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摘要

提出一種用于半導體芯片表面裂紋瞬時成像檢測的線激光鎖相熱成像新技術。該技術系統由線掃描激光源、高速紅外照相機及控制計算機組成,由線激光束掃描目標芯片表面并利用紅外相機測量熱波傳播。提出新型無基線裂紋可視化算法,裂紋可導致熱波阻擋現象,故被自動可視化和診斷,不依賴由目標芯片原始狀態所獲得的基線數據。對芯片在制造過程中產生細微裂紋進行研究,實驗證明熱成像新技術可對寬度為幾十微米的裂紋進行可視化。

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摘要

為了解決對小目標物體識別精度較差的問題,提出了一種雙注意力模型引導的目標檢測算法。該方法基于單階段檢測算法的實現原理,通過引入兩種注意力模型來提升檢測性能,尤其是對小目標物體。首先在卷積神經網絡中引入一個多尺度特征級聯注意力模塊,對原始卷積神經網絡的特征圖中各區域進行不同重要程度的關注,降低特征圖的背景及負樣本信息的干擾,特別是在淺層特征圖中可對小目標物體進行有效的關注。此外,密集連接的方式緩解了網絡反向傳播過程中梯度消失的問題。其次,對融合后的特征引入顯著通道自注意力模塊,區分特征圖不同通道,篩選出有用的通道信息,使待檢測的特征更具表征性。在目標檢測基準數據集COCO上進行測試,驗證了所提方法的有效性和先進性。

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摘要

提出一種基于馬爾科夫鏈蒙特卡羅(MCMC)框架的子圖學習方法,該方法通過構建馬爾科夫鏈實現子圖在狀態空間中的迭代,最終得到用于匹配的最優子圖,以有效提高圖匹配的精度,減少離散值的影響。在此過程中,所提方法可以在一對一的匹配約束下有效保存成對的匹配點,同時避免了離散值和畸變值的影響。實驗分別在合成圖像數據集、真實圖像數據集、3D模型數據集上展開,實驗結果證明了所提方法在圖匹配過程中的優越性。

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摘要

基于內容的醫學圖像檢索方法是近年來計算機視覺領域的研究熱點,已經廣泛應用于計算機輔助診斷的研究中。概述了基于內容的醫學圖像檢索方法的研究進展及意義,介紹了當前主流的醫學圖像檢索算法及其優缺點,旨在引導研究人員快速了解本領域的研究內容。醫學圖像檢索的研究主要分為特征提取和相似性度量兩部分。從傳統特征提取及近年來興起的基于深度學習的特征提取入手來介紹醫學圖像的特征提取方式;而相似性度量部分則詳細列舉了馬氏距離度量、詞匯樹以及哈希算法。最后概述了醫學圖像檢索領域的相關反饋技術及當前常用的圖像檢索系統,并討論了醫學圖像檢索未來可能的研究方向及相關難點。

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摘要

關聯成像以其非定域性、抗干擾能力強等特點得到研究人員的廣泛關注,在三維成像、遙感成像、生物醫療、國防軍事等領域具有廣闊的應用前景。本綜述根據發展階段的不同,詳細介紹了糾纏雙光子關聯成像、(贗)熱光關聯成像和計算關聯成像的發展歷程及應用現狀,尤其是近年來微光相機(ICCD)的出現為關聯成像發展帶來的促進作用及最新進展。針對熱光關聯成像的物理本質進行了簡單的討論,對關聯成像的實際應用進行了展望。

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摘要

為了制造高精度塑料衍射微透鏡,提出采用Taguchi方法在大范圍內選擇工藝參數,通過信噪比確定顯著影響微結構成型精度的工藝參數,并通過加權綜合評分法進行多目標優化獲得最優參數組合。結果表明保壓壓力、模具溫度和保壓時間對微結構成型精度具有顯著影響。為了提高衍射微結構成型精度,分析了衍射微透鏡注塑成型誤差的主要來源并建立了誤差補償模型。實驗結果表明注塑成型的衍射微結構高度誤差為5.69%,周期寬度誤差為6.16%,衍射微結構的注塑成型精度獲得顯著提高。

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摘要

對兩艾里-高斯光束在一維非局域非線性缺陷晶格中的相互作用進行數值研究,并分別討論了非線性非局域性、晶格性質、光束性質、光束入射角以及兩光束相位差對傳輸實驗結果的影響。實驗發現兩艾里-高斯光束在不同條件下相互作用會形成晶格孤子、準呼吸子,甚至還出現了晶格孤子對。其中,多數情況下觀察到了準呼吸子,且準呼吸子的空間大小和周期受到了非局域非線性、晶格缺陷以及光速自加速的影響。當兩艾里-高斯光束之間存在相位差入射時,它們在晶格中相互作用,形成兩個孤子對,一對孤子垂直傳輸,而另一對孤子斜向傳輸。

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摘要

利用視網膜功能測量儀對眼底進行結構成像來直接觀察體內豐富的循環系統,并對視網膜的血氧飽和度及血管直徑進行無創、定量的功能性成像測量。對糖尿病患者和健康人群進行視網膜功能成像并作定量比較分析,結果表明,在糖尿病患者中,視網膜動脈血氧飽和度相比健康人群有顯著性提高,視網膜動靜脈血氧飽和度差值有顯著性增大,視網膜黃斑中心凹無灌注區面積也有顯著增大。此外,在糖尿病患者和健康人群中,視網膜動靜脈的直徑均存在差異,且靜脈直徑總大于動脈直徑。研究結果表明通過視網膜功能成像可以檢測糖尿病患者的視網膜氧代謝和灌注率等參數的臨床變化,幫助醫生更好地觀察、評估糖尿病患者視網膜微血管的病理改變,并在糖尿病患者眼科并發癥的早期診斷和預后評估方面具有一定的應用潛力。

