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Research On 879NM Laser-Diode Endpumped ND:GDVO4 Laser With High Repetition Rate And High Brightness

Posted on:2011-03-28Degree:DoctorType:Dissertation
Country:ChinaCandidate:X D LiFull Text:PDF
GTID:1118330338989402Subject:Physical Electronics
Abstract/Summary:PDF Full Text Request
Laser-diode (LD) pumped solid-state lasers (DPSSL) have advantages of compactness, high efficiency, reliable operation and micromation. Pulsed lasers with high repetition rates and high brightness have been rapidly developed in many fields, such as lidar, electro-optical counterwork, laser manufacture and so on, and become one of the key technologies. Aimed at the difficulty of obtaining high repetition rates and high brightness together, and the slow research on pulsed lasers with high repetition rates and high brightness, we devote ourselves to explore the potential of new Nd:GdVO4 laser with high repetition rate and high brightness so that we can promote the development of pulsed lasers with high repetition rates and high brightness.Based on the fact that the effect of energy transfer upconversion (ETU) is not weak any longer when Nd:GdVO4 crystal is end-pumped by high power, we take ETU into account to the rate equation and research the influence of ETU on pump threshold. The peak power, pulse energy and pulse width are deduced from the Q-switched rate equation. The theoretical analysis shows that initial invertion population density is a key parameter to influence the pulsed laser performance. In the design of high-power pulsed laser, we should increase pump rate as greatly as possible in order to increase the initial invertion population density, and design the laser cavity reasonably to decrease the loss of cavity. They are the theoretical foundation to design all solid-state lasers with high repetition rates and high brightness in the future.Due to the influence of severe thermal effects on the performances of high-power end-pumped lasers, a series of technologies were introduced to manage the thermal effects of end-pumped Nd:GdVO4 laser. First of all, the production of thermal can be decreased. The thermal load of 24.0% decreases to 17.3% when 879nm direct pumping takes the place of 808nm indirect pumping. Secondly, four methods are used to optimize the thermal dissipation, including the adoptions of laser rod with high thermal conductivity, continuous-grown composite Nd:GdVO4 rod, dual-end pumping and microchannel sink. Thirdly, unstable resonator with convex-plane structure is adopted to compensate the thermal lensing effects caused by thermal deposited in the laser rod. These technologies can be used to relax the thermal effects in all DPSSLs, especially are suitable for end-pumped rod lasers. At the same time, it's very benefical to increase the incident pump power in end-pumped lasers. High output power and high beam quality often can not be concurrent in DPSSL in the case of high power end-pumping. In order to overcome the shortcoming, unstable resonator with convex-plane structure is introduced to improve the laser performances. Theoretical analysis shows that better mode matching can be achieved using convex-plane resonator instead of plane-plane resonator, and beam quality can be improved obviously. The selection principles of key parameters in unstable resonator are determined according to the corrected formula of thermal lensing and ABCD theory. A laser-diode end-pumped Nd:GdVO4 laser with convex-plane resonator is accomplished. The experimental results prove that high output power and high beam quality can be obtained synchronously in unstable resonator, at the same time, the pulsed laser performances are improved greatly. The guideline of designing unstable resonator with convex-plane structure is suitable for any DPSSLs with end-pumped configuration.According to the fact that ETU effects in high power end-pumped Q-switched Nd:GdVO4 laser is rather strong, theoretical analysis and experimental results demonstrate that ETU effects results in the decrease of initial invertion population density and the increase of thermal loading. For the first time, we measure and analyze the ETU spectrum of Nd:GdVO4 laser. Results show the fluorescence of 540nm, 600nm and 659nm can be attributed to the radiative transitions 4G7/2→4I9/2, 4G7/2→4I11/2 and 4G7/2→4I13/2, respectively. The weak fluorescence of 381nm and 428nm can be assigned to the transitions at 2P3/2→4I9/2 and 2P3/2→4I11/2. Meanwhile, we propose the measures of depressing the ETU effects, which will be contributed to the optimized design of high power end-pumped Q-switched Nd:GdVO4 rod laser in the future.In order to depress the influence of thermal effects on the performances of end-pumped Nd:GdVO4 laser, firstly, we reveal the advantage of direct pumping and expect that the direct pumping can be applied widely in high power DPSSL; secondly, we do some experimental researches on 879nm end-pumped Nd:GdVO4 laser. The fact that 879nm direct pumping can bring less thermal and decrease the thermal effects is proved by comparing the thermal focal length of Nd:GdVO4 rod under different wavelength pumping. The laser performances of 879nm laser-diode end-pumped Nd:GdVO4 laser are compared using conventional Nd:GdVO4 rod and composite Nd:GdVO4 rod. Experimental results show that composite Nd:GdVO4 rod is more beneficial to develop high-powered continuous and pulsed laser.The influence of cavity length, waist radius of pump beam, pump power and beam quality on pulse width are analyzed. We construct a high power 879nm laser-diode dual-end-pumped composite GdVO4/Nd:GdVO4 laser. A maximum continuous wave output power of 46.0W with Mx21.9 and My21.04 is obtained, corresponding to the slope efficiency of 71.1% to absorbed pump power and optical-optical efficiency of 53.5%. In A-O Q-switch operation, peak power of 304.1kW, 58.6kW and 23.8kW, pulse width of 7.2ns, 11.3ns and 16.2ns are obtained at the repetition rates of 10kHz, 50kHz and 100kHz, respectively. At the same time, the peak brightness at the repetition rate of 100kHz reaches to 1.87×1012W/cm2sr.
Keywords/Search Tags:879nm laser-diode, continuous-grown Nd:GdVO4 rod, high repetition rate, high brightness, thermal compensation
PDF Full Text Request
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