Broadband D2 coherent anti-stokes Raman spectroscopy for single-shot pressure and temperature determination with a Fabry-Perot etalon

A method is demonstrated that employs a Fabry-Perot etalon to modulate a broadband coherent anti-Stokes Raman spectroscopy signal beam spatially to obtain enhanced resolution and spectral information for single-shot measurements of pressure and temperature. Resulting images are analyzed by; first, fits to Fabry-Perot patterns for single rovibrational lines; second, a line-shape analysis for a single rovibrational line; and third, a mapping of the Fabry-Perot channel spectra to a linear spectrum. Measurements of the D(2) Raman Q-branch lines were made for a D(2) in Ar mixture to take advantage of the large pressure shift and rovibrational line spacing. Peaks are located to better than 0.5% of the free spectral range of the etalon (approximately 0.01 cm(-1)) and a quantitative analysis of the pressure shifting and broadening is determined for the 1-10-MPa range. Finally, temperature and pressure determination using a band-fitting analysis is demonstrated.     

The effect of Ge implantation dose on the optical properties of Ge nanocrystals in SiO(2)

Ge nanocrystallites (Ge-nc) embedded in a SiO(2) matrix are investigated using Raman spectroscopy, photoluminescence and Fourier transform infrared spectroscopy. The samples were prepared by ion implantation with different implantation doses (0.5, 0.8, 1, 2, 3 and 4) × 10(16)?cm(-2) using 250?keV energy. After implantation, the samples were annealed at 1000?°C in a forming gas atmosphere for 1?h. All samples show a broad Raman spectrum centred at w≈304?cm(-1) with a slight shift depending on the implantation doses. The Raman intensity also depends on the Ge(74+) dose. A maximum photoluminescence intensity is observed for the sample implanted at room temperature with a dose of 2 × 10(16)?cm(-2) at 3.2?eV. Infrared spectroscopy shows that the SiO(2) films moved off stoichiometry due to Ge(74+) ion implantation, and Ge oxides are formed in it. This result is shown as a reduction of GeO(x) at exactly the dose corresponding to the maximum blue-violet PL emission and the largest Raman emission at 304?cm(-1). Finally, the Raman spectra were fitted with a theoretical expression to evaluate the average size, full-width at half-maximum (FWHM) and dispersion of Ge-nc size.     

Vibrational spectroscopic studies and density functional theory calculations of speciation in the CO2-water system

Raman spectra of CO(2) dissolved in water and heavy water were measured at 22 degrees C, and the Fermi doublet of CO(2), normally at 1285.45 and 1388.15 cm(-1) in the gaseous state, revealed differences in normal water and heavy water, although no symmetry lowering of the hydrated CO(2) could be detected. Raman spectra of crystalline KHCO(3) and KDCO(3) were measured at 22 degrees C and compared with the infrared data from the literature. In these solids, (H(D)CO(3))(2)(2-) dimers exist and the spectra reveal strong intramolecular coupling. The vibrational data of the dimer (C(2h) symmetry) were compared with the values from density functional theory (DFT) calculations and the agreement is fair. Careful measurements were made of the Raman spectra of aqueous KHCO(3), and KDCO(3) solutions in D(2)O down to 50 cm(-1) and, in some cases, down to very low concentrations (> or =0.0026 mol/kg). In order to complement the spectroscopic assignments, infrared solution spectra were also measured. The vibrational spectra of HCO(3)(-)(aq) and DCO(3)(-)(D(2)O) were assigned, and the measured data compared well with data derived from DFT calculations. The symmetry for HCO(3)(-)(aq) is C(1), while the gas-phase structure of HCO(3)(-) possesses Cs symmetry. No dimers could be found in aqueous solutions, but at the highest KHCO(3) concentration (3.270 mol/kg) intermolecular coupling between HCO(3)(-)(aq) anions could be detected. KHCO(3) solutions do not dissolve congruently, and with increasing concentrations of the salt increasing amounts of carbonate could be detected. Raman and infrared spectra of aqueous Na(2) -, K(2) -, and Cs(2)CO(3) solutions in water and heavy water were measured down to 50 cm(-1) and in some cases down to extremely low concentrations (0.002 mol/kg) and up to the saturation state. For carbonate in aqueous solution a symmetry breaking of the D(3h) symmetry could be detected similar to the situation in aqueous nitrate solutions. Strong hydration of carbonate in aqueous solution could be detected by Raman spectroscopy. The hydrogen bonds between carbonate in heavy water are stronger than the ones in normal water. In sodium and potassium carbonate solutions no contact ion pairs could be detected even up to the saturated solutions. However, solvent separated ion pairs were inferred in concentrated solutions in accordance with recent dielectric relaxation spectroscopy (DRS) measurements. Quantitative Raman measurements of the hydrolysis of carbonate in aqueous K(2)CO(3) solutions were carried out and the hydrolysis degree a was determined as a function of concentration at 22 degrees C. The second dissociation constant, pK(2), of the carbonic acid was determined to be equal to 10.38 at 22 degrees C.     

