The energy-band gaps in tetrathiafulvalene-tetracyanoquinodimethane measured by far-infrared photoconductivity

The b-axis photoconductivity of TTF-TCNQ at 5 K has been measured with polarized radiation. The bolometric signal from vibrational modes was removed by increasing the chopping frequency and reducing the temperature. Band gaps of 403 K (E ∥ a) and 453 K (E ∥ b) were obtained, the former agreeing with d.c. conductivity results above 13 K. Impurity photoconductivity was observed with E ∥ b and an energy gap of 130 K explaining d.c. conductivity results below 13 K.     

Temperature dependence of the far-infrared absorption spectrum of gaseous methane

The rototranslational absorption spectrum of gaseous methane has been measured at seven different temperatures from 296 to 140 K. We have analyzed both the spectral moments and the experimental absorption shapes, assuming that only octupolar and hexadecapolar induction mechanisms contribute to the absorption. This assumption allows us to parameterize the temperature dependence of both the intensity and the shape of the absorption band. The results obtained indicate that other contributions to absorption are not negligible.     

The far-infrared absorption spectrum of electron-hole drops in silicon

We report on the first observation of the absorption spectrum of electron-hole drops in silicon. The absorption at 14°K consists of a broad peak at 34.2 ± 0.2 meV in the far-infrared spectral range. The lineshape can be well fit with a model that uses Mie theory of light absorption by small particles. The model includes both intra and interband terms. We find a plasma frequency of 51.9 ± 0.4 meV and from this we calculate a electron-hole density in the drops of (3.37 ± 0.06) × 10¹⁸ cm^?3.     

光频链接的双光梳气体吸收光谱测量

双光梳光谱技术以其无运动部件快速采样、高分辨率探测等优势成为宽带激光光谱测量中的热点技术.但受限于常用微波锁定双光梳光源间的噪声特性,双光梳光谱技术仍难以发挥其探测潜能.本文报道一种光频域互相链接的双光梳光谱探测方案.通过将两台激光器的偏置频率同时锁定到一个窄线宽激光器上,既免去了结构复杂且成本高昂的非线性自参考系统,又将双光梳间的共同参考点设置到了光频范围,抑制了双光梳光谱采样抖动,实现光谱探测性能的提升.~(13)C_2H_2的ν_1+ν_3 P支光谱数据测量数据分析结果表明:谱线位置与文献结果符合良好,光谱分辨率为0.086 cm~(-1),信噪比200:1(62.5 ms,100幅平均),相应的秒均噪声等效吸收系数达6.0×10~(-6)cm~(-1)·Hz~(-1/2).该工作为双光梳光谱测量的实际应用提供了一种高精度、低成本、易于实现的解决方案.     

Weak bands in the far-infrared spectrum of HCNO

Several weak transitions in the far-infrared spectrum of H¹²C¹⁴N¹⁶O between the (0000_v) levels with v = 2, 3, and 4 have been analyzed. Vibrational levels of improved accuracy have been calculated for both the (0000_v) series (v ≦ 5) and the (0001_v) series (v ≦ 3). For the latter, some inconsistencies in previous assignments have been removed. Two transitions from the (00020)² level have been assigned tentatively. The two lowest bands of the (0000_v) series of H¹³C¹⁴N¹⁶O have been found. Two new types of graphical plots have been used in the assignment.     

Induced far-infrared absorption in rare-gas mixtures

Translational collision-induced absorption spectra of five binary rare gas mixtures have been recorded at various densities. The experimental procedure with special control requirements is described first. The binary feature of the absorption is shown to be valid over a large density range. For this particular situation, absorption coefficients and integrated intensity values have been expressed in terms of the product of density units. Finally, a comparison between experimental and theoretical results is discussed.     

