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Study Of All-Solid-State Q-switched And Doubly Q-switched Lasers

Posted on:2010-08-10Degree:DoctorType:Dissertation
Country:ChinaCandidate:J AnFull Text:PDF
GTID:1118360278474017Subject:Optical Engineering
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All-solid-state short pulse lasers have wide applications in the fields such as laser telecommunication,remote sensing,information processing,laser processing,medical,and military,due to its advantages such as its simplicity,high efficiency,high stability,long longevity,good beam quality and has been paid much attention on.In this dissertation,by using xenon flash lamp or fiber-coupled laser-diode as the pump source,Nd:YAG,Nd:YVO4,Nd:GdVO4 and Nd:LuVO4 crystals as the gain mediums,we have studied the performance of the diode-pumped doubly Q-switched lasers with AO-GaAs or Cr4+:YAG-GaAs,the frequency doubling performance of the KTP crystal and MgO doped periodically poled LiNbO3(PPLN) crystal,as well as the pulse width control of doubly Q-switched lasers with AO-GaAs or Cr4+:YAG-GaAs.Meanwhile,the coupling rate equations under plane-wave or Gaussian distribution approximation have been established to theoretically analyze the properties of the above-mentioned Q-switched and doubly Q-switched lasers.The main content of this dissertation includes:ⅠUsing xenon flash lamp as pumping source,the doubly Q-switched Nd:YAG laser at 1.06μm with Cr4+:YAG and GaAs saturable absorbers has been realized.We also compared the laser performances of the doubly Q-switched laser with those of singly Q-switched lasers when there is only a single pulse during one pump pulse.The pulse widths and pulse symmetry factor of the three lasers versus the small signal transmission of Cr4+:YAG or the output coupler reflectivity have been given.The results show that the doubly passively Q-switched laser can improve the pulse symmetry and narrow the pulse width in comparison with the singly passively Q-switched laser.Considering the single-photon,two-photon and free carriers absorptions of GaAs,the coupling rate equations under the plane-wave approximation have been used to simulate the laser performances,the experimental results are consistent with the theoretical results.(Chapter 2-2.1)ⅡThe research on the laser performance of xenon flash lamp pumped KTP intracavity frequency-doubling Nd:YAG green laser with Cr4+:YAG and GaAs saturable absorbers have been presented.We have measured the pulse widths and symmetry factor versus small signal transmission of Cr4+:YAG for both the single passively and the doubly passively Q-switched intracavity-frequency-doubling green lasers when there is only a single pulse on the oscilloscope during one pump pulse.In addition,the dependence of pulse width,average output energy,pulse repetition,single pulse energy and peak power on incident pump energy for different Cr4+:YAG have been measured.We used the coupled rate equation under the plane-wave approximation to simulate the laser performances.The numerical solutions of the rate equations are in agreement with the experimental results.(Chapter 2-2.2)ⅢUsing both acoustic-optic(AO) modulator and GaAs saturable absorber in the same cavity,a diode-pumped doubly Q-switched c-cut Nd:GdVO4 laser has been realized.We made a comparison between c-cut and a-cut Nd:GdVO4 crystals and the experimental results shows that the doubly Q-switched c-cut Nd:GdVO4 laser can generate narrower pulse with higher peak power when the incident pump power higher than 3.4 W.Furthermore,c-cut Nd:GdVO4 laser can generate the more symmetric pulse with shorter pulse width in comparison with singly AO or GaAs Q-switched laser.Considering the turn-off time of AO Q-switch,the spatial distributions of the intracavity photon density and the population-inversion density,the population-inversion density and pump light,coupled rate equations are introduced to theoretically analyze the experimental results,and the experimental results are in fair agreement with the numerical solutions.