Factors determining the stability, resolution, and precision of a conventional Raman spectrometer

We verified the performance of a conventional Raman spectrometer, which is composed of a 30 cm single polychromator, a Si based charge-coupled device (CCD) camera, and a holographic supernotch filter. For that purpose, the time change of the peak positions of Raman spectra of naphthalene and fluorescence spectra of ruby (Cr-doped Al(2)O(3)) were monitored continually. A time-dependent deviation composed of two components was observed: a monotonous drift up to 0.4 cm(-1) and a periodic oscillation with a range of 0.15 cm(-1). The former component was stabilized at approximately 2000 s after the CCD detector was cooled, indicating that incomplete refrigeration of the CCD detector induced the drift. The latter component synchronized with the periodic oscillation of the room temperature, indicating that thermal expansion or contraction of the whole apparatus induced this oscillation. The implemental deviation is reduced when measurements are conducted using a sufficiently cooled CCD detector at a constant room temperature. Moreover, the effect of the room temperature oscillation is lowered in a spectrum acquired over a duration that is longer than one cycle of this oscillation. Applying the least squares fitting method to carefully measured spectra enhanced the precision of the determination of the peak position to 0.05 cm(-1) using the spectrometer with pixel resolution of 1.5 cm(-1).     

Structural and optical properties of tin oxide branched nanostructures

Branched nanostructures of tin oxide (SnO2) have been synthesized by Vapor-Liquid-Solid (VLS) mechanism using a gold catalyst in the temperature range of 800-850 degrees C under an ambient gas flow of 200 sccm. The microstructural and the optical properties of the as prepared products have been studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), micro-Raman, and photoluminescence (PL) studies. SnO2 branches with a rutile phase are found to have a preferential orientation along (101). Typical lengths of these branches are found to be approximately 3-5 microm and diameters in the range of 50-100 nm. Selected area electron diffraction (SAED) pattern shows that the SnO2 branches have a tetragonal cross section with [101] crystal direction. A Raman line at 631 cm(-1) (Sn-O bond) is obtained in the micro Raman spectra. Low temperature PL spectrum shows a strong green emission band near 506 nm.     

Fourier-transform instrument for high-resolution Raman spectroscopy of gases

An instrument is described for recording vibrational-rotational Raman spectra of gases with a resolution of 0.02-0.03 cm(-1). The Raman scattered light is collected by near forward scattering within the cavity of a single-mode, long-term, stabilized Ar-ion laser. The Raman light is analyzed in an ordinary step-scanned Michelson interferometer. To compensate for the low intensity of vibrational-rotational Raman spectra, the interferometer has a beam diameter of 160 mm. The movable mirror, weighing 2.7 kg, is mounted on a smoothly moving sledge, the stepwise motion being performed by three piezotranslators and controlled by three independent He-Ne laser beams. It is shown experimentally that it is possible for one to move the mirror with sufficient precision, using only 13% of the scan time in a typical experiment. In a preliminary spectrum of the fundamental vibration of(14) N(2), the width of the lines has been measured to 0.015 cm(-1).     

