This paper analyses frequency tracking characteristics of a complex-coefficient adaptive infinite-impulse response (IIR) notch filter used for suppression of narrow-band interference (NBI) with a randomly-varying freq...This paper analyses frequency tracking characteristics of a complex-coefficient adaptive infinite-impulse response (IIR) notch filter used for suppression of narrow-band interference (NBI) with a randomly-varying frequency in a quadriphase shift keying (QPSK) modulated direct-sequence code-division multiple-access (DS-CDMA) communication system. The QPSK DS-CDMA signals are transmitted over a frequency non-selective Rayleigh fading channel. The analysis is based on a first-order real-coefficient difference equation with respect to steady-state instantaneous frequency tracking error from which a closed-form expression that relates frequency tracking mean square error (MSE) with number of DS-CDMA active users and NBI power is obtained. Closed-form expressions for optimum notch bandwidth coefficient and step size constant that minimize the frequency tracking MSE are also derived. Computer simulations are included to substantiate the accuracy of the analyses.展开更多
A laser at 578 nm is phase-locked to an optical frequency comb（OFC） which is optically referenced to a subhertzlinewidth laser at 1064 nm. Coherence is transferred from 1064 nm to 578 nm via the OFC. By comparing wi...A laser at 578 nm is phase-locked to an optical frequency comb（OFC） which is optically referenced to a subhertzlinewidth laser at 1064 nm. Coherence is transferred from 1064 nm to 578 nm via the OFC. By comparing with a cavitystabilized laser at 578 nm, the absolute linewidth of 1.1 Hz and the fractional frequency instability of 1.3 × 10^-15 at an averaging time of 1 s for each laser at 578 nm have been determined, which is limited by the performance of the reference laser for the OFC.展开更多
A 60-mW solid-state deep ultraviolet(DUV)laser at 193 nm with narrow linewidth is obtained with two stages of sum frequency generation in LBO crystals.The pump lasers,at 258 and 1553 nm,are derived from a homemade Yb-...A 60-mW solid-state deep ultraviolet(DUV)laser at 193 nm with narrow linewidth is obtained with two stages of sum frequency generation in LBO crystals.The pump lasers,at 258 and 1553 nm,are derived from a homemade Yb-hybrid laser employing fourth-harmonic generation and Er-doped fiber laser,respectively.The Yb-hybrid laser,finally,is power scaling by a 2 mm×2 mm×30 mm Yb:YAG bulk crystal.Accompanied by the generated 220-mW DUV laser at 221 nm,the 193-nm laser delivers an average power of 60 mW with a pulse duration of 4.6 ns,a repetition rate of 6 kHz,and a linewidth of∼640 MHz.To the best of our knowledge,this is the highest power of 193-and 221-nm laser generated by an LBO crystal ever reported as well as the narrowest linewidth of 193-nm laser by it.Remarkably,the conversion efficiency reaches 27%for 221 to 193 nm and 3%for 258 to 193 nm,which are the highest efficiency values reported to date.We demonstrate the huge potential of LBO crystals for producing hundreds of milliwatt or even watt level 193-nm laser,which also paves a brand-new way to generate other DUV laser wavelengths.展开更多
Interference filter-stabilized external cavity diode lasers （ECDLs） have properties of simple configurations, high sta- bilities, and narrow linewidths. However, the interference filter used in common ECDL designs r...Interference filter-stabilized external cavity diode lasers （ECDLs） have properties of simple configurations, high sta- bilities, and narrow linewidths. However, the interference filter used in common ECDL designs requires an ultra-narrow bandwidth （about 0.3 nm） to achieve mode selection, that is considerably expensive and not yet available for a wide range of wavelengths. In this paper, a robust ECDL using an available broad bandwidth （about 4 nm） interference filter as the wavelength discriminator is constructed and tested. The ECDL demonstrated a narrow Lorentzian fitted linewidth of 95 kHz and a spectral purity of 2.9 MHz. The long-term frequency stability of the ECDL reaches 5.59 x 10 12.展开更多
