發(fā)布時(shí)間：2018-05-24 05:30

  本文選題：飛秒激光 + 微加工��； 參考：《上海大學(xué)》2017年博士論文

【摘要】：飛秒激光是一種超短脈沖激光,可以在單脈沖能量很低的條件下獲得GW甚至TW量級的瞬時(shí)功率,這使得飛秒激光與物質(zhì)作用時(shí)表現(xiàn)出顯著的非線性現(xiàn)象。近年來,運(yùn)用雙光子誘發(fā)光敏材料發(fā)生光聚合反應(yīng)實(shí)現(xiàn)三維微加工已經(jīng)成為微納加工領(lǐng)域的研究熱點(diǎn),并逐漸發(fā)展成為一種集超快激光技術(shù)、光化學(xué)材料技術(shù)、顯微技術(shù)、超高精度定位技術(shù)、CAD/CAM技術(shù)于一體的新型微納米加工技術(shù)。飛秒激光雙光子微加工一般采用直寫方式,按照預(yù)定軌跡在聚合物材料內(nèi)部逐點(diǎn)掃描。對于給定的加工系統(tǒng)和被加工材料,空氣和被加工材料折射率不同產(chǎn)生的像差、加工點(diǎn)光斑的橢球形分布、掃描步距的大小等因素是影響加工精度和表面質(zhì)量的重要因素。本文在像差補(bǔ)償、光斑三維整形技術(shù)以及掃描步距的優(yōu)化方法等方面開展了一些探索性的工作,主要內(nèi)容如下:1.對飛秒激光微加工實(shí)驗(yàn)系統(tǒng)的曝光控制系統(tǒng)進(jìn)行了機(jī)械和電氣改造,擴(kuò)展了三維掃描平臺的運(yùn)動(dòng)范圍,實(shí)現(xiàn)了加工對象的多樣化和多軸聯(lián)動(dòng)下的空間三維連續(xù)掃描。2.根據(jù)飛秒激光微加工機(jī)理,結(jié)合光在不同介質(zhì)中的傳播理論,分析了由于空氣和被加工材料折射率的不同對加工點(diǎn)光斑的光強(qiáng)分布產(chǎn)生的影響,并進(jìn)行了數(shù)值模擬。利用波前像差函數(shù)推導(dǎo)出了由于折射率不同引起的像差表達(dá)式,得出了隨著加工深度、物鏡數(shù)值孔徑、加工介質(zhì)折射率的增大,像差也隨之增大的結(jié)論。在此基礎(chǔ)上,建立了基于反向澤爾尼克多項(xiàng)式的像差補(bǔ)償模型,以飛秒脈沖激光在光致變色材料上進(jìn)行點(diǎn)加工為例對該補(bǔ)償模型進(jìn)行了數(shù)值模擬。仿真結(jié)果表明建立的補(bǔ)償模型能有效校正像差。初級像差補(bǔ)償后,加工點(diǎn)熒光信號強(qiáng)度衰減現(xiàn)象得到顯著改善,加工深度可接近600μm;二級像差補(bǔ)償后,信號強(qiáng)度基本不隨加工深度的改變而改變。提出了基于開普勒望遠(yuǎn)鏡系統(tǒng)的像差補(bǔ)償方法并進(jìn)行了實(shí)驗(yàn)驗(yàn)證,分析了補(bǔ)償效果。3.基于菲涅耳衍射理論,結(jié)合飛秒激光微加工焦點(diǎn)光斑橫向和軸向的歸一化光強(qiáng)分布函數(shù),對加工點(diǎn)光斑形狀進(jìn)行了數(shù)值模擬。在分別對光斑軸向和橫向整形技術(shù)的理論分析和數(shù)值模擬的基礎(chǔ)上,得到了基于光通濾波器的光斑三維整形效果的表征參數(shù),運(yùn)用全局優(yōu)化算法與遺傳算法對光束整形元件(相位板)的關(guān)鍵參數(shù)進(jìn)行了優(yōu)化設(shè)計(jì)。根據(jù)優(yōu)化設(shè)計(jì)和數(shù)值模擬的結(jié)果制作了四環(huán)復(fù)透過率相位板并進(jìn)行了驗(yàn)證實(shí)驗(yàn)。實(shí)驗(yàn)結(jié)果表明,加入相位板對激光束進(jìn)行三維整形后,加工點(diǎn)橫向和軸向尺寸明顯變小,光斑壓縮比例與理論計(jì)算結(jié)果基本吻合。介紹了通過狹縫光闌、增加柱透鏡組和增加預(yù)聚焦透鏡等三種改善加工點(diǎn)光斑非對稱性形狀的光束整形技術(shù),對其工作原理及實(shí)現(xiàn)方法進(jìn)行了詳細(xì)的分析。4.基于光強(qiáng)分布函數(shù)和自由基濃度理論,建立了飛秒激光微加工固化單元覆蓋率的數(shù)學(xué)模型,分析了覆蓋率大小對微器件表面質(zhì)量和加工效率所造成的影響。運(yùn)用曝光等效性原理,得到了微器件表面質(zhì)量特征參數(shù)與掃描步距之間的表達(dá)式,并進(jìn)行了數(shù)值模擬和實(shí)驗(yàn)。結(jié)果表明當(dāng)掃描步距遠(yuǎn)小于固化單元尺寸時(shí),其對線條表面質(zhì)量的影響較小,而當(dāng)掃描步距逐漸增大,線條表面的平滑性迅速降低,表面質(zhì)量急劇變差。針對具有不同斜率的立體器件加工,提出了連續(xù)可變間距的三維掃描方法,推導(dǎo)出了不同斜率處掃描步距的計(jì)算表達(dá)式。以球形結(jié)構(gòu)的加工為例進(jìn)行了對比實(shí)驗(yàn)。結(jié)果表明,相對于固定步距掃描法,采用連續(xù)變步距掃描法進(jìn)行微加工,能夠有效地改善微器件的表面質(zhì)量。
[Abstract]:Femtosecond laser is an ultra short pulse laser, which can obtain instantaneous power of GW or even TW at the low energy of single pulse. This makes the femtosecond laser and substance play a significant nonlinear phenomenon. In recent years, the application of photopolymerization with two-photon induced photosensitive materials to achieve three-dimensional micromachining has become a micro Naga. The research hotspots in the field of industry have gradually developed into a new micro nano processing technology, which integrates ultra fast laser technology, photochemical material technology, micro technology, ultra high precision positioning technology and CAD/CAM technology. The femtosecond laser two-photon micro machining generally uses direct writing method, and it is scanned in the polymer material point by point according to the predetermined trajectory. For the given processing system and the processed material, the aberration produced by the refractive index of the air and the processed material, the ellipsoid distribution of the spot spot of the machining point, the size of the scanning distance are the important factors that affect the machining precision and the surface quality. The main contents are as follows: 1. the mechanical and electrical transformation of the exposure control system of the femtosecond laser micromachining experiment system is carried out, the motion range of the 3D scanning platform is extended, and the spatial 3D continuous scanning.2. under the diversity of the processing objects and the multi axis linkage is realized according to the femtosecond