In situ infrared aerosol spectroscopy for a variety of nerve agent simulants using flow-through photoacoustics

We present newly measured results of an ongoing experimental program established to measure optical cross sections in the mid- and long-wave infrared for a variety of chemically and biologically based aerosols. For this study we consider only chemically derived aerosols, and in particular, a group of chemical compounds often used as simulants for the detection of extremely toxic organophosphorus nerve agents. These materials include: diethyl methylphosphonate (DEMP), dimethyl methylphosphonate (DMMP), diisopropyl methylphosphonate (DIMP), and diethyl phthalate (DEP). As reported in a prior study [Appl. Opt. 44, 4001 (2005)], we combine two optical techniques well suited for aerosol spectroscopy [i.e., flow-through photoacoustics and Fourier transform infrared (FTIR) emission spectroscopy], to measure in situ the absolute extinction and absorption cross sections over a variety of wavelengths spanning the IR spectral region from 3 to 13 mum. Aerosol size distribution(s), particle number density, and dosimetric measurements are recorded simultaneously in order to present optical cross sections that are aerosol mass normalized, i.e., m(2)/gram. Photoacoustic results, conducted at a series of CO(2) laser lines, compare well with measured broadband FTIR spectral extinction. Both FTIR and photoacoustic data also compare well with Mie theory calculations based on measured size distributions and previously published complex indices of refraction.     

Calculation and measurement of the absorption in multilayer films by means of photoacoustics

Using the photoacoustic gas cell microphone technique, absorption measurements were carried out in dielectric TiO₂/SiO₂ multilayer stacks at λ = 515 nm. For an interpretation of the results the absorption signal was calculated. By an appropriate variation in the thickness of the high and low refracting components, a separate evaluation of the volume and interface absorption became possible. For the evaporated TiO₂/SiO₂ multilayer system under investigation we found a predominance of interface absorption over volume absorption.     

基于阻抗反演技术的现场吸声测量研究

吸声系数是针对平面波入射条件下定义的声学参量.在实际(或现场)测量时,往往不满足平面波入射条件.已有的三维空间吸声测量大都基于球面波入射条件,然后加以几何修正.由于与阻抗管测量时的平面波条件不同,所以两者的结果有一定差距.利用逆滤波器原理,对扬声器频响在高低频进行了相应的补偿,消除了环境噪声的影响,在三维空间产生了光滑的butterworth宽频声脉冲.另外,由于声源辐射面积相比测试样品尺寸小很多,可将脉冲声源近似为点声源.将butterworth声脉冲入射毛毡样本,利用在时域上能够分离的入射脉冲和反射脉冲,首先计算了球面波反射系数,然后采用牛顿下山法反演得到样本的平面波阻抗比,并进一步计算了吸声系数.结果表明:较之直接利用球面波几何修正的吸声系数,反演后的吸声系数与声管测量结果更为接近.本方法采用单传声器法(两次测量),测量过程简单,为现场吸声测试提供了一种新的技术途径.     

Simultaneous measurement of temperature and chemical species concentrations with a holographic interferometer and infrared absorption

What is believed to be a new technique that allows for the simultaneous measurement of 2D temperature and chemical species concentration profiles with high spatial resolution and fast time response was developed and tested successfully by measuring a thin layer of fuel vapor created over a volatile fuel surface. Normal propanol was placed in an open-top rectangular container, and n-propanol fuel vapor was formed over the propanol surface in a quiescent laboratory environment. An IR beam with a wavelength of 8-13 mum emitted from a heated plate and a He-Ne laser beam with a wavelength of 632 nm were combined and passed through the n-propanol vapor layer, and both beams were absorbed by the vapor layer. The absorption of the IR beam was recorded by an IR camera, and the He-Ne laser was used to form a holographic interferogram. Two-dimensional temperature and propanol vapor concentration profiles were, respectively, determined by the IR absorption and the fringe pattern associated with the holographic interferogram. This new measurement technique is a significant improvement over the dual wavelength holographic interferometry that has been used previously to measure temperature and fuel concentration, and it is ready for application under different types of fire and flame conditions.     

Composition measurement of aerosols of submicrometer particles by phase fluctuation absorption spectroscopy

Phase fluctuation optical heterodyne spectroscopy is employed to obtain the first nonextractive data on size-mass distribution of submicrometer ammonium sulfate aerosols. The required theory of aerosol absorption of electromagnetic energy and subsequent thermalization is presented. Based on this theory, the predicted behavior was confirmed by experiments using IR absorption of ammonium sulfate aerosols. The results show good agreement with measurements using conventional methods including condensation nuclei counter, electron micrography, and filtration. In addition, a conversion constant for the photothermal signal of ammonium sulfate aerosols is calculated to be 2.3 microV/(microg/m3). Furthermore, the signal is shown to be linear in excitation energy and modulation frequency and scalable.     

