Mode selection by homogeneous broadening and non-linear absorption

A continuously tunable single mode can be selected from a multimode spectrum of a laser by non-linear absorbers. Theoretical and experimental investigations show that the selectivity of the method and the power of the selected mode depend considerably on the ratio of the saturation parameters of the amplifying and absorbing medium. With a He∶Ne laser having an active length of 1.70 m, a power of 35 mW was obtained in single-mode operation.     

Magnetic field dependence of cyclotron-resonance line broadening

We report that for non-degenerate electrons an electron-impurity interaction with a screening radius larger than the cyclotron orbit radius yields a cyclotron-resonance line broadening, which decreases with increasing magnetic field. This is consistent with most measured results.     

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.     

Foreign gas broadening of an IR absorption line of formaldehyde

The theory of nuclear spin state relaxation of symmetrical molecules like formaldehyde contains a collision time t_c that is interpreted as time between rotationally inelastic molecular collisions. This time traditionally is determined from measurements of pressure broadening of spectral lines. In order to test whether these collision times, which determine spin relaxation rate constants and line broadening coefficients, respectively, are the same or at least related to another, we have performed systematic measurements of the broadening of an IR line of formaldehyde by other gases of different pressures.     

Critical broadening of EPR line in molecular crystals of free radicals

Using the EPR method, the members of free radicals of the hydrazyl group have been studied within a wide temperature range. In all the samples at temperatures 0.05?3K the existence of a phase transition to an antiferromagnetic state is found out. Dynamics of critical fluctuations near the phase transition have been investigated. Two regimes of critical spin relaxation are discovered.     

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.     

Y型四能级系统中Doppler展宽对真空诱导相干性相关的探测场吸收的影响

利用数值计算结果,讨论了在Y型四能级原子系统中Doppler展宽对与真空诱导相干性(VIC) 相关的探测场吸收性质的影响.研究结果表明: 当无Doppler展宽时,只有不存在VIC时才可能产生电磁感应透明(EIT)现象; VIC将导致探测场吸收的明显改变和增益产生;在VIC存在和不存在两种情况中,吸收曲线都具有关于探测场失谐对称的双峰结构. 当有Doppler展宽时,在VIC存在和不存在两种情况中都能产生EIT现象; VIC仍将导致探测场吸收的明显改变和增益产生;不管是否存在VIC,探测场吸收都具有以下特征:吸收曲线不再具有关于探测场失谐的对称性且随Doppler展宽宽度(D)值的增大而逐渐从双峰结构变为单峰结构,探测场吸收不随D值的增大而单调增大或减小,在探测场和驱动场的传播方向相反时可获得比传播方向相同时更小的探测场吸收.     

Decoherence of excitons in multichromophore systems: thermal line broadening and destruction of superradiant emission

We study the temperature-dependent dephasing rate of excitons in chains of chromophores, accounting for scattering on static disorder as well as acoustic phonons in the host matrix. From this we find a power-law temperature dependence of the absorption linewidth, in excellent quantitative agreement with experiments on dye aggregates. We also propose a relation between the linewidth and the exciton coherence length imposed by the phonons. The results indicate that the much debated steep rise of the fluorescence lifetime of pseudoisocyanine aggregates above 40 K results from the fact that this coherence length drops below the localization length imposed by static disorder.     

Collisional broadening of saturated absorption in neon

Saturation spectroscopy involving laser light fields of two different frequencies has been applied to the investigation of Ne*-Ne collisions in an absorptive neon discharge. The pressure broadening of the saturation signals is interpreted in terms of “weak” collisions. Half the signal width results from velocity shifts of 2p ₄ atoms rather than from oscillator dephasing. The mean velocity shift is considerably larger than in collisions with helium atoms.     

Statistical thermodynamics of molecular field systems

The nonlinear generalization of the Curie-Weiss law and its relation to magnetic moment fluctuations are considered in the molecular field approximation. The temperature dependence of the energy levels is shown to lead to a generalization of the first Gibbs rule and some other thermodynamic relations. The ƒ-covariance of the fundamental thermodynamic relation is discussed.     

