Long wavelength infrared metalens fabricated by photolithography

Metasurfaces in the long wave infrared(LWIR)spectrum hold great potential for applications in ther-mal imaging,atmospheric remote sensing,and target identification,among others.In this study,we designed and experimentally demonstrated a 4 mm size,all-silicon metasurface metalens with large depth of focus opera-tional across a broadband range from 9µm to 11.5µm.The experimental results confirm effective focusing and imaging capabilities of the metalens in LWIR region,thus paving the way for practical LWIR applications of met-alens technology.

Surface-patterned chalcogenide glasses with high-aspect-ratio microstructures for long-wave infrared metalenses

Multidimensional-engineering chalcogenide glasses is widely explored to construct various infrared photonic devices,with their surface as a key dimension for wavefront control.Here,we demonstrate direct patterning high-aspect-ratio microstructures on the surface of chalcogenide glasses offers an efficient and robust method to manipulate longwave infrared radiations.Despite chalcogenide glass being considered soft in terms of its mechanical properties,we successfully fabricate high-aspect-ratio micropillars with a height of 8μm using optimized deep etching process,and we demonstrate a 2-mm-diameter all-chalcogenide metalens with a numerical aperture of 0.45 on the surface of a 1.5-mm-thick As2Se3 glass.Leveraging the exceptional longwave infrared(LWIR)transparency and moderate refractive index of As2Se3 glass,the all-chalcogenide metalens produces a focal spot size of~1.39λ0 with a focusing efficiency of 47%at the wavelength of 9.78μm,while also exhibiting high-resolution imaging capabilities.Our work provides a promising route to realize easy-to-fabricate,mass-producible planar infrared optics for compact,light-weight LWIR imaging systems.

Comparative investigation of long-wave infrared generation based on ZnGeP_2 and CdSe optical parametric oscillators

Long-wave infrared （IR） generation based on type-Ⅱ （o→e＋o） phase matching ZnGeP2 （ZGP） and CdSe optical parametric oscillators （OPOs） pumped by a 2.05μm Tm,Ho：GdVO4 laser is reported. The comparisons of the birefringent walk-off effect and the oscillation threshold between ZGP and CdSe OPOs are performed theoretically and experimentally. For the ZGP OPO, up to 419 mW output at 8.04 μm is obtained at the 8 kHz pump pulse repetition frequency （PRF） with a slope efficiency of 7.6%. This ZGP OPO can be continuously tuned from 7.8 to 8.5 μm. For the CdSe OPO, we demonstrate a 64 mW output at 8.9μm with a single crystal 28 mm in length.

Performance Comparison of Long-Wave Infrared Imaging Spectrometer Between Dyson Form and Offner Form

In view of the difficulties in traditional long-wave infrared imaging spectrometer which is hard to realize a high signal-to-noise ratio and miniaturization as well under the weak remote sensing signal,Offner convex grating spectrometer and Dyson concave grating spectrometer,both having concentric structure,are designed and analyzed in the band of 8-12 μm. The diffraction angle expressions of the two spectrometers are obtained and the diffraction characteristics are acquired. Both of the spectrometers are designed in Zemax environment under different F-numbers and different grating constants with the same slit,spatial resolution,spectral resolution and detector. The results show that Dyson grating spectrometer possesses the advantages of higher throughput and smaller volume, and Offner grating spectrometer possesses the advantage of more accessible material and the absence of chromatic aberration. The differences between Dyson form and Offner form show that the former is a better choice in the long-wave infrared imaging spectrometer.

Infrared Emissivity Study on Semiconductor Pigment of Cd-Zn-S

Semiconductor pigment of Cd-Zn-S is synthesized through the solid state reaction method and its structure and surface morphology is characterized by X-ray diffraction (XRD) and scanning electron microscope(SEM). It is demonstrated that the crystal lattice of the product is hexagonal. When the heat treatment temperature increases, the distortion of crystal lattice reduces. The samples annealed at different temperatures agglomerate to different degrees while the one annealed at higher temperature agglomerates clearly. The infrared emissivity of Cd-Zn-S at two window-bands of 3-5 μm and 8-14 μm is researched. The researched result shows that the infrared emissivity of Cd-Zn-S in 8-14 μm wave bands is much higher than that in 3-5 μm wave bands. The infrared emissivity decreases with the increasing of heat treatment temperature, which reason is that with the increasing of temperature, the infrared absorption decreases and the scatter by the particles rises.

