Nonlinear optical characteristics of carbon disulfide

The nonlinear refractive index γ of CS₂ is studied using laser pulses of various durations (from 110 fs to 75 ns). It is found that γ increases with increasing pulse duration within the picosecond region (from (3 ± 0.6) × 10^?15 cm² W^?1 at 110 fs to (3.5 ± 0.7) × 10^?14 cm² W^?1 at 75 ns) due to orientational nonlinearities. Variations in the sign of γ caused by the thermal effect at different pulse durations and repetition rates are analyzed. It is demonstrated that the fast electronic component, the component associated with molecular processes, causing positive nonlinear refraction, and the acoustic component, responsible for negative nonlinear refraction, manifest themselves simultaneously. The results of a study of the nonlinear absorption of carbon disulfide are presented. The two-and three-photon absorption coefficients of CS₂ are determined to be (5 ± 1.5) × 10^?11 cm W^?1 and (2.8 ± 0.8) × 10^?23 cm³ W^?2, respectively.     

Attenuation of ultrasound in skeletal muscle

Ultrasonic attenuation in fresh and 5% formalin fixed beef skeletal muscle has been measured, as a continuous function of frequency, in the range 1–8 MHz, for muscle fibre orientations both parallel and normal to the direction of propagation. Good agreement was found in all cases between two independent sets of measurements employing transmission and reflection techniques respectively. The data are consistent with a power law dependence of attenuation coefficient on frequency, with an exponent that is not significantly different from unity. For propagation normal to the fibres attenuation values are found as 1.1 ± 0.15 and 1.6 ± 0.15 dB cm^?1 MHz^?1 for fresh and fixed tissue respectively, the corresponding values for parallel propagation being 2.9 ± 0.23 and 4.1 ± 0.25 dB cm^?1 MHz^?1.     

Messung der Wirkungsquerschnitte für die Linienverbreiterung von Hochfrequenzübergängen im 63 P 2-Zustand des Quecksilbers durch Stöße mit Edelgasatomen

The linewidth of high frequency transitions between Zeeman-levels of the metastable 6³ P ₂-state of mercury is measured as function of the pressure of various noble gases. The measurements are made for all noble gases in the pressure range from 10^?3 to about 2 · 10^?2 Torr. The cross sections for linebroadening due to atomic collisions are derived from the pressure dependence of the linewidth. These cross sections σ were found to be (71 ± 10) · 10^?16 cm² for He, (82 ± 10) · 10^?16 cm² for Ne, (153± 12) × 10^?16 cm² for Ar, (204±28) · 10¹⁶ cm² for Kr and (291 ± 41) · 10^?16 cm² for Xe.     

Dipolar studies in CaF2 with Ce3+

Dielectric relaxation in CaF₂ doped with various amounts of Ce³⁺ (0·01 to 1·0 mol%) was measured. The value of the activation energy for orientation of the dipoles {Ce³⁺-F^? interstitial} was determined to be H = (0·46 ± 0·01) eV. The frequency factor was found to have the value τ_o = (5 ± 1) × 10^?15 sec, giving for the vibrational frequency of the interstitial the value ν_o = (5 ± 1) × 10¹³ sec^?1.The number of dipoles contributing to the dielectric loss peak was determined to be between 10¹⁷ and 8 × 10¹⁷ cm^?3 for the different doping amounts of Ce³⁺. Optical absorption measurements showed the existence of large aggregate bands. We could verify that there exists a second-order reaction of aggregation, which is responsible for the non-linearity found between optical absorption at 305 nm and the nominal concentration of Ce³⁺ in the samples. On the other hand, if we assume that the centers which contribute to optical absorption at 305 nm are those also responsible for the relaxation peak, we find that the number contributing to each process is not the same. We can define an interaction radius R as the minimum separation between two dipoles allowing them to contribute to the relaxation peak. From our experimental data R ? 3·8 × 10^?7 cm.     

Level- and line-crossing experiments in selective reflection from mercury vapour

When the technique of magnetic depolarization is applied on selective reflection of the 2537 Å resonance line from mercury vapour Doppler- and pressure-broadened level-crossing curves are received. From the pressure dependence of the damping constant, determined as: Г_c=(5.3±0.5) · 10^?9 ·N sec^?1 cm³ the cross section of resonance broadening is derived for 280 °C as: σ=(1550±150) · 10^?16 cm². Besides the zero-field level-crossing effect an additional interference effect is observed when a mixture of different isotopes is used. This line-crossing effect allows the determination of isotope shift and hyperfine structure and gives a new possibility for studying foreign gas pressure-broadening. Experiments were performed with the same apparatus in selective reflection as well as in forward-scattering. The experimental level- and line-crossing curves principally agree with curves calculated according to a theory of Series when the incident spectral distribution is considered.     

