超短脉冲激光器中色散镜的设计、制备及性能研究
文献类型：学位论文
| 作者 | 王胭脂 |
| 学位类别 | 博士 |
| 答辩日期 | 2010 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 邵建达 |
| 关键词 | 色散镜 群延迟色散 超短脉冲激光器 色散补偿 |
| 其他题名 | Design，fabrication and performance of dispersion mirrors in the ultrashort pulse laser systems |
| 中文摘要 | 超短脉冲激光器在飞秒激光加工、制造与医学等领域有着重要的研究和应用价值。在科学家们继续挑战脉冲宽度极限的过程中，可获得的脉冲宽度受到色散补偿方法和激光镜工作带宽的限制。与传统的色散补偿器件光栅和棱镜对相比，色散镜具有可重复性高、对光路不敏感、结构简单紧凑等优点，越来越多的应用到激光器中，成为10飞秒以下超短脉冲激光器必不可少的色散补偿元件。 本文在针式优化和局域优化的基础上，提出了适于设计宽带色散镜的综合优化法。这种方法交叉使用针式优化和局域优化，并且通过改变高折射率材料对评价函数产生扰动，这种结合和交叉使用有效的避免了优化过程陷入局部最小值。综合优化法结合了针式优化的准确性和局域优化的高效性，在提供高反射率的同时获得平滑的group-delay dispersion (GDD)曲线，并且自动消除最薄的膜层。通过设计不同膜系，比较了综合优化法、针式优化和局域优化方法得到的色散镜的设计结果，验证了综合优化方法的有效性和可行性。在综合优化法的基础上，设计得到了不同带宽的（150nm～500nm）色散镜：960～1110nm，700～900nm，950～1150nm， 600～900nm，900～1200nm，600～1000nm 和550～1050nm。还设计了不同类型的色散镜，包括啁啾镜对、高色散镜和低色散银镜。 为了更好的实现色散镜的设计性能，必须获得使用材料准确的折射率。因为SiO2折射率和基底折射率接近，为了尽可能得到准确的折射率值，要考虑拟合过程中可能引入误差的环节，包括测量时误差和基底折射率的影响，分析了如何更准确的获得SiO2膜的折射率值。结果表明剩余反射率的测量误差小，直接用测量镀膜前后基片的剩余反射率值可以更简便更准确地得到SiO2的折射率，能达到10-2的精度。同时还拟合了高折率材料Ta2O5的折射率。 设计和制备了中心波长1035nm的Gires-Tournois interferometer （GTI）镜，结合电场强度分布及薄膜的群延迟色散、扫描电镜的测量结果，从材料折射率、膜层厚度、敏感膜层的变化及界面粗糙度等主要因素对GTI群延迟色散性能的影响进行了分析。在理论误差分析的基础上，通过对测量值的拟合，发现当考虑膜层厚度误差和折射率不均匀性时，反演值和测量曲线相吻合，得到了实际制备时的镀膜机控制精度及制备膜层的实际厚度值和折射率不均匀度。通过分析误差产生原因，可以看出，为了得到高质量的色散镜，一是要所设计的膜系能允许更大的误差；二是不断完善制备工艺提高控制精度，减小系统误差和随机误差；三是设计时要把镀膜机的系统误差考虑进去。 制备了在700～800nm波长范围内提供约-60fs2GDD的啁啾镜，用实验室搭建的白光干涉仪进行测量，通过实验结果，可以看出离子束溅射制备得到了和设计值比较吻合的结果，并且分析了在镀膜过程中导致误差产生的原因。制备得到的非成对啁啾镜用在钛宝石激光器中进行色散补偿，分别获得了12fs和9.5fs 的激光输出脉冲。 制备了两种高色散镜，分别在780～870nm波长范围内提供-800fs2和在1030～1050nm的波长范围内-2500fs2的群延迟色散补偿。从白光干涉仪的测试结果可以看出，得到的-800fs2GDD高色散镜和设计结果吻合的比较好； -2500fs2 GDD的高色散镜用在掺Yb3+光纤激光器中很好地抑制了脉冲展宽。 |
| 英文摘要 | Femtosecond pulse generation relies on the net negative intracavity group-delay dispersion (GDD). Because of compactness, reproducibility, and insensitivity to misalignment, dispersion mirrors have been widely used in ultrafast laser system to balance the frequency-dependent positive dispersion in the laser cavity. A combined-method based on local optimization and needle optimization is proposed to design broadband dispersion mirrors. The broadband dispersion mirrors are designed by using needle optimization combined with cross application of local optimization and changing high refractive index materials. We combine high efficiency of the local optimization and accuracy of needle optimization. This method can efficiently prevent optimizing process from being captured in a local minimum and obtain higher reflectivity and more smooth GDD curves. The designed dispersion mirrors have a few numbers of layers, which don’t have the thin layers that are not easily deposited. Based on combined-method, different bandwidth and different kinds of chirped dispersion mirrors are designed and discussed. Designs of different bandwidth from 150nm to 500nm are presented. Then three types of dispersion mirrors are shown as follow: Chirped mirror (CM) pais, high dispersion mirror and low dispersion silver. As a common low refractive index material, it is difficult in accurately fitting the optical constant of SiO2 which are close to those of the substrates. Considering the error in