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摘要

針對接觸式測量高鐵機車靜態限界效率低、精度低、耗時長、勞動強度大等問題,基于回轉射線簇測量的原理,研制出新型的高鐵靜態限界二維掃描傳感器。傳感器安裝在運動導軌上,可實現靜態限界的高效自動化測量。借助高精度大理石平面對傳感器進行標定,建立測量系統的坐標系,結合外部標定,將傳感器測量結果轉換到軌道坐標系下的三維坐標,從而得到高鐵的靜態限界測量數據。實驗驗證,該傳感器精度優于1 mm,滿足了靜態限界測量的需求。

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同軸送粉噴嘴是激光金屬增材制造系統裝備的核心部件之一,直接影響著激光增材制造零件的成形精度及性能。因其重要性,國內外學者們已開發出多種新型送粉噴嘴。簡要從“光外送粉”和“光內送粉”兩種光粉相對位置不同的送粉方式概括了國內外對同軸送粉噴嘴的研究,并從激光束和粉末束是否可變焦的角度進行了分析,指明了現有同軸送粉噴嘴的特點,對未來同軸送粉噴嘴的發展進行了展望。

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摘要

基于相干瑞利散射的分布式光纖聲波傳感(DAS)技術可以實時獲取光纖沿線各位置的振動和聲場信息,具有傳感范圍大、時空精度高等獨特優勢,近年來得到了多個領域研究學者的廣泛關注。論述了DAS的基本傳感機理,概述了相干衰落抑制、響應帶寬與空間分辨率提升等關鍵科學技術問題的研究進展,介紹了DAS在安防、鐵路等領域的應用進展,并針對DAS技術未來可能的發展方向進行了評述與展望。

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采用太赫茲時域光譜系統測試黃芩苷混合物的光譜,發現黃芩苷混合物在0.3~1.5 THz波段具有明顯的吸收特征;采用二維相關光譜(2DCOS)算法進行分析后發現,混合物光譜對外擾變量(黃芩苷的濃度)變化敏感。在光譜分析的基礎上分別建立了基于支持向量機(SVM)和偏最小二乘法(PLS)的定量分析模型,采用Kenard-Stone(KS)法選擇模型的校準集和驗證集,引入相關系數和均方根誤差評價建模效果。結果表明:基于支持向量機和偏最小二乘法的定量分析模型的預測數據與實際數據均表現出良好的相關性,并且均方根誤差較小,能夠實現對黃芩苷的定量檢測;SVM模型的預測結果優于PLS模型。研究結果為藥物質量檢測提供了一種新方法,對藥物的質量檢測具有重要意義。

PDF全文中國激光 | 2020,47(03):0314001
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摘要

大氣壓力是最重要的氣象要素之一。為了實現空間激光遙感大氣壓力,需要先進行必要的地基激光雷達探測實驗研究。以單縱模Nd∶YAG激光器的二倍頻532 nm激光脈沖作為泵浦源,以KTP(KTiOPO4)晶體作為非線性轉換介質的光參量振蕩器和光參量放大器,產生了760.236 nm和760.307 nm 波長的兩種激光脈沖,脈沖能量為40 mJ,采用?350 mm望遠鏡接收大氣的后向散射,從而獲得了不同高度處與激光雷達之間雙波長的差分光學厚度。有效探測高度為500~4000 m,時間分辨率為1~5 min。實驗結果表明,差分光學厚度對應著大氣層不同高度處與激光雷達間的壓力差,其對應關系的數值表達是可以期待的。

PDF全文中國激光 | 2020,47(03):0310003
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摘要

針對齒輪故障難以識別的問題,提出了一種用于齒輪異常狀態識別的自適應噪聲補償聚合經驗模態分解方法。利用光纖布拉格光柵(FBG)傳感器提取齒輪的振動信號,通過自適應補償高斯白噪聲使振動信號頻譜均勻化,以消除經驗模態算法分解產生的模態混疊現象。利用相關系數和峭度值組成綜合評價指標來選擇有效分量,并提取其特征,采用支持向量機對齒輪故障進行識別與分類。實驗結果表明:所提方法能有效地識別齒輪的不同狀態(正常、輕度磨損、重度磨損、點蝕、裂紋以及斷齒等),識別正確率均在90%以上。

PDF全文中國激光 | 2020,47(03):0304007
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摘要

提出了一種基于最小二乘擬合的三角波調幅激光測距方法,設計了具有光程差的參考信號和測量信號兩路信道,采用改進的最小二乘直線擬合算法對兩路回波信號進行擬合,得到了關于三角波的擬合參數和奇異特征點;根據兩路信號特征點所攜帶的時移信息之間的關系,可用所提方法進行測距。在10 kHz三角波調制頻率的實驗條件下,采用幾何理論計算得出所提測距方法在測量距離為10 m時的平均測量精度能達到3.2 mm。實驗結果證明了該測距方法的有效性,在短距離激光測距方面具有一定的應用前景。

PDF全文中國激光 | 2020,47(03):0304006
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摘要