Theory of line shape of optical absorption and emission spectra in molecular crystals

We solve the equations of the coupled coherent and incoherent motion of excitons in molecular crystals and determine the optical line shapes and positions including Davydov splitting.     

Suppression of inhomogeneous line broadening of Mössbauer resonance by a spinning magnetic field

A spinning magnetic field, satisfying the so-called “magic-angle” condition, is widely used for the suppression of inhomogeneous line broadening of spin transitions in nuclear magnetic resonance (NMR) spectroscopy. We show that the redefined “magic-angle” condition can also be used for the narrowing of γ-ray nuclear transitions in the Mössbauer spectroscopy.     

High-resolution measurements of molecular absorption line profiles at 10 micrometers

Absorption line profiles of CO₂, C₂H₄ and NH₃ have been measured around a wavelength of 10 μm and under various conditions using a passive heterodyne detection technique with a resolution of 6 × 10^-4 cm^-1.     

Experimental investigation of the effect of pump incoherence on nonlinear pump spectral broadening and continuous-wave supercontinuum generation

The development of high-power cw fiber lasers has triggered a great interest in the phenomena of nonlinear pump spectral broadening and cw supercontinuum generation. These effects have very convenient applications in Raman amplification, optical fiber metrology, and fiber sensing. In particular, it was recently shown that pump incoherence has a strong impact in these processes. We study experimentally the effect of pump incoherence in nonlinear pump spectral broadening and cw supercontinuum generation in optical fibers. We show that under certain experimental conditions an optimum degree of pump incoherence yields the best performance in the broadening process. We qualitatively explain these results, and we point out that these results may have important implications in cw supercontinuum optimization.     

基于铯133原子D1线直接吸收光谱的多普勒展宽热力学温度测量

玻尔兹曼常量的定值致使温度测量逐步从协议温标向热力学温标过渡。为实现一种量子化的热力学温度测量传感方案,利用直接吸收光谱方法精密测量铯133原子D1(6S~(1/2)→6P~(1/2))跃迁吸收谱线,依据谱线多普勒展宽分量获得原子气体在该平衡态下的热力学温度。实验验证将外腔扫描激光器输出频率锁定于精密波长计,实现1000s稳定时长条件下10~(-9)量级的频率稳定度;通过振幅型声光调制器闭环控制实现优于1000∶1的测量信噪比;通过福格特线型拟合得到多普勒展宽半高全宽宽度。在室温条件下,初步结果显示温度测量误差为0.12%。由此验证了基于原子直接吸收光谱的多普勒展宽测温方法可用来实现芯片尺度、免标定的热力学温度测量。     

Collisional broadening and shifting of saturated absorption resonances in silicon tetrafluoride

The broadening and shifting of 12 saturated absorption resonances of the SiF₄ gas induced by molecular collisions have been measured in the lasing region of a low-frequency CO₂ laser at the P(30) line of the 9.4-μm band. Values of the collisional broadening are identical accurate to the measurement uncertainty. The collisional shift does not exceed 10% of the collisional broadening. This means that collisions with changes in the internal energy of molecules prevail over dephasing collisions.     

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.     

Temperature-induced line broadening, line narrowing and line shift in the luminescence of nanocrystalline ZnS:Mn

Emission spectra of nanocrystalline ZnS:Mn²⁺ have been recorded as a function of temperature between 4 and . For the two emission bands observed (a defect-related emission band around and a Mn²⁺-related emission band around ), the temperature dependence of the width and the position of the emission bands has been analyzed. The shift and the broadening of the Mn²⁺ emission can be satisfactorily explained by theoretical models and parameters for electron-phonon coupling that are similar to those for bulk ZnS. For the defect-related emission, the shift to lower energies follows the decrease in bandgap of bulk ZnS with increasing temperature. The width of the defect-related emission decreases as the temperature is raised. This anomalous behavior is explained by inhomogeneous broadening at low temperatures.