针对窄间隙熔化极气体保护焊(Gas Metal Arc Welding,GMAW)焊道侧壁处局部咬边缺陷检测困难的问题,提出了一种基于电弧声信号特征提取与处理的咬边缺陷在线检测方法。通过分析正常、临界咬边和咬边这3种焊接状态的电弧形态和电弧声信号...针对窄间隙熔化极气体保护焊(Gas Metal Arc Welding,GMAW)焊道侧壁处局部咬边缺陷检测困难的问题,提出了一种基于电弧声信号特征提取与处理的咬边缺陷在线检测方法。通过分析正常、临界咬边和咬边这3种焊接状态的电弧形态和电弧声信号特征,证实坡口侧壁引起的电弧形态变化是影响电弧声信号变化的重要因素。在此基础上采用小波包时频分析,同时引入特征类间标准差作为评价指标,确定了能有效识别3种焊接状态的敏感特征。采用Sigmoid支持向量机和五折交叉验证建立预测模型,实验结果表明该模型能较好地实现3种焊接状态的预测分类,识别准确率达到96.0%。展开更多
The objective of this study is to develop a simple tool for predicting the resonant frequency of the piston mode wave oscillation in a moonpool or a narrow gap between twin floating barges.Based on the dynamic analysi...The objective of this study is to develop a simple tool for predicting the resonant frequency of the piston mode wave oscillation in a moonpool or a narrow gap between twin floating barges.Based on the dynamic analysis and the domain-decomposition,a linear harmonic oscillator model for the fluid oscillation in a confined space is formulated,which immediately leads to an explicit dynamic solution for the resonant frequency.In the model,it is assumed that the water depth is equal to or greater than a critical value dependent on the ratio of the draft to the breadth of the floating body.The predicted resonant frequencies are compared with the numerical results of the linear potential model and the viscous fluid model,the semi-analytical potential solutions and the experimental measurements.Good agreements are observed for a wide range of geometric parameters of the moonpool and the narrow gap of either sharp or round edge shapes.The present dynamic method is also applied to predict the resonant frequency of the piston mode oscillation in the gap between a floating body and a vertical wall with a reasonable success.展开更多
本文对高重频窄脉宽多波长激光器的可靠性进行了分析及验证,建立了高重频窄脉宽多波长激光器的框图法模型。在初始设计阶段开展激光器的可靠性分析,定量计算了激光器各单元的可靠性结果,包括失效率λ和平均无故障工作时间(Mean Time Bet...本文对高重频窄脉宽多波长激光器的可靠性进行了分析及验证,建立了高重频窄脉宽多波长激光器的框图法模型。在初始设计阶段开展激光器的可靠性分析,定量计算了激光器各单元的可靠性结果,包括失效率λ和平均无故障工作时间(Mean Time Between Failure,MTBF),预计激光器整机的无故障工作时间为1798.8 h。为满足激光器的设计指标要求,通过选用高品质晶体、半导体激光器的Ⅰ级降额设计和电源控制的冗余设计,实现激光器的可靠性优化。经优化设计后,激光器整机的无故障工作时间达2260.9 h。搭建激光器整机对可靠性优化设计结果进行验证,验证结果表明:激光器无故障工作时间可达2400 h。展开更多
文摘This paper analyses frequency tracking characteristics of a complex-coefficient adaptive infinite-impulse response (IIR) notch filter used for suppression of narrow-band interference (NBI) with a randomly-varying frequency in a quadriphase shift keying (QPSK) modulated direct-sequence code-division multiple-access (DS-CDMA) communication system. The QPSK DS-CDMA signals are transmitted over a frequency non-selective Rayleigh fading channel. The analysis is based on a first-order real-coefficient difference equation with respect to steady-state instantaneous frequency tracking error from which a closed-form expression that relates frequency tracking mean square error (MSE) with number of DS-CDMA active users and NBI power is obtained. Closed-form expressions for optimum notch bandwidth coefficient and step size constant that minimize the frequency tracking MSE are also derived. Computer simulations are included to substantiate the accuracy of the analyses.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11334002,11374102,11104077,and 11127405)the National Basic Research Program of China(Grant No.2012CB821302)
文摘A laser at 578 nm is phase-locked to an optical frequency comb（OFC） which is optically referenced to a subhertzlinewidth laser at 1064 nm. Coherence is transferred from 1064 nm to 578 nm via the OFC. By comparing with a cavitystabilized laser at 578 nm, the absolute linewidth of 1.1 Hz and the fractional frequency instability of 1.3 × 10^-15 at an averaging time of 1 s for each laser at 578 nm have been determined, which is limited by the performance of the reference laser for the OFC.
基金supported by the Research Project of Aerospace Information Research Institute,Chinese Academy of Sciences (Grant Nos.E1Z1D101 and E2Z2D101)the Project of Chinese Academy of Sciences (Grant No.E33310030D)the Guangzhou Basic and Applied Basic Research Foundation (Grant Nos.2023A04J0336 and 2023A04J0021).