為實現不等壁厚復雜零件的激光增材制造,設計開發了一種基于自適應鏡的可變圓光斑激光熔覆光學系統。系統由反射式拋物準直鏡、反射式自適應鏡和反射式拋物聚焦鏡等組成。通過氣壓比例閥調節自適應鏡腔內氣壓,改變自適應鏡表面曲率半徑,使光束以不同程度的會聚角或發散角入射到反射式拋物聚焦鏡,從而改變作用在工件表面的激光光斑大小。建立了基于自適應鏡變斑光學系統的物理模型,通過Matlab和Zemax軟件仿真分析了自適應鏡焦距的變化范圍、反射式拋物準直鏡與反射式拋物聚焦鏡的焦距和位置,以及光纖激光光源參數等對系統變斑特性的影響。采用6 kW光纖激光器,按照變光斑、變功率、等速度、等功率密度的方案進行激光熔覆工藝實驗,實現了壁厚由3 mm漸變到8 mm的橢圓形工件的激光熔覆增材制造。

PDF全文中國激光 | 2020,47(03):0302007
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摘要

通過微結構結合鍍膜的方法成功設計和制備了中紅外寬帶減反射元件。首先,利用FDTD Solutions軟件,模擬了微結構周期、占空比、高度以及膜層厚度對所需波段透射率的影響規律,得到較好增透效果的微結構和膜層結構參數;根據設計參數,采用激光干涉曝光和反應離子束刻蝕技術在藍寶石表面制備出相應微結構,然后在其表面鍍制相應厚度的SiO2膜。測試結果表明:僅有單面微結構的藍寶石元件在1.5~4 μm波段的平均透射率達到92.3%,具有復合結構的藍寶石元件在該波段的平均透射率高達98.7%,相對雙面拋光藍寶石樣品透射率提升11.0%左右,實現了藍寶石表面的寬帶增透;對具有復合結構的藍寶石元件進行了濕度驗證和高低溫循環實驗,實驗前后透射率曲線無明顯變化,且無明顯水吸收,說明該元件具有很好的環境適用性。

PDF全文中國激光 | 2020,47(03):0301006
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為實現金屬光柵偏振器件在光刻機偏振照明系統中的應用,基于共振域光柵的反常偏振效應,提出一種以二氧化硅為基底、鋁與氟化鎂作為柵線材料的介質-金屬光柵偏振器。與傳統的亞波長金屬光柵偏振器相比,該偏振器的光柵周期接近入射波長(0.19~0.20 μm),表現出透射TE偏振光、反射TM偏振光的反常特性。由時域有限差分算法(FDTD)的數值模擬結果可得,當波長為0.193 μm的光垂直入射時,該光柵偏振器對TE偏振光的透過率大于60%,偏振消光比大于180。與具有相同結構參數和柵線材料的單層金屬光柵偏振器相比,該介質-金屬光柵偏振器在深紫外波段具有良好的偏振性能,TE偏振光透過率提升了約10%,偏振消光比提升了4.5倍左右(在0.193 μm波長下)。

PDF全文中國激光 | 2020,47(03):0301005
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摘要

提出了一種基于陣列透鏡和漸變多模光纖集束的調頻脈沖測試方法,該方法通過漸變折射率多模光纖提供較大的接收孔徑,通過子孔徑拼接方式取樣降低取樣光斑在光纖端面的漂移,兩者相結合可實現光束近場能量到光纖集束的高效穩定耦合。該方法中的漸變多模光纖集束可攜帶更多的取樣光能量,有利于脈沖的高對比度測量。實驗結果表明,本技術方案能夠實現調頻脈沖光束整體時間特性的保真測量,測量對比度可達630∶1。

PDF全文中國激光 | 2020,47(03):0301004
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摘要

依據自由電子激光(FEL)超快輻射脈沖電離產生光電子波包受單周期太赫茲場調制的原理,發展了光電子全動量動力學模型,并通過光電子終態能譜在太赫茲場矢勢零點的展寬來復原FEL脈沖長度。進一步分析比較不同脈沖長度的光電子波包在不同延時處脈沖復原的誤差,評估了實際測量中時間同步的精度要求。另外,還提出了一種測量雙脈沖延時的方案,并通過數值計算驗證該方案的準確性。

PDF全文HTML全文 光學學報 | 2020,40(06):0632001
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摘要

The diagnosis of osteoporosis is eventually converted to the measurement of bone mineral density (BMD) in clinical trials. Since our previous work had proved the ability of using photoacoustic spectral analysis (PASA) to efficiently detect osteoporosis, in this contribution, we proposed a fully connected multi-layer deep neural network combined with PASA to semi-quantify BMD values corresponding to varying degrees of bone loss and to further evaluate the degree of osteoporosis. Experiments were carried out on swine femur heads, and the performance of our proposed method is satisfying for future clinical screening.

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    摘要

    We propose and analyze a silicon hybrid plasmonic polarization splitter-rotator with an ultra-short footprint using an asymmetric bent directional coupler on a silicon-on-insulator platform. Benefitting from the large birefringence induced by the bent structure and plasmonic effect, the cross-polarization coupling length is only 5.21 μm. The transverse magnetic to transverse electric polarization conversion efficiency is over 99.9%, with an extinction ratio of 20.6 dB (32.5 dB) for the transverse magnetic (transverse electric) mode at 1.55 μm. Furthermore, the polarization conversion efficiency is higher than 90% while maintaining cross talk below ?19 dB within the bandwidth of 80 nm.

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      摘要

      A simple, compact, double-pass pumped Nd:YVO4 thin disk laser is demonstrated. Its continuous-wave performance with different Nd doping concentrations and thicknesses is investigated experimentally. The maximum output power of 17.7 W is achieved by employing a 0.5 at.% doped sample, corresponding to an optical-to-optical efficiency of 46% with respect to the absorbed pump power. In addition, a numerical analysis and an experimental study of the temperature distribution, and thermal lens effect of the Nd:YVO4 thin disk, are presented considering the influence of the energy transfer upconversion effect and the temperature dependence of the thermal conductivity tensor. The simulated results are in good agreement with the experimental results.