Very long wave infrared quantum cascade detector based on modular band structure

The optoelectronic performance of quantum cascade detectors(QCDs)is highly sensitive to the design of the energy level structure,leading to the inability of a single structure to achieve broad wavelength tuning.To address this issue,we propose and demonstrate a modular concept for very long wave infrared(VLWIR)QCDs based on a miniband diagonal transition scheme.The modular design makes the wavelength tuning only need to be adjusted for the absorption quantum well module rather than for the whole active region.Theoretical simulation shows that the wavelength tuning range is 39.6 meV(~14–30μm).To prove the feasibility of the scheme,three samples with different absorption well widths were fabricated and characterized.At 10 K,the response wavelengths of the three QCDs are 14,16,and 18μm,respectively,corresponding to responsivities and detectivities exceeding 2 mA/W and 1×10^(10)Jones.

Eye on the Sky: A UAP Research and Field Study off New York’s Long Island Coast

A ten-month field research study was meticulously conducted at Robert Moses State Park (RMSP) on the south shore of Long Island, NY. The objective was to determine if aerial phenomena of an unknown nature exist over a coastal location and to characterize their properties and behaviors. Primary and secondary field observation methods were utilized in this data-centric study. Forensic engineering principles and methodologies guided the study. The challenges set forward were object detection, observation, and characterization, where multispectral electro-optical devices and radar were employed due to limited visual acuity and intermittent presentation of the phenomena. The primary means of detection utilized a 3 cm X-band radar operating in two scan geometries, the X- and Y-axis. Multispectral electro-optical devices were utilized as a secondary means of detection and identification. Data was emphasized using HF and LF detectors and spectrum analyzers incorporating EM, ultrasonic, magnetic, and RF field transducers to record spectral data in these domains. Data collection concentrated on characterizing VIS, NIR, SWIR, LWIR, UVA, UVB, UVC, and the higher energy spectral range of ionizing radiation (alpha, beta, gamma, and X-ray) recorded by Geiger-Müller counters as well as special purpose semiconductor diode sensors.

nBn结构长波红外碲镉汞器件优化设计

分析了Type-I型能带对nBn结构碲镉汞器件性能的影响。通过理论计算获得了势垒层组分、掺杂浓度与能带带阶的关系,确定了nBn结构长波器件吸收层掺杂浓度与暗电流的关系。优化了nBn结构长波红外碲镉汞器件的掺杂浓度、势垒层与吸收层之间的组分过渡,建立了二维器件仿真模型并对nBn结构长波红外碲镉汞器件的能带结构进行了计算,结果表明器件结构参数的优化可以有效降低器件工作所需的开启电压,同时在吸收层内几乎不会形成耗尽区,从而有效抑制SRH产生-复合电流及隧穿电流。计算了器件结构参数优化后的长波红外碲镉汞nBn器件暗电流的变温特性,器件工作温度达到110 K以上。为高性能势垒结构长波红外碲镉汞器件的研制提供了理论依据。

变光阑长波红外连续变焦光学系统设计

非制冷长波连续变焦光学系统由于相对孔径大导致小型化和无热化设计困难,本文采用可变光阑约束物镜尺寸压缩系统总长,实现长波640×512非制冷连续变焦光学系统轻小型化设计。通过材料合理配置及主动补偿实现5片透镜的8.5×连续变焦光学系统消热设计。该系统F#恒定1.2、工作波段为8~12μm、视场变焦范围为30°×24°~3.5°×2.8°、系统总长187.5 mm,该连续变焦光学系统重量轻、总长短、透过率高、在-40℃~+60℃温度范围全视场成像质量良好。

大变倍比制冷型长波红外变焦光学系统设计

长波红外变焦光学系统相对于中波红外变焦光学系统存在可用材料少、系统高低温环境无热化难度大等难题。本文采用机械补偿变焦技术实现光学多视场变焦,利用主动补偿的消热差技术使系统在−40°C~+65°C温度范围内能够清晰成像,实现四片透镜架构的制冷型长波红外四视场光学系统设计。该光学系统四视场焦距分别为25 mm、109 mm、275 mm、400 mm,变倍比为15,光学系统包络尺寸为268 mm(长)×200 mm(宽),光学零件总质量为618 g。该光学系统具有质量轻、性能高、成本低等SWaP-C特征,在辅助导航、搜索、跟踪等安防领域中具有较大应用潜力。

