Mode-Locked Pulses with Narrowband Comb-Like Peaks Formed by Intracavity Amplitude Modulation from Gaseous Molecules

There have been extensive researches on mode-locked mid-infrared lasers [1], because they show higher spectral brightness than thermal light sources which had been used for broadband molecular vibrational spectroscopy. Those lasers usually possess smooth bell-shaped spectrum, however it is also interesting to investigate the possibility of spectrally structured sources. There are a few researches on narrowband dispersive spectral peaks formation on mode-locked pulses with intracavity gaseous molecules [[2, 3]. Recently, we have reported the symmetric spectral peaks appear on the mode-locked Cr:ZnS laser spectrum [4]. In this paper, compared to our previous report [4], we further investigate this phenomenon through numerical simulations, and clarify that the symmetric spectral peaks are formed by amplitude modulation brought from imaginary part of the molecular optical constant.