Pulsed-laser crossed-beam thermal lens spectrometry for detection in a microchannel: influence of the size of the excitation beam waist

Crossed-beam thermal lens spectrometry is especially designed for the detection of very small samples in capillary tubes and more generally in microfluidic devices. In this work, the effect of the size of the excitation beam with respect to the size of the sample microchannel has been investigated. Although the signal is inversely proportional to the size of the excitation waist into the sample, the use of large waists may provide greater sensitivities when short-pulse excitation lasers are used and allows easier optimization of the optical design. On the contrary, the use of small beam waists reduces the edge effects that can arise depending on the nature and thickness of the walls of the sample holder. Moreover, small beams provide better spatial resolution and have allowed the measurement of flow velocities as low as 1 mm s(-1).     

Multiple excitation fluorometer for in situ oceanographic applications

A new in situ fluorometer for the detection of oceanic photosynthetic pigment fluorescence is described. Emission spectra from 546 to 733 nm are recorded for each of three different visible excitation bands ten times a second. A Spectralon cell is used to improve the excitation coupling to and the collection efficiency from the sample volume. Laboratory tests demonstrated that the fluorescence emission spectra from the violet, blue, and green excitation can be used to discriminate among various algal species. The instrument was used at sea in extended in situ deployments on an undulating vehicle (SeaSoar).     

Calibration approach for fluorescence lifetime determination for applications using time-gated detection and finite pulse width excitation

Time-gated techniques are useful for the rapid sampling of excited-state (fluorescence) emission decays in the time domain. Gated detectors coupled with bright, economical, nanosecond-pulsed light sources like flashlamps and nitrogen lasers are an attractive combination for bioanalytical and biomedical applications. Here we present a calibration approach for lifetime determination that is noniterative and that does not assume a negligible instrument response function (i.e., a negligible excitation pulse width) as does most current rapid lifetime determination approaches. Analogous to a transducer-based sensor, signals from fluorophores of known lifetime (0.5-12 ns) serve as calibration references. A fast avalanche photodiode and a GHz-bandwidth digital oscilloscope is used to detect transient emission from reference samples excited using a nitrogen laser. We find that the normalized time-integrated emission signal is proportional to the lifetime, which can be determined with good reproducibility (typically <100 ps) even for data with poor signal-to-noise ratios ( approximately 20). Results are in good agreement with simulations. Additionally, a new time-gating scheme for fluorescence lifetime imaging applications is proposed. In conclusion, a calibration-based approach is a valuable analysis tool for the rapid determination of lifetime in applications using time-gated detection and finite pulse width excitation.     

Micro-array versus nano-array platforms: a comparative study for ODN detection based on SPR enhanced ellipsometry

The rapid and sensitive detection of DNA has recently attracted worldwide attention for a variety of disease diagnoses and detection of harmful bacteria in food and drink. In this paper, we carried out a comparative study based on surface plasmon resonance enhanced ellipsometry (SPREE) for the detection of oligodeoxynucleotides (ODNs) using micro- and nano-array platforms. The micro-arrayed surfaces were fabricated by a photolithography approach using different types of mask having varying size and shape. Well-ordered arrays of high aspect ratio polymeric nanotubes were also obtained using high molecular weight polystyrene (PS) and anodic aluminum oxide (AAO) membranes having 200 nm pore diameters. The SPREE sensors were then prepared by direct coupling of thiolated probe-ODNs, which contain suitable spacer arms, on gold-coated micro- and nano-arrayed surfaces. We experimentally demonstrated that, for the first time, gold-coated free standing polymeric nano-arrayed platforms can easily be produced and lead to a significant sensor sensitivity gain compared to that of the conventional SPREE surfaces of about four times. We believe that such an enhancement in sensor response could be useful for next generation sensor systems.     

Absorption phenomena in organic thin films for solar cell applications investigated by photothermal deflection spectroscopy

A high sensitive approach is presented to detect in particular the low level absorption features in pure and blended organic semiconductor films, revealing a.o. defect induced sub gap absorption and new interactions between the materials. Because sub bandgap absorption features are typically characterized by very low absorption coefficients, it is not possible to resolve them using common transmission and reflection measurements. Therefore the very sensitive and ground state spectroscopic technique of Photothermal Deflection Spectroscopy (PDS) has been developed, and introduced to characterize thin films of MDMO-PPV and PCBM, as well as films of MDMO-PPV containing an increasing amount of PCBM ranging from 5 to 90% weight fraction. The measured spectra of MDMO-PPV are interpreted in terms of defect induced absorption phenomena. The spectral position of the observed transitions in PCBM have been determined and verified. The PDS-study on MDMO-PPV/PCBM blended films revealed for the first time interaction between the two materials in the ground state. To get more insight in the interaction mechanism between the constituting materials a systematic Transmission Electron Microscopy (TEM) study has been carried out to reveal the morphology of the films. The obtained TEM-results on nanomorphology of the blended films show clear correlations with the PDS-results.     

