FEMTOSECOND VIBRATIONAL RELAXATION OF EXCITED SINGLET STATES IN ORGANIC DYES USING A TEMPORAL INTENSITY CORRELATION TECHNIQUE OF STIMULATED FLUORESCENCES.

用宽带非相干（带宽为3 ~ 7 nm）纳秒染料激光激发甲苯紫（CV）和罗丹明640（Rh-640）或高浓度DODCI溶液，在室温下产生的受激荧光的相关迹线中发现了明显的飞秒调制（量子拍）或时间峰位移信号。当持续时间为7 ns的激光束被分成波矢为k1和k2的两束光束时，其中一束相对于另一束被延迟。聚焦后用k1和k2光束照射染料。采用532 ~ 594 nm波长的激光激发染料，我们认为实验结果是由于受激荧光从两束飞秒关联光形成的动态光栅衍射所致。量子拍频可能与CV激发态的飞秒振动动力学有关。另一方面，Rh-640和其它染料的峰位移被认为是由动态光栅的深度引起的，动态光栅的深度由泵浦光的吸收和染料分子的受激荧光的有效发射之间的平衡决定。此外，Rh-640和DODCI中的拍频的缺乏可以通过这些染料的基态和激发态电位表面与CV的基态和激发态电位表面之间的不同位移和能隙来解释。

We have found striking signals which showed femtosecond modulation (quantum beat) or temporal peak shifts in correlation traces of stimulated fluorescences generated by exciting Cresyl Violet(CV) and Rhodamine 640 (Rh-640) or DODCI solution of high concentration at room temperature with broadband incoherent (bandwidth was 3- 7 nm) nanosecond dye laser. When the laser beam with a duration of 7 ns was divided into two beams with the wave vector k1 and k2, and one beam was variably delayed with respect to the other. The dye was irradiated with the k1 and k2 beams after focussed. Several wavelengths of lasers were employed to excite the dyes between 532 and 594 nm.We consider that experimental results are due to the diffraction of the stimulated fluorescence from a dynamic grating initially formed by two exciting beams with femtosecond correlation time. The quantum beats are probably related to the femto-second vibrational dynamics in the excited state of the CV. on the other hand, it is thought that the peak shifts of Rh-640 and other dyes are caused by the depth of dynamic grating determined by balance between absorption of the pump beams and effective emission of the stimulated fluorescences from dye molecules. Moreover, the lack of the beats in the Rh-640 and the DODCI can be interpreted by the different displacement and energy gap between the ground- and excited-state potential surfaces for these dyes from those for the CV.