, high thermal stability, as well as highly polarized emission. As electronic materials, they are potentially able to support high current densities, thus making it possible to realize current driven lasers. This paper mainly describes recent research progress in organic semiconductor laser crystals. The building molecules, crystal growth methods, as well as their stimulated emission characteristics related with crystal structures are introduced; in addition, the current state‐of‐the‐art in the field of crystal laser devices is reviewed. Furthermore, recent advances of crystal lasers at the nanoscale and single crystal light‐emitting transistors (LETs) are presented. Finally, an outlook and personal view is provided on the further developments of laser crystals and their applications.     

双光子吸收碱金属蒸气激光器研究进展

蓝紫激光和中红外激光在基础研究和国防工程中有重要的应用前景。单光子吸收的碱金属蒸气激光器具有量子效率高、受激发射截面大和热管理性能好等优点,近些年来已成为激光领域中研究热点之一,目前已实现k W量级的输出。双光子吸收的碱金属蒸气激光器可实现蓝紫激光和中红外激光级联输出的特性,也引起越来越多的关注。本文从碱金属原子密度、泵浦光功率、偏振和频率失调量以及调控激光等几种影响因素出发,综述了双光子吸收碱金属蒸气激光的研究进展,在此基础上分析了影响激光输出特性的原因,最后对双光子吸收碱金属蒸气激光器的发展趋势进行了展望。     

Excited-state absorption and 1064-nm end-pumped laser emission of Nd:YVO4 single-crystal fiber grown by laser-heated pedestal growth

We present an investigation of the excited-state absorption and laser emission of a 1.0-at. %-Nd3+-doped YVO4 single-crystal fiber grown by the low-cost and versatile laser-heated pedestal growth technique. Efficient laser emission at 1064 nm was achieved when the fiber was pumped, in an end-pump cavity, by a Ti:sapphire laser at 808 nm. A continuous-wave threshold of 10 mW was observed with an efficiency of 42% with respect to the absorbed pump power and the maximum output power of 200 mW. These results are excellent when compared with those of a commercial bulk crystal adapted to the same cavity (48% efficiency, 250-mW maximum output power). Thus the fibers are characterized as strong candidates for the construction of compact lasers that can also be pumped by low-cost diode lasers.     

Ⅲ–Ⅴ/Si Hybrid Laser Array with DBR on Si Waveguide

We report an eight-channel silicon evanescent laser array operating at continuous wave under room temperature conditions using the selective-area metal bonding technique.The laser array is realized by evanescentl.y coupling the optical gain of InGaAsP multi-quantum wells to the silicon waveguides of varying widths and patterned with distributed Bragg reflector gratings.The lasers have emission peak wavelengths in a range of 1537-1543 nm with a wavelength spacing of about 1.0 nm.The thermal impedances Z_T of these hybrid lasers are evidently lower than those DFB counterparts     

Generation of Terahertz radiation with two color semiconductor lasers

We discuss and analyze concepts for the generation of tuneable continuous wave terahertz (THz) radiation with two color diode lasers. First, different geometries of two color lasers are reviewed. We show that the THz power of two color lasers in combination with external photomixers becomes sufficient for scanning THz imaging applications when optical amplification with a tapered amplifier is implemented. Then, the concept of direct emission of THz radiation out of a two‐color semiconductor laser is reviewed and the potential of this concept with respect to THz bandwidth and achievable THz power is critically analyzed.     

Development of XUV lasers at the RAL Central Laser Facility

Recent progress in the development of XUV lasers by research teams using high-power and ultrashort-pulse Nd: glass and KrF laser facilities at the Rutherford Appleton Laboratory is reviewed. Injector-amplifier operation and prepulse enhanced output of the Ge XXIII collisional laser driven by a kilojoule glass laser, enhanced gain in CVI recombination with picosecond CPA drive pulses from a glass laser, and optical field ionization and XUV harmonic generation with a KrF CPA laser are described.     

光子晶体在半导体激光器中的应用

激光的发明，将人类带入光通信、光存储、光显示的高科技文明中，随着高科技的不断发展、进步和应用范围的不断扩大，对激光的要求更高，例如低阈值、高效率、高亮度、高速、小体积、好的模式特性等，这些要求在现有的传统激光器理论及技术中是难以达到的。但是当人们将光子晶体的理论与现有激光物理和技术相结合时，则有望突破传统激光器的性能瓶颈。例如，提高自发辐射速率，同时获得更高的自发辐射向受激辐射的耦合效率，实现激光器的无阈值工作；利用光子晶体对光子态的调制作用，可以获得比传统激光器大几个数量级的光学腔品质因子，大幅度提高激光的亮度、单色性；结合光子晶体微腔及其显著增加的光学腔品质因子，可以提高激光器的调制速率等，因此，人们预期光子晶体科学与技术将成为未来光电子领域发展的核心之一。文章介绍了光子晶体在半导体激光器中的应用，指出光子晶体科学技术引入发展了几十年的半导体激光器中，使半导体激光器展现出更加优异的性能。最后文章作者展望了光子晶体激光器的未来发展和应用的方向。     

光子晶体在半导体激光器中的应用

激光的发明,将人类带入光通信、光存储、光显示的高科技文明中,随着高科技的不断发展、进步和应用范围的不断扩大,对激光的要求更高,例如低阈值、高效率、高亮度、高速、小体积、好的模式特性等,这些要求在现有的传统激光器理论及技术中是难以达到的。但是当人们将光子晶体的理论与现有激光物理和技术相结合时,则有望突破传统激光器的性能瓶颈。例如,提高自发辐射速率,同时获得更高的自发辐射向受激辐射的耦合效率,实现激光器的无阈值工作;利用光子晶体对光子态的调制作用,可以获得比传统激光器大几个数量级的光学腔品质因子,大幅度提高激     

THz emission from semiconductor surfaces

We provide a review of experimental and theoretical work on electromagnetic terahertz pulse emission from semiconductor surfaces excited by femtosecond laser radiation. The main terahertz emission mechanisms are analysed. The terahertz emission from InAs and Ge is explained by the photo-Dember effect and electric field induced optical rectification. Electronic band structure and carrier scattering mechanisms are investigated by means of terahertz emission and absorption spectroscopy in InAs, InSb and Ge. To cite this article: V.L. Malevich et al., C. R. Physique 9 (2008).     

Simulation of the interplay between stimulated emission and carrier distribution in quantum-cascade lasers

We present a model for the simulation of the effect of stimulated emission on the transport and optical properties in quantum-cascade lasers. The model is based on the self-consistent solution of the Schrödinger and Poisson equations using a one-dimensional scattering rate approach, which includes the laser rate equations. We discuss the charge redistribution, the modification of the current density, and the shift of the gain maximum for various designs of mid-infrared as well as THz quantum-cascade lasers. We found that this shift varies for the different designs, but is of similar order of magnitude as due to typical fluctuations of the layer parameters such as thicknesses and composition. In some cases, the inclusion of stimulated emission results in the appearance of negative differential conductivity, which may explain the observed instabilities of the current and light output power.     

Mechanisms for lasing with cold atoms as the gain medium

We realize a laser with a cloud of cold rubidium atoms as gain medium, placed in a low-finesse cavity. Three different regimes of laser emission are observed corresponding, respectively, to Mollow, Raman, and four-wave mixing mechanisms. We measure an output power of up to 300 microW and present the main properties of these different lasers in each regime.