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Generation of ultrashort pulses in unexplored time regions and their measurement

在未探索的时间区域中超短脉冲的生成及其测量

基本信息

批准号：
14102012
负责人：
SAKAI Hirofumi
金额：
$ 68.39万
依托单位：
The University of Tokyo
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (S)
财政年份：
2002
资助国家：
日本
起止时间：
2002 至 2006
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-14102012/
关键词：
non-collinear optical parametric amp carrier envelope phase (CEP)visible to near infrared range aligned or oriented molecules high-order harmonic generation coherent vacuum ultraviolet radiation attosecond pulses polarization rate technique

项目摘要

(Visible to near infrared spectral range)We have developed a technique of non-collinear optical parametric amplification (NOPA) to generate ultrashort visible pulses. The pulses enable us to observe and analyze ultrafast dynamics of various real-time molecular vibrations whose frequencies are up to 3000 cm^<-1>. The ultrashort pulses have broadband spectrum, therefore the ultrafast dynamics of the real-time molecular vibrations can be observed in the entire broadband spectrum of the laser pulses, which gives the dependence of the ultrafast dynamics on the probe photon energy and clarifies its detailed dynamics. We have developed a multi (128 ch) double lock-in amplifier combined with spectrometer to observe the signal in the entire broadband spectrum of the ultrashort pulses. The multi channel lock-in amplifier can simultaneously measure all of the 128 probe wavelengths, which makes the measurement time 128 times shorter than before. The quick measurement enables to increase the signal … More to noise (S/N) ratio increased more than 10 times or measure the signal continuously changing parameters in good S/N ratio. Using the ultrashort visible pulses and the multi channel lock-in amplifier, we could observe the real-time signal of the sample in broadband with a fine time resolution, which can resolve the real-time molecular vibration.(Vacuum ultraviolet spectral range)We have developed an original technique to generate ultrashort light pulses in the VUV region by using high-order harmonic generation (HHG) from aligned molecules. First, we have succeeded in the optimal control of multiphoton ionization processes in aligned I_2 molecules with time-dependent polarization pulses. This means that we have developed the most advanced technique to control tunnel ionization which is the first step of HHG. Second, our novel technique to observe both ion yields and harmonic signals under the same experimental conditions enabled us to observe the first clear evidence of quantum interference of electron de Broglie waves in the recombination process, i.e., the third step of HHG from aligned CO_2 molecules. Third, we applied the polarization gate technique to HHG from non-adiabatically aligned N_2 molecules. Contrary to our expectations based on ellipticity dependence of HHG from aligned molecules, we have found that the spectral width of each harmonic tends to be broader when the molecular axis is perpendicular to the major axis of elliptical polarization. Theoretical calculations show that our observations are characteristic of time-dependent polarization pulses. This means that molecular alignment can be used as an important control parameter in addition to the carrier envelope phase when we generate attosecond pulses with polarization gated few-cycle pulses. Less

(可见光到近红外光谱范围)我们开发了一种非共线光学参量放大(NOPA)技术来产生超短可见脉冲。这些脉冲使我们能够观察和分析各种实时分子振动的超快动力学，其频率高达3000 cm^~(-1)。超短脉冲具有宽带谱，因此可以在整个激光脉冲的宽带谱上观察到实时分子振动的超快动力学，这给出了超快动力学对探测光子能量的依赖关系，并阐明了其详细的动力学。我们研制了一个多路(128路)双锁相放大器，并与光谱仪相结合，用来观测超短脉冲整个宽带谱的信号。多通道锁定放大器可以同时测量所有128个探头波长，使测量时间比以前缩短了128倍。快速测量使得能够增加信号…更多的噪声(S/N)比增加了10倍以上，或者测量的信号在良好的S/N比下连续改变参数。利用超短可见光脉冲和多通道锁定放大器，我们可以在高时间分辨率的宽带内观察到样品的实时信号，这可以解决分子的实时振动。(真空紫外光谱范围)我们发展了一种独创的技术，利用取向分子的高次谐波产生在真空紫外区产生超短光脉冲。首先，我们成功地实现了含时极化脉冲排列的I_2分子多光子电离过程的最优控制。这意味着我们已经开发出最先进的控制隧道电离的技术，这是HHG的第一步。第二，我们在相同的实验条件下同时观测离子产额和谐波信号的新技术，使我们能够第一次清楚地观察到电子德布罗意波在复合过程中的量子干涉，即来自排列的CO_2分子的高次谐波的第三步。第三，我们将偏振门技术应用于非绝热排列的N_2分子的高次谐波。相反，我们发现当分子轴垂直于椭圆偏振长轴时，各次谐波的光谱宽度会变宽，这与我们基于排列分子的高次谐波与椭圆率相关的预期相反。理论计算表明，我们的观测结果具有随时间变化的偏振脉冲的特征。这意味着当我们用偏振门控的几个周期的脉冲产生阿秒脉冲时，除了载流子包络相位之外，分子的排列也可以作为一个重要的控制参数。较少