laser micro addition. Combined with the propagation theory of light in different media, the influence of the difference of refractive index of air and the processed material on the intensity distribution of the light spot of the processing point is analyzed, and the numerical simulation is carried out. The aberration expression caused by the difference of the refractive index is derived by the wavefront aberration function. The numerical aperture of the mirror increases the refractive index of the medium and the aberration increases. On this basis, the aberration compensation model based on the reverse Zelnick polynomial is established. The compensation model is simulated with the femtosecond pulse laser processing on the photochromic material as an example. The simulation results show the compensation of the compensation model. The model can effectively correct the aberration. After the primary aberration compensation, the intensity attenuation of the fluorescent signal of the processing point is greatly improved, the processing depth can be close to 600 m. The signal intensity is basically not changed with the change of the processing depth after two stage aberration compensation. Based on the theory of Fresnel diffraction,.3. based on the theory of Fresnel diffraction and the normalized light intensity distribution function of the femtosecond laser micromachining focal spot in the transverse and axial direction, the shape of the spot light spot is simulated. Based on the theoretical analysis and numerical simulation of the axial and transverse shaping techniques of the spot, the optical filter is obtained. The key parameters of the beam shaping element (phase plate) are optimized by the global optimization algorithm and genetic algorithm. The four ring complex transmittance phase plate is made according to the optimization design and the numerical simulation results. The experimental results show that the phase plate is excited by the addition of the phase plate. After the three-dimensional shaping of the beam, the transverse and axial dimensions of the processing point are obviously smaller. The compression ratio of the spot is basically consistent with the theoretical calculation. Three kinds of optical beam shaping technology are introduced, which are through the slit aperture, adding the column lens group and increasing the prefocus lens to improve the asymmetrical shape of the spot spot. The working principle and the realization method are also introduced. A detailed analysis of.4. based on the light intensity distribution function and the free radical concentration theory is used to establish the mathematical model of the coverage rate of the solidification unit of the femtosecond laser micromachining. The influence of the coverage rate on the surface quality and the processing efficiency of the microdevices is analyzed. The surface quality characteristic parameters and scanning of the microdevices are obtained by using the exposure equivalence principle. The results show that when the scanning step is far less than the size of the curing unit, it has little effect on the surface quality of the line, and the smoothness of the line surface is rapidly reduced and the surface quality is badly changed when the scanning step is gradually increased. A three-dimensional scanning method with continuous variable spacing is proposed, and the calculation expression of the scanning step at different slopes is derived. A comparison experiment is carried out with the machining of the spherical structure as an example. The results show that the continuous step distance scanning method can effectively improve the surface quality of the microdevices with the continuous step distance scanning method.
【學(xué)位授予單位】：上海大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2017
【分類號】：TG665

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