Line strength and collisional broadening coefficients of H2O at 2.7 μm for natural gas quality assurance applications

We employed tunable diode laser absorption spectroscopy to measure the line strength, the methane (CH₄), ethane (C₂H₆) and the propane (C₃H₈) broadening coefficients for the 523–422 H₂O transition at 3619.61 cm^?1. Water amount fractions generated by a stable and accurate humidity transfer standard, traceable to the SI units via the German national humidity standard, were used to calibrate the spectroscopic line strength measurements. We focus on the traceability of the measured line data to the SI and on uncertainty assessments following the guidelines of the Guide to the Expression of Uncertainty in Measurement. We determined the line strength to be (8.42 ± 0.07)×10^?20 cm^?1/(cm^?2 molecule) corresponding to a relative uncertainty of ±0.8%. To the best of our knowledge, we report the first methane, ethane and propane broadening coefficients of (8.037 ± 0.056)×10^?5 cm^?1/hPa, (9.077 ± 0.064)×10^?5 cm^?1/hPa and (10.469 ± 0.073)×10^?5 cm^?1/hPa for the 523–422 H₂O transition at 3619.61 cm^?1, respectively. The relative combined uncertainties of the stated CH₄, C₂H₆ and C₃H₈ broadening coefficients are in the ±0.7% range.     

Coherent Stokes and anti-Stokes Raman spectra of the ν1 (A1) and ν2 (E) bands of SF6 and UF6

Coherent Stokes and anti-Stokes Raman scattering are used to study the ν₁ and ν₂ spectral band profiles of UF₆ and SF₆. Most of the observed SF₆ “hot” bands are assigned, leading to evaluations of the anharmonicity constants X_ij: X₁₂ = ?(2.80 ± 0.30) cm^?1, X₁₄ = ?(1.00 ± 0.15) cm^?1, X₁₅ = ?(1.00 ± 0.15) cm^?1. For UF₆, a tentative assignment of the “hot” bands is made: X₁₂ = ?(1.80 ± 0.30) cm^?1, X₁₃ = ?(1.60 ± 0.30) cm^?1, X₁₄ = ?(0.20 ± 0.10) cm^?1, X₁₅ = ?(0.25 ± 0.10) cm^?1, and X₁₆ = ?(0.10 ± 0.05) cm^?1. Parameters such as the vibration-rotation coupling constants are determined. For SF₆: α = (7 ± 2) × 10^?5 cm^?1 for the ν₂ band and α = ?(1.02 ± 0.01) 10^?4 cm^?1 for the ν₁ band. The calculated spectral profiles of the coherent Stokes or anti-Stokes spectra, which are in good agreement with experimental results, give values for the resonant and nonresonant parts of the susceptibility in both molecules. They also show, in some cases, the influence of neighboring combination bands.     

A high resolution FTIR spectroscopic study of the hydrogen-bonded heterodimer H3N−HCN

The spectrum of the symmetric top, hydrogen-bonded heterodimer H₃N?HCN has been recorded between 2900 and 3200cm^?1 using a high resolution FTIR spectrometer. The more intense bands are associated with the ν₂ (H?CN stretch) vibration and include hot bands associated with the low frequency modes ν₅, ν₂ and ν₁₀. Weaker difference bands of the type ν₂+(n?1) ν5?nν₅ are also observed. Analysis of the bands yields values for the band origins: ν2/0=3110·5±0·2cm^?1 and ν5/0=140±5cm^?1 and the anharmonicity constants: x _2,10=12·7±0·5cm^?1, x _2,9≈x _2,5=23±3cm^?1 and x _5,10=?5±2cm^?1. The lifetime in ν₂ with respect to vibrational predissociation, estimated from the width of the sharpest observed feature, is 100?200 ps but there is some indication that this lifetime may decrease at high J.     

Changes in Dentin Collagen After Sample Grinding and Heating

ABSTRACT

Changes to the structure of the organic matrix of the dentin tissue were determined after sample grinding and heating. Powder dentin measuring 25–38 µm and slices with a thickness of about 50 µm were employed. Spectra acquisition was conducted with a Fourier-transform infrared spectrometer. The thermal treatment was performed between 100°C and 300°C, with steps of 25°C. After grinding, two bands (1283.5 ± 0.5 cm^?1 and 1240.7 ± 0.5 cm^?1) shifted to higher wavenumbers, while three bands (1339.5 ± 0.5 cm^?1, 1283.5 ± 0.5 cm^?1, and 1202.7 ± 0.5 cm^?1) shifted to lower wavenumbers after thermal treatment in the range 100–300°C; the band at 1283.5 ± 0.5 cm^?1 shifted only 2 cm^?1. Thermal treatment produced a wavenumber shift in the opposite direction compared with the shift produced after grinding. The observed changes in the vibration modes of the structure indicate that sample preparation or sterilization involving grinding and heating must be carefully evaluated in order to preserve the natural characteristic of the collagen structure.     

