极化-光子耦合在铁电体超快太赫兹激发中的作用
Role of Polarization-Photon Coupling in Ultrafast Terahertz Excitation of Ferroelectrics
摘要：
研究了极化-光子耦合（极化-振荡-感应辐射电场）在超快太赫兹（THz）电场脉冲激发铁电薄膜中的作用。解析理论的发展预测的频率和弛豫时间的三维软模声子（本征极化振荡）是如何调制的辐射电场和外延应变。采用考虑应变-极化-光子耦合动力学的动力学相场模型，模拟了应变单畴铁电薄膜在超快太赫兹脉冲激励下的谐波极化振荡.从这种数值模拟中提取的频率和弛豫时间与分析预测吻合得很好。在相对较薄的薄膜中，预测辐射电场略微降低频率，但显著缩短弛豫时间。这些结果表明，在理解和预测铁电材料对太赫兹和更高频率的超快脉冲的响应时，考虑偏振-光子耦合的必要性。
英文摘要：
We investigate the role of polarization-photon coupling (specifically, polarization-oscillation-induced radiation electric field) in the excitation of ferroelectric thin films by an ultrafast terahertz (THz) electric-field pulse. Analytical theory is developed to predict how the frequencies and relaxation time of three-dimensional soft mode phonons (intrinsic polarization oscillation) are modulated by radiation electric field and epitaxial strain. Ultrafast THz-pulse-driven excitation of harmonic polarization oscillation in strained single-domain ferroelectric thin film is then simulated using a dynamical phase-field model that considers the coupled strain-polarization-photon dynamics. The frequencies and relaxational time extracted from such numerical simulations agree well with analytical predictions. In relatively thin films, it is predicted that the radiation electric field slightly reduces the frequencies but significantly shortens the relaxational time. These results demonstrate the necessity of considering polarization-photon coupling in understanding and predicting the response of ferroelectric materials to ultrafast pulses of THz and higher frequencies.
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