Observation of Rotational Doppler Shift for Harmonic Generation in Solids
Observation of Rotational Doppler Shift for Harmonic Generation in Solids
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DOI：
10.1109/cleo/europe-eqec52157.2021.9542453
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发表时间：
2021-06
期刊：
影响因子：
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通讯作者：
W. Komatsubara;K. Konishi;J. Yumoto;M. Kuwata-Gonokami
中科院分区：
文献类型：
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作者：
W. Komatsubara;K. Konishi;J. Yumoto;M. Kuwata-Gonokami
由电场和非线性介质对称性控制的谐波产生引起了人们的广泛关注。它可用于在极紫外区域产生相干圆偏振光束并测量手性分子[1]。这种谐波产生的基本原理可以通过考虑电场和非线性介质之间的自旋角动量（SAM）守恒来解释。例如，当圆偏振入射光束照射具有三重旋转对称性的非线性介质时，会产生如图（a）所示的反向旋转圆偏振二次谐波。入射光束光子和生成的谐波光子分别具有 2ℏ 和 -ℏ SAM。在此过程中，介质可以接收 3ℏ SAM 作为扭矩，不受 SAM 激发并保持基态。因此，满足入射光子、谐波光子和非线性介质之间的SAM守恒。这种 SAM 传递可以通过与具有平移对称性的声子 Umklapp 散射的类比来解释 [2]。一般来说，具有n重旋转对称性的介质可以接收具有多个n的SAM。
Harmonic generation controlled by electric field and nonlinear media symmetries has attracted considerable attention. It can be applied to generate coherent circularly-polarized beams in the extreme-ultraviolet regime and measure chiral molecules [1] . The underlying principles of this harmonic generation can be explained by considering the Spin Angular Momentum (SAM) conservation between the electric field and the nonlinear media. For example, when the nonlinear media with the three-fold rotational symmetry is irradiated by the circularly polarized incident beam, the counter-rotating circularly polarized second harmonic is generated as shown in Fig. (a). The incident beam photons and the generated harmonic photon have 2ℏ and -ℏ SAMs, respectively. In this process, the media can receive 3ℏ SAMs as a torque, not excited by the SAM and remaining the ground state. As a result, the SAM conservation between the incident photons, the harmonic photon, and the nonlinear media is satisfied. This SAM transfer can be explained using the analogy with the Umklapp scattering of phonons with the translational symmetry [2] . Generally, the media with the n -fold rotational symmetry can receive SAMs with multiple n .