本文關(guān)鍵詞： 皮秒激光器 MOPA 光束質(zhì)量 增益 端面泵浦 球差補償 側(cè)面泵浦 掠入射結(jié)構(gòu) 液態(tài)金屬　出處：《浙江大學(xué)》2016年博士論文　論文類型：學(xué)位論文

【摘要】：脈沖重復(fù)頻率小于1MHz的高亮度兆瓦級1064nm全固態(tài)皮秒激光器在工業(yè)微加工、非線性頻率變換等眾多領(lǐng)域具有廣泛的應(yīng)用。通常,此類激光器種子源輸出功率極低,需要采用高增益放大器(Master Oscillator Power Amplifier, MOPA)來提升輸出激光的功率及單脈沖能量,以滿足應(yīng)用需求。多級光纖放大器可以提供極高增益,但受限于光纖中的光學(xué)損傷及非線性效應(yīng),其難以實現(xiàn)高峰值功率激光輸出；再生放大技術(shù)是實現(xiàn)高增益放大的有效途徑,但其結(jié)構(gòu)復(fù)雜、價格昂貴,并不實用。近年來,基于高增益固體介質(zhì)直接放大低功率皮秒種子源技術(shù)日益得到關(guān)注。本論文對采用Nd:YVO_4晶體放大低功率的被動調(diào)Q微晶片皮秒激光器技術(shù)進(jìn)行研究,以獲得結(jié)構(gòu)簡單緊湊、成本較低的高亮度、高增益全固態(tài)皮秒激光放大器。論文主要研究內(nèi)容分為兩部分：基于端面泵浦Nd:YVO_4棒狀結(jié)構(gòu)高亮度高增益全固態(tài)皮秒激光放大技術(shù)研究；基于掠入射側(cè)面泵浦Nd:YVO_4板條結(jié)構(gòu)高亮度高增益全固態(tài)皮秒激光放大技術(shù)研究。端面泵浦Nd:YVO_4棒狀結(jié)構(gòu)散熱效果較差。為了獲得高增益及高功率激光輸出,通常需要采用強泵浦以實現(xiàn)高反轉(zhuǎn)粒子密度。這使增益介質(zhì)內(nèi)熱效應(yīng)更為嚴(yán)重,熱畸變導(dǎo)致輸出激光光束質(zhì)量退化。理論分析附加增益介質(zhì)熱致球差后激光光束質(zhì)量的演化(忽略增益飽和效應(yīng)),得到：附加增益介質(zhì)正球差的激光光束傳播經(jīng)過束腰后,波前球差會由正轉(zhuǎn)負(fù)；若將此帶負(fù)球差的激光光束通過具有相同熱效應(yīng)(熱球差)的增益介質(zhì),便可實現(xiàn)波前球差補償,使輸出激光光束質(zhì)量得到改善。指出：在端面泵浦Nd:YVO_4棒狀高增益放大器中,增益對光束強度分布起優(yōu)化作用,利于采用波前球差補償實現(xiàn)光束質(zhì)量改善。以此為基礎(chǔ),設(shè)計了基于波前球差補償?shù)母吡炼�、高增益三級全固態(tài)皮秒激光MOPA系統(tǒng)。預(yù)放大級采用特殊設(shè)計的雙通放大結(jié)構(gòu),在實現(xiàn)增益介質(zhì)波前球差自補償?shù)耐瑫r提高激光的提取效率,并有效抑制強泵浦導(dǎo)致的寄生激光,將脈沖重復(fù)頻率100kHz、脈沖寬度～95ps、光束質(zhì)量因子M~21.15的10mW低功率微晶片種子光放大到12W,光光效率20%,光束質(zhì)量因子M~21.28；主放大級為兩級單通波前球差補償結(jié)構(gòu),采用較大的泵浦光與種子光半徑,在實現(xiàn)增益介質(zhì)波前球差互補償?shù)耐瑫r有效降低增益介質(zhì)內(nèi)峰值功率密度,最終獲得了平均功率65W的激光輸出,峰值功率～7MW,單脈沖能量650μJ,光束質(zhì)量因子M~2≤1.30。與端面泵浦Nd:YV04棒狀結(jié)構(gòu)相比,掠入射側(cè)面泵浦Nd:YV04板條結(jié)構(gòu)在泵浦面附近形成一段長距離高反轉(zhuǎn)粒子密度區(qū),并具有極佳的散熱能力,是實現(xiàn)高亮度、高增益激光放大的有效途徑。對掠入射側(cè)面泵浦Nd:YV04板條增益介質(zhì)內(nèi)熱致折射率變化引起的熱透鏡及熱致畸變效應(yīng)進(jìn)行分析,指出：垂直方向泵浦光為高斯分布時,垂直方向泵浦光斑尺寸的變化對板條熱效應(yīng)影響較小,采用較小垂直方向泵浦光斑尺寸實現(xiàn)高反轉(zhuǎn)粒子密度并不會導(dǎo)致更為嚴(yán)重的熱致畸變；在掠入射角度由小變大的過程中,放大激光水平方向的熱致畸變呈先增加再減小的趨勢,采用更小的掠入射角度可以實現(xiàn)更小的水平方向熱致畸變及更高的增益(掠入射角度越小增益越高)。優(yōu)化了種子光掠入射角度、種子光在泵浦面投射寬度及泵浦寬度等參數(shù)。采用新型的液態(tài)金屬材料取代銦膜作為熱傳導(dǎo)材料,對其實用性進(jìn)行實驗驗證,極大改善地改善了板條的熱效應(yīng)。采用連續(xù)激光進(jìn)行Nd:YV04板條結(jié)構(gòu)放大實驗,對理論分析結(jié)果進(jìn)行驗證。以此為基礎(chǔ),設(shè)計了基于掠入射Nd:YV04板條結(jié)構(gòu)的高亮度、高增益兩級單通全固態(tài)皮秒激光MOPA系統(tǒng)。預(yù)放大級采用較小的泵浦光與種子光垂直半徑,實現(xiàn)高增益,將脈沖重復(fù)頻率100kHz、脈沖寬度-95ps、光束質(zhì)量因子M~2≤1.15的10mW低功率種子光放大到12W,光光效率達(dá)到22%,光束質(zhì)量M_x~2=1.23、M_y~2=1.20。主放大級采用較大的泵浦光與種子光垂直半徑,有效降低增益介質(zhì)內(nèi)峰值功率密度,最終獲得了平均功率32W的激光輸出,峰值功率～3.4MW,單脈沖能量320μJ,光束質(zhì)量因子M_x~2=1.25、M_y~2=1.20。
[Abstract]:The pulse repetition frequency is less than 1MHz high brightness megawatt 1064nm solid-state picosecond laser micro machining in industry, has been widely used in many fields of nonlinear frequency conversion. Usually, the seed laser output power is very low, the high gain amplifier (Master Oscillator Power Amplifier, MOPA) to improve the output power and the single pulse laser energy, to meet the application requirements. The multi-stage fiber amplifier can provide high gain, but limited by the optical damage and nonlinear effects in the fiber, it is difficult to achieve high peak power laser output; regenerative amplification technology is an effective way to achieve high gain amplification, but its structure is complex, expensive and not practical. In recent years, high gain solid media directly to enlarge the source of picosecond seed low power have been paid more and more attention. This paper based on the amplification of low power by using Nd:YVO_4 crystal Research on adjustable Q microchip picosecond laser technology, in order to obtain a simple and compact structure, low cost, high brightness, high gain solid-state picosecond laser amplifier. The main content of this thesis is divided into two parts: Based on Nd:YVO_4 end pumped rod structure