measurement and the influence of the substrate refractive index, the accuracies of the transmission envelop and the reflection envelop methods, by which the refractive index of SiO2 is separately obtained to invert are compared in the actual measurement and fitting. The analysis shows that the refractive index of SiO2 with 10-2 precision can be well obtained by directly using the residual reflection of substrate and films because of the few errors in actual measurement of residual reflection. The compensation of negative-dispersion mirrors has very high request on design and preparation. The reflective index and physical thickness are the necessary parameters for the realization of the capability. We design and prepare Gires-Tournois interferometer mirrors, which are analyzed from the main factors such as material refractive index, thickness, the sensitive layers and interface roughness considering the electric field distribution and the measurement result of group delay dispersion and the scanning electron microscope. Because of deviation between the measured group-delay dispersion and the designed character, based on the measured layers thickness, we fit Group delay dispersion measured values to analyse the errors produced during the deposition. When considering thickness deviation and the refractive index inhomogeneity, the fitted curve has a good agreement with the measurement result. Therefore, thickness errors and refractive index inhomogeneity are the main factors for manufacturing the Gires-Tournois interferometer mirrors. At the same time, the fitted actual manufactured thickness of every layer and the degree of the refractive index inhomogeneity are obtained from the fitted curve. The CM are designed and manufactured. The optimized CM provide GDD of around -60fs2 and average reflectivity of 99.4% with bandwidth 200nm at a center wavelength of 800nm. The CM structure consists of 52layers alternating high refractive index Ta2O5 and low refractive index SiO2. The measurement results show that the CM manufacture accuracy control can reach to our requirement by time control with ion beam sputtering. Because the GDD of CM is highly sensitive to small discrepancies between the layer thickness of calculated design and those of the manufactured mirror, we analyse the errors sources which result in thickness errors and refractive index inhomogeneous in film manufacturing. The designed and manufactured high dispersion mirrors combines the characters of chirped mirrors and Gires-Tournois interferometer(GTI) mirror and provides high dispersion compensation about -800fs2 GDD in the wavelength range 780～830nm and about -2500fs2 GDD in the wavelength range 1030～1050nm, respectively. And the dispersion mirrors are manufactured by ion beam sputtering. The performance of the mirrors have a good agreement with the designed values and can suppress the dispersion from ultrafst laser system very well. |
| 语种 | 中文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15647]  |
| 专题 | 上海光学精密机械研究所_学位论文 |
| 推荐引用方式 GB/T 7714 | 王胭脂. 超短脉冲激光器中色散镜的设计、制备及性能研究[D]. 中国科学院上海光学精密机械研究所. 2010. |
入库方式： OAI收割
来源：上海光学精密机械研究所
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