Effect of electron bombardment on a phase-inhomogeneous nanoscopic structure and the fundamental absorption spectrum of single-crystal CuO

The optical absorption spectra of single-crystal CuO bombarded with 5-MeV electrons exhibit reduced absorption in the region of the fundamental absorption edge at 17 eV, which corresponds to the b _1g →e _u transition with charge transfer in CuO ₄ ⁶⁻ . A simultaneous increase in absorption is observed in the middle infrared and in the region of high energies centered on 2.9 eV. The experimental results obtained are interpreted in terms of ideas on the phase-inhomogeneous nano-agglomorated structure in copper oxides that occurs as a result of the nucleation of polar centers (CuO ₄ ⁵⁻ , CuO ₄ ⁷⁻ ) under electron bombardment. Fiz. Tverd. Tela (St. Petersburg) 39, 2141–2146 (December 1997)     

Torsion-rotation far-infrared spectrum of O-18 methanol

High-resolution Fourier transform spectra have been recorded from 15–470 cm^–1 for the far-infrared trosion-rotation band of O-18 methanol in the vibrational ground state. So far, 57 subbands have been assigned in the 15–220 cm^–1 region for a wide range of rotational and torsional states, and their J-independent origins have been determined to an estimated accuracy of ±0.01 cm^–1. The observed origins were found to deviate in many cases by several tenths of a cm^–1 from the values calculated with the previous molecular parameters. Together with 4 known microwave origins, the new data have been fitted to a model torsion-rotation Hamiltonian in order to refine the set ofb-type molecular constants for the ground state. With the new parameter set, the experimental subband origins are reproduced with an rms error of ±0.02 cm^–1, representing a substantial improvement over the earlier situation. The spectroscopic results have also been of great assistance with our assignments of optically-pumped FIR laser emission in CH₃ ¹⁸OH, in providing FIR data for checking the identification of the IR-pump/FIR-laser transition systems through combination loop relations.     

Pure rotational spectrum of carbonyl sulfide in the far-infrared

The pure rotational spectrum of OCS has been studied by Fourier transform at room temperature over the frequency range 20–42cm⁻¹. The ground state rotational lines were observed for OC³²S up to J = 103. It has been possible also to identify the rotational lines for OC³⁴S in the ground state and for OC³²S in the ν₁ = 1 level.     

Identification of HBr isotopes in the far-infrared stratospheric spectrum

A detailed analysis is reported of high resolution IR theoretical spectra. Identification of spectral lines of HBr isotopes is made for observation conditions in the stratosphere (versus altitude, zenithal angle and concentration). The calculation of spectra suggests that a concentration of HBr higher than 6 pptv is required to detect some spectral lines of this constituent in experimental spectra.     

Interpretation of far-infrared absorption spectra in germanium

The high resolution far-infrared absorption spectra of free excitons in germanium are analyzed for the first time using a model which accurately includes both the anisotropy of the valence and condition bands and the degeneracy of the valence band. The observed structure is in good agreement with the calculated transitions between the anisotropy split ground state and the various p-like excited states.     

Calculation of the far-infrared spectrum of a water-vapor molecular laser

The theory of partial population inversion between vibrational-rotational states in molecular media is applied for a molecular laser using vapors of H₂O as active media. Two conditions of laser action in such media are discussed — population inversion and gain. The lines in the far-infrared at which such a laser can generate are predicted and the relative intensities of these lines, are calculated.The paper was mainly prepared during the author's stay at the University of Western Ontario, London (Ontario), Canada.     

Multichannel time-resolved measurement in far-infrared magnetoabsorption

A drastic innovation has been achieved in the time-resolved far-infrared magnetooptics by introducing multichannellisation of the delay time. The key section of the new system utilises a digital boxcar unit connected with a common personal computer. Making use of a test pattern signal by magneto-plasma absorption of electron-hole drops in Ge, an eight channel performance over the time window of 100 s is demonstrated.     

