一种燃烧型干扰剂的设计及其多频谱消光性能研究

为实现一剂化可见光、红外、激光的多频谱遮蔽干扰,基于铝热燃烧反应设计了一种新型燃烧型多频谱干扰剂,结合理论计算与实验获得了优选配方,并在烟箱内进行了干扰性能测试。结果表明:烟幕对可见光、近红外光（1~3 μm波段）、中红外光（ 3~5 μm波段）和波长为1.06 μm的激光可基本实现完全遮蔽;对远红外光（8~14 μm波段）的消光系数可达0.967 m²/g,对波长为10.60 μm激光的消光系数为0.655 m²/g。设计的干扰剂配方可基本实现一剂化多频谱干扰的目的,有望应用于燃烧型烟幕干扰弹。     

Applications of an extremely short strong-feedback configuration of an external-cavity laser diode system fabricated with GaAs-based integration technology

A composite-cavity laser diode is used to monitor the reflectivity or the displacement of the external-cavity mirror for micromechanical photonics devices. Optical disk bits are read out in the near field from the difference in medium reflectivity with an antireflection-coated laser diode and a photodiode. Microbeam vibration is also detected in the near field from the phase difference with an uncoated laser diode and a photodiode. In both cases the carrier-to-noise ratio is very high (more than 45 dB) because of the lack of mode-hopping noise resulting from the extremely short (less than 3 μm) external-cavity length and strong light feedback. These composite-cavity laser diode microdevices are fabricated on a gallium arsenide substrate to eliminate the need for optical alignment.     

Time-resolved reflectance and transmittance measurements of laser-induced free carriers in germanium, silicon, and zinc selenide at 10.6 microm

We present experimental results of reflectance and transmittance measurements of infrared radiation by high-density photogenerated free carriers in polycrystalline germanium, polycrystalline silicon, and chemical vapor deposition zinc selenide windows. Linearly polarized 1064 and 532 nm wavelength light from a Nd:YAG laser with a 130 ps pulse width were used to generate free carriers in the samples. Reflectance and transmittance were measured at a 10.6 microm wavelength using a linearly polarized CO2 laser.     

Great enhancement of infrared light absorption of silicon surface-structured by femtosecond laser pulses in N2 ambient

The enhanced light absorption of surface-microstructured silicon, prepared by cumulative irradiating with femtosecond laser pulses in ambient gas of N₂, was presented in this letter. The blunt conical spikes formed on silicon surface after irradiation are of elliptic conical shape due to the linearly polarized laser irradiation. Greatly enhanced light absorption of such surface-structured silicon was observed in the whole measured wavelength range from 0.3 to 16.7 μm. The light absorptance is up to 95% over the wavelength range of 0.3∼1.1 μm and as high as 75% or more in wavelength range of 8.8∼13.3 μm, though it is down to about 30% in the wavelength range of 2∼7 μm.     

High-Quality Brewster's Angle Polarizer for Broadband Infrared Application

We have designed and constructed a linear polarizer for use with visible and infrared radiation. The broadband polarizer consists of four germanium plates arranged in a chevron geometry. Input radiation is incident near Brewster's angle for the first plate such that the reflected beam is preferentially s-wave polarized. This reflected beam is steered subsequently to the successive plates, always intersecting near Brewster's angle. The beam polarization at the output of the device is almost completely s-wave polarized. The ratio of the paraxial flux of the nearly extinguished p-wave polarized light to the s-wave polarized light transmitted through the device is found to be less than 10(-5) for laser illumination at wavelengths of 0.633, 1.32, 3.39, and 10.6 mum. Calculations predict that extinction ratios less than 10(-5) are achievable over the wavelength range from 0.4 mum to beyond 500 mum. Alternative design geometries involving fewer plates are also described along with their advantages and disadvantages.     

Experimental research on the influences of smoothing by spectral dispersion on the Technical Integration Line

We describe one-dimensional smoothing by spectral dispersion (SSD) in high fluence on the Technical Integration Line. The experimental results indicate that SSD did not influence the load capacity of the laser facility. The near- and far-field analysis prove that adopting SSD could smooth the high-frequency modulations in the near field and dramatically suppress 10 μm-100 μm spatial modulations in the far field. The focal spot contrast decreases from 2.58 to 0.80 after using SSD and adaptive optics. Adopting a 0.31 nm bandwidth frequency-modulated laser pulse and a 1200 l/mm dispersion grating, experimental results proved that 97% 3ω energy passed through the laser entrance hole using a 4 m focal length wedged lens and gold foil target with an 1100 μm hole.     

