Real-time SHG imaging technique based on a 2-GHz repetition rate femtosecond Ti:sapphire laser

摘要

The problem of weak signal intensity due to the low incident average intensity limited by photodamage probability in common nonlinear light microscopy and spectroscopy can be fundamentally solved by increasing the repetition rate of the excitation light source. Since the possibility of nonlinear photodamage is determined by the incident peak intensity (or pulse energy), increasing the repetition rate of the excitation light source while keeping its peak intensity (or pulse energy) well below than damage threshold will not provoke any optical damage but will augment the average nonlinear signals. We used a femtosecond Ti:sapphire laser with a 2-GHz repetition rate as the light source of a second-harmonic-generation (SHG) microscope and strongly enhanced SHG signal was observed while no photodamage could be identified. Compared with the common 80-MHz Ti:sapphire laser, the microscopic images taken with the 2-GHz laser require shorter acquisition time and exhibit higher contrast, resulting in real-time SHG imaging capability.