Near-infrared Range Of Spectrum Research Articles

Giant circular dichroism in extrinsic chiral metamaterials excited by off-normal incident laser beams

Recently it was shown by experiments that circular dichroism (CD) can be observed in the metamaterials of non-chiral structures when they were subjected to obliquely incident light (E. Plum, et al., Physical Review Letters 102, 113902, 2009). By far, external chirality simulation was only done for a particle array embedded in a homogenous medium (V. Yannopapas, Optics Letters 34, 5, 2009); no attempt has been made on simulating and modelling of circular dichroism in layered metamaterials (e.g., thin film on substrate structure). In this paper, we present the simulation of CD effect in layered external chiral metamaterials using CST software, theoretically investigate this intriguing phenomenon through a frequency domain finite integration technique, and optimize the metamaterial unit cell configurations (size, periodicity and film thickness) to maximize the CD phenomenon in near-infrared spectrum range. We show that the CD effect can be enhanced by five times using an optimized unit cell configuration, which is more than three times higher than the existing maximum theoretical results. The CD generation mechanism was elaborated with the help of induced surface current distributions.

Layered mesoporous nanostructures for enhanced light harvesting in dye-sensitized solar cells

Incident-photon-to-current-conversion efficiency of TiO2 photoanodes is increased significantly in the visible and near infrared range of the electromagnetic spectrum by assembling films that are structured on both micrometer and nanometer length scales. Photoanodes assembled from alternating layers of TiO2 nanoparticles and mesoporous TiO2 microspheres increase the overall power conversion efficiencies of dye-sensitized solar cells by as much as 26%. This increase is due to enhanced light scattering by porous TiO2 microspheres and is achieved without sacrificing the specific surface area.

Cerebral Blood Oxygenation Measurement Based on Oxygen-dependent Quenching of Phosphorescence

Monitoring of the spatiotemporal characteristics of cerebral blood and tissue oxygenation is crucial for better understanding of the neuro-metabolic-vascular relationship. Development of new pO2 measurement modalities with simultaneous monitoring of pO2 in larger fields of view with higher spatial and/or temporal resolution will enable greater insight into the functioning of the normal brain and will also have significant impact on diagnosis and treatment of neurovascular diseases such as stroke, Alzheimer's disease, and head injury. Optical imaging modalities have shown a great potential to provide high spatiotemporal resolution and quantitative imaging of pO2 based on hemoglobin absorption in visible and near infrared range of optical spectrum. However, multispectral measurement of cerebral blood oxygenation relies on photon migration through the highly scattering brain tissue. Estimation and modeling of tissue optical parameters, which may undergo dynamic changes during the experiment, is typically required for accurate estimation of blood oxygenation. On the other hand, estimation of the partial pressure of oxygen (pO2) based on oxygen-dependent quenching of phosphorescence should not be significantly affected by the changes in the optical parameters of the tissue and provides an absolute measure of pO2. Experimental systems that utilize oxygen-sensitive dyes have been demonstrated in in vivo studies of the perfused tissue as well as for monitoring the oxygen content in tissue cultures, showing that phosphorescence quenching is a potent technology capable of accurate oxygen imaging in the physiological pO2 range. Here we demonstrate with two different imaging modalities how to perform measurement of pO2 in cortical vasculature based on phosphorescence lifetime imaging. In first demonstration we present wide field of view imaging of pO2 at the cortical surface of a rat. This imaging modality has relatively simple experimental setup based on a CCD camera and a pulsed green laser. An example of monitoring the cortical spreading depression based on phosphorescence lifetime of Oxyphor R3 dye was presented. In second demonstration we present a high resolution two-photon pO2 imaging in cortical micro vasculature of a mouse. The experimental setup includes a custom built 2-photon microscope with femtosecond laser, electro-optic modulator, and photon-counting photo multiplier tube. We present an example of imaging the pO2 heterogeneity in the cortical microvasculature including capillaries, using a novel PtP-C343 dye with enhanced 2-photon excitation cross section.

