Ultra-narrow-band tunable laserline notch filter

We report on an angularly tunable laserline notch filter from 760 to 785 nm with optical density of 5.7, 3 dB bandwidth of 9 cm⁻¹ (0.55 nm) and greater than 80% transmission. The notch filter is a single element composed of six bonded slanted reflective holographic gratings in glass.     

Raman spectrum of 12CH4 between 2850 and 3100 cm−1

The Raman spectrum of ¹²CH₄ has been recorded at high resolution between 2850 and 3100 cm^?1. A comparative study with a calculated Raman spectrum of the ν₃ band shows that, in this spectral range, about 100 lines do not belong to ν₃ and may be assigned to the ν₁ and 2ν₂ bands.     

Raman spectrum of strontium titanate

The Raman spectrum of strontium titanate has been recorded using λ 4358 of mercury as exciter. The observed spectrum consists of 7 Raman lines, one of which is of low frequency, as expected from the recent theory of Cochran. 6 of these Raman lines have been interpreted as the first order spectrum arising from a small deviation of the cubic strontium titanate from its idealized symmetry. It has been shown that one normal mode of SrTiO₃ neglected by J.T.Last, will be really active in infrared absorption in the region of 440 cm^?1 and that it has to be taken into account in the interpretation of the infrared spectra of titanates. The four vibrational modes of the unit cell of SrTiO₃ correspond to frequencies of 90, 335, 441 and 620 cm^?1 observed in Raman effect. The large width of the Raman lines and the additional lines at 256 cm^?1 and 726 cm^?1 have been attributed to a splitting of the longitudinal and transverse optical modes. With the observed frequencies it has been found possible to account for in a satisfactory manner the specific heat of SrTiO₃ in the range 54·84° K to 1800° K.     

Polarised raman and infrared spectra and vibrational analysis forα-naphthylamine

The Raman spectrum of polycrystalline α-naphthylamine was recorded in the region 100–4000 cm⁻¹. Polarisation measurements were made in CS₂ and CHCl₃ solutions. The infrared spectrum was recorded in nujol mull in the region 200–4000 cm⁻¹. The resolution was better than 2 cm⁻¹ and the accuracy of the measurements was within ± 2 cm⁻¹ for all the spectra. Vibrational assignments have been proposed for the observed frequencies. Out of the 54 normal modes of vibrations, 51 modes could be observed experimentally.     

Absorption line strengths of <Superscript>15</Superscript>NH<Subscript>3</Subscript> in the near infrared spectral region

We present initial results of an investigation of the near infrared absorption spectrum of ¹⁵NH₃ between 6468 and 6692 cm⁻¹. A widely tunable external cavity diode laser is used in a direct absorption setup to determine the line positions and line strengths of several lines in that spectral range. Line data measurements on a ¹⁴NH₃ sample are used for validation of the setup by comparison of the results with available literature data. The presented overview measurements on absorption lines of ¹⁵NH₃ have been performed to serve as a starting point for candidate line selection for prospective isotopic ratio measurements of ¹⁴NH₃ and ¹⁵NH₃.     

Spectral properties of backward stimulated scattering in liquid carbon disulfide

The spectral structure of backward stimulated scattering from a 10 cm-long CS₂-liquid cell is investigated by using Q-switched 10-ns and 532-nm laser pulses with different spectral linewidths. Under a narrow spectral line (∼0.1 cm⁻¹) pump condition, very strong sharp lines near the pump wavelength (λ ₀) position and the first-order stimulated Raman scattering (λ _s1) position can be observed. However, under a wide line (≈1 cm⁻¹) pump condition, only a strong and superbroadening spectral band can be observed mainly in the red-shift side of the pump wavelength. The different spectral features under these two conditions can be explained by a competition between stimulated Brillouin, Raman, and Rayleigh-Kerr scattering. Under both pump conditions, the broadening spectral distributions are not consistent with the predictions given by stimulated Rayleigh-wing scattering theories, but can be interpreted well utilizing the theoretical model of stimulated Rayleigh-Kerr scattering. Zh. éksp. Teor. Fiz. 112, 1563–1573 (November 1997) Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.     

