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

1. 提出了一种利用双连续波锁模染料激光器进行双光子吸收的灵敏直接的光谱学方法。发现皮秒脉冲的泵浦和探针结合高频锁相检测方法可以很好地观测到泵浦功率为100 W.2的SnO_2中的激子线。利用连续波锁模Nd-YAG激光器和染料激光器，研究了一种类似的高灵敏度方法的可行性。结果表明，该系统可用于确定TiO_2.3的最低直接带隙的性质和位置。我们研究了聚二乙炔晶体tdub的双光子吸收光谱，以澄清银对称的次低激子，如果有的话。光谱被解释为主要是由不完美引起的，尽管在一些晶体中，我们观察到一个峰值在2.84 eV，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银激子可能存在。我们成功地观察到了共振条件下PTS晶体的双光子拉曼信号，也支持了上述结论，并提供了有关非能级声子的信息。

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.