Optical Spectral Measurements Research Articles

Assessment of disease activity in patients with rheumatoid arthritis using optical spectral transmission measurements, a non-invasive imaging technique

ObjectivesIn rheumatoid arthritis (RA), treat-to-target strategies require instruments for valid detection of joint inflammation. Therefore, imaging modalities are increasingly used in clinical practice. Optical spectral transmission (OST) measurements are non-invasive...

Optical and μ-FTIR mapping: A new approach for structural evaluation of V2O5-lithium fluoroborate glasses

Collective optical and FTIR spectral measurements were carried out for undoped and V2O5 doped lithium fluoroborate glasses before and after gamma irradiation (8Mrad). The undoped glass shows strong UV absorption which is related to the presence of unavoidable trace iron (Fe3+ ions) present as unavoidable impurities. The V2O5-containing glasses reveal additional UV-near visible bands due to the presence of vanadium ions mainly in the pentavalent state with some contribution of trivalent vanadium ions. The studied glasses show marked resistance to gamma irradiation, revealing the maintenance of the optical spectral curves without variations. FTIR spectra reveal vibrational bands due to borate groups in triangular and tetrahedral coordination by the sharing of suggested (BO3F−) tetrahedral units through the modification effect of LiF on B2O3. The suggested tetrahedral units show similar vibrational modes in their wavenumbers to (BO4) units formed by alkali oxide.A new micro-FTIR mapping in combination with ordinary FTIR was also studied for further insight of the distribution of vibrational modes and structural arrangements within the studied glasses.

A digitally generated ultrafine optical frequency comb for spectral measurements with 0.01-pm resolution and 0.7-µs response time

Optical spectral measurements are crucial for optical sensors and many other applications, but the prevailing methods, such as optical spectrum analysis and tunable laser spectroscopy, often have to make compromises among resolution, speed, and accuracy. Optical frequency combs are widely used for metrology of discrete atomic and molecular spectral lines. However, they are usually generated by optical methods and have large comb spacing, which limits the resolution for direct sampling of continuous spectra. To overcome these problems, this paper presents an original method to digitally generate an ultrafine optical frequency comb (UFOFC) as the frequency ruler for spectral measurements. Each comb line provides one sampling point, and the full spectrum can be captured at the same time using coherent detection. For an experimental demonstration, we adopted the inverse fast Fourier transform to generate a UFOFC with a comb spacing of 1.46 MHz over a 10-GHz range and demonstrated its functions using a Mach-Zehnder refractive index sensor. The UFOFC obtains a spectral resolution of 0.01 pm and response time of 0.7 μs; both represent 100-fold improvements over the state of the art and could be further enhanced by several orders of magnitude. The UFOFC presented here could facilitate new label-free sensor applications that require both high resolution and fast speed, such as measuring binding kinetics and single-molecule dynamics. Optical frequency combs with ultrafine spacings look set to bring big improvements to spectral measurements and optical sensing. Yuan Bao and co-workers from China and the USA used custom-designed electrical wavefronts prepared by a digital signal processor to modulate the output of a narrow-linewidth laser. The result was an ultrafine optical frequency comb with a spacing as small as 1.46 MHz over a range of 10 GHz. Significantly, the digital signal processor prepared the comb in just 0.7 μS. Such a comb is ideal for fast, very high-resolution (0.01 pm) spectral measurements and far outperforms the scan speed and resolution of conventional grating-based optical spectrum analysers. The team demonstrated the benefits of their ultrafine comb in a highly sensitive Mach-Zehnder refractive index sensor.

