Revision on the calculation of optically pumped FIR laser spectrum with Doppler broadening and pressure broadening effects

By means of iteration method and also taking into account Doppler broadening and pressure braodening effect of IR pumping laser, the output power density of optically pumped NH₃ molecules FIR laser is calculated by solving density matrix equations of three-level system. The results of theoretical calculation shows that, in comparison with the FIR laser under the assumption of ideal monochromatic IR pumping, the output power density of FIR laser in the case of Doppler broadening and pressure broadening IR pumping decreases much more. Meanwhile, via the revision of Doppler broadening and pressure broadening effect, the theoretical value of optimum operating gas pressure reduces, which is in better agreement with the experimental value. Further study shows that the revision of Doppler broadening effect is more fit for the conventional FIR laser with a 2m sample tuble and the revision of pressure broadening effect is much more suitable for the miniature FIR laser with a short sample tube of 5 to 20cm in length.Supported by the National Natural Sciences Foundation of P.R.China and the NSF of Guangdong Province.     

The rotationally-resolved absorption spectrum of formaldehyde from 6547 to 6804 cm

The room temperature absorption spectrum of formaldehyde, H₂CO, from 6547 to 6804 cm⁻¹ (1527-1470 nm) is reported with a spectral resolution of 0.001 cm⁻¹. The spectrum was measured using cavity-enhanced absorption spectroscopy (CEAS) and absorption cross-sections were calculated after calibrating the system using known absorption lines of H₂O and CO₂. Several vibrational combination bands occur in this region and give rise to a congested spectrum with over 8000 lines observed. Pressure broadening coefficients in N₂, O₂, and H₂CO are reported for an absorption line at 6780.871 cm⁻¹, and in N₂ for an absorption line at 6684.053 cm⁻¹.     

Temperature dependence of pressure broadening of the N = 1− fine structure oxygen line at 118.75 GHz

The absorption profile of the N = 1− fine structure line of oxygen was recorded by a resonator spectrometer at a frequency range of 110-130 GHz at atmospheric pressure and different temperatures ranging from −21 °C up to +22 °C. Analysis of the observed line shape allowed determination of the temperature dependence of the line pressure broadening. The measured value of the temperature exponent is n = 0.74(5) for self-broadening. Consistency of the measurements is supported by simultaneous measurements of the line intensity, the line mixing parameter and the line center frequency, and by comparison of obtained values with previously known data.     

Influence of spectral line broadening on the mode structure of He-Kr and He-Ar gas lasers

Using the semiclassical perturbation approach, Stark broadening parameters for Kr II 469.4 nm, Ar II 476.5 nm, and Ar II 480.6 nm spectral lines have been determined. The obtained results have been used for the investigation of the role of the Stark broadening mechanism on the mode properties of hollow cathode excited noble gas mixture lasers. It has been found that for the He-KrII 469.4 nm laser broadening by neutral atom collisions is large enough to explain the single-mode operation of this laser, as opposed to the He-ArII 476.5 nm laser where Stark broadening also has to be taken into account to explain this property. Published in Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 3, pp. 405–407, May–June, 2006.     

Collisional line widths of autoperturbed N2: Measurements and quantum calculations

In this work we present new experimental and theoretical values for the line broadening coefficients of the Q-branch Raman lines of autoperturbed N₂. For the experimental determination of the coefficients, high resolution stimulated Raman spectra of the Q-branch of N₂ at different pressures were obtained at 77, 194 and 298 K. Simultaneously, quantum dynamical calculations, performed on two potential energy surfaces, were carried out for the system between 77 and 298 K, rendering a set of theoretical line broadening coefficients that could be directly compared to those obtained from the present measurements and the previous ones. Within the limit of considering the colliding molecules distinguishable we discuss the ortho and para contributions to the pressure broadening cross-sections. Because such calculations are time consuming we indicate routes to circumvent this difficulty. We observe a reasonable agreement between theoretical and experimental values of the collisional line broadening coefficients at all the studied temperatures.     

