| Since 2004,graphene has been successfully exfoliated from the bulk graphite,opening a gate of a new world based on two-dimensional(2D)materials.Two-dimensional materials,graphene as a typical one,are composed of a single atomic layer,which has many unique physical,mechanical,electronic properties,raised great researchers' attention.Now,graphene and other similar 2D materials have developed very rapidly in many fields including optics,material science,electronics,etc.For example,in display and lighting market,graphene has been used as transparent electrodes and flexible substrates in LED,etc.,lighting equipment,as well as backboard of them.Graphene was also applied in super capacitors for replacement of traditional electrolytic cells.As graphene supply and demand markets flourishing very fast,ratios of graphene trade have been increasing as well in the fields of semiconductors,electronics,batteries,stored energy,energy conversion and composite materials.The rapid development of graphene has also led to the research and development of other materials with layered structures similar to graphene.With the progress of the chemical vapor deposition(CVD)in the manufacture of 2D materials,more and more 2D materials have also been synthesized through this inexpensive and rapid manufacturing method.The unique optical and nonlinear optical properties of these 2D materials have also been gradually discovered by researchers.Due to the monolayer thickness and special optical properties of 2D materials,it has great potential for applications in the field of integrated photonics.An optical waveguide is a kind of a basic element of an integrated photonics device and is a waveguiding structure with a high refractive index surrounded by low refractive index tracks.Optical waveguide structures have the capability to confine light propagation within very small regions in the scale of micrometers or sub-micrometers,thereby achieving ultra-high optical power densities in the waveguides that cannot be easily achieved in bulk materials.Therefore,based on the optical waveguide structure combined with some functional optical materials,applications such as nonlinear optical effects or waveguide lasers can be realized or enhanced,which greatly expands the application range of the optical waveguide in the integrated photonics system.Currently,waveguide lasers provide a solution for miniaturized and high-power laser light sources for integrated optical systems.Unlike free-space lasers,waveguide lasers are excited and propagating in the micron-sized space because the light beam is confined,leading to a stronger optical density in the waveguide,and larger matched overlap area between the pump light mode and the waveguide guided mode,which can effectively reduce the laser threshold to achieve a high-brightness miniaturized laser light source.Due to the small size and high integration of integrated photonic devices such as waveguide lasers,small differences between two components in the system can cause significant pumping efficiency in overall system.Therefore,high design requirements are put forward for the various components inside the integrated system.For the components in the traditional spatial light path,it is often difficult to meet these design requirements.However,for 2D materials with only atomic layer thicknesses,size limitations are obviously not a problem.In this paper,2D materials replaced conventional organic dye and semiconductor saturable absorber mirrors(SESAMs)are used as saturable absorbers(SAs)in the waveguide laser system,which not only solved the problem of high integration or high power density of traditional components but also broaden the absorption spectrum range.Only in the aspect of waveguide laser,the combination of 2D materials and waveguide laser platforms has both unique advantages and makes a multiplier effect.The main contents of this paper include the nonlinear absorption,saturable absorption,Raman spectra,absorption spectra and other optical properties of 2D materials such as transition metal chalcogenides(TMDCs),tin diselenide,and hexagonal boron nitride.As well as combining 2D materials with crystalline optical waveguides,related applications in waveguide lasers can be realized.It also includes the use of femtosecond lasers to modify 2D materials to produce micron-scale periodic structures,and to investigate modified structures at the micron scale.According to the different classification of materials and modified materials,the main work of this paper can be summarized as follows:Several kinds of TMDCs 2D material thin films were manufactured on quartz substrate by CVD technique,including molybdenum disulfide,tungsten diselenide,molybdenum diselenide(MoS2,WSe2,MoSe2)films.The surface topography,Raman spectrum,and saturable absorption properties of these 2D material films were investigated.In Nd:YAG crystal optical waveguides,these materials were used as efficient SAs to realize passive Q-switched waveguide laser.In the experimental results,TMDCs have unique saturable absorption characters and can be applied in integrated waveguide laser light sources.Specifically,the surface morphology and Raman spectrum of few-layer MoS2 thin film of CVD were detected,and a 1 ?m passively Q-switched pulsed laser output was achieved using MoS2 as a saturable absorber at the laser pumping at 808 nm.The average output power reached 84.0 mW.The single pulse energy was 89 nJ,with a pulse width and repetition rate of 203 ns and 1.10 MHz.By varying the pump power,a tunable repetition rate from 0.51 MHz 1.10 MHz can be obtained.The surface morphology and Raman spectra of few-layer WSe2 and MoSe2 thin films of CVD