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Research On All-solid-state Nd:GdVO4Laser With High Repetition Rate And Short Pulse Width

Posted on:2014-06-01Degree:DoctorType:Dissertation
Country:ChinaCandidate:Y F MaFull Text:PDF
GTID:1108330422990355Subject:Physical Electronics
Abstract/Summary:PDF Full Text Request
Diode-laser pumped solid-state lasers (DPSSL) have advantages of high efficiency, small in size, long operation time, high beam quality and so on. Due to these merits, DPSSL is widely used in many fields, such as military, industry, medical treatment and scientif research, and it always is a research hot topic. With the advent of new material and methods, DPSSL has made great progress in recent years. But up to now, pulsed lasers with high repetition rates and short pulse width still develop slowly, and they can not meet the demand of applications in laser radar, laser processing, and laser medicine. Because of this fact, we devoted to do some effort in theoretical and experimental fields for1.06μm laser with high repetition rate and short pulse width.We gave a detailed introduction and analysis firstly for several typical DPSSL configurations and the related1.06μm laser, and we clearly knew the characteristics for these lasers. After that, the basis for the choice of Nd:GdVO4rod and the research direction for the pulsed laser with high repetition rates, high beam quality, and short pulse width were presented. Based on the four level rate equations, we did some theoretical deduction and analysis for the continuous-wave and pulsed1.06μm laser, and also for some determinant which are important to output performance. We found that the spatial pattern matching degree and the size of oscillating volume have great influence on the realization of laser with high repetition rates, short pulse width, and high beam quality. Therefore, we studied the impact of pumping parameters on the spatial pattern matching degree for plano-plano cavity, plano-convex cavity and plano-concave cavity, and we took plano-convex cavity for example to do experimental verifications in order to illustrate the correctness for theoretical research. We took the jitter of focus length for thermal induced lens into account to study the spatial pattern matching degree for these three different cavities. Furthermore, the theoretical expression of thermal stability for the laser oscillating mode was deducted based on the optical ABCD matrix and Fresnel-Kirchhoff integral theory. These theoretical researches have guiding functions for the choices of laser caivity and other parameters in the latter chapters of this thesis.Due to the fact that diffraction loss will be worse under high pump power conditions, the passively Q-switched laser rate equations containing diffraction loss was established for the purpose of obtaining high repetition rate and short pulse width passively Q-switched laser. We discussed the impact of diffraction loss on initial invertion population density, final invertion population density, intracavity photons density and lower level population density of Cr4+:YAG crystal. The modulation of passively Q-switched pulse profile was anlysised, and it maybe caused by beat frequency of intracavity transverse mode beam. In addition, a comprehensive study for passively Q-switched Nd:GdVO4laser using [100]-cut Cr4+:YAG crystal was presented. The dependence of output performance with the angle β between the polarization direction of laser and the crystallographic axis of Cr4+:YAG crystal was investigated. We adopted879nm LD to replace conventional808nm LD and used high efficiency micro-channel heat sink simultaneously to relieve the bad effect(thermal lens effect, thermal-induced diffraction loss, et al.) from end-pumped lasers. A new method based on temperature operation was proposed to control the Cr4+:YAG passively Q-switched laser energy, and Cr4+:YAG/Nd:YAG laser was used to do the experimental validation. When the environmental temperature changed from-40°C to65°C, the output energy was increased by0.73mJ. The change rate was about7%. Predictably, we can get a wider range for the output energy control under the same conditions if Nd:GdVO4rod was employed.Because of the shortages and drawbacks of purely passively Q-switching or acoustic optical(AO) Q-switching, we performed doubly Q-switching research. We confirmed the advantages of douly Q-switching technology through the comparison among passively Q-switched, AO Q-switched and douly Q-switched GdVO4/Nd:GdVO4lasers pumped by879nm LD. Furthermore, the output performance of doubly Q-switched two GdVO4/Nd:GdVO4crystals laser using directly879nm dual-end-pumping was studied. After optimization of the initial transmission of Cr4+:YAG crystal, we adopted three technologies of dual-end-pumping, π-polarized pumping, and half wave plate(HWP) insertion to relieve the thermal effect and hope to obtain a high performance laser with high repetition rate and short pulse width. Without HWP and Cr4+:YAG crystal, when the absorbed pump power was24.0W and the repetition rate of AO was10kHz and100kHz respectively, the output pulse width was12.1ns and22.7ns, respectively. After HWP and Cr4+:YAG crystal were inserted into the cavity, the output pulse width was compressed obviously with compression value of7ns and10.2ns, and it was5.1ns and12.5ns, respectively. The pulse peak power of doubly Q-switched laser of145.6kW and7.2kW was higher than125.7kW and6.8kW of single AO Q-switched laser at the absorbed pump power of24.0W and repetition rate of10kHz and100kHz, respectively.According to the fact that using pulse transmission-type method it’s hard to obtain high repetition rate and short pulse width laser when the repetition rate and gain level is considered, we proposed a pulse reflection-type pattern (cavity-dumping Q-switching) using high speed pockels cell to get high repetition rate and short pulse width laser. In order to eliminate the limit of low extinction ratio of TFP, we used a V-type cavity to do electic-optical cavity-dumped GdVO4/Nd:GdVO4laser under879nm pumping. When the absorbed pump power was29.2W, the continuous wave output power was15.7W, and the beam profile was approximate Gaussian type. In the cavity-dumping operation, a constant pulse width of3.8±0.2ns laser was obtained, and the highest repetition rate could be100kHz. This is the shortest pulse width up to now in the end-pumping rod lasers with high repetition rate. Meanwhile the highest pulse peak power for Nd:GdVO4laser was also achieved. At an absorbed pump power of29.2W, the pulse peak power for10kHz,50kHz and100kHz were252.6kW,65.9kW and34.4kW, respectively.
Keywords/Search Tags:all-solid-state laser, Q-switching, cavity-dumping, high repetition rate, short pulse width
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