Spectroscopy of red dravite from northern Tanzania

Low-Fe dravite with a formula of Na0.66Ca0.16Mg2.62Fe0.33Mn0.02Ti0.02Al5.95B3Si6.04O27(OH)4 is described from Engusero Sambu, northern Tanzania (On maps, Engusero Sambu may be found to be marked as belonging to Kenya, but in reality, it is located near the border in northern Tanzania). The sample has an unusual red color that is distinctly different from the red dravite from the Osarara, Narok district, in Kenya that was formerly studied by Mattson and Rossman (Phys Chem Miner 14:225–234, 1984) and Taran and Rossman (Am Mineral 87:1148–1153, 2002). This unique sample has been characterized by optical and Mossbauer spectral measurements to investigate underlying cause of the intense bands in absorption spectra that give rise to the red color. These features are shown to be caused by exchange-coupled Fe3+–Fe3+ interactions. Thermal annealing of the samples causes an increase in Fe3+ contents due to oxidation of [Y]Fe2+. However, heat treatment does not change the high-energy absorption edge, which is probably caused by intense ligand-to-Fe3+ charge-transfer UV bands. In fact, Mossbauer results show that high-temperature annealing initiates breakdown of the tourmaline into an Fe oxide and causes accompanying redistribution of Fe3+ within the structure. Because of the popularity of tourmaline as a gemstone, this work has implications for understanding the causes of color in tourmaline, facilitating recognition of the distinctions between naturally occurring and treated tourmalines in the gem industry and enabling heat treatments for color enhancement.

Electron emission and ultrafast low-fluence plasma formation during single-shot femtosecond laser surface ablation of various materials

Emission of erosive plasma has been observed during electric probe and optical emission spectral measurements of plumes produced by single-shot femtosecond laser ablation of optical-quality surfaces of various materials—copper, titanium, and silicon—at laser fluences well below the corresponding thermal ablation thresholds, replacing presumably electron emission at lower fluences. The onset of erosive plasma correlates on the fluence scale with saturation of dependences of self-reflectivity of the pumping femtosecond laser pulses, reflecting the “freezing” of electron dynamics (variation of electron density or temperature) during the pumping pulses, despite the monotonically increasing laser fluences.

Generation of intense supercontinuum in condensed media

Destructive nonlinear processes have limited the useful input power to a few megawatts for supercontinuum generation in bulk material. Consequently, reliable high-power, high-pulse-energy supercontinuum in condensed media has not been realized. Here, we describe an intense femtosecond supercontinuum generated in a solid medium with pulse energy and mode quality that approach those generated in the gas phase while preserving the advantages of a condensed medium of being compact, simple to operate, and highly reproducible. This is achieved by strategically placing several thin solid plates at or near the focused waist of a high-power laser pulse. The thickness of each plate is such that the optical pulse exits the plate before undesirable effects begin to take hold of the pulse. With this approach, we have obtained pulses that have an octave-spanning spectrum that covers from 450 to 980 nm at the −20 dB intensity level while converting as much as 54% of the input pulse energy to the continuum. The highest pulse energy obtained to date is 76 μJ, nearly two orders of magnitude greater than previously reported values. The transverse mode of the pulse has a M2 of 1.25. Frequency-resolved optical grating and spectral interferometric measurements indicate that the pulse is phase coherent and could be compressed to a few femtoseconds. Furthermore, the multiple-plates approach is shown to be extremely flexible and versatile. It is applicable for a broad range of input powers and materials. The generated continuum is stable and robust. Thus, multiple-plate generated femtosecond continuum could be a promising new light source in ultrafast science and extreme nonlinear optics applications.

AN OPTICAL SPECTROSCOPIC STUDY OF T TAURI STARS. I. PHOTOSPHERIC PROPERTIES

Measurements of masses and ages of young stars from their location in the HR diagram are limited by not only the typical observational uncertainties that apply to field stars, but also by large systematic uncertainties related to circumstellar phenomena. In this paper, we analyze flux calibrated optical spectra to measure accurate spectral types and extinctions of 283 nearby T Tauri stars. The primary advances in this paper are (1) the incorporation of a simplistic accretion continuum in optical spectral type and extinction measurements calculated over the full optical wavelength range and (2) the uniform analysis of a large sample of stars. Comparisons between the non-accreting TTS photospheric templates and stellar photosphere models are used to derive conversions from spectral type to temperature. Differences between spectral types can be subtle and difficult to discern, especially when accounting for accretion and extinction. The spectral types measured here are mostly consistent with spectral types measured over the past decade. However, our new spectral types are 1-2 subclasses later than literature spectral types for the original members of the TWA and are discrepant with literature values for some well known Taurus CTTSs. Our extinction measurements are consistent with other optical extinction measurements but are typically 1 mag lower than nIR measurements, likely the result of methodological differences and the presence of nIR excesses in most CTTSs. As an illustration of the impact of accretion, SpT, and extinction uncertainties on the HR diagrams of young clusters, we find that the resulting luminosity spread of stars in the TWA is 15-30%. The luminosity spread in the TWA and previously measured for binary stars in Taurus suggests that for a majority of stars, protostellar accretion rates are not large enough to significantly alter the subsequent evolution.

