Characterizing the beam properties of terahertz quantum-cascade lasers

Terahertz quantum-cascade lasers (QCLs) are very promising radiation sources for many scientific and commercial applications. Shaping and characterizing the beam profile of a QCL is crucial for any of these applications. Usually the beam profile should be as close as possible to a fundamental Gaussian TEM₀₀ mode. In order to completely characterize the laser beam the power and the wavefront have to be measured. We describe methods for characterizing the beam properties of QCLs. Several QCLs with single-plasmon waveguide and emission frequencies between 2 and 5 THz are investigated. The beam profiles of these lasers are shaped into almost fundamental Gaussian modes using dedicated lenses. The beam propagation factor M² is as low as 1.2. The wavefront is measured along the axis of propagation with a THz Hartmann sensor. Its curvature behaves as expected for a Gaussian beam. The applied methods can be transferred to any other THz beam.     

固体热容激光器:市场最佳候选者

在美国陆军空间和导弹防御指挥部的支持下,劳伦斯·利弗莫尔国家实验室与Boeing,GeneralAtomics,DRS,DecadeOpticalSystems及其工业界伙伴共同合作,正在开发研究一种用于清除地雷和战术短程防空任务的高平均功率(100kW级)移动式激光器。最终目标是开发一种能部署在多功能电动车上使用的电能固体激光器。目前有很多方法可以获得适于防御的高平均功率运转的激光器,其中化学激光器和固体激光器属于姣姣者。但化学激光器有两大缺点:①体积大,不适于移动;②在激光发射过程中产生有毒物质而破坏环境;而固体激光器体积小且有利于环境保护。如…     

高功率激光器的光束质量及其对激光加工的影响

本文介绍了光束的模式、评价光束质量的几种方法,着重介绍了国际标准化组织(ISO)提出的光束传输系数M作为评价光束质量的方法。文中还讨论了光束质量对焊接、切割加工的影响;热透镜效应对加工的影响等。     

Thermal lens and beam properties in multiple longitudinally diodelaser pumped Nd:YAG slab lasers

The focal length of the thermal lens and the beam quality factor (beam propagation factor) M² for a multiple longitudinally diode pumped slab laser is deduced for pump and output powers up to 16 and 4.5 W, respectively. Due to the geometry of the arrangement, a stronger thermal lens is observed in the plane with the larger pump spot radius as predicted by an analytical model for slab geometries. In addition, the second stable zone of an asymmetric resonator is found to be advantageous for improved beam properties at high output powers     

Nd:YAG激光器AM主动锁模稳定性的研究

本文着重介绍有关提高锁模激光器稳定性的几项重要技术:研制由三根石英棒支撑的并具有温度补偿结构的稳定谐振腔,获得腔长温度膨胀系数<0.1微米/℃、抗震性能好的结果。谱振腔还带有一个具有独特设计的精密平动微调支架,平动精度达0.01毫弧度;研制200兆赫高效率声光调制器,调制深度为18％,大于最佳锁模时所需的10％调制深度的要求。调制器能在自然空冷的条件下连续长时间稳定锁模运行;研制100兆赫高稳定度射频驱动电源,在0～8瓦输出中频率稳定度优于10~(-8)/天;在锁模激光器中成功地采用了光反馈自动稳光技术;     

GaAs:GaAlAs ridge waveguide lasers and their monolithic integrationusing the ion beam etching process

The fabrication and performance characteristics of GaAs/GaAlAs ridge waveguide lasers are discussed. Threshold currents as low as 8 mA and differential quantum efficiencies as high as 90% were obtained for 250-μm-long graded-index separate-confinement heterostructure with single quantum well (GRINSCH SQW) lasers. High-speed short-cavity ridge waveguide lasers for which both the ridge stripe and one-mirror facet were formed by Ar-ion beam etching were achieved. The dependence of threshold current and lasing spectra on the cavity length were theoretically and experimentally investigated. This process was successfully used to integrate a laser diode monolithically with a photodiode or a field-effect transistor     

Broadband over power line: once more unto the breach

This paper discusses the latest developments in broadband over power line (BPL), a technology that envisions using power lines to do double duty by delivering high-speed Internet access to customers' homes. Widespread operation of Access BPL has raised interference concerns in the protection of licensed radio services. Nevertheless, the FCC has moved the technology one step closer to implementation by issuing a notice for proposed rule making (NPRM) in February 2004, a set of regulations authorizing the operation of BPL.     

