Far infrared cw raman lasing in NH3

We report evidence that two FIR laser lines generated by cw optical pumping of ¹⁴NH₃ with CO₂ laser lines are due to stimulated Raman emission instead of the usual resonant absorption-emission process.     

Compact Raman CH3F, NH3 optically pumped FIR laser

Conclusion The compact superradiant FIR laser is developed using Herriott cell with long optical path as a FIR cell. The employment of the multipass cell gave an opportunity to increase the IR to FIR conversion efficiency in comparison with traditionally constructed FIR lasers and to observe many intensive FIR lines. The given of multipass cell can be useful for employment in continuously tunable FIR lasers.     

High power FIR NH3 laser using a folded resonator

A compact FIR laser cavity having a couple of folding mirrors was designed. By inserting this FIR cavity into the pump TE CO₂ laser resonator, we observed 19 FIR NH₃ laser lines of which 4 new lines were included. The maximum output power was over 500 W at 90 m.     

Theoretical study of multi-mode optically pumped NH3 FIR laser

The two or multi-mode optically pumped NH₃ FIR laser had been studied theoretically. The NH₃ molecular gas was assumed to be a three-level system and obeyed the time-dependent behavior of the density matrix equations. Considering the situation of playing the two or multi-mode optical pumping and the FIR laser field were same polarized. The gain coefficient and the output FIR power of the system could be calculated by using the iteration method.It had been predicted that the two or multiple longitudinal mode optically pumped NH₃ FIR laser could have a greater output power or higher lasing efficiency than single mode pumped FIR laser under suitable selected operating parameters of laser.Supported by The Education Foundation of PRC.     

Spikes in raman spectrum of miniature optically pumped NH3 fir laser

In this paper, the semiclassical density matrix equation was solved to calculate the spectral characteristics of V₂:a--sR(0,0) transition in a miniature optically pumped NH₃ far infrared laser (mini-NH₃-OPFIRL), which was pumped by CO₂-10R(6) line. The results of theoretical calculation showed that the spikes in Raman spectrum of V₂:a--sR(0,0) would appear when the operating NH₃ gas pressure was higher than a certain critical value or pumping power density was lower than a certain critical value, which was caused by Raman processes interaction of AC-Stark splitting. In our experiment, 298 µm FIR spetral line of a--sR(0,0) pumped by a TEA-CO₂ laser with 10R(6) line was observed but the spikes could not be observed owing to the limitation of the resolution of the F-P interferometer.Supported by the National Natural Sciences Foundation of P.R.China.     

Pump polarization effect in a superradiant NH3 and CH3F FIR Raman laser

The pump polarization has an evident effect on a superradiant FIR Raman laser both in NH₃ and CH₃F gases when the pump detuning from the resonant line is larger than the Raby frequency. In particular for R resonant lines the circular polarization shows a spontaneous gain about 1.5 times greater than the linear polarization as expected from the theory.     

Compact, high power FIR NH3 laser pumped in a three mirror CO2 laser cavity

A compact CO₂–NH₃ FIR laser system where an NH₃ laser cavity was inserted in pump, three mirror CO₂ laser cavity was designed. The total length of this system was about 1.8 m. Output energy of about 1 mJ (10 KW pea power) was obtained at the 152 m and 90 m lines in NH₃. Power conversion efficiency of 1.7 percent was obtained at the 90 m line.     

High power ns FIR Raman pulses in NH3 pumped by a short pulse tail-free CO2 oscillator

By using a short pulse CO₂, tail free, broadband laser it is possible to produce a compressed, high power FIR pulse in a pure Raman system when a suitable pressure and Raman cell length are used. In this way we have obtained 4ns (70KW) emission around the sR(3,0) NH₃ line pumped by 130 mJ (23ns) 9P20 CO₂ line. More resonant transitions can be also compressed at a suitable high pressure also if they show a large optical pumping and cascade processes at low pressure.     

Integrated infrared intensities in NH3

The integrated infrared intensities of the fundamental modes of NH₃ have been measured by the Wilson-Wells-Penner-Weber method. The intensities were found to be 43.9 ± 0.6, 567.6 ± 9.4 and 110.5 ± 2.0 atm^-1 cm^-2 (standard temperature and pressure) for the ν₁ + ν₃, ν₂ and ν₄ bands, respectively.     