(Chapter3-3.1)ⅣThe theoretical and experimental studies on laser diode-pumped doubly Q-switched Nd:GdVO4/KTP green lasers at 0.53μm have been presented.The rise time and fall time of the pulse,pulse widths,pulse energy and peak power have been measured under different pump power and repetition rates for the doubly and singly Q-switched lasers.Moreover,the comparison between a-cut Nd:GdVO4/KTP green laser and c-cut Nd:GdVO4/KTP green laser have been given.Considering the nonlinear loss due to the intracavity second harmonic conversion under Gaussian distribution approximation as well as the thermally induced diffraction loss and the variations of the beam radius at different positions along the cavity axis,coupled rate equations describing the doubly Q-switched intracavity frequency doubling green lasers are given.The theoretical results are consisting with experimental results. (Chapter 3-3.2)ⅤUsing three-mirror-folded cavity,diode-pumped doubly passively Q-switched KTP intracavity frequency-doubling Nd:YVO4 laser at 0.53μm with Cr4+:YAG and GaAs saturable absorbers have been realized.For three Cr4+:YAG wafers with different small signal transmission,the average output power,pulse widths,repetition rates,pulse energy,and peak powers of the doubly Q-switched laser under different pump power have been measured, respectively.In comparison with singly Q-switched laser,doubly Q-switched laser can compress the pulse width,improve the pulse symmetry and improve the pulse energy and peak power.(Chapter 3-3.3)ⅥThe method of manufacturing Nd:YVO4/YVO4,as well as its properties,has been presented.A diode-pumped actively Q-switched Nd:YVO4/YVO4 laser with AO has been carried out.The experimental studies on the output power versus the location of pumping facula in the laser crystal have been presented.The experimental results show that the maximum laser output power can be obtained when the pumping spot lies in the diffusion-bonded interface of the Nd:YVO4/YVO4 crystal.The three dimensional Possion equation has been used to analyze the steady state temperature profile in the laser crystal,and the thermal focus length of the Nd:YVO4/YVO4 composite crystal and thermal loss at different pump power are obtained.From the experimental results,we can see that the diffusion bonding crystal can reduce the thermal effect influence of laser crystal.Meanwhile, a rate-equation model for the actively Q-switched laser is used to simulate the laser performance.The numerical solutions are in agreement with the experimental results. (Chapter 4-4.1)ⅦBy using a piece of co-doped Nd3+:Cr4+:YAG crystal as saturable absorber,a laser-diode pumped passively Q-switched Nd:YVO4/YVO4 laser has been realized.The maximum laser output power of 2.452W has been obtained at the incident pump power of 8.9W for 8.8%transmission of output coupler at 1064 nm,corresponding to a slope efficiency of 30%.The other output laser characteristics of the laser have also been investigated.The laser with Nd3+:Cr4+:YAG saturable absorber has the lower threshold pump power and the higher slope efficiency compared with the laser with Cr4+:YAG saturable absorber that with the similar small-signal transmission.The dependence of the pulse width,pulse repetition, pulse energy and peak power on the pump power have also been measured.(Chapter 4-4.2)ⅧBy using GaAs as both a saturable absorber and an output coupler,a laser-diode pumped passively Q-switched Nd:LuVO4 laser has been realized for the first time to our knowledge.The uncoated GaAs forms a Fabry-Perot cavity,and the effective reflection, absorption and transmission coefficient of the GaAs wafer have been given.The characteristics of the laser such as the average output power,the pulse width,the pulse repetition rate and the peak power have been measured at different incident pump power. Compared with Nd:GdVO4 and Cr:Nd:YAG laser crystals,much shorter pulse widths can be obtained with the use of a Nd:LuVO4 laser crystal under a similar pump power level and laser cavity length.(Chapter 4-4.3)ⅨThe properties of the 5mol%MgO doped periodically poled LiNbO3(MgO-PPLN) have been demonstrated.By adding 5mol%MgO dopant impurities,the optical damage threshold as well as nonlinear coefficients of PPLN crystal is highly increased compared with that of non-doped PPLN crystal.Using the 5mol%MgO doped PPLN as the nonlinear crystal, diode-pumped cw and GaAs passively Q-switched Nd:YVO4/YVO4 green laser have been realized.The nonlinear loss due to the second harmonic wave conversion is obtained.In addition,a frequency doubling theory for quasi-phase-matched crystal PPLN are given under Gaussian distribution approximation.The coupled rate equations have been used to simulate the laser,and the theoretical analysis is consistent with the experimental results.(Chapter 5-5.1,5.2)ⅩA diode-pumped MgO-PPLN intracavity frequency doubling Cr4+:YAG passively Q-switched Nd:YVO4/YVO4 green laser has been realized in a three-mirror-folded cavity. Using two pieces of Cr4+:YAG with different small signal transmission as saturable absorber respectively,the pulse width,pulse repetition,pulse energy,and peak power of the green laser have been measured.