In situ observation of synthesized nanoparticles in ultra-dilute aerosols via X-ray scattering

In-air epitaxy of nanostructures (Aerotaxy) has recently emerged as a viable route for fast, large-scale production. In this study, we use small-angle X-ray scattering to perform direct in-flight characterizations of the first step of this process, i.e., the engineered formation of Au and Pt aerosol nanoparticles by spark generation in a flow of N₂ gas. This represents a particular challenge for characterization because the particle density can be extremely low in controlled production. The particles produced are examined during production at operational pressures close to atmospheric conditions and exhibit a lognormal size distribution ranging from 5–100 nm. The Au and Pt particle production and detection are compared. We observe and characterize the nanoparticles at different stages of synthesis and extract the corresponding dominant physical properties, including the average particle diameter and sphericity, as influenced by particle sintering and the presence of aggregates. We observe highly sorted and sintered spherical Au nanoparticles at ultra-dilute concentrations (< 5 × 10⁵ particles/cm³) corresponding to a volume fraction below 3 × 10^–10, which is orders of magnitude below that of previously measured aerosols. We independently confirm an average particle radius of 25 nm via Guinier and Kratky plot analysis. Our study indicates that with high-intensity synchrotron beams and careful consideration of background removal, size and shape information can be obtained for extremely low particle concentrations with industrially relevant narrow size distributions.

     

In situ observation and measurement of the SAW thin-film acoustoelectric effect

The thin-film acoustoelectric effect in SAW devices describes the interaction of electrical energy between a SAW in a piezoelectric medium and a thin film in the wave's propagation path. The real-time observation of the thin-film acoustoelectric interaction is useful in the design and characterization of SAW sensors (i.e., temperature, humidity, viscosity, voltage, current, Hall effects, etc.). An in situ test fixture was designed to be mechanically, thermally, and electrically stable. Data acquisition software and an electron beam evaporation system were configured for real-time thin-film characterization during film growth. Data have been observed for more than 20 SAW devices and over a wide range of frequencies (i.e., 62 MHz to 1 GHz). The results suggest that the use of the in situ procedure yielded good agreement between theoretical predictions and the measured data, which demonstrates a method for the characterization of a SAW H(2)-gas sensor in real-time.     

Numerical computation and measurement of infrared extinction of the powder of brass 70Cu/30Zn

Abstract

The FDTD method is used to calculate the specific extinction cross section of the powder of brass 70Cu/30Zn with 1.35×10⁴ to 2.56×10⁵ particles in the infrared frequency range. A digitized model of body‐center‐like structures is used for the calculations of specific extinction cross‐section. From theoretical calculations, the value of a specific extinction cross section of the powder of brass 70Cu/30Zn is between 0.14 to 4.0 m²/g. While the experimental measurement shows the value of specific extinction cross section to be between 0.58 to 3.78 m²/g. The theoretical results concur with those obtained from the experimental measurement for the cell sizes of particles in the range of 0.05 to 0.4 p.m. There are some differences between the theoretical value and measurement data of specific extinction cross section for other particle sizes outside the range of 0.05 to 0.4μm.     

In situ optical testing of infrared lenses for high-performance cameras

We propose to evaluate infrared lenses with a dedicated analyzer having the same mechanical interface as the usual cameras. The proposed analysis is based on a wavefront measurement and allows a diagnostic of possible internal defects of the analyzed lens. The infrared lens analyzer described is constituted with a quadriwave lateral shearing interferometer and works with a blackbody light. We describe the response of this interferometer and an innovative method to obtain the wavefront under test. We finally present the experimental analysis of long-wavelength infrared lenses and the particular case of a modified lens that generates a large spherical aberration.     

In situ infrared microspectroscopy of approximately 850 million-year-old prokaryotic fossils

In situ infrared (IR) and Raman microspectroscopy have been conducted on Neoproterozoic, organic-walled microfossils (prokaryotic fossils) in doubly polished, petrographic thin sections in order to detect their spectral signatures. The microfossils are very well preserved and occur in black chert from the approximately 850 million-year-old Bitter Springs Formation, Northern Territory, Australia. Raman microspectroscopy on two species of microfossils, one a filament and the other a coccoid, shows disordered peaks (D peak, 1340 cm(-1)) and graphite peaks (G peak, 1600 cm(-1)), indicating that they consist of disordered carbonaceous materials. IR micro-mapping results of the filament reveal that the distributions of peak heights at 2920 cm(-1) (aliphatic CH(2)), 1585 cm(-1) (aromatic C-C), and 1370 cm(-1) (aliphatic CH(3)) match the shape of the filamentous microfossil. These results suggest that IR microspectroscopy can be used for in situ characterization of organic polar signatures that morphologically indicate microfossils embedded in chert by using doubly-polished rock (petrographic) thin section samples. Further, these methods can be applied to controversial microfossil-like structures to test their biogenic nature.     

