Font Size: a A A

Study Of The Passively Q-switched Laser Properties Of New Saturable Absorber Co2+: LaMgAl11O19

Posted on:2008-02-16Degree:DoctorType:Dissertation
Country:ChinaCandidate:H Y QiFull Text:PDF
GTID:1118360242473647Subject:Optical Engineering
Abstract/Summary:PDF Full Text Request
The wavelength of lasers lasing around 1.6μm is in accordance with that of silica optics fibers with low dispersion and low loss,and is eye-safe.So,these lasers have widely promising in such areas:laser medical,fiber communication, optics sensing position and as a pump source for middle infrared parameter oscillator.With passively Q-switching technique,we can get stable and reliable laser pulse with short pulse cycle and high peak power in a compactness and low cost system.These Q-switched lasers were widely used in many regimes:such as radar detection,tele-sensing and laser processing.In this dissertation,according to the Q-switched properties of solid state lasers,using a new saturable absorber Co2+:LaMgAl11O19(Co:LMA)crystal as Q-switch,we finished the following experimental research:Flashlamp pumped Nd:YAG laser lasing at 1.319μm,Flashlamp pumped Er:glass laser lasing at 1.54μm,LD pumped Nd:GdVO4 lasers lasing at 1.34μm.We studied the output properties relative to input;the matching relationship between the emission cross section in gain medium and the absorption cross section of ground state and excited state in saturable absorber when these lasers operating in passively Q-switching;the optimal transmission of output coupler as the output properties were optimized;the variations of output peak power,a radical parameter in laser application,with respect to laser configuration.In addition,we also investigated the spatial distribution of KTiOAsO4(KTA)plasma induced by 1.06μm Nd:YAG laser with spectroscopic diagnose.(This publication was in Laser Phys. Lett.4,No.3,212-217(2007))The primary research works and innovations were expatiated as followings:ⅠNew saturable absorber crystal LaMgAl11O19As the second important factor,the saturable absorber also extracted more and more interesting in its research.Yumashev et al.and Ge et al.respectively invented the Co2+ions doped oxide crystal Co2+:LaMgAl11O19(abbreviated as Co:LMA).The crystal has been used in many experiments as passive Q-switches. Its outstanding performance shows the potential prospect in researches of passively Q-switched solid-state lasers.Energy levels configurations and properties of Co:LMA were deeply studied and analysed.Co:LMA crystal belongs to the hexagonal system and P63/mmc space group.La3+and Mg2+ions can be substituted by other ions,but the steady configuration of Co:LMA crystal could be kept.The complicated structure of the absorption bands is explained by splitting of the 4T1(4P)and 4T1 (4F)states in slightly distorted tetrahedral crystal field of oxygen environment around the Co2+ions.This absorption band just is the physical basis of Co:LMA as a saturable absorber in 1.3-1.6μm lasers.The broad near-infrared absorption band located at 1030-1660 nm is assigned to the 4A2(4F)'4T1(4F)transition and indicates potential application of the Co:LMA crystal as a saturable absorber Q-switch for the 1.3-1.6μm lasers.The rate equations of passively Q-switched lasers were studied by taking accout of intracavity light intensity,population inversion density of active medium and the spatial distribution of population density in ground state and excited state.The resolutions were gained.With the rate equation theory,we measured the dependence of the transmissions of Co:LMA crysta on light energy density and caculated the cross sections in groud state and excited state. (Chapter 2)ⅡFlashlamp pumped Nd:YAG lasersPassively Q-switched operation of a flashlamp-pumped 1.319μm Nd:YAG laser is realized by using Co2+:LaMgAl11O19(Co:LMA)as saturable absorber. The pumping properties of flashlamp and characteristics of Nd:YAG crystal were investigated deeply.Using plano-plano resonator and flashlamp pumping source,we studied the static and passively Q-switched operation without intracavity focusing with Co:LMA as saturable absorber.It is the first time that we obtain the experiment results with these laser configuration.The operation properties of static and dynamic operations were discussed theoretically and the operation parameters were optimized.The experimental results revealed that Co:LMA crystal was a good saturable absorber for 1.3μm passively Q-switching.It owned excellent saturable characteristics.The laser performance should be improved if the surface of Co.LMA crystal was coated.(Chapter 3)ⅢFlashlamp pumped Er:glass lasersThe operation of 1.54μm Er:glass laser pumped by flashlamp with Co2+:LaMgAl11O19(Co:LMA)as a saturable absorber was experimental demonstrated.The static and dynamic properties of this laser were studied with different transmissions of output couplers.The experiment results showed that when the transmission of output coupler was 15%,the high slop efficiency and energy conversion efficiency were got under static operation,whereas the higher single pulse energy and narrower output pulse width were got under Q-switching operation.Using Co2+:LaMgAl11O19as saturable absorber,we demonstrated the good operation of 1.54μm Er:glass laser experimently.The results indicated that the crystal Co2+:LaMgAl11O19was a good Q-switch.With this laser,we got the narrow pulse width(55ns)and high pulse peak power(0.86MW)under single output pulse.(Chapter 3)ⅣLD pumped a-cut Nd:GdVO4 lasersWe deeply analyzed the influence of the laser resonator configuration on laser pump threshod.On the basis of investigation of emission cross section of a-cut Nd:GdVO4 crystal,we obtained the good matching between this emission cross section and the absorption cross section of Co.LMA crystal and the effective area of light beam in gain medium with a plano-concave resonator.Using plano-concave resonator,we studied the properties of static and passively Q-switched operations with a-cut Nd:GdVO4 crystal as gain medium. To constructing a laser resonator,especially,we arranged a concave lens as rear mirror and a plano lens as output coupler.This configuration overcame the disadvantages of intracavity focusing under the situation when the emission cross section of gain medium was bigger than the absorption cross section of saturable absorber.For the first time,we applied Co:LMA crystal as saturable absorber in this experiment and investigated the output properties deeply with different initial transmissions of Co:LMA crystal.(Chapter 4)ⅤLD pumped c-cut Nd:GdVO4 lasersThere are many obvious difference between characteristics of a-cut Nd:GdVO4 and c-cut Nd:GdVO4 crystals.By means of studying of the characteristics and spectra properties of c-cut Nd:GdVO4 crystal,and for the first time,we investigated the properties of static and passively Q-switched operation of 1.34μm all solid state laser with Co:LMA crystal as saturable absorber.Three different output couplers with transmissions of 2%,5.5%and 7 %were used in static operation experiment.The optimal output transmission is T=7%for static operation.For Q-switched operation,with the output coupler transmission of T=5.5%,We used three different saturable absorber slabs with initial transmissions 90%,85%and 70%,respectively.But only one absorber slab(T0=90%)operated well.It meant that T0=90%matched the second threshold condition well.We investigated the output properties under this condition.Comparing with a-cut Nd:GdVO4 laser,although the realization of static and passively Q-switched operation is more easily than that of c-cut Nd:GdVO4,the c-cut Nd:GdVO4 crystal is more suitable for passively Q-switched operation and can be obtained higher output peak power.(Chapter 4)...
Keywords/Search Tags:passively Q-switched, Co2+:LaMgAl11O19 (Co:LMA) crystal, flashlamp pump, LD pump, Nd:GdVO4 crystal
PDF Full Text Request
Related items