浓度场测量的差分吸收光谱CT技术

提出了一种新的用于浓度场测量的差分吸收光谱CT技术。利用差分吸收原理进行浓度场多方位积分测量,采用少数投影最大熵重建算法进行层析图像重建。数值模拟结果表明,在0°～180°视场范围内,在4个不同的投影视角方向获取投影数据的条件下,能有效地重建出待测场分布。该技术具有较高的重建精度和良好的抗噪声性能。     

The high-resolution far-infrared spectrum of methane at the SOLEIL synchrotron

As a tetrahedral molecule, methane has no permanent dipole moment. Its spectrum, however, displays faint absorption lines in the THz region, due to centrifugal distorsion effects. This is important for planetary applications since this region is used to measure methane concentration in some planetary atmospheres, in particular on Titan. Up to now, all measurements relied either on some old low resolution infrared absorption spectra, or on high resolution Stark measurements for low J values only. Even if these results have been reexamined recently [Wishnow EH, Orton GS, Ozier I, Gush HP. The distorsion dipole rotational spectrum of CH₄: a low temperature far-infrared study. J Quant Spectrosc Radiat Transfer 2007;103:102-17], it seemed highly desirable to obtain much more precise laboratory data.The high-intensity synchrotron radiation, combined with a 151.75±0.1 m optical path in a White cell and a Bruker IFS 125 HR FTIR spectrometer at the AILES beamline of SOLEIL, enabled us to record this very weak spectrum at high resolution for the first time. Spectra were obtained in the 50-500 cm⁻¹ wavenumber range at 296 K and 9.91, 20, 50 and 100 mbar with a resolution of 0.00074, 0.00134, 0.0034 and 0.0067 cm⁻¹ (FWHM of the sinc function), respectively. The rotational clusters are fully resolved and the good signal-to-noise ratio has enabled precise measurements of transition intensities (92 cold band lines and 96 Dyad-Dyad hot band lines, with normal abundance intensities in the range 2×10⁻²⁶-1×10⁻²⁴ cm⁻¹/(mol cm⁻²)), yielding an accurate determination of the dipole moment derivatives. Such results should allow a better determination of CH₄ concentration in planetary objects.     

The far-infrared laser magnetic resonance spectrum of the CH radical

Transitions between the spin-rotational levels of the ¹³CH radical in the v=0 level of the ground state have been detected by the technique of laser magnetic resonance at far-infrared wavelengths. These measurements have been combined with the previous measurements of the lambda-doubling intervals of the molecule [J. Chem. Phys. 85 (1986) 1276 ] to determine an improved set of molecular parameters for ¹³CH. The analysis provides accurate predictions of the transition frequencies between the low-lying spin-rotational levels of the radical at zero magnetic field. A comparison is made with the values of the corresponding parameters of ¹²CH which reveals small effects due to the breakdown of the Born-Oppenheimer approximation.     

The far-infrared spectrum of fluoroform (CHF3)

The far-infrared spectrum of fluoroform has been recorded in the region between 7 and 60 cm⁻¹ at a resolution of 0.002 cm⁻¹. More than 1400 rotational transitions in the ground state have been measured and assigned up to J″ = 80. Simultaneous analyses of these measurements and of microwave and millimeter-wave data reported previously have been performed. Improved values of the ground state rotational and centrifugal distortion constants, including the sextic distortion constants reported for the first time, have been obtained. Rotational transitions in a few low-lying vibrational states have also been observed.     

基于光谱吸收型光纤传感器的煤矿瓦斯测量技术

甲烷是瓦斯的主要成分,是易燃易爆的气体。介绍了瓦斯的光谱特性以及光谱吸收法测量甲烷气体浓度的原理,给出了光谱吸收型光纤瓦斯气体传感器的主要进展和技术路径,包括差分吸收测量法和谐波吸收测量法。通过分析可看出,光谱吸收型光纤瓦斯传感器以其优良的特性得到了广泛关注,其中差分吸收法的抗干扰能力强,系统可靠性高,具有较强的工程应用价值。     

The far-infrared absorption of different types of fused silica

The absorption coefficient of various different types of fused silica (fused quartz) is measured to an accuracy of about 1% at 337 μm wavelength. Substantial systematic variations are observed. Notably, those materials produced synthetically show higher absorption than those produced from natural quartz.