Mn掺杂ZnO纳米线的拉曼散射和光致发光特性

研究了不同Mn掺杂含量的ZnO纳米线在室温条件下的拉曼散射和光致发光性能,发现Mn掺杂入ZnO后引入了部分应力,在其拉曼光谱中表现出拉曼峰的位置发生偏移,Mn的掺杂含量越高,峰偏移得越明显.Mn的掺杂对ZnO纳米线的发光性能也有影响,尽管掺杂后仍保持有较为明显的紫外发光峰,但是,随着Mn含量的增加,紫外发光峰的强度降低,并且半峰宽逐渐增大.此外,Mn的掺杂明显地改变了ZnO紫外发光峰的位置.     

Rocketborne cryogenic (10 K) high-resolution interferometer spectrometer flight HIRIS: auroral and atmospheric IR emission spectra

A Michelson interferometer spectrometer cooled to 10 degrees by liquid helium was flown into an IBC class III aurora on 1 April 1976 from Poker Flat, Alas. The sensor, HIRIS, covered the spectral range 455-2500 wave numbers (4-22 microm) with a spectral resolution of 1.8 cm(-1) and an NESR of 5 x 10-12 W/cm2 scrm(-1) at 1000 cm(-1). An atmospheric emission spectrum was obtained every 0.7 sec over an altitude range of 70-125 km. Atmospheric spectra were obtained of CO2 (nu3), NO (Deltanu = 1), O3 (nu3) and CO2 (nu2). Auroral produced excitations were observed for each band, this being the first known measurement of auroral enhancements of O3 (nu3), 9.6 microm, and CO2 (nu2), 15 microm, emissions.     

Tunable excitation source for coherent Raman spectroscopy based on a single fiber laser

We demonstrate a wavelength tunable optical excitation source for coherent Raman scattering (CRS) spectroscopy based on a single femtosecond fiber laser. Electrically controlled wavelength tuning of Stokes optical pulses was achieved with soliton self frequency shift in an optical fiber, and linear frequency chirping was applied to both the pump and the Stokes waves to significantly improve the spectral resolution. The coherent anti-Stokes Raman scattering (CARS) spectrum of cyclohexane was measured and vibrational resonant Raman peaks separated by 70?cm(-1) were clearly resolved. Single laser-based tunable excitation may greatly simplify CRS measurements and extend the practicality of CRS microscopy.     

Spatially resolved stress analysis in Al2O3/3Y-TZP multilayered composite using confocal fluorescence spectroscopy

Fluorescence piezo-spectroscopy (PS) was applied to evaluate the residual stress fields stored in a multilayered Al(2)O(3)/3Y-TZP (3 mol% Y(2)O(3)-stabilized ZrO(2)) composite using the chromophoric fluorescence spectra of Al(2)O(3). The PS results were compared with a theoretical stress distribution in the laminate, calculated according to a repeating unit cell model. However, in practical fluorescence spectroscopy, each measurement point corresponded to a finite volume of material, within which the scattered light experienced fluorescence wavelengths characteristic of the local (weight-average) stress fields. Because of the finite volume of material probed in PS measurements, a comparison between the experimental and calculated values requires that the calculated stresses be convoluted according to the depth-response function of the probe. A pinhole aperture incorporated in the Raman microprobe was used to control the collection probe depth and to modulate the portion of the whole fluorescence emission reaching the detector. According to calibrations of the probe depth and probe response function, probe-convoluted stresses were obtained and a spatially resolved mapping of residual stresses could be obtained.     

