Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA.
Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803, USA.
Phys Rev Lett. 2014 Apr 18;112(15):153001. doi: 10.1103/PhysRevLett.112.153001. Epub 2014 Apr 14.
High harmonic generation (HHG) is used to measure the spectral phase of the recombination dipole matrix element (RDM) in argon over a broad frequency range that includes the 3p Cooper minimum (CM). The measured RDM phase agrees well with predictions based on the scattering phases and amplitudes of the interfering s- and d-channel contributions to the complementary photoionization process. The reconstructed attosecond bursts that underlie the HHG process show that the derivative of the RDM spectral phase, the group delay, does not have a straightforward interpretation as an emission time, in contrast to the usual attochirp group delay. Instead, the rapid RDM phase variation caused by the CM reshapes the attosecond bursts.
高次谐波产生（HHG）用于测量氩中复合电偶极矩矩阵元（RDM）的光谱相位，其频率范围很宽，包括 3p 库珀极小值（CM）。所测量的 RDM 相位与基于互补光致电离过程中 s 通道和 d 通道干涉的散射相位和幅度的预测非常吻合。HHG 过程所依据的重建的阿秒脉冲串表明，RDM 光谱相位的导数，即群延迟，不能直接解释为发射时间，这与通常的阿秒啁啾群延迟不同。相反，CM 引起的 RDM 相位的快速变化会改变阿秒脉冲串的形状。
