CuO纳米空心球的制备及其NO_x气敏研究

为了制备高灵敏度、快速响应、高选择性的室温NO_x气体传感器,采用简单的一步液相回流法合成出CuO纳米空心球气敏材料。通过XRD、SEM等表征手段对所合成材料的结构和形貌进行研究。结果表明,制备的CuO是由层状纳米片CuO组装成的直径约为500 nm的中空球状颗粒;将其作为电极材料组装成气敏元件,其在室温下对NO_x表现出很好的气敏性能:该材料对体积分数100×10~(–6) NO_x的响应时间为2.5 s,灵敏度可达70.96%;对NO_x最低检测限为体积分数2×10~(–6),灵敏度为13.23%。     

Remote sensing

With the advent of powerful workstations and affordable software, data from remote-sensing satellites are at last being winnowed and sifted for special-purpose information, sometimes in combination with other inputs. Still more data will become available with the launch of new commercial satellites with high-resolution remote sensing. The author discusses the image processing aspects of remote sensing, describing how the digital images are transformed into maps. In particular the author discusses data fusion and how the spatial resolution limits are overcome by using spectral signatures of objects     

A slot microring sensor with feedback spiral waveguide for trace gas CH4 sensing in mid-infrared region

In this paper, a slot microring resonator with a piece of spiral feedback waveguide for CH4 sensing application is proposed. This sensor is based on silicon-on-insulator (SOI) substrate and with the operation wavelength in mid-infrared region. To reach high sensitivity and good selectivity, slot cross section and spiral feedback waveguide are carefully tailored. The sensor shows ppb-scale trace gas sensing potential and is easy to be packaged in integrated photonics circuits. Calculation results show that the sensitivity reaches 1.4×10-2 dB/ppm and the detection limit achieves 700 ppb in the case of Lspiral=100Lr.     

Coupling losses in hollow waveguide laser resonators

Hollow waveguide gas lasers of the type described by Smith have some inherent loss in coupling radiation from the guide into free space and back into the guide. This paper calculates that loss for the EH11lowest order waveguide mode as a function of mirror position and mirror radius. It is shown that some mirror positions and radii are optimum, in that they provide low coupling loss and are relatively insensitive to mirror position.     

Transverse modes of active hollow waveguide resonators

The effect of an active medium on the mode structure of a hollow waveguide resonator is investigated. A coupled-mode approach is employed. The field propagation through the resonator is described by a propagation matrix; thus, the solution is found by solving the generally nonlinear eigenvalue problem of the matrix for complete resonator round-trip. This has been performed numerically using an appropriate iteration procedure. The method was applied to duel-case I resonators. It was found that thermally induced refractive index profiles and, in the case of larger guide cross sections, the gain properties can also alter the mode structure significantly. These alterations influence the power gain coefficient as well as the conditions for single-transverse-mode operation     

Transversely excited waveguide gas lasers

This paper summarizes the work done on transversely excited (TE) waveguide lasers since the first proposal in 1973 and reports on the current state of the art. We describe the development of waveguide designs and of techniques for discharge control which permit high-pressure operation and high output power densities to be obtained.     

A spherical scatterer inside a circular hollow dielectric waveguide

A theoretical investigation is presented of scattering characteristics of a perfectly conducting spherical object placed inside a quasi-optical transmission line of the millimeter and submillimeter waves in the form of a circular hollow dielectric waveguide (HDW). From the analytical expressions obtained, backscattering and extinction cross sections of this object are derived via the excitation coefficient of the dominantHE ₁₁ mode of the circular HDW and the HDW geometrical parameters. The agreement of the results with the corresponding data for the scattering of a plane homogeneous wave is shown.     

介质覆盖的金属中空波导的制作及其传输特性

采用液相沉积的方法，在直径为530μm的玻璃管中制备出了用于CO2激光传输的Agl覆盖的Ag中空波导。在对波导中Agl和Ag层的厚度进行控制，并对波导进行有效的冷却后，测出直波导中的损耗为1.56dB/m。     

Coaxially fed hollow cylindrical monopole in a rectangular waveguide

A formally exact solution that can easily be put in a form suitable for accurate numerical calculation is presented for a hollow coaxially fed cylindrical monopole in a rectangular waveguide. The solution utilises a well known Fourier-transform technique in conjunction with a Cheby?shev polynomial representation for the unknown function. The result is an almost diagonalised infinite matrix?a form eminently suitable for the purpose of numerical inversion.     

Remote sensing of dipole rings

Historical satellite-derived sea surface temperature (SST) data are reanalyzed with a zebra color palette and a thermal separatrix method. The new results from this reanalysis are as follows: (a) thirteen observational sequences of six rings from the Gulf Stream and the Brazil Current, which have historically been interpreted as solitary vortices or monopoles are shown to have a dipolar character; (b) some of these dipole rings have been observed in the open ocean, thereby eliminating the possibility that they are sustained by topographic interactions with the continental slope; (c) whether interacting with other features or evolving as isolated circulations, dipoles are seen to rotate within a relatively narrow range of approximately 4-8° day ^-1 (interacting) and 10-15° day-1 (isolated); and (d) feature tracking delineates energetic fluid in both vortices and eliminates the possibility of interpreting dipole rings as transient features produced by active monopoles and patches of entrained fluid     

Small-bore hollow waveguide for delivery of near singlemode IRlaser radiation

A hollow waveguide whose bore size is 250 μm in diameter is fabricated by depositing a dielectric and a metal layer inside a thin-wall silica tube. This small bore waveguide has an advantage over the larger bore guides in that it maintains a nearly pure HE¹¹ mode of a CO₂ laser even when it is bent to small radii     

