Experimental Studies On Pulsed Solid State Lasers Based On Several New Broadband Saturable Absorbers

Due to the advantages of durable stability,large single pulse energy,muli-wavelength range availability,and so on,pulsed solid state lasers capture a significant portion of the micro machining laser market.In order to conform the low-cost and diversified development trends of commercial pulsed lasers,researchers are working on some new cheap and high performance materials which could replace the expensive traditional laser devices.In recent years,as the important pulse modulators in pulsed lasers,some new saturable absorbers including carbon nanotubes,Graphene,and other nonlinear nanomaterials have received researchers'attentions.These nanomaterials are cheaper and easier to make than semiconductor saturable absorber mirror?SESAM?.Especially,the saturable absorbers based on Graphene,transition-metal dichalcogenide and black phosphorus?BP?possess excellent nonlinear optical responses over the broad waveband from ultraviolet to infrared and are known as the broadband saturable absorbers.At present,the research on new style broadband saturable absorbers has become a hotspot.However,the intrinsic instability of most nanomaterials leads to low damage threshold of saturable absorption devices,also the immature preparation technology results in large insertion losses,which would be the hindrances to their applications in high power pulsed solid state lasers.Under this background,the paper studies not only the mode locked pulsed solid state laser based on SESAM but also the nonlinear optical properties of carboxyl graphene-oxide?GO-COOH?,tungsten disulfide?WS₂?,BP,and ferroferric-oxide?Fe₃O₄?nanomaterials.Based on these nanomaterials,different types of saturable absorption devices with low insertion loss and high damage threshold for high power pulsed solid state lasers are fabricated by improving the fabrication techniques.Inserting them in the solid state laser resonators,we obtain the pulsed lasers with high output power.The main research works are as follows:1.Based on the passive mode locking principle of solid state laser,we apply a home-made SESAM to a Nd:YVO₄ laser resonator and obtain a stable passive mode-locking operation.The average output power is 5.11 W,the pulse width is 25.1ps,and the repetition rate is 124 MHz.Moreover,the light-light conversion efficiency is 36.5%and the slope efficiency is 47.1%,which confirm the technique progress of the home-made SESAM.2.We prepared WS₂ solution and thin film saturable absorbers by liquid-phase-exfoliation method and vertical evaporation method,respectively.The rapid cooling effect of the solvent improves the thermal damage threshold of WS₂solution absorber.Then,the WS₂ solution is held in a coated quartz cell and inserted into the solid state laser cavity.By comparison text,we investigate the effects of different concentrations of WS₂ solution on laser pulses.The passively Q-switched laser with the average output power of 720 mW is obtained based on the WS₂solution with the optimal concentration ratio.By contrast,the uniform WS₂ thin film coated on the quartz substrate by the vertical evaporation method possesses thinner thickness.Also,the optical loss of quartz substrate is lower than that caused by quartz cell and solvent of solution saturable absorber.Thus,based on it,we get high slope efficiency Q-switched pulsed laser with watt level average output power and high repetition rate of above 1 MHz.3.The nonlinear absorption properties of BP nanoplates and Fe₃O₄nanoparticles are investigated,respectively.They not only exhibit excellent nonlinear optical response,but also possess broader operation wavelength band than WS₂ nanomaterials.However,considering of the poor stability of two nanomaterials in the air,we exploit the packaging method of solution saturable absorber to reduce the contact time between nanomaterials and air,extending the service life.In addition,the solvent of solution saturable absorber is improved.the selection of N-methylpyrrolidone?NMP?solvent with high boiling point and light transmittance further decreases the solution absorber'insertion loss and further increases the resistance to thermal damage.Ultimately,based on BP solution saturable absorber,the passively Q-switched laser of watt level average output power is achieved.Meanwhile,it is the first time that Fe₃O₄ nanomaterial has been successfully applied to the pulsed generation of passively Q-switched solid state laser.4.We propose the fabrication scheme of Langmuir-Blodgett?LB?film to prepare a uniform ultra-thin saturable absorption film.The technique can improve the uniformities of nanoplates'distributions,and the thickness of film can be easily controlled by times of film-forming,promoting the repeatability of the saturable absorber.In addition,its membrane environment only need normal temperature and pressure conditions,avoiding the damage of nanomaterials.Based on the high dispersibility of nonlinear GO-COOH nanomaterial in aqueous solution,we realize the uniform and ordered arrangement of GO-COOH nanosheets on the quartz plate and get a low insertion loss transmissive GO-COOH saturable absorber device.By using it into the Nd:GdVO₄ laser,the passive Q-switching operation with maximum average output power of 1.1 W is achieved.The corresponding slope efficiency is35.6%.Furthermore,a passive Q-switched mode-locking operation is also observed.Its average output power can reach 1.33 W,which shows the application preponderance and potential of the GO-COOH LB film in high power pulsed solid state laser.