Femtosecond laser is an ultrashort pulse laser with a certain repetition rate, which is realized by mode-locking mechanism. The repetition frequency is inversely proportional to the length of the laser resonator. The longer the resonator length, the lower the repetition frequency. The general cavity length is 1.5m, and the corresponding repetition frequency is 100MHz. If there is a direct output single pulse, that is, one pulse every 1 second, how long will it take? The whole earth can't let go, can it? Therefore, the single shot is selected by photoelectric elements or even mechanical shutters. For example, if you want to take a single shot, I will filter out the remaining 99,999,999 pulses to achieve a single pulse. A single pulse is not directly output.

Femtosecond and picosecond belong to ultra-short and ultra-fast lasers, but the difference is that the output pulse width of picosecond laser is several picoseconds (10-12nd power second), and the output pulse width of femtosecond laser is several femtoseconds (10-15th power second), which does not exceed 1000.

The spectral width of picosecond laser and femtosecond laser is generally different. Femtosecond laser has a wider spectral width, covering tens to hundreds of nanometers, while picoseconds only need a few nanometers.