High-resolution photothermal microscope: a sensitive tool for the detection of isolated absorbing defects in optical coatings

The photothermal deflection technique allows us to highlight the presence of inhomogeneities of absorption in optical components. This nondestructive tool is of great interest to the study of the role of contaminants, inclusions, and impurities in the laser-induced damage process. We show that the detection of nanometer-sized isolated absorbing defects requires the development of an adapted photothermal setup with high detectivity and high spatial resolution. Thus it is essential to improve the resolving power up to its theoretical limit.     

Spherical beam volume holograms for spectroscopic applications: modeling and implementation

The spherical beam volume hologram, recorded by a plane wave and a spherical beam, is investigated for spectroscopic applications in detail. It is shown that both the diffracted and the transmitted beam can be used for spectroscopy when the hologram is read with a collimated beam. A new method is introduced and used for analysis of the spherical beam volume hologram that can be extended for analysis of arbitrary holograms. Experimental results are consistent with the theoretical study. It is shown that the spherical beam volume hologram can be used in a compact spectroscopic configuration when the transmitted beam is monitored. Also, on the basis of the properties of the spherical beam hologram, the response of a hologram recorded by a plane wave and an arbitrary pattern is predicted. The information can be used to optimize holographic spectrometer design.     

Radiation shielding features for various tellurium-based alloys: a comparative study

We investigate the radiation shielding properties for four Te-based alloys. X-ray diffraction patterns revealed pure phases in all studied samples; however, a secondary phase is detected in the CrTe sample in good agreement with the literature. All samples’ densities were measured using the Archimedes principle. The mass attenuation coefficient (MAC) was calculated using Geant4 MC Toolkit and then compared with the XCOM data. Many photon-shielding properties were computed for all investigated samples based on the MAC. The Phy-X and SRIM were used to determine the fast neutron removal cross-section (Σ_R) and projected range, respectively. As a result, PbTe shows superior shielding features compared to the rest of the investigated samples to use this sample in different shielding applications.

     

Innovation in non-contact ultrasonic analysis: applications for hidden objects detection

 This paper describes unusual applications of ultrasound that are based upon recent advances in transduction efficiency in air and gaseous media. Piezoelectric transducer devices – capable of generating extremely high intensity ultrasound in ambient air up to 5 MHz – have been successfully developed and tested. This is in addition to the obvious uses for gas analysis, remote sensing, liquid level, gap, and thickness measurement, and proximity analysis. These new generation transducers make it possible to analyze solids and liquids not only non-destructively, but also without physically contacting the test sample. Among various applications to the non-destructive characterization (NDC) of industrial materials, we also describe the feasibility of a forensic application. This concerns the detection of objects such as knives, guns, contraband drugs, dead bodies, etc., hidden inside false compartments or walls. Received: 15 October 1997 / Accepted: 24 October 1997     

Mode-selective excitation and detection of ultrasonic guided waves for delamination detection in laminated aluminum plates

Selective modes of guided Lamb waves are generated in a laminated aluminum plate for damage detection using a broadband piezoelectric transducer structured with a rigid electrode. Appropriate excitation frequencies and modes for inspection are selected from theoretical and experimental dispersion curves. Dispersion curves are obtained experimentally by short time Fourier transform of the transient signals. Sensitivity of antisymmetric and symmetric modes for delamination detection are investigated. The antisymmetric mode is found to be more reliable for delamination detection. Unlike other studies, in which the attenuation of the propagating waves is related to the extent of the internal damage, in this investigation, the changes in the time-of-flight (TOF) of guided Lamb waves are related to the damage progression. The mode conversion phenomenon of Lamb waves during progressive delamination is investigated. Close matching between the theoretical and experimentally derived dispersion curves and TOF assures the reliability of the results presented here.     

Basic considerations in the use of coded excitation for color flow imaging applications

Coded excitation is now a well-established technique in medical ultrasound for B-mode imaging applications. It enables a gain in depth of penetration, without sacrificing the spatial resolution and maintaining an acceptable peak intensity for patient safety. The rationale of this technique for velocity estimation applications still has to be formulated in more precise terms. In particular, differences in the situation that arise in color flow imaging (CFI) applications from typical B-mode imaging conditions, such as signal-to-noise ratio conditions, pulsing strategy, and safety requirements, need to be specifically addressed to assess more quantitatively the potential of this technique. This paper discusses the potential improvement in sensitivity, resolution, and statistical performance provided by coded excitation for CFI applications from theoretical considerations and simulations.     