were investigated.The nonlinear absorption of the two samples was tested using a 1.06?m picosecond laser(pulse width of 22 ps)and obtained saturation intensity of 0.007 GW/cm2 and 0.006 GW/cm,respectively,modulation depths of 5.4%and 11.4%.At 808 nm laser pumped in 1 ?m waveguide lasers using WSe2 and MoSe2 as saturable absorbers have been achieved.The Q-switched laser pulse has a maximum output power of 115.1 mW and 45.7 mW,a slope efficiency of 7.4%and 7.0%,and a minimum laser threshold of 189.7 mW and 275.1 mW.Both have 35.9 nJ(19.0 nJ)of maximum single pulse energy,and adjustable pulse repetition rate from 0.995 to 3.334 MHz(0.781 to 2.938 MHz)in MoSe2(WSe2).SnSe2 thin films were manufactured on a sapphire substrate using CVD technology.The surface topography,linear absorption spectrum,Raman spectrum,and saturable absorption characteristics of the film were investigated.In a Nd:YAG crystal optical waveguide,a passive Q-switch waveguide laser of 1 ?m was realized using this sample as a saturable absorber.As experimental results demonstrating,SnSe2 has a unique linear absorption spectrum and saturable absorption,has a certain prospect in low power density nonlinear optical applications.Specifically,this sample was obtained from a non-linear coefficient from-13596 cm/GW to-2967.3 cm/GW by an ultra-fast 1.03-?m Z-scan system.The saturation intensity is-23.78 GW/cm2 saturable absorption characteristics.In the waveguide platform,few-layer SnSe2 thin film is used as the saturable absorber to realize a 1064 nm Q-switched laser pumped at 808 nm.The output laser pulse has a maximum output power of 102.3 mW,a slope efficiency of 11.9%,and a minimum laser threshold of 287 mW.The pulsed laser has tunable repetition rate frequencies and pulse widths of 0.337 to 2.294 MHz and 129 ns to 299 ns.The maximum single pulse energy is 44.5 nJ and the maximum peak power is 347.0 mW.The few-layer hexagonal boron nitride(h-BN)thin film with boron vacancies(Bv)defects was manufactured on the sapphire substrate by CVD technique.Raman spectroscopy,photoluminescence,linear absorption transitions,and nonlinear absorption effects of Bv-defective h-BN films were investigated by micro-fluorescence/Raman spectroscopy,spectrophotometry,and ultrafast laser Z-scan techniques.By utilizing VASP software,the lattice structure of the defect state was simulated and verified.In the Nd:YAG waveguide laser platform,a 1 ?m passively Q-switched mode-locked waveguide pulsed laser was realized using this material as a saturable absorber.The experimental results show that the h-BN sample,to which was introduced a single atom,Bv defect has impurity absorption at 1 ?m 1 eV)and photoluminescence of light,indicating that Bv-defective h-BN has near-infrared and visible bands for nonlinear and photoluminescence applications.Specifically,the surface morphology,absorption spectrum,and Raman spectrum of a few layers of CVD h-BN thin film were measured;the sample was found to have two linear impurity peaks at<1 eV and 1 eV to 2 eV using spectrophotometry,where 1 The absorption energy gap of eV-2eV corresponds to 1.16 eV;the Bv-defective h-BN photoluminescence was excited by a 532 nm laser,and the emitted wavelength was 694 nm(1.79 eV);the single atom was simulated by VASP software based on density functional theory.In the Bv-defective state,the corresponding energy band structure and absorption spectrum were simulated,which were highly consistent with the experimental results.The 1.03 ?m ultrafast laser Z-scan system was used to investigate the sample with a power density of up to 160.36 GW/cm2.The sample has a saturation absorption intensity I=1.03 GW/cm2 and a modulation depth of 1%.In the waveguide platform,a few-layer Bv-defective h-BN film is used as a saturable absorber to achieve 1.06 ?m lasing with 808-nm-wavelength optical pumping.The Q-switched laser pulse output,repetition rate and pulse duration have varied depending on the polarization and incident power of the pump light,ranging from 0.79 MHz to 2.42 MHz and 130 ns to 456 ns,and the maximum peak power is 252.8 mW,the maximum single pulse energy is 35.0 nJ.By adjusting the resonant cavity,Q-switched mode-locked pulsed laser is further obtained.The repetition rate of the mode-locked pulse is 8.7 GHz and the pulse duration is 55 ps.Using a femtosecond laser to irradiate a single-layer graphene film on a sapphire substrate,a micron-scale periodic permanent modified structure is obtained on the film.The modified structure was found by atomic force microscopy(AFM)and scanning electron microscopy(SEM).Raman spectroscopy to 1 ?m spatial resolution using ?-Raman spectroscopy was used to investigate the modified structure including layer numbers,defects,and lattice structure.As a result of the experiment,modifications present a regular variation along the radial direction from a central ablated region.Based on the obtained micro-Raman spectrum and the reflective micro-spectrum of laser-irradiated graphene,structural modification with periodic variations containing several spectral regimes has been observed.This work helps to provide a theoretical basis for the further applications of femtosecond lasers to process microstructures on graphene.Specifically,a Raman spectrum with a spatial resolution of 1 ?m was obtained by Raman spectroscopy,and four modified regions corresponding to different mechanisms I-IV were identified by the position,width,and intensity ratio of characteristic peaks in Raman spectra.The change of graphene properties in different regions was determined,including layer number,defect distance,defect density,refractive index,etc. |
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