| Because of its special working wavelength and excellent beam quality,mid-infrared fiber laser has been widely used in molecular spectroscopy,laser radar,material processing,biomedicine and other fields.The mid-infrared pulsed laser technology based on the saturable absorber has the characteristics of simple structure and easy implementation,high beam quality,high energy pulse and high stability,so it has become a hot spot in this field.Currently,semiconductor saturable absorption mirrors have been commercialized,but their working range is limited to near infrared band,and there are some problems such as low damage threshold,high cost and complex preparation.Two-dimensional(2D)material saturable absorber has the advantages of broadband response and easy integration,so it has become a research hotspot in pulsed fiber laser technology.At present,the saturable absorbers based on transition metal sulfur compounds are mostly prepared by liquid phase method or chemical vapor deposition.2D materials prepared by liquid phase method have many problems such as impurities and defects,while the materials prepared by chemical vapor deposition have problems such as the pollution and damage induced by the film transfer process.Both routes,will increase the optical loss of 2D materials saturable absorbers,and reduce the stability of pulsed laser modulation.In order to solve the above problems,taking group Ⅷtransition metal sulfur compounds as the research object,this paper proposes a general method of preparing saturable absorption mirror by in-situ growing 2D Fe and Ni-based chalcogenide compounds on optical glass surface,avoiding the typical transfer process of 2D materials,and directly applying in 2.8μm pulsed laser modulation experiment.The stable output of Q-switched pulses is realized.The main research contents are as follows:(1)Controlled growth of 2D FeS,FeSe,NiS and NiSe materials.2D transition metal chalcogenide compounds have been grown on optical glass substrates by a space-confined chemical vapor deposition process.Specifically,2D materials such as FeS,FeSe,NiS and NiSe were grown on sapphire and mica substrates at 520-630 ℃ using iron and nickel iodide,as well as sulfur and selenium powders as precursors.The morphology,thickness,crystal quality and elemental composition of the as-prepared materials were analyzed by optical microscopy,electron microscopy,Raman spectroscopy,atomic force microscopy and X-ray photoelectron spectroscopy.The results show that the lateral size of 2D FeS,FeSe,NiS and NiSe materials are 3-10 μm,the thicknesses are 3-230 nm,and the crystal quality is relatively high.The nonlinear optical properties of the samples were tested by Z-scanning technique based on a 2.8 μm ultrafast laser.The results show that these materials exhibit good saturation absorption properties in mid-infrared fiber lasers and are suitable for pulse modulation in mid-infrared fiber lasers.(2)Preparation of FeS,FeSe,NiS and NiSe saturable absorption mirrors and their characteristics of Q-switched laser.Four kinds of mid-infrared saturable absorption mirrors were prepared by magnetron sputtering gold films on the back of optical substrates loading samples,and their applications in 2.8 μm mid-infrared fiber lasers were studied.The results show that the width of Q-switched pulse generated by2 D FeSe and NiSe materials reaches the order of microsecond.The width of Q-switched pulse generated by2 D FeS and NiS materials reaches to the order of nanosecond,and Q-switched mode-locked signal appears in the pulse train based on 2D NiS materials,which provides the possibility for further compression of pulse width.This research provides a new idea for the development of mid-infrared saturable absorption mirrors of 2D materials. |
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