腔型结构对LD端面泵浦Nd:YAG激光器输出特性的影响

在腔长为 2 47mm的LD端面泵浦Nd :YAG激光器的谐振腔中加入一片凸透镜 ,改变腔型结构 ,发现输出功率由 0 .3 5W增至 1.19W ,M2 因子由 1.0 9增至 2 .6,阈值功率由 2 .78W降至 0 .68W ,与腔长为 2 0mm的谐振腔阈值功率相同。分析表明 ,由于透镜的变换作用 ,使得泵浦端面上振荡光斑与泵浦光斑的比例发生变化 ,在晶体后端面处泵浦光斑确定的情况下 ,激光器的输出功率和阈值功率主要取决于该处的振荡光斑大小 ,与有效模体积无直接关系     

Nd:YAG激光器增大线偏振输出功率的实验研究

由热应力双折射产生的热退偏是限制Nd:YAG激光器线偏振输出功率的重要因素。本文理论分析并实验证明,相比于传统的[111]方向切割的Nd:YAG晶体棒,使用[100]方向切割的Nd:YAG晶体棒能够改善Nd:YAG激光器的线偏振态输出功率。在理论分析的基础上,实验中采用半导体侧面泵浦不同切割方向的Nd:YAG棒状晶体,比较[111]、[100]方向切割晶体的线偏振输出特性,实验证明[100]方向切割的Nd:YAG棒状晶体,有最小的晶体热退偏方向,可以提高激光器的线偏振输出功率。     

InGaAsP/InP double-heterostructure lasers: Simple expressions for wave confinement, beamwidth, and threshold current over wide ranges in wavelength (1.1-1.65 µm)

For InGaAsP/InP devices emitting in the wavelength range of1.1-1.65 mum, we present novel and accurate analytical approximations of the crucial parameters in laser design: the radiation confinement factorGamma; the effective refractive index Neff; and the transverse beamwidththeta_{perp}. It is found thatGammais independent of wavelength or step-index difference andtheta_{perp}becomes independent of wavelength as the active layer thicknessesddecreases below 0.15 μm. An explicit analytical expression is derived for the threshold current density Jth. The new linear gain-current relationshipg(cm^-1) = 28.5(J/d) - 50is deduced from a critical assessment of recent experimental data. A theoretical framework is provided to explain experimental observations such as: the Jthversusdcurve is independent of wavelength, the threshold has a negligible variation over the0.1-0.3 mum active-layer thickness range, and the normalized threshold current density (J_{th}/d, ford geq 0.5 mum) varies strongly (3-5 kA/cm²/μm) with cavity length.     

Effect of 1/f noise on the spectral linewidth of corrugation-pitch-modulated multiquantum-well distributed feedback lasers at high output power

The mechanism by which spectral linewidth reduction saturates in CPM-MQW-DFB (corrugated-pitch-modulated multiquantum-well distributed feedback) lasers at high output powers is investigated by measuring the spectral power density of their FM noise. Linewidth saturation is caused by the 1/f component of this noise.<>     

Thermoelectric power of the n-InSb in a transverse quantizing magnetic field at a large temperature gradient

The thermoelectric power of the n-type indium antimonide was studied in the transverse magnetic field (0–80 kOe) at T _aV =160 K and different temperature gradients. It was found that the electron component of the thermoelectric power at a small temperature gradient is consistent with the theory that takes into account the electron spin, whereas, for a large temperature gradient, the value determined by the variation of the Benedicks thermoelectric power in the magnetic field is added to this component.     

低轨星座系统的可控波束到地功率通量密度研究

功率通量密度是评估空间业务系统保护地面业务系统的一项干扰评价指标。给出了低轨星座系统可控波束的功率通量密度的计算方法和特定可控角下功率通量密度限值的符合性判定算法。在此基础上,提出了一种基于仰角遍历的功率通量密度限值的符合性判定算法。结合低轨星座系统的特征,论证了简化最大功率通量密度计算需要满足的条件。以Starlink系统为分析场景,计算分析了其Ka/E频段馈电波束的功率通量密度,并与SpaceX公开的结果对比验证了所提方法的正确性。结果表明,Starlink系统Ka频段馈电波束到地功率通量密度在仰角低于20°时不满足《无线电规则》规定的限值要求。     

light intensity at the return place and encirclement power ratio for the distorted reflected beam based on cat-eye effect

