Development of a new method of twe-photon absorption measurement and study of electronic structure of polydiacetylene crystals

1.提出了一种利用两个连续锁模染料激光器实现双光子吸收的灵敏、直接的光谱方法。结果表明，在抽运功率为100W.2的情况下，皮秒脉冲泵浦和探测相结合的高频锁定探测方法可以很好地观测到SnO_2中的激子线。此外，还研究了使用连续锁模的Nd-YAG激光器和染料激光器的类似的高灵敏度方法的可行性。结果表明，本系统对于确定TiO2.3的最低直接带隙的性质和位置是非常有用的。我们研究了聚二乙炔晶体TCDU-B的双光子吸收光谱，以澄清银对称性的第二低激子。光谱被解释为主要是由缺陷引起的，尽管在一些晶体中我们观察到2.84 eV的峰值可能是由于激子。我们发现，在能量为2.32 eV的双光子激发下，在PTS晶体中可以观察到一条发射线。这一事实有力地表明了银激子的存在。我们成功地观测到了PtS晶体在共振条件下的双光子喇曼信号，也支持了上述结果，并提供了关于非吉拉德声子的信息。

1. A sensitive and direct method Of two-photon absorption by utilizing two cw mode-locked dye-lasers was developed for spectroscopic use. It is found that the pump and probe method of the picosecond pulses with combined use of a high-frequency lock-in detection works well enough to observe the exciton lines in SnO_2 with the pump power Of 100 W.2. Feasibility of a similar, highly sensitive method with the use of a cw mode-locked Nd-YAG laser and a dye-laser was also investigated. As the result, the present system was found to be useful enough to determine the nature as well as location of the lowest direct band gap of TiO_2.3. We studied the two-photon absorption spectrum in a polydiacetylene crystal, TCDU-B to clarify the second-lowest, exciton, if any, of Ag symmetry. The spectrum was interpreted as arising mostly from imperfection, though in some crystals we observed a peak at 2.84 eV due presumably to the exciton.4. We found that an emission line could be observed in a PTS crystal when two-photon-excited with the energy 2.32 eV. This fact strongly suggests that the Ag exciton might exist.5. We succeeded in observing the two-photon Raman signal from a PTS crystal under the resonant condition, also supporting the above as well as providing information about ungerade phonons.