Investigation on the spectrum smoothing effect in an ultrafast Tm-doped fiber chirped pulse amplifier

We investigate the spectrum smoothing effect of the amplified soliton pulse in an ultrafast Tm-doped fiber chirped pulse amplifier, in which the soliton pulse is amplified to 7.3 W with a pulse duration of similar to 350 fs. The experimental investigation reveals that the spectrum smoothing effect arises from the polarization filtering effect of the grating-based pulse compressor, which is further confirmed by a theoretical simulation. This effect not only smooths the amplified laser spectrum, but also improves the pulse contrast ratio.