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        摘要

        This erratum1 is issued by the authors to note that the caption of Fig. 10 refers the reader to Table III in the published version of the manuscript, while the correct reference is to Table II.

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          摘要

          The Editors of Matter and Radiation at Extremes (MRE) wish to express their deepest gratitude to the following individuals who generously provided advice on manuscripts as reviewers for MRE in the year of 2019 (names are listed in alphabetical order).

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            摘要

            Recent reports of the superconductivity in hydrides of two different families (covalent lattice, as in SH3 and clathrate-type H-cages containing La and Y atoms, as in LaH10 and YH6) have revealed new families of high-Tc materials with Tc’s near room temperature values. These findings confirm earlier expectations that hydrides may have very high Tc’s due to the fact that light H atoms have very high vibrational frequencies, leading to high Tc values within the conventional Bardeen–Cooper–Schrieffer phonon mechanism of superconductivity. However, as is pointed out by Ashcroft, it is important to have the metallic hydrogen “alloyed” with the elements added to it. This concept of a metallic alloy containing a high concentration of metal-like hydrogen atoms has been instrumental in finding new high-Tc superhydrides. These new superhydride “room-temperature” superconductors are stabilized only at very high pressures above 100 GPa, making the experimental search for their superconducting properties very difficult. We will review the current experimental and theoretical results for LaH10?x and YH6?x superhydrides.

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              摘要

              The first Dense Z-Pinch (DZP) conference, in 1984, marked an attempt to use then-modern pulsed power with a Z-pinch to work toward thermonuclear fusion energy. This 11th DZP conference in China is a good time to look back, to comment on progress since, and to project forward. What follows is a personal perspective: scattered comments from a sympathetic outsider and one-time participant. In these 35 years, Z-pinch theory has evolved from little more than cartoons to fully 3D MHD computer simulations, measurements have gone from mostly time- and spatially integrated diagnostics to monochromatic imaging, highly resolved x-ray spectroscopy, and active laser probing. Large pulsed power generators now drive x-ray-producing Z-pinches that are powerful enough for many applications; thermonuclear fusion may work single-shot in the future.

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                摘要

                Properties of atoms and molecules undergo significant changes when subjected to spatial confinement. We study the excitation spectra of lithium-like atoms in the initial 1s22s electronic configuration when confined by an impenetrable spherical cavity. We implement Slater’s X-α method in Hartree–Fock theory to obtain the excitation spectrum. We verify that as the cavity size decreases, the total, 2s, 2p, and higher excited energy levels increase. Furthermore, we confirm the existence of crossing points between nsnp states for low values of the confinement radius such that the nsnp dipole transition becomes zero at that critical pressure. The crossing points of the sp states imply that instead of photon absorption, one observes photon emission for cavities with radius smaller than the critical radius. Hence, the dipole oscillator strength associated with the 2s → 2p transition becomes negative, and for higher pressures, the 2s → 3p dipole oscillator strength transition becomes larger than unity. We validate the completeness of the spectrum by calculating the Thomas–Reiche–Kuhn sum rule, as well as the static dipole polarizability and mean excitation energy of lithium-like atoms. We find that the static dipole polarizability decreases and exhibits a sudden change at the critical pressure for the absorption-to-emission transition. The mean excitation energy increases as the pressure rises. However, as a consequence of the critical transition from absorption to emission, the mean excitation energy becomes undetermined for higher pressures, with implications for material damage under extreme conditions. For unconfined systems, our results show good to excellent agreement with data found in the literature.

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                  摘要

                  Z-pinch experiments with a hybrid configuration of a deuterium gas puff have been carried out on the HAWK (NRL, Washington, DC) and GIT-12 (IHCE, Tomsk) pulsed power generators at 0.7 MA and 3 MA currents, respectively. On GIT-12, neutron yields reached an average value of 2 × 1012 neutrons, and deuterons were accelerated up to an energy of 30 MeV. This was 50 times the ion energy provided by the generator driving voltage of 0.6 MV and the highest energy observed in z-pinches and dense plasma foci. To confirm these unique results independently on another device, we performed several experimental campaigns on the HAWK generator. Comparison of the experiments on GIT-12 and HAWK helped us to understand which parameters are essential for optimized neutron production. Since the HAWK generator is of a similar pulsed power architecture as GIT-12, the experiments on GIT-12 and HAWK are important for the study of how charged-particle acceleration scales with the current.

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                    摘要

                    Using the SG-III prototype laser at China Academy of Engineering Physics, Mianyang, we irradiated polystyrene (CH) samples with a thermal radiation drive, reaching conditions on the principal Hugoniot up to P ≈ 1 TPa (10 Mbar), and away from the Hugoniot up to P ≈ 300 GPa (3 Mbar). The response of each sample was measured with a velocity interferometry diagnostic to determine the material and shock velocity, and hence the conditions reached, and the reflectivity of the sample, from which changes in the conductivity can be inferred. By applying the self-impedance mismatch technique with the measured velocities, the pressure and density of thermodynamic points away from the principal Hugoniot were determined. Our results show an unexpectedly large reflectivity at the highest shock pressures, while the off-Hugoniot points agree with previous work suggesting that shock-compressed CH conductivity is primarily temperature-dependent.