with high brightness and high gain all solid state picosecond laser amplification technology research; Study on the amplification of grazing the incident side pumped Nd:YVO_4 slab with high brightness and high gain solid-state picosecond laser end pumped Nd:YVO_4 rod. Based on poor heat dissipation. In order to obtain high gain and high power laser output, usually need to use strong pump to achieve high density inversion. This makes the gain medium thermal effect is more serious, resulting in degradation of the quality of the output of thermal distortion laser beam. The theoretical analysis of additional gain medium in the thermal evolution of laser beam quality caused by aberration (ignoring the effect of gain saturation), added: The gain medium positive spherical aberration laser beam propagation through the waist, wavefront aberration will turn from positive to negative; if the laser beam with negative spherical aberration by having the same thermal effect (hot spherical aberration) of the gain medium, we can realize the wavefront compensation of spherical aberration, the quality of the output laser beam is improved. It is pointed out that: in the end pumped Nd:YVO_4 rod high gain amplifier, gain of function optimization of beam intensity distribution, to improve the beam quality of the wavefront spherical aberration compensation. On this basis, the design of high brightness compensation based on wavefront aberration, high gain three level solid-state picosecond laser MOPA system. Pre amplifier uses a specially designed double pass structure in gain medium self compensation at the same time improve the wavefront aberration of laser extraction efficiency, and effectively suppress the parasitic laser caused by strong pumping, the pulse repetition frequency of 100kHz, pulse width 95ps, beam quality 10mW low power factor M~21.15 microchip to 12W seed optical amplification, 20% optical optical efficiency and beam quality factor M~21.28; the main amplification level two for single pass wavefront spherical aberration compensation structure, the larger the pump and seed light radius, while achieving the gain medium mutual compensation can effectively reduce the wavefront aberration of gain medium in the peak the power density, finally obtained the average laser output power of 65W, peak power 7MW, single pulse energy of 650 J, beam quality factor M~2 is less than or equal to 1.30. and end pumped Nd:YV04 rod structure compared to grazing side pumped Nd:YV04 slab to form a long distance high inversion density area near the surface of the pump, and heat capacity excellent, is to achieve high brightness, high gain laser amplification. The effective way of grazing side pumped Nd:YV04 slab gain medium heat induced thermal lens and thermal refractive index change caused by The distortion effect is analyzed, pointed out: the vertical pump for the Gauss distribution, influence the change of vertical pump spot size on slab thermal effect, with a smaller vertical pump spot size to achieve high density inversion does not lead to more serious heat distortion; the grazing angle changes from small to large in the process in the horizontal direction, amplified laser thermal induced distortion was first increased and then decreased, the grazing angle smaller can realize the horizontal thermal induced distortion smaller and higher gain (grazing incidence angle is small. The higher the gain) to optimize the seed light grazing angle, the seed width and surface projection in pump the pump width and other parameters. The liquid metal new material to replace indium film as thermal conductive material, the practicality of experimental verification, greatly improved to improve the thermal effect of the slab. By adopting continuous 嬋，

本文編號：1481306