论文标题
时间域和频谱光谱中的声子共振的光谱变窄
Spectral narrowing of a phonon resonance in time-domain sum-frequency spectroscopy
论文作者
论文摘要
总频产生（SFG）光谱学为研究非中心对称培养基和界面提供了多功能方法。在这里，使用可调的皮秒红外（IR）脉冲来自自由电子激光器，已通过红外可测量的振动振动SFG光谱探测了4H-SIC的非线性光学响应，4H-SIC的非线性光学响应是硅碳化硅的常见多型。在SFG光谱中，我们观察到纵向光学声子频率附近的尖锐共振，这是由于IR渗透率的Epsilon-Near-Zero rengime而引起的。在时域中，SFG强度的堆积与诱导的相干IR极化的自由诱导衰减有关。当接近声子共振的频率时，与非谐振的IR激发相比，观察到较慢的极化。因此，通过引入IR和可见的上转脉冲之间的时间延迟，我们可以证明声子SFG共振的光谱缩小，这是通过模型计算证实的。
Sum-frequency generation (SFG) spectroscopy provides a versatile method for the investigation of non-centrosymmetric media and interfaces. Here, using tunable picosecond infrared (IR) pulses from a free-electron laser, the nonlinear optical response of 4H-SiC, a common polytype of silicon carbide, has been probed in the frequency- and time-domain by infrared-visible vibrational SFG spectroscopy. In the SFG spectra we observe a sharp resonance near the longitudinal optical phonon frequency, arising from linear optical effects due the epsilon-near-zero regime of the IR permittivity. In the time domain, the build-up of the SFG intensity is linked to the free-induction decay of the induced coherent IR polarization. When approaching the frequency of the phonon resonance, a slower polarization dephasing is observed as compared to off-resonant IR excitation. Thus, by introducing a temporal delay between the IR and the visible up-conversion pulse we are able to demonstrate spectral narrowing of the phonon SFG resonance, as corroborated by model calculations.
