多通道扫描型红外光纤气体测量系统研究

提出了一种将声光可调滤光器技术应用于气体浓度测量的红外光谱系统。该系统以氙灯作为光源,TeO2晶体作为声光介质的色散元件,InGaAs光电二极管阵列作为多通道检测器,利用光纤探测和传输光信号,由计算机处理数据和显示结果。通过声光调制将宽带光变为单色光,通过超声射频的变化实现光谱扫描,可对不同气体进行快速测量,无机械调谐机构,结构简单。通过对甲烷气体的实验表明,该系统的有效光谱测量范围为900~1900nm,光谱分辨率为60nm,可用于对有害气体的在线检测。     

Near-ultraviolet Incoherent Broadband Cavity Enhanced Absorption Spectroscopy for OClO and CH2O in Cl-initiated Photooxidation Experiment (cited: 3)

Chlorine dioxide (OClO) is an important indicator for Cl-activation. The monitoring of OClO appears to be crucial for understanding the chemistry of Cl-initialed oxidation and its impact on air quality in polluted coastal regions and industrialized areas. We reportthe development of a Xe arc lamp based near-ultraviolet (335-375 nm) incoherent broad-band cavity enhanced absorption spectroscopy (IBBCEAS) spectrometer for quantitative assessment of OClO in an atmospheric simulation chamber. The important intermediate compound CH₂O, and other key atmospheric trace species (NO₂) were also simultaneously measured. The instrumental performance shows a strong potential of this kind of IBBCEAS instrument for field and laboratory studies of atmospheric halogen chemistry.     

固相微萃取纤维研究进展

固相微萃取是一种新型的萃取分离技术. 由于它具有富集能力强、分析速度快、操作简便及便于现场分析和仪器联用等优点,成为痕量物质分离检测分析的重要工具. 固相微萃取技术的核心是固相微萃取纤维. 总结了固相微萃取纤维在稳定性、使用寿命及选择性方面的一些特点,并综述了近年来在这些方面所进行的研究工作及发展方向.     

Approximate analytical expressions of apertured broadband beams in the far field

The approximate analytical expressions of the apertured broadband beams in the far field with Gaussian and Laguerre-Gaussian spatial modes are presented.For the radially polarized Laguerre-Gaussian beam,the result reveals that the electromagnetic field in the far field is transverse magnetic.The influences of bandwidth(Γ) and truncation parameter(C 0) on the transverse intensity distribution of the Gaussian beam and on the energy flux distribution of radially polarized Laguerre-Gaussian beam are analysed.     

Real‐Time and Broadband Terahertz Wave Scattering Manipulation via Polarization‐Insensitive Conformal Graphene‐Based Coding Metasurfaces

Here, for the first time, the real‐time and broadband manipulation of terahertz (THz) waves are acquired by introducing a multifunctional graphene‐based coding metasurface (GBCM). The designed structure consists of subwavelength patterned graphene units whose operational statuses can be dynamically switched between two digital states of “0” and “1”. By engineering the spatial distribution of chemical potentials across the GBCM, various scattering patterns having single, two, four, and numerous reflection beams are elaborately achieved just within one planar structure. To compute the far‐field pattern of GBCM, an inverse discrete Fourier transform (IDFT) is established, providing a fast and efficient design method. The proposed GBCM provides a low reflection bellow ?10 dB over a broad frequency band ranging from 1 THz to 1.9 THz. In addition, the metasurface retains its low reflection behavior in a wide range of incident wave angles for both TE and TM polarizations. According to conformal invariance of graphene sheets, the stealth property of GBCM is well preserved while wrapping around a curved object. The proposed technique of real‐time scattering manipulation leads to multifunctional THz devices, opening new routes contributing to numerous applications such as imaging and stealth technology.     