In situ infrared ellipsometric study of stimuli-responsive mixed polyelectrolyte brushes

The switching behavior of stimuli-responsive mixed polymer brushes (d = 11 nm) was monitored for the first time in liquid phase in situ by infrared spectroscopic ellipsometry (IRSE). IRSE is presented as a new, sensitive in situ tool for online analysis of chemical changes in a thin complex film at the solid/liquid interface. Responsive behavior (protonation and deprotonation reaction) of the poly(acrylic acid)/poly(2-vinylpyridine) (PAA-mix-P2VP) brush was probed in aqueous solutions with pH ranging from pH 2 to pH 10. Structural and chemical changes in a thin polymer brush layer were identified from the analysis of infrared ellipsometric tanPsi spectra during the variation of pH. Systematic change in pH confirmed the reversible switching behavior of the PAA-mix-P2VP brush between three different states: swollen P2VP and compact PAA chains at pH 2, a compact "P2VP...PAA" complex at pH 6.5, and swollen PAA and compact P2VP chains at pH 10.     

Backscatter signatures of biological aerosols in the infrared

To develop a deeper understanding of the optical signatures of both biological aerosols and potential interferents, we made field measurements of optical cross sections and compared them to model-based predictions. We measured aerosol cross sections by conducting a hard-target calibration of a light detection and ranging system (LIDAR) based on the Frequency Agile Laser (FAL). The elastic backscatter cross sections are estimated at 19 long-wave infrared (LWIR) wavelengths spanning the range from 9.23 to 10.696 μm. The theoretical modeling of the elastic backscatter cross sections is based on the measured refractive index and size distribution of the aerosols, which are used as inputs into Mie calculations. Both model calculations and experimental measurements show good agreement and also indicate the presence of spectral features based on single particle absorption in the backscatter cross sections that can be used as a basis for discrimination for both standoff and point sensors.     

In situ examination of the chemical etching of SiO2-Si structures using an atomic force microscope

First results are reported of in situ visualization of the chemical etching of P⁺-ion implanted SiO₂-Si structures in an aqueous HF solution using an atomic force microscope. The rates of SiO₂ etching were determined and the kinetics of the photostimulated chemical etching of Si were investigated. Pis’ma Zh. Tekh. Fiz. 24, 81–86 (November 12, 1998)     

In situ measurement of crystal growth rate of zeolite

To clarify the growth behavior of zeolite crystals under hydrothermal synthesis conditions, the growth process of ZSM-5 type zeolite crystals was studied using two kinds of in situ observation apparatus. Direct observation of ZSM-5 crystals from amorphous gels during steaming and silicalite crystals from clear aqueous solutions was performed. During the stationary growing stage, a constant rate of crystal growth of zeolites was observed directly for both zeolite crystals. In the case of ZSM-5 zeolites from gels, it was also found that after a certain induction time, crystals grew to 10–20 μm in size, after which no further growth was observed. On the other hand, in the case of silicalite crystals from aqueous solutions, the induction time hardly existed. The size distribution of crystals and the activation energy for crystal growth are also discussed.     

The generation and measurement of aerosols

Aerosols are of extreme importance to many branches of science and technology although this is seldom realized by non-specialists. The disperse phase of an aerosol may consist of virtually any known material and so includes liquids, pure and unadulterated, as well as solids of simple composition and regular shape in one extreme to complex materials which may be radioactive, electrically charged and of complex shape in the other extreme.The basic characteristics and some of the most important methods of generating aerosols are reviewed. The difficulties that arise in attempting to produce standard aerosols are indicated. In considering measurements on aerosols the difficultues in collecting representative samples are outlined. Diagnostic methods which do not perturb the aerosol such as photographic and holographic techniques as well as light interaction methods are considered in some detail.     

化学气相沉积金刚石薄膜生长的原位反射率测量

报道了化学气相沉积金刚石薄膜生长的原位反射率测量,提出了监控金刚石薄膜生长的激光反射多光束干涉的数学模型。通过原位反射率的测量,精确监控了金刚石薄膜的生长厚度,成功地制备了红外增透增,这种方法的测量装置简单、紧凑而且可靠。     

Design and analysis of a flow-through integrating cavity absorption meter

We present a design for a flow-through integrating cavity absorption meter. This instrument, in principle, is capable of measuring the spectral optical absorption coefficient of natural waters in situ independently of scattering effects. Monte Carlo simulations are used to determine the design parameters and evaluate instrument performance. We investigate both detector response and the distribution of radiant energy inside the instrument and present empirical equations describing these quantities as a function of the absorption coefficient. The effects of changing the instrument geometry are illustrated. Finally, we discuss the effects of scattering on the instrument performance and verify that they are negligible for natural waters.