Cerebral Blood Oxygenation Measurement Based on Oxygen-dependent Quenching of Phosphorescence

Monitoring of the spatiotemporal characteristics of cerebral blood and tissue oxygenation is crucial for better understanding of the neuro-metabolic-vascular relationship. Development of new pO2 measurement modalities with simultaneous monitoring of pO2 in larger fields of view with higher spatial and/or temporal resolution will enable greater insight into the functioning of the normal brain and will also have significant impact on diagnosis and treatment of neurovascular diseases such as stroke, Alzheimer's disease, and head injury. Optical imaging modalities have shown a great potential to provide high spatiotemporal resolution and quantitative imaging of pO2 based on hemoglobin absorption in visible and near infrared range of optical spectrum. However, multispectral measurement of cerebral blood oxygenation relies on photon migration through the highly scattering brain tissue. Estimation and modeling of tissue optical parameters, which may undergo dynamic changes during the experiment, is typically required for accurate estimation of blood oxygenation. On the other hand, estimation of the partial pressure of oxygen (pO2) based on oxygen-dependent quenching of phosphorescence should not be significantly affected by the changes in the optical parameters of the tissue and provides an absolute measure of pO2. Experimental systems that utilize oxygen-sensitive dyes have been demonstrated in in vivo studies of the perfused tissue as well as for monitoring the oxygen content in tissue cultures, showing that phosphorescence quenching is a potent technology capable of accurate oxygen imaging in the physiological pO2 range. Here we demonstrate with two different imaging modalities how to perform measurement of pO2 in cortical vasculature based on phosphorescence lifetime imaging. In first demonstration we present wide field of view imaging of pO2 at the cortical surface of a rat. This imaging modality has relatively simple experimental setup based on a CCD camera and a pulsed green laser. An example of monitoring the cortical spreading depression based on phosphorescence lifetime of Oxyphor R3 dye was presented. In second demonstration we present a high resolution two-photon pO2 imaging in cortical micro vasculature of a mouse. The experimental setup includes a custom built 2-photon microscope with femtosecond laser, electro-optic modulator, and photon-counting photo multiplier tube. We present an example of imaging the pO2 heterogeneity in the cortical microvasculature including capillaries, using a novel PtP-C343 dye with enhanced 2-photon excitation cross section. Click here to view the related article Synthesis and Calibration of Phosphorescent Nanoprobes for Oxygen Imaging in Biological Systems.

Facile direct integration of self-doped titanium oxide nanonails on silicon by solid-state-reaction

Self-doped titanium oxide nanonails are directly grown on silicon with a thermal oxide by the solid-state-reaction of the TiN/Ni/TiN growth pad at a relatively low growth temperature, 800 °C, made possible in the presence of a carbon precursor. The nanonails are doped by the constituent elements of the multilayer and carbon of the hydrocarbon. The spontaneously-doped titanium oxide nanonails show cathode luminescence in a visible and near-infrared spectrum range. The nail head can be controlled by tuning the vertical location of the catalyst layer in the multilayer growth pad.

Generation of intense frequency-tunable few-cycle femtosecond pulses in hollow fiber

We theoretically show an approach to generate intense frequency-tunable few-cycle femtosecond pulses by molecular phase modulation combined with self-phase modulation. An intense pump pulse propagates through a gas-filled hollow fiber to excite alignment of the gas molecule, which induces temporal modulation of the refractive index. Then the spectrum of a time-delayed intense probe pulse is continuously tuned by the alignment and broadened simultaneously by self-phase modulation. The modification to the pump-induced alignment by the intense probe pulse is considered. Frequency-tunable intense few-cycle pulses in the visible and near-infrared spectrum range are obtained using initial 20 fs, 800 nm pulses.

Using Near-Infrared Spectrophotometry for the Identification of Pharmaceuticals and Drugs

The near infrared range (NIR) of the electromagnetic spectrum extends from 800 to 2500 nm, being confined between the middle IR and visible spectral regions. The method of NIR spectroscopy is based on a combination of spectrophotometry and statistical methods of multifactor analysis, which provides excellent possibilities for drug identification and quality control even without opening the package. We have studied a series of drugs including cefazolin sodium and generic drugs based on enalapril maleate. True and falsified variants of a given drug X were classified into groups according to “drug name,” “drug manufacturer,” and “falsified product” by means of NIR spectroscopic analyses performed using the NIR Fourier-transform instruments Multi Purpose Analyzer (Bruker, Germany) and Antaris (Thermo Electron Corporation, USA). The potential of this method for the identification of drugs without violation of their packing shows good prospects for introducing it into the drug quality control system. This method should be recommended for introduction into the future Russian State Pharmacopoeia as a general method of drug analysis.