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                      摘要

                      The emergence of a new era reaching beyond current state-of-the-art ultrashort and ultraintense laser technology has been enabled by the approval of around € 850 million worth of structural funds in 2011–2012 by the European Commission for the installation of Extreme Light Infrastructure (ELI). The ELI project consists of three pillars being built in the Czech Republic, Hungary, and Romania. This challenging proposal is based on recent technical progress allowing ultraintense laser fields in which intensities will soon be reaching as high as I0 ~ 1023 W cm?2. This tremendous technological advance has been brought about by the invention of chirped pulse amplification by Mourou and Strickland. Romania is hosting the ELI for Nuclear Physics (ELI-NP) pillar in M?gurele near Bucharest. The new facility, currently under construction, is intended to serve the broad national, European, and international scientific community. Its mission covers scientific research at the frontier of knowledge involving two domains. The first is laser-driven experiments related to NP, strong-field quantum electrodynamics, and associated vacuum effects. The second research domain is based on the establishment of a Compton-backscattering-based, high-brilliance, and intense γ beam with Eγ ? 19.5 MeV, which represents a merger between laser and accelerator technology. This system will allow the investigation of the nuclear structure of selected isotopes and nuclear reactions of relevance, for example, to astrophysics with hitherto unprecedented resolution and accuracy. In addition to fundamental themes, a large number of applications with significant societal impact will be developed. The implementation of the project started in January 2013 and is spearheaded by the ELI-NP/Horia Hulubei National Institute for Physics and Nuclear Engineering (IFIN-HH). Experiments will begin in early 2020.

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                        摘要

                        Classical wisdom of wave–particle duality regulates that a quantum object shows either the particle or wave nature but never both. Consequently, it would be impossible to observe simultaneously the complete wave and particle nature of the quantum object. Mathematically the principle requests that the interference visibility V and which-path distinguishability D satisfy an orthodox limit of V2+D21. The present work reports a new wave–particle duality test experiment using single photons in a modified Mach–Zehnder interferometer to demonstrate the possibility of breaking the limit. The key element of the interferometer is a weakly scattering total internal reflection prism surface, which exhibits a pronounced single-photon interference with a visibility of up to 0.97 and simultaneously provides a path distinguishability of 0.83. Apparently, the result of V2+D21.63 exceeds the orthodox limit set by the classical principle of wave–particle duality for single photons. We expect that more delicate experiments in the future should be able to demonstrate the ultimate limit of V2+D22 and shed new light on the foundations of contemporary quantum mechanics.

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                          摘要

                          A novel type of mid-IR microresonator, the chalcogenide glass (ChG) microfiber knot resonator (MKR), is demonstrated, showing easy fabrication, fiber-compatible features, resonance tunability, and high robustness. ChG microfibers with typical diameters around 3 μm are taper-drawn from As2S3 glass fibers and assembled into MKRs in liquid without surface damage. The measured Q factor of a typical 824 μm diameter ChG MKR is about 2.84×104 at the wavelength of 4469.14 nm. The free spectral range (FSR) of the MKR can be tuned from 2.0 nm (28.4 GHz) to 9.6 nm (135.9 GHz) by tightening the knot structure in liquid. Benefitting from the high thermal expansion coefficient of As2S3 glass, the MKR exhibits a thermal tuning rate of 110 pm·°C?1 at the resonance peak. When embedded in polymethyl methacrylate (PMMA) film, a 551 μm diameter MKR retains a Q factor of 1.1×104. The ChG MKRs demonstrated here are highly promising for resonator-based optical technologies and applications in the mid-IR spectral range.

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                            摘要

                            Investigating closely stacked GaN/AlN multiple quantum wells (MQWs) by means of cathodoluminescence spectroscopy directly performed in a scanning transmission electron microscope, we have reached an ultimate spatial resolution of σCL=1.8 nm. The pseudomorphically grown MQWs with high interface quality emit in the deep ultraviolet spectral range. Demonstrating the capability of resolving the 10.8 nm separated, ultra-thin quantum wells, a cathodoluminescence profile was taken across individual ones. Applying a diffusion model of excitons generated by a Gaussian-broadened electron probe, the spatial resolution of cathodoluminescence down to the free exciton Bohr radius scale has been determined.

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                              摘要

                              Single-photon detectors are ubiquitous devices in quantum-photonic-based communication, computation, metrology, and sensing. In these applications, N-fold coincidence photon counting is often needed, for example, to characterize entanglement. However, N-fold coincidence photon counting typically requires N individual single-photon detectors and associated bias and readout electronics, and these resources could become prohibitive if N goes large and the detectors need to work at cryogenic temperatures. Here, to break this limit on N, we propose a device architecture based on N cascaded photosensitive superconducting nanowires and one wider nanowire that functions as a current reservoir. We show that by strategically designing the device, the network of these superconducting nanowires can work in a synergic manner as an n-photon detector, where n can be from 1 to N, depending on the bias conditions. We therefore name the devices of this type superconducting nanowire multi-photon detectors (SNMPDs). In addition to its simple one-port bias and readout circuitry, the coincidences are counted internally in the detector, eliminating the need for external multi-channel, time-correlated pulse counters. We believe that the SNMPDs proposed in this work could open avenues towards conveniently measuring high-order temporal correlations of light and characterizing multi-photon entanglement.

