Through simultaneous five-photon absorption, scientists observe efficient frequency-upconverted stimulated emission from the mid- or near-infrared to the visible region in a novel fluorophore. The fifth-order dependence on the input light intensity provides much stronger spatial confinement than lower-order nonlinear absorption, thus offering much higher contrast for imaging.
- Qingdong Zheng
- Haomiao Zhu
- Xueyuan Chen