Wavelength tunable ultra-short pulses based on a flat broadband spectrum generated in a nonlinear ytterbium-doped fiber amplifier

We present a nonlinear ytterbium-doped fiber amplifier based on enhanced nonlinear effects that can produce a flat broadband spectrum ranging from 1050–1225 nm with a maximum average output power of 7.8 W at 14 W pump power.Its repetition rate is 89 MHz. Using a pair of gratings and two knife edges as a filter, wavelength tunable picosecond pulses of tens to hundreds of milliwatts can be obtained in the broadband spectrum range. The output power, pulse width, and spectrum(center wavelength and linewidth) are adjusted by tuning the distance of the grating pair and/or the knife edges.Fixing the distance between the two gratings at 15 mm and keeping the output spectrum linewidth at approximately 20 nm,the shortest pulse width obtained is less than 1 ps centered at 1080 nm. The longest wavelength of the short pulses is around1200 nm, and its output power and pulse width are 40 m W and 5.79 ps, respectively. The generation of a flat broadband spectrum is also discussed in this paper.     

Single-layer broadband planar antenna using ultrathin high-efficiency focusing metasurfaces

Phase gradient metasurfaces(PGMS) offer a fascinating ability to control the amplitude and phase of the electromagnetic(EM) waves on a subwavelength scale, resulting in new applications of designing novel microwave devices with improved performances. In this paper, a reflective symmetrical element, consisting of orthogonally I-shaped structures, has been demonstrated with an approximately parallel phase response from 15 GHz to 22 GHz, which results in an interesting wideband property. For practical design, a planar antenna is implemented by a well-optimized focusing metasurface and excited by a self-designed Vivaldi antenna at the focus. Numerical and experimental results coincide well. The planar antenna has a series of merits such as a wide 3-d B gain bandwidth of 15–22 GHz, an average gain enhancement of 16 d B, a comparable aperture efficiency of better than 45% at 18 GHz, and also a simple fabrication process. The proposed reflective metasurface opens up a new avenue to design wideband microwave devices.     

机载腔增强吸收光谱系统应用于大气NO_2空间高时间分辨率测量

介绍了一套用于机载平台测量的非相干宽带腔增强吸收光谱(IBBCEAS)系统,并应用于实际大气NO_2空间分布的高时间分辨率观测.为满足机载测量中对时间分辨率的需求,系统采用离轴抛物面镜代替消色差透镜提高光学耦合效率;并运用Allan方差,对系统性能进行了分析.通过腔增强吸收光谱系统与长光程吸收光谱系统对实际大气NO_2的对比测试,两者线性相关系数R~2达到0.86.将IBBCEAS系统应用于机载平台,在时间分辨率为2 s的情况下,探测限达到95 ppt(1σ).通过机载观测,获得了华北地区石家庄等地上空对流层大气NO_2的廓线信息.     

宽带磁共振T/R开关的设计与实现

磁共振系统中的发射/接收（transmit/receive,T/R）开关用于收发通路的切换,要求在隔离大功率信号的同时具有较小的插入损耗;另外,在宽带磁共振谱仪中,一般的窄带T/R开关也不再适用.本文基于PIN（positive-intrinsic-negative）二极管设计了工作频率为10~100 MHz的宽带磁共振T/R开关.通过减小电平跳变、优化开关过冲和解决二极管被动导通等问题,获得了插入损耗小于1 dB、大功率信号隔离度大于75 dB、开关时间1 μs的整体性能.用本文设计的宽带T/R开关替代一般探头中的窄带T/R开关,在0.5 T核磁共振（NMR）波谱仪上测得了氢核和氟核两个不同频率的磁共振信号,验证了宽带T/R开关的宽带性能.     

Strong and broadband terahertz absorber using Si02-based metamaterial structure

We design and experimentally demonstrate a broadband metamaterial absorber in the terahertz （THz） band based on a periodic array of aluminum （A1） squares with two different sizes. A thin silicon dioxide （SiO2） film rather than a conventional polyimide （PI） layer is used as a dielectric spacer to separate A1 squares from the platinum （Pt） ground plane in our design, which significantly improves the design precision and the feasibility of the device fabrication. The combination of different sizes of AI squares gives rise to an absorption bandwidth of over 210 GHz with an absorption of over 90%. Our results also show that our device is almost polarization-insensitive. It works very well for all azimuthal angles with an absorption of beyond 80%.