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                                摘要

                                The experimental investigation of mode distortion induced by stimulated Raman scattering (SRS) in a high-power fiber amplifier, which includes the evolutions of optical spectra, spatial beam profiles, and time-frequency characteristics, has been carried out in detail. Temporal-frequency characteristics have been studied for the first time, to the best of our knowledge, by using a low-speed camera and high-speed photodiode traces, which revealed that temporal-frequency characteristics of SRS-induced mode distortion are different from traditional dynamic mode instability (MI). The experimental results show that the output beam profile remains stable before the mode distortion occurs and fluctuates obviously after the onset of SRS-induced MI but on a time scale of seconds, which is much lower than that of Yb-gain-induced MI featuring millisecond-level beam profile fluctuation. It also shows that the mode distortion became measurable in company with the onset of inter-mode four-wave mixing (IM-FWM) when the ratio of Raman light reaches 3%; further, the beam quality factor M2 degrades gradually from 1.4 to 2.1 as the ratio of Raman light increases. The mode distortion is accompanied by an obvious temperature increase of the output passive fiber, which further confirms that the mode distortion originates from SRS. The cause of the mode distortion induced by SRS has been explained in the context of core-pumped SRS effect, and the investigation on the accompanying IM-FWM effect indicates that the main content of the SRS-induced high-order mode is the LP21 mode.

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                                  摘要

                                  We report on the performance of AlGaN-based deep ultraviolet light-emitting diodes (UV-LEDs) emitting at 265 nm grown on stripe-patterned high-temperature annealed (HTA) epitaxially laterally overgrown (ELO) aluminium nitride (AlN)/sapphire templates. For this purpose, the structural and electro-optical properties of ultraviolet-c light-emitting diodes (UVC-LEDs) on as-grown and on HTA planar AlN/sapphire as well as ELO AlN/sapphire with and without HTA are investigated and compared. Cathodoluminescence measurements reveal dark spot densities of 3.5×109 cm?2, 1.1×109 cm?2, 1.4×109 cm?2, and 0.9×109 cm?2 in multiple quantum well samples on as-grown planar AlN/sapphire, HTA planar AlN/sapphire, ELO AlN/sapphire, and HTA ELO AlN/sapphire, respectively, and are consistent with the threading dislocation densities determined by transmission electron microscopy (TEM) and high-resolution X-ray diffraction rocking curve. The UVC-LED performance improves with the reduction of the threading dislocation densities (TDDs). The output powers (measured on-wafer in cw operation at 20 mA) of the UV-LEDs emitting at 265 nm were 0.03 mW (planar AlN/sapphire), 0.8 mW (planar HTA AlN/sapphire), 0.9 mW (ELO AlN/sapphire), and 1.1 mW (HTA ELO AlN/sapphire), respectively. Furthermore, Monte Carlo ray-tracing simulations showed a 15% increase in light-extraction efficiency due to the voids formed in the ELO process. These results demonstrate that HTA ELO AlN/sapphire templates provide a viable approach to increase the efficiency of UV-LEDs, improving both the internal quantum efficiency and the light-extraction efficiency.

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                                    摘要

                                    Supercapacitors (SCs) have broad applications in wearable electronics (e.g., e-skin, robots). Recently, graphene-based supercapacitors (G-SCs) have attracted extensive attention for their excellent flexibility and electrochemical performance. Laser fabrication of G-SCs exhibits obvious superiority because of the simple procedures and integration compatibility with future electronics. Here, we comprehensively summarize the state-of-the-art advancements in laser-assisted preparation of G-SCs, including working mechanisms, fabrication procedures, and unique characteristics. In the working mechanism section, electric double-layer capacitors and pseudo-capacitors are introduced. The latest advancements in this field are comprehensively summarized, including laser reduction of graphene oxides, laser treatment of graphene prepared from chemical vapor deposition, and laser-induced graphene. In addition, the unique characteristics of laser-enabled G-SCs, such as structured graphene, graphene hybrids, and heteroatom doping graphene-related electrodes, are presented. Subsequently, laser-enabled miniaturized, stretchable, and integrated G-SCs are also discussed. It is anticipated that laser fabrication of G-SCs holds great promise for developing future energy storage devices.

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                                      摘要

                                      Metasurfaces have found broad applicability in free-space optics, while its potential to tailor guided waves remains barely explored. By synergizing the Jones matrix model with generalized Snell’s law under the phase-matching condition, we propose a universal design strategy for versatile on-chip mode-selective coupling with polarization sensitivity, multiple working wavelengths, and high efficiency concurrently. The coupling direction, operation frequency, and excited mode type can be designed at will for arbitrary incident polarizations, outperforming previous technology that only works for specific polarizations and lacks versatile mode controllability. Here, using silicon-nanoantenna-patterned silicon-nitride photonic waveguides, we numerically demonstrate a set of chip-scale optical couplers around 1.55 μm, including mode-selective directional couplers with high coupling efficiency over 57% and directivity about 23 dB. Polarization and wavelength demultiplexer scenarios are also proposed with 67% maximum efficiency and an extinction ratio of 20 dB. Moreover, a chip-integrated twisted light generator, coupling free-space linear polarization into an optical vortex carrying 1? orbital angular momentum (OAM), is also reported to validate the mode-control flexibility. This comprehensive method may motivate compact wavelength/polarization (de)multiplexers, multifunctional mode converters, on-chip OAM generators for photonic integrated circuits, and high-speed optical telecommunications.