Theoretical study on gain and tuning characteristics of infrared-microwave pumped NH3 FIR laser

Based on the semi-classical density matrix equation theory, the gain and tuning characteristics of infrared-microwave pumped NH₃ FIR laser were studied. It was shown that quasi-continuously tuning could be obtained by the tuning of microwave frequency and the efficiency of the laser could be enhanced by electric dipole transition enhancement effect, but compromise should be made between FIR laser output and frequency tuning range.     

NMR spectral densities and two dimensional diffusion in TiS2(NH3)1.0 and TaS2(NH3)x

NMR measurements of proton spin-lattice relaxation times T₁ and T_1? in the layered intercalation compounds TiS₂(NH₃)_1.0 and TaS₂(NH₃)_x (x = 0.8, 0.9, 1.0) are reported as functions of frequency and temperature (100 K – 300 K). These observations probe the spectral density of magnetic fluctuations due to motions of the intercalated molecules at frequencies accessible to the T₁ (4–90 MHz) and T_1? (1–100 kHz) measurements. Since the average molecular hopping time (τ) can be changed by varying temperature, different regions of the spectral density can be examined. For T > 200 K, both T^?1₁ and T^?1_1? vary logarithmically with frequency, reflecting the two dimensional character of the molecular diffusion. The temperature dependence of T₁ suggests that a more accurate picture of the short time dynamics is required. No dependence of relaxation rate on vacancy concentration is found.     

Vibrational modes symmetry and raman scattering in SnI4 crystals

A group-theoretical vibrational modes symmetry analysis of SnI₄ crystals has been made for the Brillouin zone center and polarized Raman scattering study in these crystals has been carried out. Correlation diagram showing the correspondence between the crystal vibrational modes and the free SnI₄ molecule modes has been built. The nature and peculiarities of the low frequencies spectrum have been considered.     

(NH4)2SO4，NH4NO3和(NH4)2SO4/NH4NO3混合气溶胶吸湿质量增长因子的快速测量方法

气溶胶颗粒的吸湿性决定了其尺寸、浓度、化学组成以及相态,从而显著影响着全球气候、大气异相化学以及人类健康。运用在线、原位、连续扫描衰减全反射傅里叶变换红外光谱（ATR-FTIR）技术, 结合线性湿度（RH）控制系统,实现了RH连续变化条件下气溶胶FTIR-ATR光谱的快速测量。根据水弯曲振动谱带（~1 640 cm-1）峰面积随RH的变化,得到了(NH₄)₂SO₄,NH₄NO₃和(NH₄)₂SO₄/NH₄NO₃混合气溶胶的质量增长因子（MGFs）、潮解点（DRH）和风化点（ERH）。与气溶胶的E-AIM模型预测值相比较,实验结果表现出良好的一致性,证实该方法是一种测量大气气溶胶MGFs,ERH和DRH的快速测量方法。     

The electrooptic effect in NH4IO3

The static electrooptic coefficients of NH₄IO₃ at room temperature are r₄₃ = 4.9, r₆₁ = 1.0, r₁₂n²₁ ? r₃₂n³₃ = 59.6, r₂₂n³₂ ? r₃₂n³₃ = 116.8 [ X 10^-12m/V]. The electrooptic effect depends on temperature and shows two ph ase transitions at 82.5°C and near 120°C.     

Partly tunable mid-infrared NH3 laser

Using a continously tunable pulsed 20-atmosphere CO₂ laser as a pump source, we generated pulses of mid-infrared radiation, partly tunable in frequency intervals in the range between 200 and 900 cm^–1 via stimulated Raman scattering in gaseous ammonia. As a Raman cell we used a multiple pass cell. We observed for¹⁴NH₃ and¹⁵NH₃ laser lines at 52 different frequencies with 39 lines observed for the first time. Tuning ranges up to 150 GHz and peak powers of several MW were achieved. The quantum efficiency reached 40 %.     