The forbidden (J → J + 1) spectrum of CH4 in the ground vibronic state

The pure rotational R-branch spectrum of CH₄ arising from the centrifugal distortion moment has been studied using a simple 12.10-m light-pipe cell and a conventional interferometer. Ten forbidden (J → J + 1) transitions for J = 7 to J = 16 have been observed in the spectral region 80–200 cm^?1 with a theoretical resolution of 0.5 cm^?1. The integrated intensity of the six strongest lines has been measured and was found to be of the order of twice that calculated from the distortion moment obtained earlier from a molecular beam study of the (J = 2) rotational level. In the approximation that frequency shifts due to this excess intensity are neglible, it has been determined that the rotational constant B₀ = (5.245 ± 0.004) cm^?1 and the scalar distortion constant D_S = (1.19 ± 0.09) × 10^?4 cm^?1. It is argued that the excess intensity is due to higher-order terms in the dipole moment operator and the validity of the frequency analysis is considered in this context.     

Observations on the electronic spectrum of gaseous FeO

About 400 lines are assigned to FeO emission bands in the region 5580 to 6265 Å. The lower state of all the bands analyzed is identified as the ground state of the molecule, for the value of the lower-state vibration frequency (ω_e = 880.61 ± 0.02 cm^?1) is in excellent agreement with that observed in low-temperature matrix isolation, itself confirmed by isotopic substitution. This state is also observed as the lower state in laser-induced fluorescence. However, 880 cm^?1 is significantly smaller than the value found in laser photodetachment studies of FeO^? (970 ± 60 cm^?1). The rotational analysis is consistent with a parallel transition, ΔΛ = 0, but the value of Λ is not determined. According to theoretical calculations, the orange bands most probably arise from a ⁵Σ-⁵Σ transition. There is at least one nearby excited state, for all analyzed upper levels are perturbed.     

High-resolution measurement and analysis of the infrared spectrum of nitric acid near 1700 cm−1

The infrared spectrum of the ν₂ band of nitric acid (HNO₃) has been measured with a tunable diode laser in the frequency interval from 1690 to 1727 cm^?1. A total of 430 assigned transitions have been analyzed to yield a set of nine rovibrational constants for the upper state with a standard deviation of 0.0012 cm^?1. The band is primarily B type with a band center at 1709.568 ± 0.005 cm^?1. Because of the absence of perturbations, the band constants can be used to calculate transition frequencies and relative intensities with a high degree of accuracy.     

Laser Stark spectroscopy of FCN

Using a CO₂ laser, Stark shifted resonances have been measured for the CF stretching fundamental (ν₃) of FCN near 9.3 μm, and for two nearby “hot” bands. The band centers measured are 1076.492007 ± 0.000013 cm^?1 for 00⁰1-00⁰0, 1085.741046 ± 0.000050 cm^?1 for 01¹1-01¹0, and 1091.16222 ± 0.00015 cm^?1 for 02⁰1-02⁰0. The ground state dipole moment of FCN is found to be 2.1203 ± 0.0010 D and dipole moments are also given for the other states observed. Values are given for the rotational constant and l-doubling constant for the 01¹1 state.     

Raman-brillouin light scattering determination of the structural correlation range in ges2 glass

Polarized Brillouin and low frequency (3 cm^?1 ? ω ? 40 cm^?1) Raman spectra of GeS₂ glass have been measured. Parameters determined from the Brillouin spectra have been used in the theory of Martin and Brenig to obtain from a fit of the Raman spectrum the structural correlation range, 2σ. We find 2σ = 8 ± 1 Å.     

Measurement of integrated intensities of acetylene bands at 3·04, 7·53 and 13·7 μm

Integrated intensities of acetylene bands at 3·04, 7·53 and 13·7 μm have been measured at 300°K using the Wilson-Wells-Penner-Weber technique and a spectral resolution of 0·6 cm^?1. Our best estimates of the intensities are 294 ± 6 cm^?2atm^?1 for the 3·04 μ bands, 87 ± 2 cm^?2atm^?1forthe 7·53 μband and 729 ± 28 cm^?2atm^?1 for the 13·7 μ band at 300°K.     