用于地表温度探测10μm~11μm带通滤波器的研制

多谱段光谱成像仪搭载长波红外探测器可以提供空间高分辨率的地表温度信息,研究地表温度在全球能量平衡和气候变化中具有重要意义。本文采用10μm~11μm滤波器作为红外探测器的窗口进行地表温度探测,分别采用Ge和ZnS作为高低折射率材料,在Ge基板上设计一种宽截止、高透射的长波红外带通滤光膜;采用真空镀膜技术在Ge板两面分别制备长波通和短波通滤光膜以实现带通,其中Ge和ZnS薄膜分别以电子束和电阻热蒸发的方式沉积,膜厚采用晶控仪控制,通过Matlab软件建立膜厚沉积数学模型,模拟并修正多层膜的Tooling以减少厚度误差。测试结果表明:10μm~11μm波段平均透射率达到94.3%,透射区波纹幅度为1.6%;4μm~9.5μm和11.5μm~16μm波段平均透射率小于0.1%,各项耐环境测试表明滤波器满足使用要求。

Urban land-use classification by combining high-resolution optical and long-wave infrared images

Multi-sensor and multi-resolution source images consisting of optical and long-wave infrared (LWlR) images are analyzed separately and then combined for urban mapping in this study.The framework of its methodology is based on a two-level classification approach.In the first level,contributions of these two data sources in urban mapping are examined extensively by four types of classifications,i.e.spectral-based,spectral-spatial-based,joint classification,and multiple feature classification.In the second level,an objected-based approach is applied to decline the boundaries.The specificity of our proposed framework not only lies in the combination of two different images,but also the exploration of the LWlR image as one complementary spectral information for urban mapping.To verify the effectiveness of the presented classification framework and to confirm the LWlR's complementary role in the urban mapping task,experiment results are evaluated by the grss_dfc_2014 data-set.

大视场小型无热化长波红外镜组设计

跟随红外镜头小型化、大视场化的趋势,利用ZEMAX设计了一款大视场无热化小型长波红外镜组。系统匹配384×288@17μm的非制冷型长波红外探测器,工作波段为8~12μm。系统F数为1.6,相比于传统红外镜头,视场角更大,全视场达72°,尺寸更小,总长仅为6.96 mm。主镜头仅用3片镜片,通过两种红外光学材料的搭配以及6面非球面实现像差的校正和光学系统的无热化,工作温度范围覆盖-40~60℃。仿真结果表明,在空间频率15 lp/mm处,全视场的调制传递函数大于0.5,空间频率30 lp/mm处,全视场调制传递函数大于0.15。同时为了增大红外探测器的填充因子,提高能量利用率,在系统中搭配设计了放置于红外传感器前的微透镜阵列。实现了红外光学系统的小型化,为红外热像仪在智能手机上的应用提供了解决方案。

红外与可见光双模导引头光学系统设计

为了提升导弹在复杂环境下的寻的制导能力,设计了一种红外与可见光双模式导引头光学系统。该方案中采用分光镜透射红外光反射可见光,使结构布局更加紧凑,实现红外与可见光共口径,同时配合红外材料选取,实现光学被动消热差设计。中红外模式视场角3°×2.3°,可见光模式视场角5°×4°,工作温度20℃条件下,双模式在截止频率处,MTF(Modulation Transfer Function)值均大于0.4。红外与可见光双模式光学系统适合应用于复杂环境的导弹制导,对温度有良好的适应性,具有较好的成像质量,满足系统的性能要求。

基于兰姆波谐振器和超表面的谐振式热红外探测器研究

设计了一种基于氮化铝(AlN)兰姆波谐振器和超表面的谐振式热红外探测器,基于超表面的吸收器用于对特定波长红外辐射的吸收,再利用AlN兰姆波谐振器的温度频率效应检测红外辐射。首先,对兰姆波谐振器的电极周期、电极宽度、AlN薄膜厚度和支撑轴尺寸进行优化设计,设计了电极周期分别为12μm和1.2μm的谐振器结构,其工作频率分别为365 MHz和2544 MHz。其次,设计了方形结构超表面的等离子体吸收器,并研究分析其红外吸收机理及结构尺寸对吸收性能的影响规律。通过集成超表面红外吸收器并调节吸收结构尺寸,实现可调谐、近100%的双带吸收性能,在3μm~5μm和8μm~12μm处的吸收率均超过99.5%,谐振式热红外探测器的响应时间低于0.8 ms、热噪声等效功率低于10^(-11)Hz/μW。

深低温工作甚长波面阵红外探测器封装技术

基于甚长波红外探测器对低于液氮温度工作环境的需求,提出了一种深低温工作甚长波红外探测器封装技术。通过对杜瓦组件漏热和芯片电学引出结构的优化设计,可控制芯片在30 K低温工作时整个杜瓦组件的静态热耗为0.65 W,最冷端位置的静态热耗为0.3 W,与之适配的两级脉管制冷机冷量可以满足上述热耗需求。完成了探测器组件的封装测试。结果表明,在制冷机膨胀机热端空气冷却测试条件下,探测器芯片部分可达到35 K的温度;杜瓦的外轮廓小于Φ130 mm×180 mm。该项技术成果促进了深低温工作的甚长波面阵红外探测器封装技术的发展。

