| 题名 | 飞秒数字全息及相关技术研究 |
| 作者 | 朱林伟 |
| 学位类别 | 博士 |
| 答辩日期 | 2011 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 周常河 |
| 关键词 | 飞秒激光 数字全息 位相差 热透镜效应 脉宽测量 |
| 其他题名 | Femtosecond Digital Holography and Related Technology |
| 中文摘要 | 数字全息结合泵浦探测技术是一种研究飞秒激光诱导物体动态变化的很好的方法。众所周知，数字全息干涉技术是一种非常灵敏的测量方法，它可以同时记录和再现物体的振幅和相位信息。飞秒脉冲数字全息干涉测量的超快时间分辨和极高的空间分辨使人们能够研究这些超快动力学现象和阐明其基本的物理机制。 本博士论文主要研究飞秒脉冲数字全息及其相关技术用来探测飞秒激光脉冲与物质的相互作用中的物理现象。主要完成了以下几个方面的研究工作： 1. 提出了一种飞秒脉冲离轴数字全息干涉记录装置，此装置中同时集成了反射式的迈克尔逊干涉仪与透射式的马赫-泽德干涉仪。利用此实验装置，研究了铬金属薄膜在飞秒激光脉冲能量低于和高于烧蚀阈值的两种情况激发下，铬金属薄膜的表面形变和内部折射率的动态变化。反射式的迈克尔逊干涉仪可以用来研究探测飞秒激光脉冲激发铬金属薄膜表面的形态变化；透射式的马赫-泽德干涉仪可以用来研究铬金属薄膜内部的折射率变化。实验结果表明，利用数字全息再现可以定性的解释飞秒激光脉冲诱导铬金属薄膜产生的物理现象。 除此之外，此实验装置同样可以应用于其它材料在飞秒激光脉冲激发下的动态变化和监测飞秒激光脉冲烧蚀材料过程中的动态变化。同时，利用此装置我们还研究了铬金属光栅在飞秒激光脉冲激发下的相位变化。 2. 报道了飞秒泵浦光脉冲能量低于烧蚀阈值情况下激发铬膜产生的热透镜效应。用菲涅尔衍射理论来解释在模式不匹配组态下的飞秒激光诱导铬膜产生的热透镜效应。基于菲涅尔衍射理论，可以很好的解释飞秒光激发铬膜中的热透镜现象。理论模拟得出的探测光强度分布与实验结果相一致。为了描述热透镜效应，定义了一种热透镜效应的强度对比度，并且发现探测光在特征距离处的热透镜效应强度对比度的值最大。我们同时研究了热透镜效应强度对比度随泵浦光能量和延迟时间的变化情况。理论模拟与实验结果相符。 3. 报道了双光束飞秒激光在低于烧蚀阈值下激发铬金属薄膜的相位动态变化。利用热传导和热弹性理论来解释飞秒激光激发铬膜产生的表面形变和折射率的变化。利用数字全息技术可以再现铬金属薄膜经双光束诱导产生的纳米尺度的表面形变和铬膜内部的相位变化。提出一个简化的物理模型来定性的解释铬金属薄膜经飞秒激光激发后产生的热物理过程。理论数值模拟与实验结果相一致 4. 提出了一种新的飞秒脉冲合成孔径数字全息方法，用来获得高分辨率和宽视场的再现图像。用于合成孔径的子全息图仅仅通过改变物光和参考光的延迟时间来获得。利用图像处理算法，合成孔径全息图可以准确的拼接。理论分析和实验结果表明，合成孔径数字全息可以很好的消除飞秒脉冲离轴数字全息的弱相干性。利用此合成孔径数字全息技术可以有效提高再现像的空间分辨率和再现视场。 5. 介绍了实验室自组装的二次谐波强度自相关测量装置，利用此装置可以用来测量皮秒激光的脉冲宽度。测量了一种基于新晶体Yb:SSO（Yb:Sc2SiO5）的二极管抽运被动锁模激光器出射的皮秒脉冲宽度，其中心波长为1061nm，重复频率52MHz。同样，借助此装置也测量了中心波长为1064nm，重复频率1KHz的锁模皮秒激光放大器中的脉宽。此测量装置与商业的自相关仪相比，具有大的测量范围、高的灵敏度、高稳定性的特点。另外，借助于高分辨率的光谱仪，利用此装置我们可以用二次谐波-频率分辨光开关法来测量皮秒脉冲在时域和频域上的特性。利用高分辨率光谱仪的二次谐波-频率分辨光开关法，我们同样测量了二极管抽运被动锁模Yb:BBO激光器出射的皮秒脉冲宽度。实验结果表明，我们的实验装置可以很好的来测量皮秒脉冲激光器出射的脉冲宽度。利用此装置对脉冲的测量，有助于进一步的优化二极管抽运皮秒激光器。除此之外，利用本实验室的飞秒激光器，我们在PDMS上加工出了光栅结构，可用于压印技术。 |
| 英文摘要 | Digital holography, combined with the pump-probe technique, is a good choice for studying dynamic changes. Digital holographic interferometry is a well-known powerful method, allowing both of the amplitude and phase of a specimen to be simultaneously observed. The development of ultrafast time- and space-resolved optical interferometry makes it possible to study the dynamics of these ultrafast phenomena and clarifies the underlying basic physical mechanisms. This work is mainly aiming to study the femtosecond digital holography and its relevant technology for probing ultrafast phenomenon in femtosecond light–matter interaction. The content of this work mainly includes: 1. We present a femtosecond off-axis digital holography for investigating the dynamic reversible surface change induced by femtosecond laser pulses with fluences near the ablation threshold. A reflection Michelson interferometer (RMI) and a transmission Mach–Zehnder interferometer (TMZI) are integrated in the same setup for recording digital holograms. Using this experimental technique, we study the surface deformation and refraction index change of the Cr film produced by irradiation with femtosecond laser pulses both below and above the ablation threshold. The RMI is used to measure the laser induced surface deformation of the metal film, while the TMZI is used to analyze the refraction index change of the metal film induced by the femtosecond laser pulses. Experimental results show that both surface modification and refraction index change of chromium metal film can be observed when femtosecond laser pulses are below and above the ablation threshold. Based on the experimental results, the physical processes of the metal induced by femtosecond laser pulses are given qualitatively. In addition, this setup can also be helpful for studying the transient dynamics in other materials, and this setup can also be useful for monitoring the ablation process of micromachining for practical applications. Using this setup, we also study the phase change of the Cr film grating induced by femtosecond laser pulse below the ablation threshold. 