Study Of Singly And Doubly Q-switched Laser Characteristics And Frequency Conversion Characteristics

Diode-pumped solid-state Q-switched lasers have wide applications such as optical communication, laser medical, industry, laser measuring and information processing, due to its simplicity, high stability, short pulse width and high pulse energy. By using single and double Q-switching technique, diode-pumped solid-state Q-switched laser can obtain shorter pulse width, higher pulse peak power and more symmetrical pulse shape, etc.In this dissertation, by using LD as the pump source, Nd:LuVO4crystal as the laser gain medium, an AO—GaAs active-passively Q-switched1064nm laser and a Cr4+:YAG—GaAs doubly passively Q-switched1064nm laser have been realized, respectively; with AO—GaAs and Cr+:YAG—GaAs, intracavity frequency doubling Nd:LuVO4/KTP active-passively and doubly passively Q-switched532nm lasers have been studied, respectively; using Nd:GdVO4crystal as the laser gain medium, we have studied an AO—V3+:YAG active-passively Q-switched1342nm laser and a V3+:YAG—Co:LMA doubly passively Q-switched1342nm laser, respectively; using single-walled carbon nanotube (SWCNT) as the saturable absorber, we have realized a Nd:Lu0.33Y0.37Gd0.3VO4passively Q-switched1064nm laser and an intracavity frequency doubling Nd:SSO/KTP passively Q-switched540nm laser, respectively, in addition, with EO—SWCNT, a Nd:Lu0.33Y0.37Gd0.3VO4doubly Q-switched laser has been obtained too. The main contents of this dissertation include:I. A diode-pumped1064nm doubly Q-switched Nd:LuVO4laser with AO and GaAs has been realized. The pulse profile of the doubly Q-switched Nd:LuVO4laser has almost absolutely symmetric shape. The dependences of pulse width, single pulse energy and peak power on incident pump power under10KHz and20KHz of AO are measured. By considering the Gaussian transversal distribution of intracavity photon density and the longitudinal distribution of photon density along the cavity axis, the coupled rate equations of the laser are given. These coupled rate equations are solved numerically and the theoretical results are in agreement with the experimental results.(Chapter2,2.1)Ⅱ. By using GaAs saturable absorber as the output coupler, we demonstrated a diode-pumped doubly passively Q-switched Nd:LuV04laser with Cr4+:YAG and GaAs. This laser can generate a shorter and more symmetric pulse profile when compared with pure GaAs. Two different small-signal transmission of Cr4+:YAG saturable absorbers, which are T0=O.71and T0=0.81, have been used in the experiment. The average output power, the dependences of pulse width, the pulse repetition and single pulse peak power have been measured.(Chapter2,2.2)Ⅲ. A532nm intracavity frequency doubling Nd:LuV04/KTP doubly Q-switched green laser with AO and GaAs has been realized. This doubly Q-switched green laser can obtain the more symmetric and the shorter pulses than the singly Q-switched Nd:LuVO4/KTP green laser with AO or GaAs. By taking the walk-off effect of KTP crystal, the Gaussian transversal and longitudinal distributions of the intracavity photon density into account, the coupled rate equations of the doubly Q-switched intracavity frequency doubling Nd:LuV04/KTP green laser with AO and GaAs are given to simulate Q-switched process of the green laser numerically. The experimental results are consistent with the theoretical simulations.(Chapter3,3.1)Ⅳ. By simultaneously using Cr4+:YAG and GaAs saturable absorbers in the cavity, an intracavity frequency doubling doubly Q-switched Nd:LuV04/KTP green laser has been presented. The experimental results show that the doubly passively Q-switched green laser can generate more symmetric pulse shape and the shorter pulse width with higher peak power compared with the singly passively Q-switched intracavity frequency doubled green laser with Cr4+:YAG or GaAs saturable absorbers. The pulse symmetry in the doubly passively Q-switched green laser depends on the ratio of the small-signal transmissions of both saturable absorbers. By reasonably choosing the small-signal transmissions of both saturable absorbers, the doubly passively Q-switched green laser can generate the symmetric pulse profile. The doubly passively Q-switched green laser can obtain more symmetric pulse profiles and the pulse symmetry for T0=0.81is better than that for T0=O.91and0.71. The coupled rate equations considering the Gaussian transversal and longitudinal distributions of the intracavity photon density are solved to simulate the passively Q-switched process of the laser. The theoretical solutions are basically identical with the experimental results.(Chapter3,3.2)Ⅴ. A diode-pumped active-passively doubly Q-switched Nd:GdVO41342nm laser with AO and V3+:YAG has been realized. By considering the thermal lens effect of the laser gain medium, the coupled rate equations for the doubly Q-switched laser at1342nm under Gaussian approximation are given. The average output powers and the pulse widths of the singly and doubly Q-switched lasers are measured. The characteristics of the singly and doubly Q-switched lasers at high AO repetition rate (10-100kHz) are also studied. The numerical results of the equations are consistent with the experimental results.