Comparative spectral and shielding studies of binary borate glasses with the heavy metal oxides SrO, CdO, BaO, PbO or Bi2O3 before and after gamma irradiation

This work aims to compare the experimental shielding behavior of some prepared binary borate glasses with SrO, CdO, BaO, PbO or Bi2O3 towards successive gamma irradiation by investigating their combined optical and FTIR spectral measurements before and after gamma irradiation. Optical spectra of all the samples reveal strong UV absorption which is related to the presence of unavoidable trace iron impurities (Fe3+ ions) contaminated within the raw materials which were used for the preparation of the studied glasses. Additional near visible bands are observed in the two lead borate and bismuth borate glasses due to characteristic absorption of Pb2+ and Bi3+ ions. Gamma irradiation causes varying responses depending on the type of glass. Bismuth borate glass shows highly marked shielding towards successive gamma irradiation while lead borate glass reveals resistance in low dose (4Mrad) and produces induced defects at high dose (8Mrad). The other glasses show obvious generation of induced defects upon gamma irradiation. FTIR spectra of the glasses reveal vibrational modes characteristic to combined presence of triangular and tetrahedral borate units in their specific different wavenumbers besides the presence of interfering structural PbO and BiO linkages in the lead borate and bismuth borate glasses. Gamma irradiation produces limited changes in the FTIR spectra specifically the intensity of some vibrational modes while the bismuth borate glass has proved to be the best radiation-shielding candidate when comparing the combined spectral results after successive gamma irradiation.

Optical and structural properties of WO3-doped silicophosphate glasses for gamma-ray applications

Optical and FTIR spectral measurements were carried out for prepared base undoped sodium silicophosphate glass together with samples of the same composition containing (0.5%, 0.75%, 1% and 1.25%) WO3 in order to characterize the valence states of tungsten ions in such host mixed forming oxides glass. The same combined spectral studies were repeated after subjecting the prepared samples to gamma irradiation with a dose of 8Mrad (8×104Gy). The base undoped glass exhibits a strong UV absorption band which is related to the presence of unavoidable trace iron (Fe3+) ions impurities contaminated within the raw materials used for the preparation of the base glass. WO3-doped glasses exhibit bluish color and reveal distinct optical absorption peaks which are attributed to the presence of both W6+ and W5+ ions. Infrared absorption spectra of the studied glasses reveal distinct broad IR bands which are attributed to the sharing modes of vibrations of both phosphate and silicate networks. The addition of the dopants (0.5–1.25%) WO3 did not cause marked changes in the IR spectral vibrational bands. Gamma irradiation conducts no variations in the number or position of main IR characteristic absorption bands due to the stability of the glassy network containing combined structural building groups together with the presence of tungsten ions. E.S.R. spectra of WO3-samples reveal spin resonance indicating the presence of unpaired tungsten ions and support the optical result.

Two‐Dimensional Nanostructures by the Assembly of n‐Type Tetraazaanthracene‐Based Conjugated Molecules

On the basis of our previous communication concerning a new family of thiophene-armed tetraazaanthracene molecules, we present a further intensive investigation on this class of compounds substituted with different alkyl chains and their self-assembled two-dimensional (2D) nanostructures. These tetraazaanthracene molecules with different alkyl chains were prepared in good yields using the synthetic strategy we developed. In addition to the expected typical n-type character, one compound exhibited aggregation behavior upon electrochemical reduction. Moreover, all molecules in the neutral state showed a strong tendency to aggregate in a binary solvent, as confirmed by optical spectral measurements. To investigate such self-assembly behavior, a phase-transfer method with a dichloromethane/methanol (2:3) binary solvent system was used to prepare the nanostructures. By means of atomic force microscopy, transmission electron microscopy, and X-ray diffraction, we found that the morphology of assembled 2D sheet-like structures could be adjusted by varying the alkyl chain. The weak interactions arising from the heteroatoms (N and S) in the conjugated backbones play a key role in the formation and stabilization of layered structures.