Improved convergence of a non-perturbative semi-classical pressure broadening model

It is shown that by including the second term of Magnus expansion, improved convergence can be achieved for the non-perturbative pressure broadening formalism proposed by Neilson and Gordon (J. Chem. Phys. 58 (1973) 4131). The present method was applied to the line broadening calculations of CO in a bath of Ar.     

Pressure broadening and shifting parameters for the spectral lines in the fundamental vibration-rotation bands of HBr and HI in mixtures with rare gases

We report measurements of the line broadening and shifting coefficients in the (1 ← 0) fundamental absorption bands of the HBr and HI molecules in mixtures with rare gases He, Ne, Ar, Kr, and Xe. Comparison is given with the published data on other HHal-Rg systems. The measured line shifts are separated into terms symmetric and asymmetric in the line number m. The magnitudes of the symmetric shifts change in a regular manner in the series of rare gases and reach perturber-specific asymptotic values at higher ∣m∣. It is found that the asymptotic values of the symmetric line shifts linearly correlate with the respective C₆ potential energy constants and that the slopes of these correlations are proportional to the vibrational ground state dipole moments squared of the hydrogen halide molecules.     

Comparison of quantum, semiclassical and classical methods in hydrogen broadening of nitrogen lines

We use an accurate N₂-H₂ab initio potential energy surface (PES) in order to inter-compare various methods commonly employed to calculate pressure broadening coefficients. Close-coupling (CC) calculations of the collisional linewidths of the isotropic Raman lines of N₂ perturbed by H₂ are performed for temperatures between 77 and 2000 K. The CC results compare well with available experimental values. Three less exact methods of calculation are also used: the full classical (FC) model of Gordon, the semiclassical (SC) formalism of Robert and Bonamy and the quantum dynamical coupled states (CS) method. The CS method provides good agreement with CC calculations for all studied temperatures, FC calculations can be considered as accurate above room temperature while the SC method gives overestimated values by about 20-30% in all cases. The temperature dependences of pressure broadening coefficients provided by each method are very similar at elevated (above room) temperatures.     

Pressure broadening and shifting parameters for the spectral lines in the first overtone vibration-rotation bands of HBr and HI in mixtures with rare gases

We present experimental data on the previously unknown line broadening and shifting coefficients in the (2 ← 0) overtone vibration-rotation bands of the HBr and HI molecules in mixtures with several rare gases. The vibrational dependence of the isotropic and anisotropic components of the binary interaction potential is probed by separating the measured line shifts into parts symmetric and asymmetric in the line number m and by comparing with the previously published similar data for the fundamental bands of the same molecules. It is shown that the line shifts are dominated by the vibrational dependence of the isotropic potential. A linear correlation is found between the asymptotic values of the symmetric shifts in the overtone bands for all HX-Rg (X = F, Cl, Br, I) pairs and the respective C₆ long-range potential energy constants. Line broadening parameters in the overtone band of pure HBr are also reported.     

Nitrogen-induced broadening and shifts of rotation-vibrational lines in the fundamental, first, second and third overtone bands of HI

We report experimental results on the previously unknown broadening and shifting coefficients in the fundamental and three overtone vibration-rotation bands of the HI molecule in mixtures with nitrogen gas. Our data are compared with the previously published results for the fundamental bands of the HF and HCl molecules. It is shown that the line shifts are dominated by the vibrational dependence of the isotropic part of the intermolecular interaction potential.     

Calculation and simulation of absorption line broadening in water vapor by noble gas atoms

Semiclassical methods have been applied to calculate the collisional broadening of water vapor absorption lines by noble gas atoms (Ar, He, Ne, and Kr). An analytical model has been proposed for line half-widths. The model parameters have been determined for the ν₂ band of the H₂O molecule for all the buffer gases under consideration, as well as for the bands 3ν₁ + ν₃ and 2ν₁ + 2ν₂ + ν₃ in the case of the broadening by argon. In the latter case, the model parameters that determine the temperature dependence of the half-widths of the water vapor lines of the ν₂ band have been found. The model proposed describes well the known experimental data and permits a relatively simple calculation of the H₂O line half-widths for the bands and the buffer gases under consideration in a wide range of rotational quantum numbers. For the ν₂ band, the model calculations in the case of the broadening by argon can be performed up to temperatures of 2500 K.     

