Investigation On Preparation,Characterization And Optical Modulation Performance Of Novel Two-dimensional Saturable Absorbers For 3?m Lasers

Mid-infrared lasers emitting at the eye-safe wavelength of 3 ?m locate at the well-known "molecular fingerprint" spectral region,which makes it possessing broad applications in analysis of trace gases,weather diagnostics,electro-optic countermeasure and remote sensing.Compared with continuous-wave operation,pulsed lasers possessing a high output energy or peak power are of particular attractive for practical uses.Due to a strong interaction with water,which is the most significant component making up the tissue cells,ultrafast laser sources at 3 ?m are highly demanded in tissue cutting and stitch,ophthalmology,neurosurgery,urology and dentistry.Furthermore,high-power 3 ?m lasers can be used as pump sources for driving mid-infrared lasers at longer wavelength,optical parametric processes,super-continuum lasers and terahertz generations.In the theoretical part of this thesis,the electronic band structures of novel two-dimensional nano-materials(Transitional metal dichalcogenides.Black phosphorus and graphite carbon nitride)have been simulated via first principles density functional theory calculation.In the experimental part,the nanosheet layer samples have been prepared and a series of systematical characterizations with respect to the microstructure,morphology,linear and nonlinear absorption properties at 3 ?m have been analyzed.The home-fabricated two-dimensional saturable absorbers have also been employed in several Q-switched 3 ?m laser systems based on Er3+ or Ho3+-doped crystals.The results validate that two-dimensional nano-materials are promising candidates as optical modulators for mid-infrared pulse lasers and have great potential in ultrafast photonics applications.The main contents are as follows:1.To explore the theoretical mechanism of the broadband optical absorption in transitional metal dichalcogenides(TMDs),the electronic structures of typical TMDs(MoS2 and WS2)with 2H structure,special TMD(ReS2)with lT structure and TMD alloy(MoWS2)with S vacancy defects have been analyzed by using first principles density functional theory calculation.2.The electronic structure of black phosphorus(BP)has been theoretical investigated.The direct and narrow energy gaps of monolayer and bulk black phosphorus have been assessed.3.Two possible structural units in graphite carbon nitride(g-CN)have been built.After ionic relaxation,the unit with a lower total energy has been picked for band structure analyses.Further calculation has been carried out to determine the evolution of spectrum response depended on N vacancy defects.4.Bulk MoWS2 and graphite carbon nitride powder samples have been synthesized by utilizing chemical vapor transport and thermal polymerization methods,respectively.Few-layer MoS2,ReS2,MoWS2,black phosphorus and graphite carbon nitride nanosheet samples have been prepared by employing liquid phase exfoliation method.Different two-dimensional saturable absorbers with application potential for 3 ?m band have been fabricated by using drop coating.spin coating and vertical evaporation.5.For a systematic characterization of the structure,composition and morphology of the products,several measurements such as x-ray diffraction,energy dispersive spectroscopy,inductively coupled plasma spectrometry,Raman spectroscopy,transmission electron microscopy,scanning electron microscopy and atomic force microscopy have been taken.To explore the linear and nonlinear optical properties of the nanosheet two-dimensional film samples,UV/VIS/NIR spectrophotometer and nonlinear optical response measurement at 3 ?m have been utilized.6.Laser diode pumped continuous wave Er:Lu2O3,Er:SrF2 and Ho,Pr:LuLiF4 lasers have been demonstrated for experimental breakthroughs in Er3+ and Ho3+ laser systems at 3 ?m.7.MoS2,MoWS2,ReS2 and g-CN have been employed for passively Q-switched operations in 3 ?m lasers for the first time.The layer-dependent saturable absorption properties of black phosphorus at 3 ?m have been experimentally demonstrated for the first time.According to a set of theoretical and experimental investigations,we have explored the saturable absorption properties of TMDs,BP and g-CN at the spectral range of 3 ?m.We aim to fabricate a series of novel modulation devices for 3 ?m with advantages of low costs,feasible preparation and controllable modulation parameters.The results in this thesis would provide research basis for ultrafast laser systems at the mid-infrared wavelength of 3 ?m.