Microwave determination of the conformation and dipole moment of 1,3-difluoroacetone

The microwave spectra of the ground state and several low-lying vibrational modes of 1,3-difluoroacetone have been assigned and analyzed. The assigned form has a molecular conformation in which one fluorine atom lies cis and the other trans to the oxygen atom. The rotational constants of the ground state species were determined using a centrifugal distortion analysis: A = 6024.843 ± 0.006 MHz, B = 2454.414 ± 0.001 MHz, C = 1783.897 ± 0.001 MHz. The molecular dipole moment components of the ground state species lie along the a and b principal axes with μ_a = 2.38 ± 0.03 D, μ_b = 0.89 ± 0.03 D, and μ_T = 2.54 ± 0.03 D. Comparative intensity measurements with OCS microwave lines indicate that the assigned form constitutes only 20% to 30% of the total gas mixture, the remainder presumably consisting of one or more other conformers, perhaps the gauche-gauche form. The lowest vibrational frequency (82 ± 12 cm^?1) is attributed to the trans-CH₂F torsion, while the next-higher vibrational frequency (127 ± 15 cm^?1) is believed to be the cis-torsion. A low-frequency in-plane bending motion is found at 285 ± 25 cm^?1.     

Torsion of the nitro group in nitroethylene

Eight NO₂-torsional transition frequencies obtained from interferometric far infrared measurements are reported. These data provide accurate information on the potential function for torsional angles up to 50°. The potential parameters are V₂ = 1642.7 ± 3.9 cm^?1 and V₄ = ?88.0 ± 1.7 cm^?1 for a rigid frame/rigid top model and V₂ = 1690.6 ± 4.2 cm^?1 and V₄ = ?90.8 ± 1.8 cm^?1 for a refined model allowing for distortions of the NO₂-group upon torsion. V₆ and V₈ terms are not significant.     

Investigation of third-order optical nonlinearity in KBe2BO3F2 crystal by Z-scan

The third-order optical nonlinearity of deep-ultraviolet (DUV) nonlinear optical (NLO) crystal KBe₂BO₃F₂ (KBBF) was investigated using single-beam Z-scan technique for the first time. The Z-scans were performed on a c-cut KBBF crystal and a KBBF prism-coupling device (PCD) with picosecond pulses at 355?nm. No two-photon absorption was observed in the experiment. The measured nonlinear refraction index n ₂ showed positive signs, indicating self-focusing Kerr effects. The n ₂ values were estimated to be (1.75±0.35)×10^?15?cm²/W with the c-cut sample and (1.85±0.37)×10^?15?cm²/W with the PCD, corresponding to the third-order nonlinear optical susceptibilities $\chi_{\mathrm{eff}}^{(3)}$ of (0.99±0.20)×10^?13?esu and (0.94±0.19)×10^?13?esu, respectively. The results are expected to promote the investigation of frequency conversion processes with ultra-short laser in KBBF crystal.     

Direct observation of the torsional fundamental of gaseous C2F6 in the far infrared

The forbidden a_1u torsional vibration of C₂F₆ has been observed in far-infrared absorption at 67.5 cm^?1 with an integrated intensity of 0.20 ± 0.08 × 10^?2 cm^?2. The observed intensity is compared with that expected theoretically from Coriolis coupling of the torsion to the infarred-active a_2u and e_u vibrations. For certain force fields and choices of sign for the dipole moment derivatives the agreement is satisfactory. The potential barrier to internal rotation has been recomputed from the observed torsional frequency to be 1367 cm^?1. (3.91 kcal mole^?1). This value is compared with those of ethane and partially fluorinated ethanes.     

Raman study of charge-density-wave phase transition in quasi-one-dimensional conductor (TaSe4)2I

Polarized Raman spectra were obtained in the quasi-one-dimensional conductor (TaSe₄)₂I above and below the charge-density-wave (CDW) transition temperature (T_c=263 K). The Raman intensities of many peaks become intenser and two of the phonon peaks shift to higher frequency with decreasing temperature. Moreover a new broad peak at about 90 cm^?1 and a new peak around 166 cm^?1 appear in the low-temperature phase. The polarization characteristic shows that the former is assigned to totally symmetric mode. The damping constant of the phonon at 90 cm^?1 increases markedly with increasing temperature. The frequency shifts to higher frequency as the temperature increases and the coupling coefficient is approximately proportional to (T_c?T)^{$\text{1}\text{2}$}. This peak becomes Raman active owing to the CDW phase transition. The temperature dependence of the damping constant and the frequency shift may have a relation to the dynamical properties of the CDW phase transition.