The phase shifts leading to the broadening and shift of spectral lines

The classical theory of collisional broadening and shift parameters (β, δ) of an isolated spectral line was used to obtain simple analytical formulas for calculating both β and δ. These formulas were obtained on the assumption that the short range interaction is effective only in the broadening while the long range is effective in the shift of the spectral line. These parameters β and δ depend on the limiting phase shifts responsible for broadening η_b and shift ηδ. It was found that the values of η_b and η_δ are not equal to each other as was proposed by Weisskopf η_b=η_δ=1. The maximum and average values of η_b (η_b max, η_b av) and η_δ (η_δ max, η_δ av) were obtained by numerical evaluation, using different inverse power potentials. By introducing these parameters into the approximated formulas for β and δ using Van der Waals and Lennard-Jones potential, it was found that the results of calculations for (β and δ) with different atomic transitions perturbed by different inert gases are in close agreement with earlier results. Those results, obtained earlier, were based on the Lindholm-Foley theory especially with the average values of η_b [η_b av=0.6057] and the maximum values of η_δ [η_δ max=1.57625]. The impact parameters ρ_b and ρ_δ leading to the broadening and shift of the spectral line were also obtained for different interactions. It was found that the end parameter for the broadening ρ_b is not equal to the starting parameter for the shift ρ_δ.     

Y型四能级系统中Doppler展宽对VIC相关的双光子吸收的影响

利用数值计算结果讨论了Doppler展宽对Y型四能级原子系统中真空诱导相干 性(VIC)相关的双光子吸收的影响. 研究结果表明: 1)在无Doppler展宽的情况中, 不存在VIC时, 吸收曲线具有双峰结构并产生电磁感应透明(EIT)现象, 存在VIC时吸收曲线具有单峰结构而EIT现象不再发生; 2)在有Doppler展宽的情况中, 不管是否存在VIC, EIT现象都能发生; 不存在VIC时, 不管探测场和驱动场传播方向相同还是相反, 随Doppler展宽宽度D值的增大, 吸收先增大后减小, 吸收曲线逐渐从双峰结构变为单峰结构; 存在VIC时, 若探测场和驱动场传播方向相同, 随D值的增大, 吸收先增大后减小, 吸收曲线逐渐从单峰结构变为双峰结构; 若探测场和驱动场传播方向相反, 随D值的增大, 吸收单调减小, 但吸收曲线仍保持单峰结构.     

紫铜等离子体特征谱线及其展宽形成机制

利用波长为1064 nm,最大能量为500 mJ的 Nd:YAG脉冲激光器对紫铜进行冲击,并且改变激光能量,获得一系列等离子体特征谱线,结果表明:本实验条件下,获得铜原子谱线不完整,只有5条明显激发谱线,分别为:CuⅠ 406.33 nm, CuⅠ 458.69 nm, CuⅠ 521.8 nm, CuⅠ 529.25 nm, CuⅠ 578.2 nm。根据跃迁原理,得出激光不能使铜原子完全受到激发;选取CuⅠ 521.8 nm原子光谱与CuⅠ 578.2 nm的原子光谱谱线线型作为分析对象,发现其展宽线型不同,分别为Lorenz线型与Gauss线型。通过对应线型曲线方程分析得出,同一原子光谱不同波段对应形成光谱展宽机制不同。     

紫铜等离子体特征谱线及其展宽形成机制

利用波长为1064 nm,最大能量为500 mJ的 Nd：YAG脉冲激光器对紫铜进行冲击,并且改变激光能量,获得一系列等离子体特征谱线,结果表明：本实验条件下,获得铜原子谱线不完整,只有5条明显激发谱线,分别为：CuⅠ 406.33 nm, CuⅠ 458.69 nm, CuⅠ 521.8 nm, CuⅠ 529.25 nm, CuⅠ 578.2 nm。根据跃迁原理,得出激光不能使铜原子完全受到激发;选取CuⅠ 521.8 nm原子光谱与CuⅠ 578.2 nm的原子光谱谱线线型作为分析对象,发现其展宽线型不同,分别为Lorenz线型与Gauss线型。通过对应线型曲线方程分析得出,同一原子光谱不同波段对应形成光谱展宽机制不同。     