Investigation of the water vapor emission spectrum in the region 9600–12000 cm−1

To record weak emission spectra, a high-sensitivity diffraction spectrometer, operating in the region 400–1100 nm, has been designed on the basis of a DFS-452 spectrograph and a photodiode reader with a spectral resolution of 0.14 cm^?1. A Multiplaz-2500 plasmatron, generating intense molecular emission spectra in the visible and near-IR regions, served as a source of the water vapor emission spectrum at temperatures above 3000 K. Water vapor emission spectra have been recorded for the first time in the range above 10 000 cm^?1. The analysis of the spectra obtained has shown that the plasmatron emission spectrum also includes the lines of the OH radical.     

新型透射式全息窄带带阻滤光器的光谱特性分析

滤光器在光谱学、光学测量和激光物理中有着极其重要的应用。全息滤光器是一种新型滤光器,特别是利用重铬酸明胶(DCG)记录的全息透射式窄带滤光器,其主要特点为对主谱线有很窄的带宽。文章主要用紫外-可见分光光度计测定用DCG记录的透射式全息窄带带阻滤光器的光谱特性,测量结果分析表明,滤光器在可见光区域(400～800 nm)对其中心波长的相对透射率小于2%,其他谱线的相对透射率大于85%。且滤光器有较窄的带宽,其半宽度小于12 nm,十分之一宽度小于15 nm。对氩离子激光(Ar+)主谱线514.5 nm有优良的滤光特性。     

Absorption spectrum of carbon dioxide at 4.3 μm

The absorption spectrum of carbon dioxide has been recorded in the wavenumber region 2395-2216 cm^?1 with a spectral resolution between 0.02 and 0.03 cm^?1. About twenty transitions have been identified and the molecular constants of the levels involved have been evaluated. In view of the interest of this region in atmospheric studies a map of the entire spectrum recorded by using a normal sample of carbon dioxide is presented including the identifications for the different bands. About 90% of the lines observed have been interpreted. Some of them have been assigned to transitions originating from higher excited states of ¹²C¹⁶O₂ not considered before in interpreting this spectral region. For the first time, bands of ¹²C¹⁶O¹⁷O have been identified in the 4.3-μm spectra obtained with the natural sample.     

Spectroscopy of phonon and vibronic states of YbAl3(BO3)4 single crystal

The polarized Raman and reflection spectra of a single crystal YbAl₃(BO₃)₄ at room temperature were studied. Raman active vibrational modes A ₁, E _TO, and E _LO are identified. In the Raman spectrum, we detected an intense line at a frequency of 1018 cm⁻¹, which refers to internal vibrations of the BO₃ group and is known to be promising for use in amplifiers based on stimulated Raman scattering. From the simulation of reflection spectra by the method of dispersion analysis the frequencies of A ₂ vibrational modes were determined. Intense bands observed in the low-temperature transmission spectra in the range of f-f transitions in the Yb³⁺ ion are attributed to electron-phonon transitions. The Raman lines are compared with electron-phonon lines in the transmission spectrum.     

Narrowing of the vibrational spectrum under compression of liquid carbon dioxide

The broadening and shift of the Q bands of the 1388/1285-cm⁻¹ Fermi doublet of carbon dioxide have been measured by means of the spectroscopy of coherent anti-Stokes Raman scattering in a wide density range realized at compression in dense gaseous and liquid states. The spectrum of the low-frequency Q band exhibits an essential narrowing upon the compression of the liquid in the density range of 320–400 amagat from a maximum width of about 2.2 cm⁻¹ to about 1.7 cm⁻¹ determined by elastic dephasing. The observed dependence is connected with the progressive narrowing of the spectral contribution attributed to the collapsed rotational structure.     