Quantitative analysis of the in situ Fourier transform infrared absorption and emission spectrum of gas-phase SiO (Deltav = 1 and 2) produced in Si-N-O fiber growth

The in situ Fourier transform infrared (FT-IR) spectrum of gasphase SiO produced in silicon oxynitride fiber growth has been quantitatively analyzed. Both absorption and emission FT-IR spectra at a spectral resolution of 0.5 cm(-1) were produced from the reaction zone at 1450 degrees C. The fundamental and hot bands were observed with vibrational levels up to v = 7. For the purposes of quantitative analysis the individual vibration-rotation integrated line strengths for the three main isotopes,( 28)SiO,( 29)SiO, and( 30)SiO, were calculated based on ab initio quantum chemical calculations of the electric dipole moment function and the transition moment. Vibrational anharmonicity and Hermann-Wallis correction factors were also incorporated. From the line strengths at specific temperatures and the known Dunham coefficients, the absorbance spectrum was simulated with best fits giving the averaged SiO concentration in the 400 mm reaction zone of 1.0 x 10(17) molecules/cm(3). Such quantitative measurements demonstrate the power of in situ infrared (IR) spectroscopy combined with quantum chemical calculations. The rapid determination of synthetic calibration datasets for chemometric analysis can thus lead to correlation of gas-phase species concentrations with fiber growth properties and subsequently to real-time process control.     

Crystallinity of bamboo-based carbon filaments for incandescent lamps examined by Raman spectroscopy as a nondestructive means of analysis

The crystallinities of bamboo-based carbon filaments have been examined by Raman spectroscopy as a nondestructive means of analysis of the historical lamp (ca. 1890s) manufactured by Ichisuke Fujioka of Japan, and the results have been compared with results from the study of Edison's lamp (ca. 1889) and replica lamps produced in 1979. The crystallinities for the three carbon filaments have been evaluated in terms of the intensity ratio I(D)/I(G), where I(D) is the intensity at 1350 cm(-1) for the D band originating from the defect of graphite and I(G) is the intensity at 1585 cm(-1) for the G band due to the stretching vibration of graphite layers. The ratios obtained are 0.3-0.4, 0.28-0.3, and 0.25-0.28 for the Fujioka, Edison, and replica lamps, respectively. The Raman spectrum of the bamboo-based carbon filament produced by thermal pyrolysis at 1273 K in a nitrogen atmosphere is significantly different from those of filaments inside the incandescent lamps. The raw bamboo filament was analyzed by ultraviolet (UV) Raman spectroscopy using an excitation wavelength of 325 nm from a HeCd laser to avoid the strong interference due to photoluminescence. An intense peak at 1585 cm(-1) was recognized, which was ascribed to the C=C bond vibration for the lignin component in the bamboo. The upper shift of the D band for the carbon filament pyrolyzed at 1273 K was confirmed by varying the excitation wavelength at 514.5 nm to 325 nm, and this behavior was interpreted on the basis of the double resonance Raman scattering mechanism.     

Generation of 224-nm radiation by stimulated Raman scattering of ArF excimer laser radiation in a mixture of H2 and D2

Raman shifting of tunable ArF excimer laser radiation in a mixture of H(2) and D(2) produces tunable radiation in the 224-nm region as a result of Stokes shifting the frequency of the fundamental radiation (193 nm) once in both H(2) and D(2). At a total pressure of 25 bars, a 19% H(2) in D(2) mixture is found to provide a maximum conversion efficiency (2.5%) to the 224-nm range. Both fundamental and 224-nm radiation were used to record laser-induced fluorescence excitation spectra of nitric oxide produced in an oxyacetylene flame. From the excitation spectra, we determined the tuning range of the 224-nm radiation to be 270 cm(-1) with a linewidth of 0.9 cm(-1), which is similar to the fundamental laser radiation. We derived the exact Raman shift of the generated radiation by comparing both excitation spectra which was found to be 7142.3(5) cm(-1).     