吸收谱线Doppler展宽对原子多步光电离的影响

原子法激光同位素分离的核心之一是如何高效地将原子激发电离.本文从原子法激光同位素分离的实际情况出发,研究了原子吸收谱线的Doppler展宽对原子电离率的影响.研究中使用的理论工具是原子激发电离的密度矩阵方程,并利用数值计算方法对方程进行求解.研究结果表明:当吸收谱线有Doppler展宽时,在激光参数不变的条件下原子电离率会降低;且当激光功率固定时,存在使原子电离率为最大的线宽值.这与已发表文献中无Doppler展宽时的计算结果有很大不同.为了追求最佳的原子电离效果,在原子法激光同位素分离系统中激光应该尽可能地工作在最佳线宽条件下.如果激光线宽有不可控的随机波动,在技术上让激光线宽略大于最佳线宽更为有利.无论如何控制激光线宽,尽可能地降低原子吸收谱线的Doppler展宽都有利于原子电离率的提高.     

Spectral line broadening in quantum wells due to Coulomb interaction of current carriers

A theoretical analysis of emission line broadening due to Coulomb interaction of carriers is performed. An analytical approximation for the spectral line shape function with exponential decays is derived by using the perturbation theory for many-body electron–hole systems for both non-degenerate and degenerate conditions. An explanation of the experimentally observed spectral line asymmetry and the linewidth change as a function of the temperature and the excitation level is given.     

Pressure shift and broadening of 110-101 water vapor lines by atmosphere gases

This paper is devoted to the measurement of pressure shift and broadening parameters of water-vapor lines of the pure rotational transition 1₁₀-1₀₁ in the ground vibrational state of H₂¹⁶O at 556.936 GHz, H₂¹⁷O at 552.02 GHz, H₂¹⁸O at 547.676 GHz, and the vibrationally excited state v₂=1 line of H₂¹⁶O at 658.003 GHz. The broadening coefficients of the line at 556.936 GHz (for N₂ and O₂ as perturbing gases) coincide within the errors with the values obtained recently by Seta et al. [Pressure broadening coefficients of the water vapor lines at 556.936 and 752.033 GHz. JQSRT 2008;109:144-50] by means of a very different technique (THz-TDS). Pressure shift and broadening for other lines were measured for the first time. Comparison of our results with previous measurements and theoretical calculations is presented.     

Pressure broadening and collisional shift of the Rb D2 absorption line by CH4, C2H6, C3H8, n-C4H10, and He

The pressure broadening and shift rates of the rubidium D2 absorption line 5²S_1/2→5²P_3/2 (780.24 nm) with CH₄, C₂H₆, C₃H₈, n-C₄H₁₀, and He were measured for pressures ≤80 Torr using high-resolution laser spectroscopy. The broadening rates γ_B for CH₄, C₂H₆, C₃H₈, n-C₄H₁₀, and He are 28.0, 28.1, 30.5, 31.3, and 20.3 (MHz/Torr), respectively. The corresponding shift rates γ_S are −8.4, −8.8, −9.7, −10.0, and 0.39 (MHz/Torr), respectively. The measured rates of Rb for the hydrocarbon buffer gas series of this study are also compared to the theoretically calculated rates of a purely attractive van der Waals difference potential. Good agreement is found to exist between measured and theoretical rates.     

The relativistic Doppler broadening of the line absorption profile

The classical results of Doppler broadening of the line absorption profile are generalized to a relativistic gas in thermal equilibrium by taking into account the relativistic variance of the volume absorption coefficients of the gas, as derived by L.H. Thomas. This variance produces a small correction, even in the non-relativistic approximation.