New χ (3)-nonlinear-laser manifestations in tetragonal LuVO4 crystal: more than sesqui-octave Raman-induced Stokes and anti-Stokes comb generation and cascaded self-frequency “tripling”

We report the experimental investigations of nonlinear-laser effects in LuVO₄ vanadate under one-micron picosecond Nd³⁺:Y₃Al₅O₁₂ pumping. In this tetragonal host-crystal for Ln³⁺ lasants for the first time we excited ultra-broad, more than one and half octave (13500 cm⁻¹) Raman induced Stokes and anti-Stokes generation combs and observed multi-step cascaded parametric χ ⁽³⁾-lasing in UV spectral region. All generation lines were identified and attributed to SRS-promoting modes of the crystal (ω _SRS1≈900 cm⁻¹ and ω _SRS2≈113 cm⁻¹). We classified this vanadate as a promising material for self-Raman laser converters.     

Raman scattering of light and IR absorption in carbon nanotubes

Raman light scattering and IR absorption spectra of samples containing multilayer carbon nanotubes in different stages of purification by the selective oxidation technique have been investigated. It was found that the Raman spectra of carbon nanotubes exhibit softening of the mode at 1582 cm⁻¹ corresponding to E _2g vibrations of graphite hexagons and a line at 120 cm⁻¹ due to the radial vibrations of nanotubes. In IR absorption spectra measured in the region of 0.07–0.3 eV, several sets of lines with a spacing of 15 meV (120 cm⁻¹) between lines of each group have been detected. We suggest that each group corresponds to electron transitions generating electron-hole pairs in semiconducting nanotubes and contains a phononless 00-line and its phonon replicas with spacing between them equal to the “breathing” mode energy of 120 cm⁻¹. Measurements of electric conductivity at a frequency of 9300 MHz indicate that, in addition to semiconducting nanotubes, the samples contain nanotubes with properties of a highly disordered semimetal. Zh. éksp. Teor. Fiz. 113, 1883–1891 (May 1998)     

Anomalous low-frequency phonons in ZrB<Subscript>12</Subscript>

The influence of pressure and temperature on low-frequency lines (100–300 cm^–1) in Raman spectra of ZrB₁₂ and LuB₁₂ single crystals has been investigated. These spectral features have been identified as one-phonon and two-phonon excitations of the acoustic branches of the phonon spectrum. It has been found that the observed spectra of ZrB₁₂ single crystals are more structured and indicate the development of phonon anomalies with a decrease in the temperature. Despite the fact that the low-frequency features in the phonon spectrum of ZrB₁₂ are characterized by a high value of the isothermal Grüneisen parameter, their isobaric Grüneisen parameter has a negative value. This indicates large contributions from the fourth-order anharmonicity, which significantly exceed the volume effects. The appearance of narrow lines in the frequency range from 155 to 175 cm^–1 at temperatures T < 100 K suggests the possibility of a structural transition with an incomplete softening of the lattice.     

High-resolution coherent stokes Raman spectroscopy of theν 1 andν 3 bands of methane

Coherent Stokes Raman spectra of the ν₁ and ν₃ bands of CH₄ have been recorded in mixing two pulsed lasers (ruby and dye) of very good spectral and spatial quality. The results show a resolution of about 0.010 cm⁻¹ for a 10 Torr pressure, corresponding in great part to Doppler broadening.     

