Isothermal dependences of Raman scattering intensity i (ω′; T = const) on frequency Ω = ω₀ − ω′ and isofrequency temperature dependences of i (Ω = ω₀ − ω′ = const; T) in quartz crystals in a wide temperature range, including the α−β phase transition point (ω₀ and ω′ are the excitation and Raman frequencies, respectively) have been compared. The isofrequency temperature dependences exhibit an intensity peak (near the phase-transition point), whose spectral position and magnitude depend on the fixed frequency Ω = ω₀ − ω′. A theory of these dependences is developed for the crystals undergoing structural phase transitions. The theory predicts a soft-mode effect in the form of Raman opalescence: an anomalous increase in the spectral intensity of the isofrequency maximum i₀ (Ω, T) with a decrease in frequency Ω near the phase-transition temperature (T ≈ T_c). Agreement is established between the experimentally observed spectral intensity anomalies and the developed theory of isofrequency temperature dependences and processes of interaction of the fundamental soft mode with a low-frequency high-Q oscillator.

中文翻译：

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石英晶体拉曼散射强度的等温温度异常

拉曼散射强度的等温依赖性我（ω '; Ť =常数）上频率Ω= ω ₀ - ω '的和isofrequency温度依赖性我（Ω= ω ₀ - ω '=常数; Ť）在石英晶体在一宽的温度范围，包括α-β相转变点（ω ₀和ω'分别是激励频率和拉曼频率）。所述isofrequency温度依赖性表现出强度峰（相转变点附近），其光谱位置和大小依赖于固定频率Ω= ω ₀ - ω '。针对经历结构相变的晶体，开发了这些依赖性的理论。理论预测，拉曼乳光形式的软模式的效果：在isofrequency最大的光谱强度的异常增加我₀（Ω，Ť）与频率Ω的相转变温度附近的降低（Ť ≈ Ť _Ç）。在实验观察到的频谱强度异常与等温温度相关性的发展理论以及基本软模与低频高Q振荡器的相互作用过程之间建立了一致。