Title: Enhanced Raman scattering by fast GaN phonon-polaritons Show Chinese title

Title: 快速GaN声子极化子增强的拉曼散射

Abstract: Phonon-polaritons propagating in crystal volume offer the possibility of transferring information throughout matter (via phonons) at high (photon-like) velocity and tunable frequency/wavelength in the far-infrared. However, from the phonon-polariton Raman cross section, the phonon and photon advantages seem mutually exclusive. Either the phonon-polaritons are fast (photon-like) but hardly supported by the lattice (not phonon-like), or they are well supported by the lattice (testified by a high Raman efficiency) but slow (not photon-like). An optimal phonon-photon coupling is currently searched for in hexagonal-GaN by near-forward Raman scattering across parallel crystal faces with in-plane singular c-axis. Two accessible phonons, i.e., the ordinary A1 and E1 ones, plus two refractive indices, i.e., the ordinary and extraordinary ones, generate various phonon-polariton candidates. Notably, in perfect forward Raman scattering and in crossed polarizations of the incident (along c) and scattered lights, which, altogether, maximizes the transferred wavevector to the crystal at minimum scattering angle, a fast phonon-polariton, stemming from the bottleneck of the E1 dispersion on entry to the deep photon-like regime, is activated. It is well supported by the lattice since its Raman signal is strong and sharp, enhanced by multi-reflection of the laser beam between crystal faces at near-normal incidence. This fast Raman-enhanced phonon-polariton is interesting for infrared-photonics in that it cumulates the advantages of a photon (speed) and of a phonon (Raman intensity). Besides, it commutates from a phonon-polariton to a phonon by deviating from normal incidence or by permuting the incident and scattered polarizations, with potential applications as a vibrational/optical switch. Show Chinese abstract

Abstract: 声子极化激元在晶体体积中传播，提供了通过声子在整个物质中以高速（类似光子）和可调频率/波长的远红外传输信息的可能性。 然而，从声子极化激元的拉曼散射截面来看，声子和光子的优势似乎相互排斥。 要么声子极化激元是快速的（类似光子），但很难被晶格支持（不类似声子），要么它们被晶格很好地支持（由高拉曼效率证明），但速度慢（不类似光子）。 目前，在六方氮化镓中通过平行晶体面的近前向拉曼散射寻找最佳的声子-光子耦合。 两个可获得的声子，即普通的A1和E1声子，加上两个折射率，即普通和异常的折射率，生成了各种声子极化激元候选。 值得注意的是，在完美的前向拉曼散射和入射光（沿c轴）与散射光的交叉偏振情况下，总体上在最小散射角下最大化传递到晶体的波矢，一种快速的声子极化激元被激活，这种声子极化激元源于E1色散在进入深光子类似区域时的瓶颈。 它由于其拉曼信号强且尖锐而被晶格很好地支持，这是由于激光束在近法向入射下在晶体面之间的多反射增强的。 这种快速的拉曼增强的声子极化激元对于红外光子学具有吸引力，因为它结合了光子（速度）和声子（拉曼强度）的优点。 此外，通过偏离法向入射或交换入射和散射的偏振方向，它可以从声子极化激元转换为声子，潜在的应用作为振动/光学开关。