(Chapter4,4.1)Ⅵ. By using both V3+:YAG and Co:LMA saturable absorbers in the cavity, a doubly passively Q-switched Nd:GdVO41342nm laser has been studied. The experimental results show that the doubly passively Q-switched laser can generate the shorter pulse width with higher peak power in comparison to the singly passively Q-switched laser with V3+:YAG or Co:LMA saturable absorber. By considering the thermal lens effect of the laser gain medium, the coupled rate equations for the doubly passively Q-switched laser at1342nm under Gaussian approximation are given and the simulation solutions of the equations are basically identical with the experimental results. The simulation results also show that the doubly passively Q-switched laser can generate shorter pulse width than the singly passively Q-switched laser even though they have the same initial signal transmissions.(Chapter4,4.2)Ⅶ. A passively Q-switched Nd:Lu0.33Y0.37Gd0.3VO4laser with SWCNT has been demonstrated. At the incident pump power9.1W, the minimum pulse width of52ns and the maximum peak power66.5W can be obtained. In order to compare different gain media, the passively Q-switched Nd:LuVO4and Nd:Lu0.15Y0.85VO4lasers under the same laser cavity have been also investigated. The experimental results show that Nd:Lu0.33Y0.37Gd0.3VO4crystal is more suitable for passively Q-switched laser with SWCNT than Nd:LuVO4or Nd:Lu0.15Y0.85VO4crystals.(Chapter5,5.1)VIII. An intracavity frequency doubling Nd.SSO/KTP passively Q-switched540nm green laser with SWCNT has been obtained. The maximum average output power is0.89W at the incident pump power of11.8W, corresponding to an optical conversion efficiency of7.5%and a slope efficiency of10.2%. At the same incident pump power, the minimum pulse widths of94.8ns and the maximum peak power of19.1W can be obtained. The fluorescence spectrum of the Nd:SSO crystal is measured. The central wavelength of the fluorescence band is1080.1nm with a full width at half-maximum of3.4nm.(Chapter5,5.2)IX. By simultaneously using EO and SWCNT in the cavity, an active-passively doubly Q-switched Nd:Lu0.33Y0.37Gd0.3VO4laser has been realized. The experimental results show that this doubly Q-switched Nd:Lu0.33Y0.37Gd0.3VO4laser can generate shorter pulse width and higher peak power compared to the singly Q-switched Nd:LuYGdVO4laser with only EO or SWCNT. At the incident pump power11.43W and f=2kHz, the minimum pulse width17.6ns and the maximum pulse peak power19886W can be obtained.(Chapter5,5.3) The main innovations include:I. By using Nd:LuVO4crystal as the laser gain medium, an AO—GaAs active-passively doubly Q-switched1064nm laser have been realized for the first time. The pulse profile of the doubly Q-switched Nd:LuVO4laser has almost absolutely symmetric shape. By considering the Gaussian transversal distribution of intracavity photon density and the longitudinal distribution of photon density along the cavity axis, the coupled rate equations of the laser are given, the theoretical results are in agreement with the experimental results Ⅱ. A diode-pumped1064nm doubly Q-switched Nd:LuVO4laser with Cr4+:YAG and GaAs has been operated firstly. This laser can generate a shorter and more symmetric pulse profile when compared with pure GaAs.Ⅲ. By taking the walk-off effect of KTP crystal, the coupled rate equations of the intracavity frequency doubling Nd:LuVO4/KTP AO—GaAs active-passively doubly Q-switched532nm green lasers have been given firstly; An intracavity frequency doubling Nd:LuVO4/KTP Cr4+:YAG—GaAs doubly passively Q-switched532nm green laser have been invesitaged for the first time, By reasonably choosing the small-signal transmissions of both saturable absorbers, the doubly passively Q-switched green laser can generate the symmetric pulse profile.IV. By considering the thermal lens effect of the laser gain medium, the coupled rate equations for the doubly Q-switched laser at1342nm under Gaussian approximation are given firtstly. In the experiment,1342nm Nd:GdVO4AO—V3+:YAG active-passively doubly Q-switched and V3+:YAG—Co:LMA doubly passively Q-switched lasers have been realized for the first time, respectively. The simulation results show that the doubly passively Q-switched laser can generate shorter pulse width than the singly passively Q-switched laser even though they have the same initial signal transmissions.Ⅴ. By using SWCNT as the saturable absorber, we have realized a1064nm Nd:Luo.33Y0.37Gd0.3VO4passively Q-switched laser and a540nm intracavity frequency doubling Nd:SSO/KTP passively Q-switched laser for the first time, respectively. In addition, with EO—SWCNT, an active-passively doubly Q-switched Nd:LuYGdVO4laser has been obtained firstly too.