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                                        摘要

                                        首次以等離子旋轉電極(Plasma Rotating Electrode Process,PREP)制備的GCr15高碳鋼粉末為實驗原料,采用選區激光熔化(Selective Laser Melting,SLM)制備GCr15高碳軸承鋼。研究了SLM成形過程中激光功率(P)、掃描速度(v)、體能量密度(Volumetric Energy Density,VED)對GCr15成形性能的影響和成形后的組織轉變。實驗結果表明,在參數可調節的范圍內,激光功率、掃描速度、體能量密度與相對密度成線性

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                                        摘要

                                        毛竹筍生長與毛竹產量及固碳能力有密切的關系,研究毛竹筍蓄積量與生物量之間的關系,探討毛竹筍生物量變化規律,有利于了解毛竹筍的生長特性。本文利用地面LiDAR技術獲取毛竹筍三維點云數據,進而構建毛竹筍三維模型,并計算其體積,嘗試建立毛竹筍蓄積量轉換為生物量的數學模型。實驗結果表明:利用毛竹筍三維模型計算的體積與利用公式(本文選用區分求積式)計算的體積兩者相關性高;通過樣本檢驗,毛竹筍

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                                        摘要

                                        為增強42CrMo鋼表面硬度及耐磨性,利用半導體激光器在基體表面制備了含0 %、10 %、20 %、30 %及40 % nano-WC粉末的Ni60增強涂層。采用OM、SEM、EDS、XRD對試樣的微觀組織與相成分進行了表征,利用顯微硬度計和高溫摩擦磨損試驗機進行了力學及摩擦學性能測試。結果表明:納米WC增強Ni60涂層表面成形良好。增強涂層的組織形貌呈條狀、樹枝狀、魚骨狀、塊狀和粒狀。物相以Ni-Fe相為主,nano-WC一部分保留下來,一

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                                        摘要

                                        本文在分析傳統光學相位編碼技術特性基礎上,提出了一種可實用化的光學相位防偽掩膜設計方法。該方法采用二維條碼編碼技術,將用于防偽的文本或圖像信息編碼為二維條碼,然后基于傳統相位編碼技術將該二維條碼編碼為光學相位防偽掩膜。解碼時,采用較低量化階數的防偽掩膜在解碼后,經圖像形態學相關算法即可成功恢復原二維條碼的準確編碼信息,進而二維條碼解碼得到原始的文本和圖像。該設計方法不但有效解決

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                                        摘要

                                        理論分析和實驗數據表明,當背景發生波動時,背景加權直方圖修正算法(CBWH)在目標跟蹤過程會存在波動跟隨的現象,從而產生波動誤差。為了改善背景波動下的跟蹤效果,減小波動誤差,本文在CBWH的基礎上提出了背景梯度修正直方圖算法(BGCH),利用相鄰幀的背景梯度信息對目標模型進行二階加權修正,在機制上提前阻斷了背景加權直方圖修正算法(CBWH)的波動跟隨過程。實驗結果表明,該方法顯著減小了背景波動時CB

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                                        軌道板作為承載軌道的基礎,其制造精度與列車的運行安全息息相關。承軌臺作為軌道板的一部分,其幾何尺寸是衡量軌道板制造質量的重要指標。針對現有承軌臺檢測方法中存在的問題,本文提出了一種基于改進的雙目線結構光傳感器的承軌臺測量方法,測量時雙目傳感器中兩個相機與承軌臺之間的相對位置保持不變,通過傳感器內置的驅動裝置控制線激光器移動完成承軌臺的掃描,獲得點云數據,提高了承軌臺預埋套管位置

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                                        京雄城際鐵路機場隧道DK46+092~DK53+300區間位于區域地面沉降明顯地段,為了更加迅速、直觀的了解隧道在施工和后期運營過程中的安全情況,掌握隧道結構的健康狀態,需要對其進行安全監測。本文基于光纖光柵感測原理,在京雄高鐵在建隧道中進行了隧道襯砌環向應變感測、隧道襯砌變形縫相對位移感測、隧道周邊分層沉降監測;詳細介紹了傳感元件的布設安裝工藝,實現了大斷面隧道結構健康監測的自動化、遠程化控

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                                        城區激光雷達點云建筑物提取技術是近年來發展的熱點,但是如何準確區分植被、建筑物以及人造物,提高分類精度一直是研究難點。本文針對分類精度較低的問題,提出一種基于隨機森林的點云分類算法。首先使用改進布料濾波算法對點云數據進行地面濾波;構建決策樹并進行基于最大互信息系數的相關性分析,選出相關系數最小、精度最高的決策樹,得到弱相關隨機森林模型;接著對決策結果進行加權投票處理,最終得到一

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                                        土壤有機質(SOM)是衡量土壤肥力的重要指標,可見光-近紅外反射光譜(Vis-NIR)技術為快速易行估算土壤有機質提供可能。然而,土壤光譜僅反映土壤理化屬性的微弱信號,從高維數據中挖掘敏感信息仍需進一步探索。因此,本文采集艾比湖濕地89個典型樣點和土壤實測光譜數據(350~2500nm),所測土壤光譜進行一階微分變換預處理,膺選475個波段(r>0.25,顯著性檢驗閾值P ?? =0.01),利用連續投影算法(SPA)

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                                        在基于壓縮感知的計算關聯成像中,散斑設計是高質量圖像重構的關鍵。傳統散斑生成方法存在冗余性高、關聯成像質量低的問題,為此提出一種基于主成分分析的散斑優化方法,該方法的核心是通過線性變換將高維空間中的數據投影到低維空間中,使低維空間上的投影方差最大化。結合圖像先驗知識,通過樣本訓練的方法得到一組測量矩陣,在低采樣率的情況下,提高成像質量。實驗結果表明,與傳統方式相比,在采樣率相同