多波长测量技术

给出了3种多波长测量技术的应用实例，采用多波长二极管激光器干涉仪测量表面轮廓，3个二极管激光器分别发射780nm、823nm和825nm3种近红外光波，可以得到2个近似15μm和29μm的合成波长，激光二极管的注入电流用1MHz左右的3种不同频率调制，以获得干涉仪的相位调制，这3个干涉信号用1个光电检测器和锁相放大器检测，采用同样的干涉仪，仅用2种波长进行了圆度偏差测量，论述了相移干涉测量技术，其试件的长度表示为光源波长的倍数，如果只使用1种波长，则要求确切知道整数干涉级；而使用多种波长，如532nm、633nm和780nm时，可得到几个独立的长度，此时整数衍射级不同，可以通过“精确小数法”计算得到，PTB精密干涉仪长度测量不确定度很小，其单值性范围约0.6mm，因此其近似的长度估算足以满足超精密长度测量的要求。     

Al-Sm2O3/聚氨酯复合涂层的近红外低反射与8~14 μm低发射率性能

以Al粉与Sm₂O₃为复合颜料,聚氨酯（PU）为黏合剂,制备了Al-Sm₂O₃/PU复合涂层。系统研究了涂层的微结构、红外发射率、近红外反射性能及力学性能。研究结果表明：Sm₂O₃的存在可有效降低涂层对1.06 μm近红外光的反射率,Al粉的存在可有效降低涂层在8~14 μm波段的红外发射率。通过调节Al粉与Sm₂O₃质量比,涂层在8~14 μm波段的红外发射率可在0.556~0.834范围内调节,涂层对1.06 μm近红外光的反射率可在35.1%~57.7%范围内调节。所制备Al-Sm₂O₃/PU涂层具备优良的力学性能,在不同Al-Sm₂O₃质量比下,其附着力与耐冲击强度分别可达到1级和50 kg·cm。Al-Sm₂O₃/PU复合涂层有望成为一种新型的具备低近红外光反射率与优良力学性能的低红外发射率涂层材料。     

Diabolo nanoantenna for enhancing and confining the magnetic optical field

In this Letter, we introduce a new nanoantenna concept aimed at generating a single magnetic hot spot in the optical frequency range, thus confining and enhancing the magnetic optical field on the background of a much lower electric field. This nanoantenna, designed by applying Babinet's principle to the bowtie nanoaperture, takes the shape of a diabolo. It differs from the well-known bowtie nanoantenna in that the opposing pair of metal triangles are electrically connected through their facing tips. Thus instead of a large charge density accumulating at the air gap of the bowtie nanoantenna, leading to a large electric field, a high optical current density develops within the central "metal gap" of the diabolo nanoantenna, leading to a large magnetic field. Numerical simulation results on the first nanodiabolo geometries show a 2900-fold enhancement of the magnetic field at a wavelength of 2540 nm, confined to a 40-by-40 nm region near the center of the nanoantenna.     

Alignment control of columnar liquid crystals with wavelength tunable CO2 laser irradiation

Infrared-induced alignment change with wavelength tunable CO₂ laser irradiation for columnar liquid crystal domains was investigated for a liquid crystalline triphenylene derivative. A uniformly aligned alignment change of domains was observed when a chopped linearly polarized infrared laser light corresponding to the wavelength of the aromatic C-O-C stretching vibration band (9.65 μm) was irradiated. The results strongly imply that the infrared irradiation is a possible technique for device fabrication by use of columnar mesophase as a liquid crystalline semiconductor.     

Methane detection with a narrow-band source at 3.4 µm based on a Nd:YAG pump laser and a combination of stimulated Raman scattering and difference frequency mixing

We report the characterization of a 10-Hz pulsed, narrow-band source that is coincident with a fundamental ν(3) rovibrational absorption of methane at 3.43 μm. To generate this midinfrared wavelength, an injection-seeded 1.06-μm Nd:YAG laser is difference frequency mixed with first Stokes light generated in a high-pressure methane cell (1.06 ? 1.54 μm) to result in light at a wavelength of 3.43 μm, that is, the ν(1) Raman active frequency of methane (~2916.2 cm(-1)). With a modest-energy Nd:YAG laser (200 mJ), a few millijoules of this midinfrared energy can be generated with a pulse width of ~7 ns (FWHM). The methane ν(1) frequency can be pressure tuned over 8-32 atm (corresponding to ~13 GHz) and scanned across part of the ν(3)P(10) rovibrational level of methane, resulting in a peak measured methane absorption coefficient of 4.2 cm(-1) atm(-1).     