Vibrational Spectroscopic Characterization of the Arsenate Mineral Barahonaite: Implications for the Molecular Structure

The mineral barahonaite is in all probability a member of the smolianinovite group. The mineral is an arsenate mineral formed as a secondary mineral in the oxidized zone of sulphide deposits. We have studied the barahonaite mineral using a combination of Raman and infrared spectroscopy. The mineral is characterized by a series of Raman bands at 863 cm^?1 with low wavenumber shoulders at 802 and 828 cm^?1. These bands are assigned to the arsenate and hydrogen arsenate stretching vibrations. The infrared spectrum shows a broad spectral profile. Two Raman bands at 506 and 529 cm^?1 are assigned to the triply degenerate arsenate bending vibration (F ₂, ν₄), and the Raman bands at 325, 360, and 399 cm^?1 are attributed to the arsenate ν₂ bending vibration. Raman and infrared bands in the 2500–3800 cm^?1 spectral range are assigned to water and hydroxyl stretching vibrations. The application of Raman spectroscopy to study the structure of barahonaite is better than infrared spectroscopy, probably because of the much higher spatial resolution.     

The absorption spectrum of D<Subscript>2</Subscript>O in the region of 0.97 μm: the 3ν<Subscript>1</Subscript> + ν<Subscript>3</Subscript> vibrational–rotational band

The vibrational–rotational absorption spectrum of D₂O in the range from 10 120 to 10 450 cm^–1 is recorded on a Fourier transform spectrometer with a resolution of 0.05 cm^–1. The measurements were performed using a multipass White cell with an optical path length of 24 m. A light-emitting diode with brightness higher than that of other devices was used as a radiation source. The signal-to-noise ratio was about 10⁴. The spectrum is interpreted as consisting of lines of more than 400 transitions. The spectral characteristics of lines (centers, intensities, and half widths) are determined by fitting the Voigt profile parameters to experimental data by the least-squares method. The intensities of lines and the experimental rotational energy levels of the (301) vibrational state of the D₂ ¹⁶O molecule with high rotational quantum numbers are determined for the first time.     

Raman scattering in dried DNA and crystalline amino acids

Raman spectrum characteristics of dried deoxyribonucleic acid (DNA) and two types of crystalline amino acids (L-lysine, D-asparagine) are compared in a wide range of frequencies, including the regions of lattice (7 to 200 cm^?1) and intramolecular (200 to 4000 cm^?1) vibrations. It is found that the spectral position of the low-frequency band in the Raman spectrum of DNA with a peak near 26 cm^?1 correlates with the Raman spectrum of high-Q low-frequency modes that manifest themselves in the crystalline amino acids under investigation. The low-frequency band of DNA refers to a twist-like vibrational mode of nucleobases. The intensities of this DNA mode and the high-Q lattice modes of the crystalline amino acids L-lysine and D-asparagine are several times as high as those of the Raman lines corresponding to the intramolecular modes. Resonant coupling of low-frequency modes of DNA and amino acid molecular chains is analyzed.     

Polarized Raman scattering and low frequency infrared study of hydroxyapatite

A detailed investigation of the polarized Raman spectrum of monoclinic hydroxyapatite (OHAp) and a careful study of the low frequency infrared spectrum of polycrystalline OHAp, is reported. Most of the spectral details of Raman scattering are consistent with the local pseudo-hexagonal C₆ factor group symmetry of OHAp. However, some features, for example the absence of TO-LO splitting for particular E₁ phonon geometries and the splitting of the lowest frequency Raman line, are a reflection of the centrosymmetric monoclinic lattice of OHAp. Between 0 and 50cm^?1, a temperature-dependent background, having E₁ symmetry, and probably associated with OH^? disordering flucuations, was observed in OHAp. Both OHAp and FAp displayed low frequency Raman lines which softened with decreasing temperature. However, no evidence for a phase transition was found in either OHAp or FAp in the 12–295 K temperature range.     

Directional dispersion of extraordinary phonons in layer compound InSe

The resonant Raman scattering of polar optical phonons has been measured in trigonal γ-InSe at the E'₁ exciton edge. The two-phonon scattering spectrum widely spreads over the frequency range of 50 cm^-1 with an extremely asymmetric lineshape. This spectrum has been interpreted in terms of the directional dispersion of extraordinary LO and TO phonons.