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A new coaxial pulsed plasma thruster (PPT) laboratory model is designed and employed in this study. A Teflon sleeve is connected with the anode, which is shaped as a nozzle, and a cathode is mounted in the cavity of the Teflon sleeve and kept in close contact with it. A thread is then designed in the internal surface of the Teflon sleeve, and because of the strong field strength of the cathode triple junction (CTJ), vacuum flashover occurs and a plasma jet is acquired behind the anode. The electric field distribution of the designed coaxial PPT laboratory model is simulated by MAXWELL 3D simulation software, and the plasma density and thrust are measured by a Langmuir probe and a piezoelectric thin-film sensor, respectively. Through a series of comparative experiments, we discuss the impact of optimal designs, such as the thread and the nozzle-shaped anode, on the discharge characteristics of the coaxial PPT. The experimental and simulation results indicate that the designed coaxial PPT laboratory model presents better discharge characteristics in view of its higher plasma density and greater thrust.

A space-borne differential optical absorption spectrometer was designed on the basis of a four channel Offer imaging spectrometer with a convex grating.It could acquire high accuracy radiation scattered by earth surfaces or air in a nadir push-broom mode,and could quantitatively obtain the trace gas distribution based on the "fingerprint" absorption of the trace gas at different spectral information and the differential optical absorption spectrum algorithm.According to the characteristics of large field,wide wavelength range,high spatial and spectral resolution of the spectrometer,the corresponding methods of spectral calibration and radiometric calibration were presented,and a calibration system was built.Then the spectral and radiometric calibrations of the spectrometer were realized,and the calibration uncertainty was analyzed.Experimental results show that spectral calibration uncertainty of the instrument is 0.027 nm and the radiation uncertainty is 2.96%.The calibration accuracy meets the given requirements and can provide a foundation for quantitatively inversion of the instrument.

When UV-Nanoimprint Lithography(NIL) is used in manufacturing gratings of Distributed Feedback Laser Diodes(DFB LDs),the resist often turns into a high polymer after curing and can not be eliminated completely.To eliminate the residual resist,a multi-mask layer process was demonstrated.In this process,a 50 nm SiO2 hard mask was deposited between the wafer and the UV-curable resist and then traditional nanoimprint lithography based on soft stamp UV-imprinting was executed.Following that,the Inductively Coupled Plasma(ICP) dry etching was used to transfer the pattern on the substrate.Finally,it was rinsed with Buffered Oxide Etchant(BOE)for a few seconds.The effect of etching time on the duty ratio of grating was explored and the grating morphologies processed by traditional method and proposed method were compared.A scanning electron microscope image of rinsed grating shows that the grating with about 240 nm pitch and 82 nm depth offers a clean surface and a good feature.Therefore.The proposed method not only can eliminate the residual resist effectively but also can avoid the morphologic damage.

In order to improve the resolution of an Extreme Ultraviolet(EUV) photon counting imager,this paper analyzed the influence of the crosstalk between Wedge Strip Zigzag(WSZ) anodes and the false trigger resulted from out-range signals on image quality.First,the reasons which caused the crosstalk were analyzed,and the range of crosstalk coefficient and its optimum value were determined by measuring interelectrode capacitance.Then,the crosstalk coefficient was used to process photons and determine a proper energy interval(upper and lower limit).Finally,the image obtained in the setting energy interval was compared with an original image.The comparison shows that the image quality has been improved obviously.The results demonstrate that the image edge becomes stronger further and image resolution is improved by eliminating the crosstalk between WSZ anodes and removing fake data from real data.

Mid-infrared spectral region is favorable for high sensitivity trace gas detection.The development and characterization of a compact mid-infrared laser spectrometer for high resolution spectroscopic detection of trace gases is reported.Continuous-wave mid-infrared radiation is generated by difference-frequency mixing of outputs of two commercial narrow linewidth diode lasers.A maximum mid-infrared radiation power of 1 μW at 3.31 μm is generated,and the wavelength tuning region is around 3.2 μm to 3.7 μm.The high-resolution spectroscopy capability of this spectrometer is evaluated by trace CH4 measurement,the line at 3 028.751 cm-1 of v3 fundamental vibrational band of CH4 is chosen as target analysis line for this line is relatively free of interference by other gas species.The detection sensitivity for CH4 is estimated to be 0.8 ppm for 10 cm optical path length at atmospheric pressure,and the limitation is supposed mainly from the etalon noise of optical surfaces.