Vibration-inversion-rotation spectra of ammonia: Centrifugal distortion, Coriolis interactions, and force field in NH3, NH3, ND3, and NT3

An effective inversion-rotation Hamiltonian has been developed for NH₃ which avoids the necessity of having to include high powers of the inversion motion coordinate in the Taylor expansions of the potential energy and the inverse moment of inertia tensor. This nonrigid bender Hamiltonian describes the centrifugal distortion and the Coriolis interactions in the ground and excited inversion states. It also describes the inversion doublings in the ground and excited vibration-inversion states of ammonia. A least-squares procedure that includes the numerical integration of the Schrödinger wave equation has been used to determine the harmonic force field and the double-minimum inversion potential function for (¹⁴NH₃, ¹⁵NH₃) and for (¹⁴ND₃ and ¹⁴NT₃).The anomalous rotational dependence of the inversion doublings in the (±l) components of the v₄ = 1 state of ¹⁴NH₃ has been explained by the Coriolis interactions between v₂=1, v₄ = 1, v₂ = 2, v₂ = 1, v₄ = 1, and v₂ = 3 vibration-inversion states.     

Line Broadening and Mixing in NH3 Inversion Doublets Perturbed by NH3, He, Ar, and H2

Measurement of absorption by pure ammonia and NH₃–(H₂, He, and Ar) mixtures in the P branch of the ν₄ band at room temperature have been made with a high-resolution Fourier transform spectrometer. Least squares fits of the spectra using different techniques are used for the analysis of the evolution with pressure of the absorption shape for a number of ^PP inversion doublets. Intensities, half-widths, and line-coupling parameters are determined, demonstrating the great importance of line-mixing effects. The results are compared with values calculated using a semiclassical model. The latter explains most of the features of the line-broadening and the J and K dependencies of line-coupling for pure NH₃, whereas poorer results are obtained for line-mixing in mixtures. The most striking and original result is the very large amount of coupling between the symmetric and antisymmetric components, which can reach up to 80% of the width in the case of pure NH₃. Also remarkable is the very strong influence of the rotational quantum number K.     

Kinetic study of NH3/ND3 exchange in TaS2 by neutron diffraction

Tracer exchange of TaS₂·NH₃ by liquid ND₃ was investigated at 215 and 223 K by neutron diffraction. The results suggest only a molecular exchange on the time-scale of quasielastic neutron scattering measurements.     

Calorimetric and x-ray diffraction studies of the (NH4)3WO3F3 and (NH4)3TiOF5 perovskite-like oxyfluorides

The heat capacity and unit cell parameters of the (NH₄)₃WO₃F₃ and (NH₄)₃TiOF₅ perovskite-like oxyfluorides were measured in the temperature interval from 80 to 300 K; the existence of two and one phase transitions in these compounds, respectively, was demonstrated, and their thermodynamic parameters were determined. The effect of a hydrostatic pressure of up to 0.5 GPa on the phase transition temperatures was studied. Triple points and high-pressure phases were found in the T vs. p diagrams. An analysis of entropy changes suggests that all the structural transformations revealed are associated with the ordering of structural blocks. __________ Translated from Fizika Tverdogo Tela, Vol. 46, No. 5, 2004, pp. 888–894. Original Russian Text Copyright ? 2004 by Flerov, Gorev, Fokina, Bovina, Laptash.     

Chlorine K X-ray absorption-edge structures of CIS-[Pt(NH3)2Cl2], trans-[Pt(NH3)2Cl2], trans-[Pd(NH3)2Cl2] and (NH4)2PdCl4

The K absorption-edge spectra of the ligand chlorine ion in square-planar complex compounds cis- and trans-[Pt(NH₃)₂Cl₂], trans-[Pd(NH₃)₂Cl₂], and (NH₄)₂PdCl₄ are reported and discussed in connection with the chlorine K absorption spectra of K₂PtCl₄ and K₂PdCl₄, reported previously. The observed chemical shift of a white line at the absorption threshold is interpreted in terms of the difference of the ligand-field splitting of electronic states for metal ions. The white line is attributed to the electronic transition from the Cl^? ls level to the lowest unoccupied antibonding molecular orbital (MO), which is specified by a $\text{MO}\text{b}{}_{\mathrm{1g}}\text{(σ}{}^1\text{)}$ in the square-planar complex with D_4h symmetry. The other absorption structures are regarded as continuum “shape resonances” of the outgoing electron trapped by the cage of the surrounding atoms. The effect of geometrical isomerism is found in the chlorine K absorption spectra of cis- and trans-[Pt(NH₃)₂Cl₂].