SAT0501 Assessment of Disease Activity in Patients with Rheumatoid Arthritis using Optical Spectral Transmission Measurements, a Non-Invasive Operator-Independent Imaging Technique.

BackgroundIn rheumatoid arthritis (RA), treat-to-target strategies require instruments for valid detection of joint inflammation. With the use of imaging modalities such as ultrasonography (US) and magnetic resonance imaging (MRI), it...

Chemistry of Anthracene–Acetylene Oligomers. XXI. Structures and Stereochemistry of Chiral Anthracene–Acetylene Dimers with an Intra-Annular Alkoxy Group

Abstract Anthracene–acetylene cyclic dimers having a methoxy or an ethoxy group at the intra-annular position were synthesized by cross-coupling reactions. DFT calculations suggested that the alkoxy–alkyl groups were perpendicular to the planar rigid framework leading to a chiral structure. The enantiomers were resolved by chiral HPLC and their chiroptical properties were characterized by optical rotation and CD spectral measurements. Their absolute stereochemistries were assigned by the theoretical calculation of CD spectra by using the TDDFT method. Kinetic measurements revealed that the barriers to enantiomerization were 122 and >142 kJ mol−1 for the methoxy and ethoxy compounds, respectively. The structures and stereochemistries are compared with those of intra-annular alkyl derivatives.

Human tissue color as viewed in high dynamic range optical spectral transmission measurements

High dynamic range optical-to-near-infrared transmission measurements for different parts of human body in the spectral range from 650 to 950 nm have been performed. Experimentally measured spectra are correlated with Monte Carlo simulations using chromaticity coordinates in CIE 1976 L*a*b* color space. Both a qualitative and a quantitative agreement have been found, paving a new way of characterizing human tissues in vivo. The newly developed experimental and computational platform for assessing tissue transmission spectra is anticipated to have a considerable impact on identifying favorable conditions for laser surgery and optical diagnostics, while providing supplementary information about tissue properties.

Potential of optical spectral transmission measurements for joint inflammation measurements in rheumatoid arthritis patients

Frequent monitoring of rheumatoid arthritis (RA) patients enables timely treatment adjustments and improved outcomes. Currently this is not feasible due to a shortage of rheumatologists. An optical spectral transmission device is presented for objective assessment of joint inflammation in RA patients, while improving diagnostic accuracy and clinical workflow. A cross-sectional, nonrandomized observational study was performed with this device. In the study, 77 proximal interphalangeal (PIP) joints in 67 patients have been analyzed. Inflammation of these PIP joints was also assessed by a rheumatologist with a score varying from 1 (not inflamed) to 5 (severely inflamed). Out of 77 measurements, 27 were performed in moderate to strongly inflamed PIP joints. Comparison between the clinical assessment and an optical measurement showed a correlation coefficient r=0.63, p<0.001, 95% CI [0.47, 0.75], and a ROC curve (AUC=0.88) that shows a relative good specificity and sensitivity. Optical spectral transmission measurements in a single joint correlate with clinical assessment of joint inflammation, and therefore might be useful in monitoring joint inflammation in RA patients.

An ethanol vapor detection probe based on a ZnO nanorod coated optical fiber long period grating

A new ethanol vapor detection probe based on an optical fiber long period grating overlaid with a zinc oxide (ZnO) nanorods layer is presented. The ZnO nanorod layer was developed onto the cladding of the fiber using aqueous chemical growth, seeded by a thin layer of metallic Zn. The growth of the ZnO nanorods overlayer onto the long period grating cladding is monitored in real time for investigating its effect on the spectral properties of the device and its subsequent role in the sensing mechanism. Results are presented, on the correlation between the growth time of the ZnO layer and the ethanol vapor detection performance. Reversible spectral changes of the notch extinction ratio of more than 4 dB were recorded for ~50 Torr of ethanol vapor concentration. In addition, photoluminescence emission studies of the ZnO overlayer performed simultaneously with the optical fiber spectral measurements, revealed significant ethanol induced changes in the intensity of the bandgap peak.

