Spencer Austin P, Li Hebin, Cundiff Steven T, Jonas David M
†Department of Chemistry and Biochemistry, University of Colorado, Boulder, Colorado 80309-0215, United States.
‡JILA, University of Colorado and National Institute of Standards and Technology, Boulder, Colorado 80309-0440, United States.
J Phys Chem A. 2015 Apr 30;119(17):3936-60. doi: 10.1021/acs.jpca.5b00001. Epub 2015 Apr 16.
A solution to Maxwell's equations in the three-dimensional frequency domain is used to calculate rephasing two-dimensional Fourier transform (2DFT) spectra of the D2 line of atomic rubidium vapor in argon buffer gas. Experimental distortions from the spatial propagation of pulses through the sample are simulated in 2DFT spectra calculated for the homogeneous Bloch line shape model. Spectral features that appear at optical densities of up to 3 are investigated. As optical density increases, absorptive and dispersive distortions start with peak shape broadening, progress to peak splitting, and ultimately result in a previously unexplored coherent transient twisting of the split peaks. In contrast to the low optical density limit, where the 2D peak shape for the Bloch model depends only on the total dephasing time, these distortions of the 2D peak shape at finite optical density vary with the waiting time and the excited state lifetime through coherent transient effects. Experiment-specific conditions are explored, demonstrating the effects of varying beam overlap within the sample and of pseudo-time domain filtering. For beam overlap starting at the sample entrance, decreasing the length of beam overlap reduces the line width along the ωτ axis but also reduces signal intensity. A pseudo-time domain filter, where signal prior to the center of the last excitation pulse is excluded from the FID-referenced 2D signal, reduces propagation distortions along the ωt axis. It is demonstrated that 2DFT rephasing spectra cannot take advantage of an excitation-detection transformation that can eliminate propagation distortions in 2DFT relaxation spectra. Finally, the high optical density experimental 2DFT spectrum of rubidium vapor in argon buffer gas [J. Phys. Chem. A 2013, 117, 6279-6287] is quantitatively compared, in line width, in depth of peak splitting, and in coherent transient peak twisting, to a simulation with optical density higher than that reported.
利用三维频域中的麦克斯韦方程组解来计算氩缓冲气体中原子铷蒸汽D2线的重相位二维傅里叶变换（2DFT）光谱。在针对均匀布洛赫线形模型计算的2DFT光谱中模拟了脉冲通过样品时空间传播产生的实验失真。研究了在高达3的光密度下出现的光谱特征。随着光密度增加，吸收和色散失真从峰形展宽开始，发展到峰分裂，最终导致分裂峰出现之前未被探索的相干瞬态扭曲。与低光密度极限情况不同，在低光密度极限下布洛赫模型的二维峰形仅取决于总退相时间，在有限光密度下二维峰形的这些失真会通过相干瞬态效应随等待时间和激发态寿命而变化。探索了特定实验条件，展示了样品内光束重叠变化和伪时域滤波的影响。对于从样品入口开始的光束重叠，减小光束重叠长度会减小沿ωτ轴的线宽，但也会降低信号强度。一种伪时域滤波器，将最后一个激发脉冲中心之前的信号从FID参考的二维信号中排除，可减少沿ωt轴的传播失真。结果表明，2DFT重相位光谱无法利用可消除2DFT弛豫光谱中传播失真的激发 - 检测变换。最后，将氩缓冲气体中铷蒸汽的高光密度实验2DFT光谱[《物理化学杂志A》2013年，117卷，6279 - 6287页]在线宽、峰分裂深度和相干瞬态峰扭曲方面与光密度高于所报道值的模拟进行了定量比较。
