Joint Attosecond Science Laboratory, National Research Council of Canada and University of Ottawa, 100 Sussex Drive, Ottawa, K1A 0R6, Canada.
Phys Rev Lett. 2012 Oct 5;109(14):143001. doi: 10.1103/PhysRevLett.109.143001. Epub 2012 Oct 4.
Molecular frame high-harmonic spectra of aligned N2 molecules reveal a Cooper-like minimum. By deconvolving the laboratory frame alignment distribution, what was previously thought to be a maximum of emission along the molecular axis is found to be maxima at 35 degrees off axis, with a spectral minimum on axis. Both of these features are supported by photoionization calculations that underline the relationship between high-harmonic spectroscopy and photoionization measurements. The calculations reveal that the on axis spectral minimum is a Cooper-like minimum that arises from the destructive interference of the p and f partial wave contributions to high-harmonic photorecombination. Features such as Cooper minima and shape resonances are ubiquitous in molecular photoionization or recombination.
分子框架中取向 N2 分子的高次谐波谱揭示了类似库珀的最小值。通过对实验室框架取向分布进行反卷积，发现之前被认为是分子轴线上发射的最大值实际上是在轴 35 度处的最大值，而轴线上的光谱最小值。这些特征都得到了光致电离计算的支持，该计算强调了高次谐波光谱学和光致电离测量之间的关系。该计算表明，轴上光谱最小值是类似库珀的最小值，它是由高次谐波光复合中 p 和 f 部分波贡献的相消干涉引起的。类似库珀最小值和形状共振等特征在分子光致电离或复合中普遍存在。