Based on the definition of second order moment and the approximate three-dimensional analytical formula for probe detected laser beam passing through a cat-eye optical lens with center shelter and oblique detector, the analytical expression of the encirclement power ratio of the cat-eye effect reflected light under far-field condition has been deduced. Variable laws of light intensity at the return place and encirclement power ratio are performed by numerical calculation, and are analyzed physically. The results show that the light intensity at the return place decreases monotonically with the increases of the diameter, incidence angle, tilted angle of the detector and the center shelter ratio, but the relationships between these parameters and the encirclement power ratio are all nonmonotonic. The reasonable choice of the focal shift size would result in the largest light intensity at the return place and the largest erirclenent power ratio.     

Limits of the output power in Er3+:ZBLAN singlemodefibre lasers

The saturation of the 2.71 μm laser output has been measured in erbium-doped ZBLAN singlemode fibres with Er³⁺ concentrations of 1000, 5000 and 10000 ppm mol. Limits of the single-mode-laser output are discussed     

The self-heated 442-nm He-Cd laser: Optimizing the power output, and the origin of beam noise

Power output and beam noise parametric results are obtained for the blue transition of the self-heated He-Cd laser in tubes of 0.10-0.16-cm bore diameter. Presentation of this data in the form of performance contour maps shows that the usual scaling laws for laser discharges are accurate for this laser (<12-percent parameter variation for a 60-percent diameter variation) and is a convenient form for use in tube design. The contour maps imply the existence of a direct connection between the output and noise of this laser. A theory is proposed that the noise in the He-Cd discharge arises from the rapid increase in ionization rate due to Penning collisions as Cd is added to the He discharge. This produces a high gain in the discharge column for the growth of striation waves (which modulate the output). The theory correctly predicts the details of the laser noise behavior, showing that both the noise and output share a common origin in the Penning effect. The dependence of Cd vapor density on tube current is found, from sidelight studies, to be more pronounced in self-heated tubes (as opposed to tubes with externally heated Cd sources). A threshold dissipation value is given for puncture of the hot glass bore by the discharge (this is a common failure mode in the He-Cd laser).     

Double resolution microwave holography: The resolving power of a laboratory system versus the Rayleigh limit for a conventional hologram

It is demonstrated that the resolving power of a laboratory double-resolution microwave hologram can be significantly greater than the maximum resolving power theoretically attainable from the equivalent conventional hologram of the same size and recorded in the same plane.     

热效应对高功率b轴Nd:YAP、Nd Cr:YAP连续激光器输出的影响

本文在文献[1]的基础上提出了含有椭圆折射率分布介质谐振腔的设计方法,分析了b轴Nd:YAP、Nd Cr:YAP连续激光器中热效应对激光横向场分布、输出偏振方向以及输出功率的影响。 Nd:YAP晶体的热焦距f_(x=0)~((z))和f_(z=0)~((z))较短,这就使得在较大的输入功率时,激光的输出特性发生变化。在非对称(A=16厘米,B=11.9厘米)平面腔中,当输入功率为3.615千瓦时,沿a轴和c轴偏振的激光,在a轴和c轴位置腔的g值都处在稳定区(0≤g_1g_2≤1),由于c轴偏振跃迁截面大,所以激光以c轴偏振的1.0795微米起振。随着泵浦功率的提高,热焦距缩短,增加到6.3千瓦时,c轴偏振在c轴位置腔的g参数落在稳定和非稳定区的交界处,而在a     

Theory of the power characteristics of quantum-well lasers with asymmetric barrier layers: Inclusion of asymmetry in electron- and hole-state filling

The power characteristics of quantum-well lasers with asymmetric barrier layers, which represent a novel type of injection laser, are calculated on the basis of an extended model taking into account asymmetry in the filling of electron and hole states. The electron–hole asymmetry is shown to have no significant effect on the characteristics of these lasers. Even in the presence of intermediate layers (located between the quantum well and each of the two asymmetric barrier layers), where parasitic electron–hole recombination does occur, the internal differential quantum efficiency of such a laser exhibits only a weak dependence on the pump current and remains close to unity; therefore, the light–current characteristic remains linear up to high pumping levels.