Infrared Generation by Coherent Excitation of Polaritons
Infrared Generation by Coherent Excitation of Polaritons
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通过极化子相干激发产生红外线
DOI：
10.1103/physrevb.4.4556
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发表时间：
1971
影响因子：
3.7
通讯作者：
F. Martini
中科院分区：
文献类型：
--
作者：
F. Martini
这项工作提出了由三波非线性参数相互作用激发的极化子波在立方晶体中传播的瞬态理论。混合过程的耦合系数是使用第二量子化公式中的量子力学微扰方法计算的，并在理论中明确包括相互作用的相位和动量失配。描述驱动光脉冲演化的偏微分方程的解得出极化子脉冲传播瞬态问题的完整公式。在极化子波的驱动脉冲f(z,t)的持续时间大于阻尼参数Г−1的情况下，瞬态问题得到完全解决：这是一种具有一般物理相关性的情况，包括锁模激光器产生的短脉冲的光学行为。特别是，该问题的解决导致了对特征相互作用长度和时间的定义，该特征相互作用长度和时间取决于初始条件并以关键方式影响“相干激发”过程的效率。拉曼混合过程作为极化激元过程的一个特例进行了简要讨论。然后在半经典的基础上考虑红外产生的过程，特别强调边界条件的传播效应的讨论。特别讨论了传播方程自由解的非齐次特征。该理论进一步扩展到对剩余斯特拉尔带的非线性光学行为的简要讨论，从而导致考虑 ω= ω LO 处的无限非线性后向反射率。然后描述了一个实验，其中将磷化镓晶体中的相干红外产生应用于偏振子区域中线性和非线性光学参数的一系列精确测量。波长 λ= 29.2、2 9. 9 和 34.6 μ 处发射的红外强度的角度分布以及准共线运动配置中极化子场的空间演化导致了晶体在这些波长下的折射率的确定，并首次直接测量了大极化子色散区域中的吸收系数。基于我们的结果，我们可以验证Barker提出的描述GaP晶格振荡的多振荡器理论模型的正确性。最后，通过不同频率下的红外强度来确定非线性光学磁化率模量的色散| d|的晶体。假设在非线性区域中晶格的一阶近似单振荡器模型，我们可以测量特征非线性参数 C= S (d Q′ d E′)。我们发现C=− 0.48±0.01。本工作中描述的实验方法对于光学和红外频率范围内的固体非线性光谱具有普遍意义。
The work presents a transient theory of the propagation in a cubic crystal of a polariton wave excited by a three-wave nonlinear parametric interaction. The coupling coefficient of the mixing process is calculated using a quantum-mechanical perturbation approach in the second-quantization formulation and including explicitly in the theory the phase and momentum mismatches of the interaction. The solution of the partial differential equations describing the evolution of the driving optical pulses leads to a complete formulation of the transient problem for the polariton pulse propagation. The transient problem is fully solved in the case in which the duration of the driving pulse f (z, t) of the polariton wave is larger than the damping parameter Γ− 1: a case of general physical relevance including the optical behavior of short pulses generated by mode-locked lasers. In particular the solution of the problem leads to the definition of a characteristic interaction length and time depending on the initial conditions and affecting in a critical way the efficiency of the" coherent excitation" process. The Raman mixing process is briefly discussed as a particular case of the polariton process. The process of infrared generation is then taken into account on a semiclassical basis, with particular emphasis on the discussion of the propagation effects of the boundary conditions. In particular, the inhomogeneous character of the free solutions of the propagation equations is discussed. The theory is further extended to a brief discussion of the nonlinear optical behavior of the reststrahl band, leading to the consideration of an infinite nonlinear backward reflectivity at ω= ω LO. An experiment is then described in which the coherent infrared generation in a crystal of gallium phosphide is applied to a series of accurate measurements of the linear and nonlinear optical parameters in the polariton region. The angular distribution of the emitted infrared intensity at wavelengths λ= 29.2, 2 9. 9, and 34.6 μ and the spatial evolution of the polariton field in the quasicollinear kinematical configuration lead to the determination of the index of refraction of the crystal at these wavelengths and to the first direct measurement of the absorption coefficient in the zone of large polariton dispersion. On the basis of our results, we could verify the correctness of the multiple-oscillator theoretical model proposed by Barker in order to describe the lattice oscillation in GaP. Finally, the infrared intensity at the various frequencies leads to the determination of the dispersion of the modulus of the nonlinear optical susceptibility| d| of the crystal. Assuming in first approximation a single-oscillator model for the lattice in the nonlinear regime, we could measure the characteristic nonlinear parameter C= S (d Q′ d E′). We found C=− 0.48±0.01. The experimental methods described in the present work are of general interest for the nonlinear spectroscopy of solids in the optical and infrared range of frequencies.