Ceraso Arianna, Mou Sen, Rubano Andrea, Paparo Domenico
Department of Physics, Politecnico di Milano, Piazza Leonardo da Vinci, 32, I-20133 Milano, Italy.
INFN and Dipartimento di Fisica, Università di Roma 'La Sapienza', Piazzale A. Moro 2, I-00185 Roma, Italy.
Materials (Basel). 2019 Nov 23;12(23):3870. doi: 10.3390/ma12233870.
Recently we have demonstrated a new nonlinear optical effect in the THz interval of frequencies. The latter is based on the use of femtosecond optical pulses and intense, sub-ps, broadband terahertz (THz) pulses to generate a THz-optical four- and five-wave mixing in the investigated material. The spectrum of the generated signal is resolved in time and wavelength and displays two pronounced frequency sidebands, Stokes and anti-Stokes, close to the optical second harmonic central frequency 2 ω L , where ω L is the optical central frequency of the fundamental beam, thus resembling the spectrum of standard hyper-Raman scattering, and hence we named this effect 'THz hyper-Raman'-THYR. We applied this technique to several crystalline materials, including α-quartz and gallium selenide. In the first material, we find that the THYR technique brings spectroscopic information on a large variety of low-energy excitations that include polaritons and phonons far from the Γ-point, which are difficult to study with standard optical techniques. In the second example, we show that this new tool offers some advantages in detecting ultra-broadband THz pulses. In this paper we review these two recent results, showing the potentialities of this new THz technique.
最近，我们在太赫兹频率区间展示了一种新的非线性光学效应。后者基于利用飞秒光脉冲和高强度、亚皮秒、宽带太赫兹（THz）脉冲，在被研究材料中产生太赫兹光学四波和五波混频。所产生信号的频谱在时间和波长上得到分辨，并显示出两个明显的频率边带，即斯托克斯和反斯托克斯边带，靠近光学二次谐波中心频率2ωL，其中ωL是基波的光学中心频率，因此类似于标准超拉曼散射的频谱，所以我们将这种效应命名为“太赫兹超拉曼”-THYR。我们将这项技术应用于几种晶体材料，包括α-石英和硒化镓。在第一种材料中，我们发现THYR技术能带来关于多种低能激发的光谱信息，这些激发包括远离Γ点的极化激元和声子，而用标准光学技术很难对其进行研究。在第二个例子中，我们表明这种新工具在检测超宽带太赫兹脉冲方面具有一些优势。在本文中，我们回顾这两个近期的结果，展示这种新太赫兹技术的潜力。
