Study of hyper-Raman scattering excited by dye-laser for spectroscopic use in solids

1. 我们首次利用重复脉冲染料激光器成功地观测到了固体中光学声子的超拉曼信号。为此，我们研制了一种高灵敏度的探测系统。因此，我们首次在实验上研究了Tio_2和SrTiO_3晶体中超拉曼散射效率的频率色散，在这样的范围内，相关光子能量，即入射光子能量的两倍，2hwi和散射光子能量的两倍，hws在基本吸收边缘上。结果发现，当2hwi从下方接近带隙Eg时，在90散射几何结构中允许声子模式的效率显著提高。这一事实将使人们能够在未来进行更灵敏的超拉曼实验。我们还表明，上述结果可以合理地解释为与Eg.4的双光子持续共振。我们发现在金红石晶体中，在反向散射几何中通常被禁止的纵向声子在带隙处表现出尖锐而引人注目的双光子共振行为。起因可能是由于q依赖- Fro^^ lich相互作用引起的与激子的共振。我们在SrTiO_3中也观察到由LO声子引起的类似谐振行为。我们把这一现象解释为由弗洛里希相互作用引起的。因此，上述意义上的共振超拉曼光谱是一种很有前途的技术，可以揭示固体中电子能带结构的特定临界点，特别是在紫外线区域。值得注意的是，光跃迁能的一半的光子能量是足够的。

1. For the first time, we have succeeded in observing the hyper-Raman signals of optic phonon in solids by using a repetitively pulsed dye laser. For this purpose, we have developed a high-sensitive detection-system.2. Thereby, we have for the first time studied experimentally the frequency dispersion of the hyper-Raman scattering efficiency in Tio_2 and SrTiO_3 crystals, in such a range that the relevant photon energies, i.e., twice the incident one, 2hwi and the scattered one, hws are across the fundamental absorption edge. As the result, it is found that the efficiency of the allowed phonon modes in the 90ﾟ scattering geometry increases remarkably, as 2hwi approaches the band gap Eg from below. This fact will enable one to perform more sensitive hyper-Raman experiments in the future.3.We have also shown that the above result can be reasonably interpreted in terms of a two-photon ongoing resonance with Eg.4. We have found that the forbidden longitudinal phonon normally forbidden in the backward scattering geometry in a rutile crystal shows a sharp and striking two-photon resonant behavior at the band gap. The origin may be attributed to the resonance with the excitons due to the q-dependent- Fro^^"lich interaction. we have also observed a similar resonant behavior due to the LO phonon in SrTiO_3. we have interpreted this phenomenon as arising from the Fro^^"lich interaction.5. As a consequence, the resonant hyper-Raman spectroscopy in the above sense is a promising technique to unravel specific critical points of electronic band structure in solids, particularly in the ultraviolet region. It is noted that a photon energy of half the optical transition energy is sufficient.