Fourier-transform infrared and optical absorption spectra of P-N,N-dimethylaminobenzylidenemalononitrile (DBM) thin films

Thin films of P-N,N-dimethylaminobenzylidenemalononitrile (DBM) were prepared for the first time using thermal evaporation technique. The molecular structure and electronic transitions of DBM films were investigated by Fourier-transform infrared (FTIR), X-ray diffraction (XRD), and ultraviolet–visible (UV–vis) spectra. The observed vibrational wavenumbers in FTIR spectra were analyzed and assigned to different normal modes of the molecule. UV–vis optical absorption spectral measurements of DBM films were analyzed to obtain the type of the optical transitions. The values of the optical gap ( E opt ), the transport gap ( E t ), the exciton binding energy ( E B ), the urbach's energy ( E u ), the dispersion parameters, the molar extinction coefficient ( ɛ mol), the oscillator strength ( f), and the electric dipole strength ( q 2) were also reported.

Cr doping induced structural, phonon and excitonic properties of ZnO nanoparticles

We report systematic study of structural, phonon and optical properties of Cr-doped ZnO nanoparticles. These particles are synthesized through simple sol–gel technique. Structural studies carried out by X-ray diffraction method, confirm that the prepared particles are in hexagonal wurtzite structure and lattice parameters change considerably while increasing the doping. Raman and Fourier transform infrared spectral studies show that the intensity of the phonon modes decreased and also blue shift due to ion doping, respectively. Apart from this, transmission electron microscopic studies show reduction in particle size where the particle diameters reduced from 36 to 11 nm. Optical absorption spectral measurements show a blue shift in the band-gap and increment in excitonic oscillator strength. Photoluminescence studies show doping altered the near-band edge emission but there is no change in the other emission bands which is due to oxygen vacancy, surface defects and surface dangling bonds.

Optical spectral reflectance of human articular cartilage – relationships with tissue structure, composition and mechanical properties

The information from spectral reflectance of articular cartilage has been related to the integrity of the tissue. This study explores more in detail the interrelations between the cartilage composition, structure and mechanical properties, and optical spectral reflectance. Using human osteochondral samples the reflectance spectral images of articular cartilage were captured and analyzed by using CIELAB color space as well as principal component analysis. With both analysis methods statistically significant correlations were observed between the reflectance and histological integrity, as assessed by Mankin scoring, tissue proteoglycan content and dynamic modulus. In thick human cartilage, the reflectance was found to be independent of the cartilage thickness, suggesting negligible influence of the underlying subchondral bone. Based on the present results diagnostically relevant information on cartilage quality can be extracted using optical spectral reflectance measurements. These measurements could be feasible during arthroscopic surgery when more in-depth information of the properties of articular cartilage is needed.

On the use of stimulated Brillouin scattering as a calibration method for group delay and differential group delay measurements

We propose a novel group delay and differential group delay calibration method for polarization-dependent optical spectral characterization measurements. The calibration method is based on the dispersive nature of stimulated Brillouin scattering and its polarization dependent spectral response. The main advantage of the calibration method is its tunability in wavelength, bandwidth and magnitude, what makes it suitable for different measurement setups.

Multilevel Analysis of Oscillation Motions in Active Regions of the Sun

We present a new method that combines the results of an oscillation study made in optical and radio observations. The optical spectral measurements in photospheric and chromospheric lines of the line-of-sight velocity were carried out at the Sayan Solar Observatory. The radio maps of the Sun were obtained with the Nobeyama Radioheliograph at 1.76 cm. Radio sources associated with the sunspots were analyzed to study the oscillation processes in the chromosphere-corona transition region in the layer with magnetic field B=2000 G. A high level of instability of the oscillations in the optical and radio data was found. We used a wavelet analysis for the spectra. The best similarities of the spectra of oscillations obtained by the two methods were detected in the three-minute oscillations inside the sunspot umbra for the dates when the active regions were situated near the center of the solar disk. A comparison of the wavelet spectra for optical and radio observations showed a time delay of about 50 seconds of the radio results with respect to optical ones. This implies a MHD wave traveling upward inside the umbral magnetic tube of the sunspot. Besides three-minute and five-minute ones, oscillations with longer periods (8 and 15 minutes) were detected in optical and radio records.