Stimulated Raman effect and four-wave mixing in a hollow waveguide

A theoretical and experimental investigation of stimulated Raman scattering and four-wave mixing in a gas-filled hollow waveguide was performed. The four-wave mixing processes, specifically the generation of the third Stokes component at ω₃ when ω₃ =2ω₂-ω₁, show a strong resonance-like behavior as a function of wavelength. These resonances are caused by the phase matching required for efficient four-wave mixing, because the hollow waveguide supports only certain propagation directions leading to the development of waveguide modes. The theoretical results are compared with experimental data for TEM₀₀ and TEM₁₀ fundamental dye-laser beams generating third Stokes wavelengths between 2.6 and 7.5 μm     

Investigation on propagation properties of terahertz waveguide hollow plastic fiber

The propagation properties of terahertz (THz) waveguide plastic hollow fiber have been investigated in this paper. The effects of radiation frequency, bore diameters and dielectric coating layers on the waveguide property have been shown and discussed. The results show that the attenuation loss of TM mode increases and that of TE mode decreases as radiation frequency increases. The attenuation loss decreases with the increasing of fiber bore diameter. The attenuation loss decreases as the refractive index of dielectric coating layer and the ratio of the refractive index of outer dielectric layer to that of inner dielectric layer increase.     

Narrow-core hollow optical waveguide with nanostructured SOI as ultra-low loss platform for efficient photodetection

A nanostructured hollow optical waveguide based on high-index contrast grating (HCG) embedded SOI is proposed. An ultra-low propagation loss of 1.22 dB/m even at narrow, 1-\(\upmu \)m thick, air-core is reported. A high-performance photodetection is realized by the introduction of hollow core in form of intrinsic region in the photodetection (PIN) layer within HCG-assisted narrow-core waveguide. A sufficiently high responsivity of 0.8 A/W and quantum efficiency of 64% are obtained at 1550-nm which is possible because of the presence of surface modes within HCG which get coupled in the photodetection layer leading to a strong optical confinement in that layer. High reflectivity, small penetration length and coupling of lateral surface modes in HCG make it possible to offer improved waveguiding and hence photodetection.     

Remote sensing of the Earth's surface with an airborne polarizedlaser

A new remote sensing instrument, the Airborne Laser Polarization Sensor (ALPS), is making the first multispectral radiometric and polarization measurements of the Earth's surface using a polarized laser light source. Results from data flights taken over boreal forests in Maine at 1060 and 532 nm, using a Nd:YAG laser source, showing depolarization signatures for three broadleaf and five coniferous tree species, are discussed. Measurements made over nonforest ground cover had a large dynamic range in depolarization values at both wavelengths. The ALPS system use twelve photomultiplier tube detectors configurable to measure desired parameters such as the total backscatter and the polarization state, including the azimuthal angle and ellipticity, at different ultraviolet to near-infrared wavelengths simultaneously. Measurements of the azimuth and ellipticity of the backscatter polarization were variable and no specific conclusions have yet been drawn     

Remote sensing by nuclear quadrupole resonance

Detection of explosives has the flavor of those mathematical problems that are not invertible. It is easier to hide explosives than to find them. Many approaches have been proposed and executed for the remote detection of explosives, contraband materials, weapons of mass destruction, currency, etc. Most detection technologies suffer from a common problem: the features they look for, such as discontinuities in electrical conductivity, are not unique properties of the target but are contained, to some degree, in the more benign surroundings. Such a degeneracy leads to “clutter” in the response. For example, resolving the false alarms generated by this clutter can determine the rate of advance of a conventional electromagnetic metal detector employed as a landmine detector. One approach that provides a “unique” signature is nuclear quadrupole resonance (NQR) (the technique is also called QR, to avoid confusion with strictly nuclear techniques). This paper outlines the important physical principles behind the use of NQR for remote detection, indicates areas of applicability, and presents results of field trials of a prototype landmine detection system     

Remote temperature sensing using polarisation-preserving fibre

A fibre-optic temperature sensor is described in which the change in modal birefringence of a short length of polarisation-preserving fibre is monitored in reflection through a 90 m length of input fibre. The system shows high sensitivity and good downlead insensitivity.     

Modeling of radar scattering conditions inside a circular hollow dielectric waveguide

A new ray representation of electromagnetic field inside a quasi — optical structure in the form of a circular hollow dielectric waveguide is suggested and confirms the possibility for the unusual application of such a waveguide as an off-beat microanechoic chamber for electromagnetic modeling in the near millimeter and submillimeter wave regions.     

Local attenuation and field changes in uniformly bent overmodedslab hollow waveguide

A new efficient method has been employed to evaluate fields and losses in overmoded bent hollow waveguide by using the finite difference beam propagation method (FD-BPM) which considers the second field derivative along the propagation direction. The transition losses near the straight and curved sections are shown to be considerably smaller than those predicted by available theory     

共享激光器的分布式光纤气体传感系统

为了实现远端多节点的高效检测并降低成本,设计了一种新颖的分布式光纤气体传感系统。该系统采用共享一个工作于特种波长的分布反馈半导体激光器,将其置于一个本地控制节点内并通过双向光纤链路串联各远端检测节点,同时使用特殊设计的远端节点结构和光纤段,在每个检测节点,用两个Y型耦合器接入气室,将系统中信号分为上行流和下行流,避免来自其它节点信号影响并直接实现时分复用;并以三节点系统的瓦斯体积分数检测为例进行数值计算和实验。结果表明,激光二极管占总成本比重可由约60%降至约38%,且增加循环检测次数能使各节点测定气体体积分数的相对误差降低,首个节点的相对误差可降至0.2%以下,甚至更低,该方案能够精简高效地实现共享光源的分布检测。