In consideration of the effect of stray light on the measurement accuracy of a space-borne differential optical absorption spectrometer for monitoring atmospheric trace gases,several stray light removing mechanisms including a light shield and other baffles were developed to suppress the stray light,and the properties of the stray light were analyzed.With TracePro model,the stray light removing of UV channel 1(240-315nm) in the system was evaluated,then the first and second order scattering paths were determined by simulation analysis.On the basis of stray light paths,the stray light removing for revised system was analyzed,and Point Source Transmittance(PST) was calculated.The obtained PST value shows that the light shield and other mechanisms have suppressed the stray light effectively,PST values are less than 3×10-5,and stray radiation ratio in a central field is 5.472 ×10-4.Furthermore,the final stray light suppressing level of the system satisfies the requirement of design index.Moreover,the edge filter method is used to measure the stray light level,and the results indicate that the stray light in the central field is 8.167×10-4,which is close to the simulation results and proves the simulation result to be credible.

A series of Ce3+ and Eu2+ doped Ca8Mg(SiO4)4Cl2 powder were synthesized by high-temperature solid-state reaction.The crystal structure was investigated by X-ray diffraction(XRD) and the fluorescence spectra were also recorded and analyzed.The relative spectral power distribution was obtained by spectral power calibration curve,and the emission color coordinates of samples were calculated and characterized.The XRD spectrum indicate that the phosphor is Ca8Mg(SiO4)4Cl2 with face centered cubic lattice.Ce3+ and Eu2+ doped Ca8Mg(SiO4)4Cl2 samples present purplish-blue and green colors under the excitation of ultraviolet radiation,and the corresponding color coordinates are(0.157 3,0.052 8) and(0.154 0,0.466 3),respectively.In Ce3+/Eu2+ codoped Ca8Mg(SiO4)4Cl2 powder,the introduction of Ce3+ changes the luminescent color obviously,and with the increasing of concentration Ce3+,the color coordinates shift to the greenish blue color region.

Arrayed waveguide grating(AWG)-type optical components are widely used in optical transmission system,and the low cost AWG chips are in more and more urgent need.Among all the methods for lowering the AWG cost,reducing the AWG chip size is one of the most effective methods.A novel compact AWG based on low refractive index contrast silica-on-silicon(SoS) technology was proposed.In this AWG,only the segments connected with the slab waveguides in the input and output waveguides are air trench(AT) waveguides.By using these AT segments,the distance between the adjacent output waveguides connected with the output slab was decreaced greatly,so the focuses of slab waveguides,and the number of arrayed waveguides were decreaced greatly.Thus,the size of AWG chip was decreased dramatically.The arrayed waveguides and the segments coupling to fibers in the input or output waveguides were all fabricated with low refractive index contrast waveguides,for the purpose to obtain low coupling losses with fibers and good performances as traditional SoS AWGs.The size of an AWG designed consisting 40 channels on 100 GHz ITU grid is only 23.88 mm×10.5 mm,which area is about 1/6 of a traditional AWG with the same function.

The yield of curve-shape arrayed waveguide grating(AWG) chips is twice of the square-shape ones.However,the center wavelength of curve-shape AWG is easily influenced by the packaging stress,which is introduced by the linear expansion coefficient difference between the packaging box and the ribbon fibers coupled to the AWG chip.The experimental results showed the AWG center wavelength varied with the thermal stress linearly.The variation of the center wavelength for a thermally stabled AWG module was as large as 46 pm,when the ambient temperature varied from-20 ℃ to 65 ℃,even the ribbon fibers were bonded to the packaging box with soft silicon rubber.In this paper,a new low stress thermal stabled AWG packaging was introduced.In this package,a borosilicate glass plate was bonded to the ceramic heater,and the ribbon fibbers were bonded to it with silicon rubber.For the linear expansion coefficient difference between the borosilicate glass plate and ribbon fiber is very samll,the thermal stress of ribbon fibber or AWG chip is very small.Experimental results showed the typical center wavelength variation for thermally stabled AWG modules manufactured with this technique was smaller than 5 pm,and the typical thermal stress was smaller than 0.029 MPa,when the ambient temperature varied from-20 ℃ to 65 ℃.

It is difficult to obtain a nanoimprint stamp with low cost and high quality in fabrication of Distributed Feedback(DFB)gratings.In this paper,the quartz stamp for semiconductor DFB gratings was fabricated by using double-layer metal mask and lift-off lithography.Firstly,the photoresist pattern of a DFB grating was written on a Ti coated quartz substrate by electron beam lithography,then a layer of metal Ni was sputtered on it to obtain a corresponding pattern by metal lift-off technology.Finally,the Inductively Coupled Plasma(ICP)dry etching was used to transfer the pattern on the quartz substrate.The scanning electron microscope image of the fabricated stamp shows good uniformity with sufficiently low line edge roughness.The stamp is suitable to fabricate DFB grating for 1 310 nm semiconductor laser diodes using UV nanoimprint lithography.