Eco-friendly plasmonic sensors: using the photothermal effect to prepare metal nanoparticle-containing test papers for highly sensitive colorimetric detection

Convenient, rapid, and accurate detection of chemical and biomolecules would be a great benefit to medical, pharmaceutical, and environmental sciences. Many chemical and biosensors based on metal nanoparticles (NPs) have been developed. However, as a result of the inconvenience and complexity of most of the current preparation techniques, surface plasmon-based test papers are not as common as, for example, litmus paper, which finds daily use. In this paper, we propose a convenient and practical technique, based on the photothermal effect, to fabricate the plasmonic test paper. This technique is superior to other reported methods for its rapid fabrication time (a few seconds), large-area throughput, selectivity in the positioning of the NPs, and the capability of preparing NP arrays in high density on various paper substrates. In addition to their low cost, portability, flexibility, and biodegradability, plasmonic test paper can be burned after detecting contagious biomolecules, making them safe and eco-friendly.     

城市道路视频中小像素目标检测

视频图像中的小像素目标难以检测。针对城市道路视频中的小像素目标,本文提出了一种改进YOLOv3的卷积神经网络Road_Net检测方法。首先,基于改进的YOLOv3,设计了一种新的卷积神经网络Road_Net;其次,针对小像素目标检测更依赖于浅层特征,采用了4个尺度检测方法。最后,结合改进的M-Softer-NMS算法来进一步提高图像中目标的检测精度。为了验证所提出算法的有效性,本文收集并标注了用于城市道路小像素目标物体检测的数据集Road-garbage Dataset,实验结果表明,本文算法能有效地检测出诸如纸屑、石块等在视频中相对于路面的较小像素目标。     

Use of modulated excitation signals in medical ultrasound. Part II: Design and performance for medical imaging applications

In the first paper, the superiority of linear FM signals was shown in terms of signal-to-noise ratio and robustness to tissue attenuation. This second paper in the series of three papers on the application of coded excitation signals in medical ultrasound presents design methods of linear FM signals and mismatched filters, in order to meet the higher demands on resolution in ultrasound imaging. It is shown that for the small time-bandwidth (TB) products available in ultrasound, the rectangular spectrum approximation is not valid, which reduces the effectiveness of weighting. Additionally, the distant range sidelobes are associated with the ripples of the spectrum amplitude and, thus, cannot be removed by weighting. Ripple reduction is achieved through amplitude or phase predistortion of the transmitted signals. Mismatched filters are designed to efficiently use the available bandwidth and at the same time to be insensitive to the transducer's impulse response. With these techniques, temporal sidelobes are kept below 60 to 100 dB, image contrast is improved by reducing the energy within the sidelobe region, and axial resolution is preserved. The method is evaluated first for resolution performance and axial sidelobes through simulations with the program Field II. A coded excitation ultrasound imaging system based on a commercial scanner and a 4 MHz probe driven by coded sequences is presented and used for the clinical evaluation of the coded excitation/compression scheme. The clinical images show a significant improvement in penetration depth and contrast, while they preserve both axial and lateral resolution. At the maximum acquisition depth of 15 cm, there is an improvement of more than 10 dB in the signal-to-noise ratio of the images. The paper also presents acquired images, using complementary Golay codes, that show the deleterious effects of attenuation on binary codes when processed with a matched filter, also confirmed by presented simulated images.     

Preparation and properties of RF sputtered indium-tin oxide thin films for applications as heat mirrors in photothermal solar energy conversion

In the present research, in order to deposit indium-tin oxide (ITO) thin films the method of RF reactive sputtering was used. Sputtering of two types indium-tin targets in the presence of oxygen as reactive gas was made. The technological parameters were optimized to obtain films with good quality on different substrates. The films' microstructure was studied by TEM and SAED. To identify the optical properties of the films the methods of infrared spectrometry and laser ellipsometry were used. UV-VIS spectrophotometry showed the high visible transmittance of the RF sputtered ITO films. Heating of the substrates during the films sputtering and their post deposition thermal treatment also were studied. The ultimate goal of the present research activities was to develop new technological processes leading to low-cost, highly effective optical coatings for application in photo thermal solar energy conversion and utilization.     

Transport- and diffusion-based optical tomography in small domains: a comparative study

We compare reconstructions based on the radiative transport and diffusion equations in optical tomography for media of small sizes. While it is well known that the diffusion approximation is less accurate to describe light propagation in such media, it has not yet been shown how this inaccuracy affects the images obtained with model-based iterative image reconstructions schemes. Using synthetic nondifferential data we calculate the error in the reconstructed images of optical properties as functions of source modulation frequency, noise level in measurement, and diffusion extrapolation length. We observe that the differences between diffusion and transport reconstructions are large when high modulation frequencies and noise-free data are used in the reconstructions. When the noise in data reaches a certain level, approximately 12% in our simulations, the differences between diffusion- and transport-based reconstructions become almost indistinguishable. Given that state-of-the-art optical imaging systems operate at much lower noise levels, the benefits of transport-based reconstructions of small imaging domains can be realized with most of the currently available systems. However, transport-based reconstructions are considerably slower than diffusion-based reconstructions.     

