With the aid of lasers, researchers have developed various two-photon absorption (2PA) based applications, which include biological imaging, 3-dimentional microfabrication, frequency up-converted lasing, optical power limiting, and photodynamic therapy etc. Unlike 2PA, five-photon absorption (5PA) related phenomenon, is more difficult to observe due to the low transition probability of the 5PA process. Furthermore, the realization of five-photon pumped stimulated emission will be even more difficult because it requires the 5PA to be large enough for creating population inversion in the gain medium.
Prof. Zheng Qingdong’s group at Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences (FJIRSM) has reported on the first experimental observation of five-photon induced stimulated emission in collaboration with Prof. Chen Xueyuan’s group at FJIRSM.
By rational molecular design, a multi-photon absorbing material IPPS with the molecular configuration of Donor-Pi-Acceptor was prepared and selected from a large number of multi-photon active chromophores. Through simultaneous five-photon absorption, stimulated emission from IPPS was realized for converting the 2100nm invisible infrared laser into the visible 501nm blue-green laser.
At the same time, by direct three-photon absorption, the IPPS system exhibited a high net conversion efficiency of 10.4 percent, which thus enable the realization of novel frequency up-converted lasing in practical device applications. The results have been published in Nature Photonics.
This work is the first real application for five-photon absorption, which belongs to a ninth-order nonlinear process with extremely low probability. For the 5PA process, its 5th-order dependence on the input light intensity would provide a much stronger spatial confinement so that a much higher contrast in imaging can be achieved as compared to lower-order nonlinear absorption.