發(fā)布時(shí)間：2018-03-23 03:39

  本文選題：YAG激光器　切入點(diǎn)：MOPA結(jié)構(gòu)　出處：《華中科技大學(xué)》2015年碩士論文　論文類型：學(xué)位論文

【摘要】：本論文對千瓦級長脈沖Nd:YAG固體激光放大器進(jìn)行了理論分析和實(shí)驗(yàn)研究。首先,在時(shí)間域和空間域?qū)す馄髡袷幖壓头糯蠹夁M(jìn)行了分析和模擬,得到了耦合輸出鏡透過率、輸出功率、提取效率、高斯光束傳輸特性以及增益特性等方面的理論分析結(jié)果,確定了激光器的結(jié)構(gòu)參數(shù)。該結(jié)構(gòu)保證各級之間高斯光束匹配,使入射光束恰好充滿介質(zhì)棒的端面,充分利用有效模體積的同時(shí)進(jìn)行自孔徑選模,抑制熱致球差對M2因子的負(fù)面作用。經(jīng)過調(diào)整各級的間距和熱焦距的匹配,得到放大級不改變傳輸光束BPP的結(jié)果。然后,針對強(qiáng)泵浦、高功率固體激光器,基于非線性模型進(jìn)行了熱效應(yīng)分析。研究了[111]切割方向Nd:YAG激光介質(zhì)熱致雙折射與其偏振特性,給出了激光介質(zhì)縱向截面內(nèi)熱致雙折射橢圓分布圖。根據(jù)對非線性模型的光程差擬合分析,得出半徑相關(guān)的二次項(xiàng)對熱焦距產(chǎn)生貢獻(xiàn),而四次項(xiàng)決定了熱透鏡球差,高功率情況下熱致球差不能忽略,并且會影響光束質(zhì)量的結(jié)論。根據(jù)熱致雙折射所導(dǎo)致的折射率變化重新分析了基于非線性模型的熱焦距,實(shí)測值與理論值的吻合度比線性模型更高。最后,實(shí)驗(yàn)采用單級振蕩兩級放大的MOPA結(jié)構(gòu),在重復(fù)頻率為90 Hz,脈沖寬度為1 ms時(shí),得到1024 W的平均輸出功率,輸出激光的單脈沖能量11.4 J,峰值功率11.4 kW,電光效率3.41%,BPP=20.9 mm×mrad。其中振蕩級BPP=19.8 mm×mrad,通過兩級放大,BPP在誤差范圍內(nèi)基本保持不變,符合預(yù)期設(shè)計(jì)目標(biāo)。與同級別千瓦級的腔內(nèi)串接固體激光器比較,MOPA結(jié)構(gòu)固體激光器的BPP更小,電光效率較高,另外還能避免腔內(nèi)激光介質(zhì)和光學(xué)元件的光損傷,從而降低系統(tǒng)的組裝、調(diào)試以及維護(hù)等方面的復(fù)雜度。
[Abstract]:In this paper, the theoretical analysis and experimental study of kilowatt-class long-pulse Nd:YAG solid-state laser amplifier are carried out. Firstly, the laser oscillation stage and amplifier stage are analyzed and simulated in time domain and space domain, and the transmittance of coupling output mirror is obtained. The theoretical analysis results of output power, extraction efficiency, beam propagation characteristics and gain characteristics of Gao Si have determined the structural parameters of the laser. The incident beam is filled with the end surface of the dielectric rod, and the self-aperture mode selection is carried out by making full use of the effective mode volume to suppress the negative effect of the thermal spherical aberration on the M2 factor. The results of the amplification stage without changing the propagating beam BPP are obtained. Then, the thermal effect analysis is carried out based on the nonlinear model for strongly pumped, high-power solid-state lasers. The thermally induced birefringence and polarization characteristics of the Nd:YAG laser medium with the cut direction are studied. The thermal birefringence ellipse distribution in the longitudinal section of laser medium is given. According to the optical path difference fitting analysis of the nonlinear model, the quadratic term related to the radius contributes to the thermal focal length, and the fourth term determines the spherical aberration of the thermal lens. The conclusion that thermal spherical aberration can not be ignored and will affect the beam quality under high power condition is concluded. The thermal focal length based on nonlinear model is reanalyzed according to the refractive index variation caused by thermally induced birefringence. The agreement between the measured and theoretical values is higher than that of the linear model. Finally, a single-stage oscillatory two-stage amplified MOPA structure is used to obtain an average output power of 1024 W at a repetition rate of 90 Hz and a pulse width of 1 Ms. The single pulse energy of the output laser is 11.4 J, the peak power is 11.4 kW, the electro-optic efficiency is 3.41 and the BPP is 20.9 mm 脳 mrad.Oscillation stage BPP=19.8 脳 mrad. through two-stage amplification, the BPP remains basically unchanged within the error range. The BPP of MOPA-structured solid-state laser is smaller, the electro-optic efficiency is higher, and the optical damage of the laser medium and optical elements in the cavity can be avoided, compared with the intracavity series solid-state laser with the same level of kilowatts. In order to reduce the system assembly, debugging and maintenance and other aspects of the complexity.
【學(xué)位授予單位】：華中科技大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TN722

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本文編號：1651761