Fiber-optic probes for in vivo Raman spectroscopy in the high-wavenumber region

In vivo Raman spectroscopy, using fiber-optic probes is hindered by the intense background signal, which is generated in the fused-silica fibers, in the fingerprint region of the Raman spectrum (approximately 0-2000 cm(-1)). Optical filtering is necessary to obtain tissue spectra of sufficient quality. The complexity of fiber-optic probes for fingerprint Raman spectroscopy, in combination with size constraints and flexibility requirements for in vivo use have been a major obstacle in the development of in vivo diagnostic tools based on Raman spectroscopy. A setup for remote Raman spectroscopic tissue characterization in the high-wavenumber region ( approximately 2400-3800 cm(-1)) is presented. It makes use of a single, unfiltered, optical fiber for guiding laser light to the sample and for collecting scattered light and guiding it back to a spectrometer. Such a simple configuration is possible because the fused-silica core and cladding of the fiber present almost no Raman background signal at these wavenumbers. Several commercially available optical fibers were tested with respect to Raman signal background, to determine their suitability for in vivo Raman spectroscopy measurements in the high-wavenumber region. Different fiber core, cladding, and coating materials were tested. Silica core-silica clad fibers, with an acrylate coating and a black nylon jacket, proved to be one of the best candidates. In vitro measurements on brain tissue of a 6-month-old pig were obtained with a remote high-wavenumber Raman setup. They illustrate the low background signal generated in the setup and the signal quality obtained with a collection time of 1 s.     

Off-line direct deposition gas chromatography/surface-enhanced Raman scattering and the ramifications for on-line measurements

Surface-enhanced Raman spectra (SERS) of molecules separated by gas chromatography (GC) were measured off-line by condensing the analyte on a moving, liquid-nitrogen-cooled ZnSe window on which a 5 nm layer of silver had been formed by physical vapor deposition. After the components that eluted from the chromatograph had been deposited, the substrate was allowed to warm up to room temperature and transferred to the focus of a Raman microspectrometer where the spectrum of each component was measured. Band intensities in the spectrum of 3 ng of caffeine prepared in this way were approximately the same as in the spectrum of bulk caffeine. By making some logical assumptions, it was shown that identifiable GC/SERS spectra of 30 pg of many molecules could be measured over a 300 cm(-1) region in real-time and that if an optimized substrate were used the minimum identifiable quantity could be reduced to 1 pg or less.     

Raman spectra of proteinaceous materials used in paintings: a multivariate analytical approach for classification and identification

This work presents Raman spectra obtained from thin films of protein materials which are commonly used as binding media in painted works of art. Spectra were recorded over the spectral range of 3250-250 cm(-1), using an excitation wavelength of 785 nm, and several bands have been identified in the fingerprint region that correspond to the various proteins examined. Differences in the C-H vibrations located between 3200 and 2700 cm(-1) can be accounted for with reference to the amino acid composition of the protein-based binding media as well as the presence of fatty acid esters, in the case of egg yolk. In addition, the discrimination of different proteins on the basis of variations in spectra between 3200 and 2700 cm(-1) can be achieved following multivariate analysis of a large data set of spectra, providing a novel and nondestructive alternative based on Raman spectroscopy to other methods commonly used for the analysis of proteins.     

Estimation of crystallinity in isotropic isotactic polypropylene with Raman spectroscopy

The Raman spectrum of isotactic polypropylene (iPP) has been found to exhibit vibrational peaks in the region of 750 to 880 cm(-1) that are sensitive to the degree of crystallinity. These features are broadly assigned to various modes of methyl group rocking, rho(CH2), and there have been various attempts to assess crystallinity based on the integrated intensities of these bands. Various vibrational analyses performed in the past in combination with experimental studies have concluded that the presence of crystalline order with trans-gauche conformation gives rise to a peak at 809 cm(-1), which is assigned to a rho(CH2) mode coupled with the skeletal stretching mode. However, the presence of additional peaks at 830 cm(-1), 841 cm(-1), and 854 cm(-1), within the same envelope, have been the subject of controversy. In this work isotropic films of iPP derived from the same precursor of identical tacticity have been subjected to various degrees of annealing and the integrated intensities of the Raman bands were measured. The results showed that true 3d crystallinity in isotropic iPP can only be expressed by the 809 cm(-1) band whereas the band at 841 cm(-1) corresponds to an uncoupled rho(CH2) fundamental mode and thus is a measure of the amorphous content. The less intense satellite bands at 830 cm(-1) and 854 cm(-1) of solid iPP cannot be distinguished from the 841 cm(-1) band in the melt and are generally considered as intermediate phases possibly related to non-crystalline components with 3(1)-helical conformations. Independent differential scanning calorimetry (DSC) crystallinity measurements were in broad agreement with the Raman measurements based on the normalized intensity of the 809 cm(-1) Raman band. By comparing the Raman with the DSC data a new value for the theoretical heat of fusion for the 100% crystalline iPP has been proposed.     