Frequency tuning due to nonlinear effects in whispering gallery mode laser based on InAsSb/InAsSbP heterostructure

Frequency tunable infrared whispering gallery mode (WGM) semiconductor laser with a disk cavity has been created that operates at a wavelength of 3.5 μm at a temperature of 79 K. The laser radiation spectra have been studied. Smooth tuning of the main WGM toward shorter wavelengths by 11 Å due to nonlinear optical effects has been observed.     

Improved Near-Infrared Spectral Responsivity Scale

A cryogenic radiometer-based system was constructed at the National Institute of Standards and Technology for absolute radiometric measurements to improve detector spectral power responsivity scales in the wavelength range from 900 nm to 1800 nm. In addition to the liquid-helium-cooled cryogenic radiometer, the system consists of a 100 W quartz-tungsten-halogen lamp light source and a 1 m single-grating monochromator for wavelength selection. The system was characterized and the uncertainty in spectral power responsivity measurements evaluated. A variety of photodetectors, including indium gallium arsenide photodiodes (InGaAs), germanium (Ge) photodiodes, and pyroelectric detectors, were subsequently calibrated. Over most of the spectral range, the spectral power responsivity of the photodetectors can be measured with a combined relative standard uncertainty of 0.4 % or less. This is more than a factor of two smaller than our previous capabilities, and represents a significant improvement in the near infrared (NIR) spectral power responsivity scale maintained at NIST. We discuss the characterization of the monochromator-based system and present results of photodetector spectral power responsivity calibrations.     

Triggering and Monitoring Plasmon‐Enhanced Reactions by Optical Nanoantennas Coupled to Photocatalytic Beads

Plasmonic metal/semiconductor nanocomposites promise to be a breakthrough for boosting and investigating photon‐assisted processes at the nanoscale, with exciting perspectives for energy conversion and catalysis. However, the efficiency and selectivity of these surface processes are still far from being controlled. Here, shown for the first time, is a new class of photocatalyst which is based on the synergistic combination of bowtie‐like gold nanoantennas and SiO₂/TiO₂ core/shell oxide beads. These systems are exploited as efficient near‐field optical light concentrators, stimulating photon‐driven processes at the metal‐semiconductor interface. Extraordinary enhancements of photodegradation rates (minutes instead of hours) result from matching the nanoantenna surface plasmon resonance with the optical absorption of organic dyes and the excitation source wavelength. Moreover, strong Raman enhancements are observed allowing for direct in‐situ monitoring of reaction progress of different analytes on the same site.     

人造水雾粒度测试及红外消光因子计算分析

在大型半密闭空间内发生具有不同粒度分布的水雾体系,用喷雾激光粒度仪测试粒度分布规律并采用Van Der Hulst公式计算不同大小水雾粒子对红外辐射的散射效率因子、吸收效率因子和消光效率因子。结果表明:试验条件下水雾粒子的平均直径在5~65μm范围内。计算结果显示:水雾粒子对3～5、8～14μm红外辐射的消光作用主要取决于散射效应而非吸收效应。当水雾粒子的直径大于等于红外辐射的波长时,水雾体系对该波长红外辐射能够产生较强的消光效果。综合分析水雾体系的稳定性和消光特性,直径在3~30μm之间的水雾粒子对3～5、8～14μm红外辐射的衰减效果更为明显。     

Broadband photovoltaic effect of n-type topological insulator Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript> films on p-type Si substrates

We report the photovoltaic effects of n-type topological insulator (TI) Bi2Te3 films grown on p-type Si substrates by chemical vapor deposition (CVD).The films containing large nanoplates with a smooth surface formed on p-Si exhibit good p-n diode characteristics under dark and light illumination conditions and display a good photovoltaic effect under the broadband range from ultraviolet (UV) to near infrared (NIR) wavelengths.Under the light illumination with a wavelength of 1,000 nm,a short circuit current (Isc) of 19.2 μA and an open circuit voltage (Voc) of 235 mV are achieved.The maximum fill factor (FF) increases with a decrease in the wavelength or light density,achieving a value of 35.6％ under 600 nm illumination.The photoresponse of the n-Bi2Te3/p-Si device can be effectively switched between the on and off modes in millisecond time scale.These findings are important for both the fundamental understanding and solar cell device applications of TI materials.     

