Activities of neurons are generally completed on a time scale of 10 milliseconds, which makes it hard for conventional microscopes to observe these phenomena directly. On the contrary, two-photon microscopy works by delivering ultrafast pulses of infrared laser light to the sample, where it interacts with fluorescent labels to create an image. It is extensively used for biological researches because of its ability to produce high-resolution 3D images up to a depth of one millimeter in a living tissue or to monitoring activities from hundreds of neurons simultaneously. These advantages, however, come with a limited imaging speed of the two-photon microscopy because of the weak fluorescent signal.
Reference:C. Wen, M. Ren, F. Feng, W. Chen, and S. Chen, “Compressive Sensing for Fast 3-D and Random-access Two-photon Microscopy,” Optics Letters, 44(17): 4343-46, 2019.