Mo6 cluster-based compounds for energy conversion applications: comparative study of photoluminescence and cathodoluminescence

Abstract

We report the photoluminescence (PL) and cathodoluminescence (CL) properties of face-capped [Mo₆Xⁱ₈L^a₆]^2? (X = Cl, Br, I; L = organic or inorganic ligands) cluster units. We show that the emission of Mo₆ metal atom clusters depends not only on the nature of X and L ligands bound to the cluster and counter-cations, but also on the excitation source. Seven members of the A_xMo₆Xⁱ₈L^a₆ series (A = Cs⁺, (n-C₄H₉)₄N⁺, NH₄⁺) were selected to evaluate the influence of counter-cations and ligands on de-excitation mechanisms responsible for multicomponent emission of cluster units. This study evaluates the ageing of each member of the series, which is crucial for further energy conversion applications (photovoltaic, lighting, water splitting, etc.).     

LSPR生物传感器在临床医学检测应用中的研究进展

肿瘤标志物在人类医学及恶性肿瘤的早期诊断、治疗监测及预后评估方面具有重要作用。目前血清肿瘤标志物的检测方法主要有放射免疫法(RIA),酶联免疫吸附法(ELISA)及化学发光免疫法(CLEIA)等,这些方法各自存在放射性污染、操作繁琐、检测时间长、价格昂贵等缺点,限制了血清肿瘤标志物在临床医学及肿瘤检测中的应用。新近出现的基于局域表面等离子体共振效应(LSPR)的传感器因在生物医学检测领域极具优势而成为研究热点。基于局域表面等离子体共振效应的生物传感器,利用贵金属纳米结构对周围介质环境变化敏感的基本原理,可将生物分子吸附引发的金属纳米颗粒外界介质折射率的改变转化为可测量的LSPR峰值吸收波长有规律的移动以实现对传感器表面样品的检测,具备检测灵敏度高、特异性好、免标记、设备便携、成本低的优点,具备临床检测潜力。但到目前为止,利用此传感器检测与疾病及肿瘤相关的肿瘤标志物的类似研究报道较少。在本文中,我们针对LSPR生物传感器的传感原理、国内外的研究进展以及我们在此方面的主要研究成果进行了综述。

     

UV Raman imaging--a promising tool for astrobiology: comparative Raman studies with different excitation wavelengths on SNC Martian meteorites

The great capabilities of UV Raman imaging have been demonstrated on the three Martian meteorites: Sayh al Uhaymir, Dar al Gani, and Zagami. Raman spectra without disturbing fluorescence and with high signal-to-noise-ratios and full of spectral features were derived. This result is of utmost importance for the development of powerful instruments for space missions. By point scanning the surfaces of the meteorite samples, it was possible for the first time to construct UV-Raman images out of the array of Raman spectra. Deep-UV Raman images are to the best of our knowledge presented for the first time. The images were used for a discussion of the chemical-mineralogical composition and texture of the meteorite surfaces. Comparative Raman studies applying visible and NIR Raman excitation wavelengths demonstrate a much better performance for UV Raman excitation. This comparative study of different Raman excitation wavelengths at the same sample spots was done by constructing a versatile, robust sample holder with a fixed micro-raster. The overall advantages of UV resonance Raman spectroscopy in terms of sensitivity and selectivity are demonstrated and discussed. Finally the application of this new technique for a UV Raman instrument for envisaged astrobiological focused space missions is suggested.     

Anti-Stokes Raman spectrometry with 1064-nm excitation: an effective instrumental approach for field detection of explosives

Anti-Stokes Raman spectra of 28 explosive materials were obtained with 1064-nm excitation using fiber-optic sampling and a dispersive spectrograph equipped with a charge-coupled device (CCD) array detector. By using a silicon CCD detector, anti-Stokes features could clearly be observed for the majority of samples from -250 to -1650 cm(-1). Using the fiber-optic probe, spectra were routinely obtained from samples positioned up to twelve meters from the spectrograph within 240 s. The utility of an anti-Stokes correction routine is demonstrated, which routine allowed anti-Stokes spectra measured with 1064-nm excitation to be successfully searched and identified against libraries of Stokes spectra obtained using a Fourier transform (FT) Raman system equipped with a 1064-nm Nd:YAG laser.