Experimental study on spectral morphological changes of narrow pulse width picosecond lasers

Using ytterbium doped single-clad/double-clad fiber amplifiers, different amplification experiments were conducted on narrow pulse width picosecond light, and the influence of self-phase modulation on pulse frequency domain characteristics during amplification was analyzed. A self developed picosecond oscillator based on semiconductor saturable absorber mirror (SESAM) mode locking is used to directly enter the main amplifier device. The oscillator has a pulse width of 6.8 ps, a repetition rate of 20.76 MHz, and a center wavelength of 1064.3 nm. After amplification, the maximum output power is 315 mW, with an energy of about 15 nJ. The phenomenon of spectral changes caused by selfphase modulation of picosecond pulsed light during amplification is explored. When the output pulse optical power is about 200 mW and the pulse energy is about 10 nJ, and the injection power is 39.4 mW, 134 mW, 229.2 mW, and 326.8 mW, respectively, the corresponding spectral widths are 0.187 nm, 0.522 nm, 0.53 nm, and 0.588 nm, respectively. Experimental research shows that under the same output pulse energy conditions, the smaller the injected optical power, the better the output pulse spectral morphology. As the injected optical power decreases, the effect of pulse shape on self-phase modulation in fiber lasers decreases.