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                                        基于多元函數泰勒公式和最優控制原理,首先,在塔克拉瑪干沙漠部分中心區域(反演區域),利用2014年1月FY-3C微波成像儀10.65GHz垂直極化的觀測亮溫、CRTM輻射傳輸模式的模擬亮溫等資料,在原有地表發射率與2個影響因子的函數關系基礎之上,構建了該區域1月份微波地表發射率與2個、4個影響因子之間的線性反演模型。其次,以觀測亮溫為參考,分別將兩種線性反演模型所得的地表發射率提供給CRTM輻射傳輸模式模擬亮

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                                        針對人工檢測編織袋缺陷的正確率低與效率較低的問題,提出一種高效的在線檢測編織袋缺陷方法。在線采集編織袋圖像并進行圖像處理,消除干擾項,準確檢測編織袋的缺陷。使用均值濾波器、灰度開閉操作對圖像進行預處理,消除圖像中干擾缺陷檢測的黑白條紋與灰度不均勻,降低噪聲。使用差分圖像二值化對圖像進行背景分割,提取出孔洞缺陷、拉絲缺陷及過大的絲線縫隙、褶皺和黑色物。進行開閉運算處理,將斷裂的缺

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                                        結合多徑路由(Multipath Routing,MPR)、流量疏導(Traffic Grooming,TG)和自適應調制(Adaptive Modulation,AM)三者的優點,以解決軟件定義彈性光網絡(Software Defined Elastic Optical Networks,SD-EON)中持續時間感知的路由與頻譜分配(Routing and Spectrum Assignment,RSA)問題,建立了以最小化頻譜資源占用為優化目標的整數線性規劃模型,并提出一種基于流量疏導的時間感知多徑RSA算法(Hol

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                                        利用由棱鏡和金屬膜組成的Kretschmann模塊,以及由有機膜、金屬膜和玻璃片組成的襯底模塊,當兩個模塊相互接近時,構成以納米空氣間隙和有機膜為導波層的雙面金屬包覆波導結構。通過激發雙面金屬包覆波導結構中的導模共振,根據導模共振角與導波層納米空氣間隙厚度的變化關系的原理,選擇其中一個模式的反射率曲線作為探測信號,通過測量其共振角的變化實現納米空氣間隙的測量。通過數值模擬計算結果表明,本

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                                        針對光量子噪聲加密的高速信息防護傳輸系統,提出一種有效的密鑰同步方案。設計了同步幀結構及同步過程,并周期性測量信道傳輸時延,迭代估算傳輸時延差以修正解密密鑰到達時刻,完成高速信息傳輸下解密密鑰與密文的同步。實驗分析了影響密鑰同步的重要參數,驗證了該方案的可行性,并在實驗所得數據的基礎上分析了同步方案成功率和誤碼率等關鍵性能指標。

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                                        針對暗通道先驗去霧算法透射率估計不準確以及天空區域或大面積白色區域去霧后存在顏色失真等問題,提出了一種基于超像素分割和暗亮通道結合的單幅圖像去霧方法。首先采用超像素方法對有霧圖像進行分割,將得到的超像素塊代替暗通道固定方形濾波窗口;其次,采用暗通道與亮通道先驗理論結合的方法獲取透射率,使透射率估計更準確;然后,在天空區域通過閾值分割結合亮通道先驗理論確定大氣光值,并利用融合梯度

                                        PDF全文 激光與光電子學進展 | 2020,57(16):161023
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                                        本文分別采用脈沖調制模式和連續模式激光作為選區激光熔融工藝的熱源,研究了不同激光平均功率和脈沖占空比對TC4鈦合金試樣致密度、表面粗糙度和顯微組織等的影響。相對于連續激光,采用占空比在60%~70%的脈沖激光可顯著提高零件表面質量(表面粗糙度最低達3.6327μm),使試樣晶粒寬度由(1.14±0.23)μm減小到(0.85±0.18)μm,并能有效消除連續激光加工時因熱應力累積導致的3mm左右的翹曲變形。

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                                        利用Leica C05三維激光掃描儀和南方全站儀以多種特征的植物表面為觀測目標,獲取點云數據和距離參考值,研究不同植物表面的顏色、粗糙度和測站距離對點云的測距精度和激光回波強度的影響。試驗結果表明:(1)測站距離小于100m時,掃描儀測距誤差為1mm~5mm,超過90m時,測站距離每增加10m,激光點云測距誤差約增加1mm;(2)顏色、粗糙度和測站距離對三維激光掃描儀的激光回波強度和測距精度有影響;(3)顏色

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                                        針對火焰檢測定位精度與檢測精度不高的問題,提出了基于定位置信度和區域全卷積網絡的火焰檢測方法。首先使用擴大的可分離卷積提高感受野,減少模型參數量,提高檢測速度;其次對預測候選框進行平移和伸縮操作,提高了候選區域的完整性;然后引入定位置信度思想,解決了非極大值抑制(NMS)方法采用分類置信度作為判斷標準導致錯誤抑制的問題,提高了候選框的定位精度以及檢測精度;最后加入新的標簽(L-Fire,S-

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                                        高危作業現場環境復雜,危險系數高,容易發生跌倒事故,造成人員傷亡。為了檢測工人跌倒行為,提出了一種基于Kinect傳感器的人體跌倒檢測方法。利用Kinect獲取深度圖像,提取關節點信息,通過計算關節點相對位置熵和速度變化,判斷人體是否發生跌倒。通過對比實驗,確定了一組跌倒識別率最高的骨架關節點:頭、雙肩、雙膝、中心點。實驗數據表明該方法可以更快速準確地檢測跌倒行為。

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