2. The thermal lens (TL) effect in chromium film induced by femtosecond laser pulses with the laser power below the ablation threshold is reported. A Fresnel diffraction theory is used to explain the TL effect. Based on this theory, the TL effect induced by femtosecond laser pulses can be explained clearly. The intensity profile of the TL calculated by the theoretical model is in agreement with the experimental results. In order to describe the TL effect, we define a contrast ratio of the intensity of the TL, and we find that the maximum contrast ratio of the TL effect is obtained when the probe beam is recorded at a characteristic distance. The dependence of the contrast ratio of the TL on different pump laser power levels and delay times is also investigated. Numerical simulations are also consistent with the experimental results. 3. Phase changes induced by two focused femtosecond pulsed lasers in metal film are studied using digital holography (DH) when the pump power is below the ablation threshold. The theory of heat conduction and thermoelasticity is used to explain the surface deformation and the refraction index change caused by the laser-induced nonuniform temperature distribution. Using the DH, both the nanoscale surface deformation and the phase change of the film can be reconstructed. A simplified model for the phase change of the sample in the transmission is presented to qualitatively determine the physical properties of metal film induced by femtosecond laser. Numerical simulations are also well consistent with the experimental results. 4. A new aperture-synthesis approach in femtosecond pulse digital holography for obtaining a high-resolution and a whole field of view of the reconstructed image is proposed. The sub-holograms are recorded only by changing the different delay time between the object and reference beams. In addition, by using image processing techniques, the synthesis aperture digital hologram can be superposed accurately. Our analysis and experimental results show that the walk-off in femtosecond off-axis digital holography caused by low coherent can be well eliminated. The resolution of the reconstructed image can be improved effectively. 5. We describe a home-made apparatus for measuring picosecond laser pulses using a second-harmonic generation (SHG) intensity autocorrelator. It is clear that an intensity autocorrelation can be used for measuring the pulse length of the ultrashort pulses laser. Using this SHG intensity autocorrelator, we measured the pulse length of a diode pumped picosecond passively mode-locked Yb:SSO laser which emits at a central wavelength of 1061nm at a repetition rate of 52MHz, and we also measured the pulse width of a mode-locked picosecond laser amplified system with the centered wavelength of 1064nm at a pulse repetition frequency of 1K HZ. Compared with the commercial autocorrelator, this setup has a larger measurement range, higher accuracy, and more reliable results. In addition, using a high resolution spectrum instrument, the apparatus becomes a second-harmonic-generation frequency-resolved optical gating measurement (SHG-FROG) apparatus. Based on the apparatus, we also report on the measurement of picosecond pulses with a FWHM bandwidth of about 1nm generated by a diode-pumped picosecond passively mode-locked Yb:SSO laser. The experimental results indicate that the full intensity and phase evolution of picosecond pulses can be retrieved successfully, using a high spectral resolution spectrometer. The phase information is useful for further optimization of the diode pumped picosecond laser. |
| 语种 | 中文 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15663]  |
| 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 | 朱林伟. 飞秒数字全息及相关技术研究[D]. 中国科学院上海光学精密机械研究所. 2011. |
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