Optical and field emission properties of Zinc Oxide nanostructures

Zinc Oxide (ZnO) nano-pikes were produced by oxidative evaporation and condensation of Zn powders. The crystalline structure and optical properties of the ZnO nanostructures (ZnONs) greatly depend on the deposition position of the ZnONs. TEM and XRD indicated that the ZnONs close to the reactor center, ZnON-A, has better crystalline structure than the ZnONs away from the center, ZnON-B. ZnON-A showed the PL and Raman spectra characteristic of perfect ZnO crystals, whereas ZnON-B produced very strong green emission band at 500 nm in the photoluminescence (PL) spectrum and very strong Raman scattering peak at 560 cm(-1), both related to the oxygen deficiency due to insufficient oxidation of zinc vapor. ZnON-B exhibited better field emission properties with higher emission current density and lower turn-on field than ZnON-A.     

Transmission fourier transform Raman spectroscopy of pharmaceutical tablet cores

Transmission Fourier transform (FT) Raman spectroscopy of pharmaceutical tablet cores is demonstrated using traditional, unmodified commercial instrumentation. The benefits of improved precision over backscattering Raman spectroscopy due to increased sample volume are demonstrated. Self-absorption effects on analyte band ratios and sample probe volume are apparent, however. A survey of near-infrared (NIR) absorption spectra in the FT-Raman spectral range (approximately 0 to 3500 wavenumber shift from 1064 nm, or 1064 to 1700 nm) of molecules with a wide range of NIR-active functional groups shows that although absorption at the laser wavelength (1064 nm) is relatively small, some regions of the Raman spectrum coincide with NIR absorbances of 0.5 per cm or greater. Fortunately, the pharmaceutically important regions of the Raman shift spectrum from 0 to 600 cm(-1) and from 1400 to 1900 cm(-1) exhibit low self-absorption for most organic materials. A statistical analysis of transmission FT-Raman noise in spectra collected from different regions of a pharmaceutical tablet provides insight into both spectral distortion and reduced sampling volume caused by self-absorption.     

Infrared and Raman spectral signatures of aromatic nitration in thermoplastic urethanes

The spectral signatures of nitro attack of the aromatic portion of thermoplastic urethanes (TPU) were determined. Eight fragment molecules were synthesized that represent the nitrated and pristine methylenediphenyl section common to many TPUs. Infrared (IR) and Raman (785 nm illumination) spectra were collected and modeled using the B3LYP/6-31G(d)//B3LYP/6-31G(d) model chemistry. Normal mode animations were used to fully assign the vibrational spectra of each fragment. The vibrational assignment was used to develop a diagnostic method for aromatic nitro attack in thermoplastic urethanes. The symmetric NO(2) stretch coupled out of phase with the C-NO(2) stretch (1330 cm(-1)) was found to be free from spectral interferences. Spectral reference regions that enable correction for physical differences between samples were determined. The carbonyl stretch at 1700 cm(-1) was the best IR reference region, yielding a limit of quantitation (LOQ) of 0.66 +/- 0.02 g N/100 g Estane. Secondary IR reference regions were the N-H stretch at 3330 cm(-1) or the urethane nitrogen deformation at 1065 cm(-1). The reference region in the Raman was a ring stretching mode at 1590 cm(-1), giving an LOQ of 0.69 +/- 0.02 g N/100 g Estane. Raman spectroscopy displayed a larger calibration sensitivity (slope = 0.110 +/- 0.004) than IR spectroscopy (slope = 0.043 +/- 0.001) for nitration determination due to the large nitro Raman cross-section. The full spectral assignment of all eight molecules in the infrared and Raman is presented as supplemental material.