Preparation and characterization of sol–gel processed GeO2/methyltrimethoxysilane hybrid thin films

We report on preparation and characterization of GeO₂/methyltrimethoxysilane hybrid thin films processed by the sol–gel spin coating technique. Acid catalyzed solutions of methyltrimethoxysilane mixed with germanium isopropoxide have been used as precursors for the hybrid materials. The optical properties of the thin films, including refractive index, thickness, and transparency as well as structural characterization, have been studied by using a prism coupling technique, atomic force microscopy, thermal gravimetric analysis, UV–visible spectroscopy, and Fourier transform infrared spectroscopy. The results indicate that a crack-free, low absorption, and high transparency in the visible range optical films with a thickness of about 1.3 μm could be obtained by a single spin-coating process and at low heat treatment temperature. A strong UV absorption region at short wavelength ∼200 nm, accompanied with a shoulder peaked at ∼240 nm, due to the neutral oxygen monovacancies defects, has also been identified.     

Lidar aerosol backscatter cross sections in the 2-νm near-infrared wavelength region

Lidar backscatter cross-sectional measurements at 1.064, 0.532, and 1.54 μm were acquired during November 1989 and May-June 1990 around the Pacific region by the NASA DC-8 aircraft as part of the Global Backscatter Experiment. The primary motivation for the Global Backscatter Experiment was the study of lidar backscatter cross sections for the development of a spaceborne wind-sensing lidar. Direct backscatter measurements obtained by the NASA Goddard Space Flight Center visible and infrared lidar are compared with backscatter cross sections calculated from aerosol size distributions obtained by particle counters. Results for one flight with pronounced aerosol layers in the upper troposphere southeast of Japan are presented. Because 2-μm region wavelengths are possible candidates for a spaceborne wind-sensing lidar, the visible and infrared lidar backscatter cross sections at 1.064, 0.532, and 1.54 μm are extrapolated to the 2-μm region. The extrapolated 2-μm cross sections are compared with lidar measurements at 9 μm. A significant range in the ratio of 2-9-μm backscatter cross sections is found, but a large number of points concentrate near ratios of three to ten. A large number of 1.064- and 1.54-μm cross sections were binned to provide an estimate of backscatter for various percentiles for the flight. The ratio of the 50-percentile backscatter values at 1.064 and 1.54 μm suggest a λ(-1.9) to λ(-3.0) wavelength dependence of aerosol backscatter cross section in the near infrared for the observational case.     

Optical response of laser-doped silicon carbide for an uncooled midwave infrared detector

An uncooled mid-wave infrared (MWIR) detector is developed by doping an n-type 4H-SiC with Ga using a laser doping technique. 4H-SiC is one of the polytypes of crystalline silicon carbide and a wide bandgap semiconductor. The dopant creates an energy level of 0.30 eV, which was confirmed by optical spectroscopy of the doped sample. This energy level corresponds to the MWIR wavelength of 4.21 μm. The detection mechanism is based on the photoexcitation of electrons by the photons of this wavelength absorbed in the semiconductor. This process modifies the electron density, which changes the refractive index, and, therefore, the reflectance of the semiconductor is also changed. The change in the reflectance, which is the optical response of the detector, can be measured remotely with a laser beam, such as a He-Ne laser. This capability of measuring the detector response remotely makes it a wireless detector. The variation of refractive index was calculated as a function of absorbed irradiance based on the reflectance data for the as-received and doped samples. A distinct change was observed for the refractive index of the doped sample, indicating that the detector is suitable for applications at the 4.21 μm wavelength.     

Radiation filters and emitters for the NIR based on periodically structured metal surfaces

Abstract

The spectrally selective optical properties of wavelength selective radiation emitters and filters based on periodically microstructured metal surfaces were investigated. Metal surfaces were structured by the use of a holographic mask and subsequent etching processes. Due to the microstructure, thermally excited surface plasmons couple to electromagnetic radiation. Therefore a structured tungsten surface can act as a selective radiation emitter. The calculation of the absorptance by a rigorous diffraction theory allows the prediction of the emissivity of such structures. The angle dependent emissivity of tungsten gratings with periods of 1.4 μm and 2.0 μm was measured. A peak emissivity of 70% at a wavelength of 1.6 μm was achieved. Band pass filters for the near infrared spectral range based on perforated metal films were investigated theoretically and experimentally. Filters with a grating period of 2.0 μm were produced. A peak transmittance of 80% at a wavelength 2.9 μm was achieved. The optical properties of the diffractive elements described partly show a strong angle dependence