Configurable-bandwidth imaging spectrometer based on an acousto-optic tunable filter

This article presents a new imaging spectrometer called autonomous tunable filtering system. The instrument acquires sequential images at different spectral wavelengths in the visible and near infrared range of the electromagnetic spectrum. The spectral selection is performed by an acousto-optic tunable filter (AOTF), which is driven by a custom radio-frequency (rf) generator based on a direct digital synthesizer (DDS). The DDS allows a high flexibility in terms of acquisition speed and bandwidth selection. The rf power is dynamically controlled to drive the AOTF with the optimum value for each wavelength. The images are formed through a carefully designed optical layout and acquired with a high performance digital camera. The application software controls the instrument and acquires the raw spectral images from the camera. This software optionally corrects the image for the AOTF nonidealities, such as diffraction efficiency variations, spatial nonuniformity, and chromatic aberration, and generates a single multiband image file. Moreover, the software can calculate the reflectance or transmittance of the acquired images. The instrument has been calibrated to give precise and repetitive measurements and has been validated against a high performance point spectrometer. As a case example, the instrument has been successfully used for the mapping of chlorophyll content of plant leaves from their multispectral reflectance images.

Peptide-coated semiconductor nanocrystals for biomedical applications.

We have developed a new functionalization approach for semiconductor nanocrystals based on a single-step exchange of surface ligands with custom-designed peptides. This peptide-coating technique yield small, monodisperse and very stable water-soluble NCs that remain bright and photostable. We have used this approach on several types of core and core-shell NCs in the visible and near-infrared spectrum range and used fluorescence correlation spectroscopy for rapid assessment of the colloidal and photophysical properties of the resulting particles. This peptide coating strategy has several advantages: it yields probes that are immediately biocompatible; it is amenable to improvements of the different properties (solubilization, functionalization, etc) via rational design, parallel synthesis, or molecular evolution; it permits the combination of several functions on individual NCs. These functionalized NCs have been used for diverse biomedical applications. Two are discussed here: single-particle tracking of membrane receptor in live cells and combined fluorescence and PET imaging of targeted delivery in live animals.

Isotope-shift and hyperfine-constant measurements of near-infrared xenon transitions in glow discharges and on a metastableXe(3P2)beam

In this paper we discuss the hyperfine structure and isotope shift of the xenon atom. The study was performed using a semiconductor diode laser mounted in an extended-cavity configuration and emitting in the near-infrared range of spectrum. Doppler-free spectra of four transitions between 820 and 830 nm were obtained by using either a saturation spectroscopy technique in a cell or a laser-induced fluorescence technique on a collimated atomic metastable beam. The hyperfine coupling constants of ${}^{129}\mathrm{Xe}$ and ${}^{131}\mathrm{Xe}$ were determined for the levels ${1s}_{5},$ ${1s}_{4},$ ${1s}_{2},$ ${2p}_{2},$ ${2p}_{4},$ and ${2p}_{6}$ (Paschen notation). Moreover, a systematic study of the isotope shift was performed for the ${1s}_{3}\ensuremath{\rightarrow}{2p}_{4}$ $(\ensuremath{\lambda}=820.8\mathrm{nm})$ and ${1s}_{5}\ensuremath{\rightarrow}{2p}_{6}$ (\ensuremath{\lambda}=823.3 nm) transitions for which all the stable isotopes ${}^{128--131}\mathrm{Xe},$ ${}^{132}\mathrm{Xe},$ ${}^{134}\mathrm{Xe},$ and ${}^{136}\mathrm{Xe}$ were fully resolved.

Smoke data determination for various types of fuel

Abstract Fire protection assessment is of major interest in industrial environments. Among the resulting threats, smoke production is the object of growing attention. In this context, a proper analysis of smoke generated by four of the most commonly used oils in the Electricite de France production units, as well as heating oil, often implicated in everyday life accidental fires, is reported. The convenient relative measure of smoke emission, the specific extinction area, is identified as the variable to be used. Results show that all these fuels have a high propensity to generate soot particles. The evolution of extinction coefficient and wavelength, modelled as K e ∼ λ -n , reveals small-size, mainly absorbing particles. However, the dispersion coefficient n appears not spectrally constant. Despite the few data points, giving an exploratory nature to the work, a slope discontinuity of the curves, more or less marked as a function of the atomic ratio H/C of the fuel, appears between the visible and near infrared range of the spectrum. Theoretical predictions using appropriate values of soot optical constants show a satisfactory agreement with experiment. Beyond a simple classification of the different fuels, the results are valuable as input values in radiative exchange modelling.

New generation of spectrometers for measurement of spectral reflective characteristics

A review is made on the design philosophy of groundbased multichannel spectrometers for measurements of solar irradiation reflected from various natural formations within the visible and near infrared range of the electromagnetic spectrum. Important specifics of the new generation ground-based spectrometers are the improved functional possibilities for the scientific experiments, management and for the specialized data processing. The instruments enable the performance both of automated mode of operation and within the payload of complex measurement equipment. The incorporation of proper computer techniques accounts for the increased intelligence and adaptivity which provides for the precise resolution necessary for the scientific methodology and applicable tasks.