Enhanced thermal emission from metal-free,fully epitaxial structures with epsilon-near-zero InAs layers

We introduce a novel method to create mid-infrared(MIR)thermal emitters using fully epitaxial,metal-free structures.Through the strategic use of epsilon-near-zero(ENZ)thin films in InAs layers,we achieve a narrow-band,wide-angle,and p-polarized thermal emission spectra.This approach,employing molecular beam epitaxy,circumvents the complexities associated with current layered structures and yields temperature-resistant emission wavelengths.Our findings contribute a promising route towards simpler,more efficient MIR optoelectronic devices.

Holography in the invisible. From the thermal infrared to the terahertz waves: outstanding applications and fundamental limits

Since its invention,holography has been mostly applied at visible wavelengths in a variety of applications.Specifically,non-destructive testing of manufactured objects was a driver for developing holographic methods and all related ones based on the speckle pattern recording.One substantial limitation of holographic non-destructive testing is the setup stability requirements directly related to the laser wavelength.This observation has driven some works for 15 years:developing holography at wavelengths much longer than visible ones.In this paper,we will first review researches carried out in the infrared,mostly digital holography at thermal infrared wavelengths around 10 micrometers.We will discuss the advantages of using such wavelengths and show different examples of applications.In nondestructive testing,large wavelengths allow using digital holography in perturbed environments on large objects and measure large deformations,typical of the aerospace domain.Other astonishing applications such as reconstructing scenes through smoke and flames were proposed.When moving further in the spectrum,digital holography with so-called Terahertz waves(up to 3 millimeters wavelength)has also been studied.The main advantage here is that these waves easily penetrate some materials.Therefore,one can envisage Terahertz digital holography to reconstruct the amplitude and phase of visually opaque objects.We review some cases in which Terahertz digital holography has shown potential in biomedical and industrial applications.We will also address some fundamental bottlenecks that prevent fully benefiting from the advantages of digital holography when increasing the wavelength.

长波红外大孔径长焦距无热化光学系统设计

对于长波红外长焦距光学系统,大孔径能使系统具有更好的成像亮度,但也带来了孔径边缘像差较大且难以校正的问题。利用折反射式结构减少光学系统总长,采用两块反射镜结构作为基础,在其后搭配一组校正折射透镜构成光学系统,并应用光焦度分配、消热差及消色差条件,设计出大孔径、长焦距的长波红外无热化光学系统。该光学系统工作波段为8~12μm,焦距为800 mm,全视场角为0.6°,F数为2.5,遮拦比为0.2,光学系统总长为344.62 mm;在-40~60℃工作温度范围内,全视场角的调制传递函数值在奈奎斯特频率20 lp/mm处均大于0.25。设计的长波红外大孔径长焦距光学系统由2块反射镜和4块折射透镜组成,系统结构紧凑,成像性能稳定,可为类似此类光学系统设计提供参考。

长焰煤与糠醛渣共热解动力学、热力学及快速热解产物特性

对糠醛渣和低阶长焰煤共热解特性进行系统性研究,通过采用热重分析仪(TG)、红外快速热解反应器考察升温速率对等比例混合的长焰煤和糠醛渣共热解产物分布的影响以及二者之间的协同效应。TG结果表明在300~600℃的热解区间内糠醛渣中纤维素与长焰煤热解产生的含碳有机组分发生交互作用。Kissinger-Akahira-Sunose(KAS)和Flynn-Wall-Ozawa(FWO)法计算的活化能分别在69.80~256.04 kJ/mol和71.24~253.43 kJ/mol之间;在升温速率20、30和40℃/min时,平均指前因子分别为2.55×10^(11)/s(KAS)和4.22×10^(11)/s(FWO)。糠醛渣和长焰煤红外快速共热解实验结果表明:当升温速率从10℃/s提高到30℃/s时,焦油产率先从8.67%增加到9.24%,随后又降低到8.30%,水产率从15.92%降低到14.73%又增到15.26%,气体产率从25.12%增加到26.66%而半焦从50.29%下降到49.78%。模拟蒸馏结果也表明焦油成分中轻质组分含量约为70%,重质组分相对较少,表明红外快速加热下糠醛渣与长焰煤的共热解有助于焦油提质,产生正协同作用。