文摘A 60-mW solid-state deep ultraviolet(DUV)laser at 193 nm with narrow linewidth is obtained with two stages of sum frequency generation in LBO crystals.The pump lasers,at 258 and 1553 nm,are derived from a homemade Yb-hybrid laser employing fourth-harmonic generation and Er-doped fiber laser,respectively.The Yb-hybrid laser,finally,is power scaling by a 2 mm×2 mm×30 mm Yb:YAG bulk crystal.Accompanied by the generated 220-mW DUV laser at 221 nm,the 193-nm laser delivers an average power of 60 mW with a pulse duration of 4.6 ns,a repetition rate of 6 kHz,and a linewidth of∼640 MHz.To the best of our knowledge,this is the highest power of 193-and 221-nm laser generated by an LBO crystal ever reported as well as the narrowest linewidth of 193-nm laser by it.Remarkably,the conversion efficiency reaches 27%for 221 to 193 nm and 3%for 258 to 193 nm,which are the highest efficiency values reported to date.We demonstrate the huge potential of LBO crystals for producing hundreds of milliwatt or even watt level 193-nm laser,which also paves a brand-new way to generate other DUV laser wavelengths.
基金Project supported by the Foundation of Based Technology of China(Grant No.YXBGD20151JL01)the National Natural Science Foundation of China(Grant Nos.61376049,61604007,11674016,61378058,61575008,and 61574011)+1 种基金the Natural Science Foundation of Beijing City,China(Grant Nos.4172009 and4152003)the Beijing Municipal Commission of Education of China(Grant Nos.PXM2017 014204 500034 and PXM2016 014204 500018)
文摘Interference filter-stabilized external cavity diode lasers （ECDLs） have properties of simple configurations, high sta- bilities, and narrow linewidths. However, the interference filter used in common ECDL designs requires an ultra-narrow bandwidth （about 0.3 nm） to achieve mode selection, that is considerably expensive and not yet available for a wide range of wavelengths. In this paper, a robust ECDL using an available broad bandwidth （about 4 nm） interference filter as the wavelength discriminator is constructed and tested. The ECDL demonstrated a narrow Lorentzian fitted linewidth of 95 kHz and a spectral purity of 2.9 MHz. The long-term frequency stability of the ECDL reaches 5.59 x 10 12.
文摘针对窄间隙熔化极气体保护焊(Gas Metal Arc Welding,GMAW)焊道侧壁处局部咬边缺陷检测困难的问题,提出了一种基于电弧声信号特征提取与处理的咬边缺陷在线检测方法。通过分析正常、临界咬边和咬边这3种焊接状态的电弧形态和电弧声信号特征,证实坡口侧壁引起的电弧形态变化是影响电弧声信号变化的重要因素。在此基础上采用小波包时频分析,同时引入特征类间标准差作为评价指标,确定了能有效识别3种焊接状态的敏感特征。采用Sigmoid支持向量机和五折交叉验证建立预测模型,实验结果表明该模型能较好地实现3种焊接状态的预测分类,识别准确率达到96.0%。
基金Project supported by the National Nature Science Foundation of China(Grant No.51490673)the National Key R&D Program of China(Project ID:2016YFE0200100).
文摘The objective of this study is to develop a simple tool for predicting the resonant frequency of the piston mode wave oscillation in a moonpool or a narrow gap between twin floating barges.Based on the dynamic analysis and the domain-decomposition,a linear harmonic oscillator model for the fluid oscillation in a confined space is formulated,which immediately leads to an explicit dynamic solution for the resonant frequency.In the model,it is assumed that the water depth is equal to or greater than a critical value dependent on the ratio of the draft to the breadth of the floating body.The predicted resonant frequencies are compared with the numerical results of the linear potential model and the viscous fluid model,the semi-analytical potential solutions and the experimental measurements.Good agreements are observed for a wide range of geometric parameters of the moonpool and the narrow gap of either sharp or round edge shapes.The present dynamic method is also applied to predict the resonant frequency of the piston mode oscillation in the gap between a floating body and a vertical wall with a reasonable success.
文摘本文对高重频窄脉宽多波长激光器的可靠性进行了分析及验证,建立了高重频窄脉宽多波长激光器的框图法模型。在初始设计阶段开展激光器的可靠性分析,定量计算了激光器各单元的可靠性结果,包括失效率λ和平均无故障工作时间(Mean Time Between Failure,MTBF),预计激光器整机的无故障工作时间为1798.8 h。为满足激光器的设计指标要求,通过选用高品质晶体、半导体激光器的Ⅰ级降额设计和电源控制的冗余设计,实现激光器的可靠性优化。经优化设计后,激光器整机的无故障工作时间达2260.9 h。搭建激光器整机对可靠性优化设计结果进行验证,验证结果表明:激光器无故障工作时间可达2400 h。
