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Research On High Repetition Rate High Peak Power Blue Lasers By Frequency Doubling Of Nd3+-Doped Lasers

Posted on:2012-08-17Degree:DoctorType:Dissertation
Country:ChinaCandidate:F ChenFull Text:PDF
GTID:1118330362950232Subject:Physical Electronics
Abstract/Summary:PDF Full Text Request
Diode-pumped solid-state lasers (DPSSL) have attracted much attention in recent years for the advantages of high efficiency, high brightness and compactness. For diode-end-pumped high repetition rate, high peak power Nd3+-doped lasers, the four-level laser system at the wavelength of 1.06μm and green laser by frequency-doubling have been studied extensively, and the laser performances of them can satisfy the requirements in many industries, such as laser radar, laser processing, and optoelectronic countermeasures so on. As the quasi-three-level laser system, the lasers emission at the wavelength around 0.9μm and blue lasers by frequency-doubling are developed slowly for they are restricted by many factors. However, blue lasers have many important applications. Especially, the pulsed blue lasers can be used in the laser underwater communication and underwater detection. In view of this condition and background, this dissertation intends to make efforts on the investigation of the high repetition rate high peak power blue lasers, and hopefully we can make some contribution on the development and the application of pulsed blue lasers.First of all, we make a comprehensive overview and analysis on the development of all-solid-state blue lasers. The main problems existing in these subjects are concluded and the direction for realizing the high repetition rate high peak power blue laser is pointed out. Furthermore, a detailed overview on the development of diode-pumped Nd3+-doped quasi-three-level lasers and frequency-doubling blue lasers are present. According to the methods of finite element analysis and interferometry, the end-face thermal deformation of Nd:GdVO4 laser medium is calculated theoretically and measured experimentally. Then, the Yong's modulus of elasticity and the Poisson's ratio for Nd:GdVO4 is estimated to be E=135GPa andν=0.35, respectively. To evaluate the serious thermal effect in Nd3+-doped quasi-three-level laser operation, the thermal focus length as a function of incident pump power is measured for continuous wave (CW) 912nm Nd:GdVO4 laser. The fractional thermal loading is deduced to be 0.36 during CW 912nm laser operation, and the rationality is certified by modelling the end-face deformation of Nd:GdVO4 crystal. Moreover, the thermal rupture limit of the laser medium in diode-end-pumped CW Nd:GdVO4 laser is analyzed, and it provides a theoretical basis for the following laser design.When the Nd3+-doped quasi-three-level lasers are operated at room temperature, there are thermal population on the lower laser level, and the reabsorption of the oscillating laser is induced, which will influence the output laser performance. Based on the rate equations, the theoretical model including reabosrption effect for CW Nd3+-doped quasi-three-level lasers is established. Considering reabosrption effect, the laser threshold, slope efficiency and output power are calculated, and the parameters of Nd3+-doped concentration, length of laser medium, space distribution of pump laser and oscillating laser, and the transmissivity of output mirror are optimized. After optimization in experiments, high power CW Nd3+-doped quasi-three-level lasers are obtained, with the highest output power of 16.2W 912nm laser, 15.5W 914nm laser and 17.2W 946nm laser, respectively. To evaluate the reabosrption effect during quasi-three-level laser operation using different Nd3+-doped laser mediums, the reabosrption cross-sectionσr is estimated by comparing the experimental results with calculational results, withσr about (1.0±0.5)×10-20cm2, (0.5±0.5)×10-20cm2 and (0.5±0.5)×10-20cm2 for 912nm, 914nm and 946nm lasers, respectively. To improve the thermal dissipation in diode-end-pumped Nd3+-doped quasi-three-level lasers, the micro-channel heat-sink is designed and applied, and the technology of indium-solder is explored initially.To obtain the pulsed Nd3+-doped quasi-three-level lasers with high repetition rate, short pulse width and high peak power output, the model of high repetition rate acoustic-optically (AO) Q-switched laser is established, and the AO Q-switched 912 nm performance as a function of incident pump power and repetition rate is calculated. On this basis, the high repetition rate AO Q-switched Nd3+-doped quasi-three-level laser output performance is investigated experimentally, and the highest peak power of 9.13kW 912nm laser, 6.25kW 914nm laser, 12.0kW 946nm laser are obtained at 10kHz, with the pulse width of 25.2ns, 33.6ns, 24.4ns, respectively. To compensate the serious thermal focal lensing effect during Q-switched Nd3+-doped quasi-three-level laser operation, the thermal compensation plano-convex unstable cavity is designed and applied in the pulsed 946nm laser operation, and the highest peak power of 31.5kW 946nm laser is obtained at 10kHz, with the pulse width of 13.7ns. Moreover, the beam quality is improved obviously. Finally, the output performance of Cr4+:YAG passively Q-switched laser is modeled on theory, and the passively Q-switched 912nm Nd:GdVO4 laser is investigated experimentally.To realize a pulsed blue laser with high repetition rate and high peak power output, the intracavity frequency-doubling AO Q-switched blue laser is investigated experimentally using a thermal insensitive V-type laser cavity. The highest peak power of 3.51kW 456nm laser, 2.25kW 457nm laser, and 4.0kW 473nm laser are obtained at 10kHz, with the pulse width of 37ns, 37.4ns, 33.1ns, respectively. Furthermore, the intracavity frequency-doubling of Cr4+:YAG passively Q-switched 456nm pulsed laser is also studied in the same V-type laser cavity. To compress the pulse width and to improve the peak power of blue laser, by using an extracavity frequency-doubling of AO Q-switched Nd3+-doped quasi-three-level laser configuration, the high repetition rate high peak power blue lasers are obtained combining with the technologies of thermal compensation unstable cavity and high efficiency frequency-doubling. The highest peak power of 2.3kW 456nm laser and 16.7kW 473nm laser are obtained at 10kHz, with the pulse width of 21.3ns and 9ns, respectively, and the maximum operating repetition rate are 100kHz and 50kHz, respectively. The beam quality factors for 473nm laser at the maximum output power are Mx2=1.5 and My2=1.36, and the power instability is less than 1% in 20 minutes test.
Keywords/Search Tags:all-solid-state laser, Nd3+-doped quasi-three-level laser, Q-switch, frequency doubling, high repetition rate, high peak power
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