(Chapter 5-5.3)ⅪThe methods to control the pulse width of a laser-diode end-pumped doubly Q-switched Nd:YVO4/YVO4 composite crystal laser with acoustic-optic(AO) and GaAs saturable absorber has been theoretically and experimentally studied.By varying one or two Q-switchers in the laser cavity and the pumping facula in the gain medium,we provide two kinds of efficient means to control the pulse duration.The average pumping radius versus the location of pumping facula in the laser crystal,as well as the transfer matrix and formula for calculating the beam radius of arbitrary position in the cavity,have been presented.The coupled rate equations are used to analyze the process of the laser.The experimental results are consistent with the theoretical results.(Chapter 6-6.1)ⅫWe have theoretically and experimentally studied the methods to control the pulse duration of a diode-pumped doubly passively Q-switched Nd:YVO4/YVO4 composite crystal laser with Cr4+:YAG and GaAs saturable absorbers.By varying the position of saturable absorbers in the laser cavity or the pumping facula in the gain medium,we can vary the pulse duration of the laser pulse.The coupled rate equations are introduced to simulate the process of the laser,and the theoretical calculation results agree with the experimental results.The main innovations of this dissertation are as follows:ⅠUsing xenon flash lamp as pumping source,we first demonstrated the Cr4+:YAG-GaAs doubly Q-switched Nd:YAG 1.06μm laser and KTP intracavity frequency-doubling 0.53μm green laser.The pulse widths and pulse symmetry factor of the three lasers versus the small signal transmission of Cr4+:YAG or the output coupler reflectivity have been given.The results show that the doubly passively Q-switched laser can improve the pulse symmetry and narrow the pulse width in comparison with the singly passively Q-switched laser.Considering the single-photon,two-photon and free carriers absorptions of GaAs,the coupling rate equations under the plane-wave approximation have been used to simulate the laser performances.ⅡUsing both acoustic-optic(AO) modulator and GaAs saturable absorber in the same cavity,diode-pumped doubly Q-switched c-cut Nd:GdVO4 1.06μm laser and KTP intracavity frequency-doubling 0.53μm green laser has been first demonstrated.In comparison with a-cut Nd:GdVO4 laser,c-cut Nd:GdVO4 laser can generate narrower pulse width and higher peak power when the incident pump power higher than 3.4W and 4.4W for 1.06μm laser and 0.53μm green laser,respectively.Considering the turn-off time of AO Q-switch,the spatial distributions of the intracavity photon density and the population-inversion density,the population-inversion density and pump light,coupled rate equations are introduced to theoretically analyze the experimental results,and the experimental results are in fair agreement with the numerical solutions.ⅢBy using GaAs as both a saturable absorber and an output coupler,a laser-diode pumped passively Q-switched Nd:LuVO4 laser has been realized for the first time to our knowledge.The characteristics of the lasers such as the average output power,the pulse width, the pulse repetition rate and the peak power have been measured at different incident pump power.Compared with Nd:GdVO4 and Cr:Nd:YAG laser crystals,much shorter pulse widths can be obtained with the use of a Nd:LuVO4 laser crystal under a similar pump power level and laser cavity length. ⅣUsing the 5mol%MgO doped PPLN as the nonlinear crystal,diode-pumped GaAs and Cr4+:YAG passively Q-switched Nd:YVO4/YVO4 green laser have been first presented. By adding 5mol%MgO dopant impurities,the optical damage threshold as well as nonlinear coefficients of PPLN crystal is highly increased compared with that of non-doped PPLN crystal.By considering the second harmonic conversion as a nonlinear loss of the fundamental wave,we used a rate-equation model considering the quasi-phase-matching theory to simulate the laser performance,and the numerical solution are consistent with the experimental ones.ⅤThe methods to control the pulse width for laser-diode end-pumped AO-GaAs and Cr4+:YAG-GaAs doubly Q-switched Nd:YVO4/YVO4 composite crystal laser has been theoretically and experimentally studied.By varying one or two Q-switchers in the laser cavity and the pumping facula in the gain medium,we provide two kinds of efficient means to control the pulse duration.The average pumping radius versus the location of pumping facula in the laser crystal,as well as the transfer matrix and formula for calculating the beam radius in intracavity arbitrary position,have been presented.The coupled rate equations are used to analyze the process of the laser.The experimental results are consistent with the theoretical results.
Keywords/Search Tags:All-solid-state, Double Q-switching, Quasi-phase-matching, Pulse width control, Rate-equation model
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