5.3　Confocal Laser Scanning Microscope

Fluorescence imaging is an imaging mode that has gradually developed in the biomedical field in recent years.Fluorescence is the process whereby a molecule in the lower and stable of two electronic states（generally the ground state）is excited to a higher and unstable electronic state by radiation whose energy corresponds to an allowed absorption transition.After absorbing photon，electrons may reach the high vibrational energy level or the first excited state.The second excited state then undergoes internal conversion or relaxation oscillation process to reach the lowest vibrational energy level of the first excited state.Since the excited state is an unstable state，the electron returns to the ground state from the lowest vibrational energy level of the first excited singlet state，followed by the emission at the same time.Fluorescence imaging has the advantages of real-time image acquisition，high sensitivity，non-toxicity，and abundant fluorescent contrast agents.It is widely used in basic scientific research and clinical practice.With the development of science and technology，fluorescence microscopy has also made significant progress，and a series of technologies such as confocal laser scanning microscopy，and two-photon confocal laser scanning microscopy，have emerged，which play key roles in biomedical research and clinical diagnosis.(https://www.daowen.com)