Nanometer scale real-time mapping of vibrations in pico second tempral region

在这项研究中，我们的目标是开发一种既具有纳米空间分辨率又具有皮秒时间分辨率的新型显微镜。它可以通过扫描探针显微镜和超短激光脉冲时间分辨测量技术相结合来实现。前者具有纳米级的空间分辨率，后者具有皮秒级的时间分辨率。超高速光开关与超短激光脉冲和扫描隧道显微镜的结合已经沿着这条道路被提出。然而，当隧道电流切换得很快时，样品和显微镜针尖之间的杂散电容大大降低了空间分辨率。为了解决上述问题，我们提出了一种扫描探针显微镜，它可以探测超短激光脉冲激发的超短声子脉冲。锁模钛宝石激光器的超短光脉冲分为两个光路。使用光学延迟线在两路脉冲之间引入±1 ns的时间差。通过每条线路的脉冲用不同的频率进行调制。用调制光脉冲照射金属薄膜样品，产生超短声声子脉冲。利用原子力显微镜对产生的周期性表面位移进行检测。我们从理论上考虑了这种方法，并进行了实际实验。此外，我们还对利用超声力显微镜测量纳米空间分辨率的局域弹性以及半导体量子阱结构产生超高频声子的技术进行了相关研究。

In this research, we aim to develop a new microscope which has both nanometer spatial resolution and picosecond temporal resolution. It can be realized by the combination of the scanning probe microscope and the time-resolved measurement technique with ultrashort laser pulses. The former has the nanometer spatial resolution and the latter the picosecond temporal resolution. The combination of the ultra high speed optical switch with ultra short laser pulses and the scanning tunneling microscope has been already proposed along this way. It is proved, however, that the stray capacity between the sample and the microscope tip substantially reduces the spatial resolution when the tunnel current is switched very fast. As a way getting around the above problem, we propose a scanning probe microscope that detects ultrashort phonon pulses excited by ultrashort laser pulses.The ultrashort light pulses from a mode-locked Ti-sapphire laser are divided into two optical paths. An optical delay line is used to introduce a time difference of ± 1 ns between the pulses in two paths. The pulses passing each line are modulated with different frequencies. A metal thin film sample is irradiated by the modulated light pulses to generate the ultrashort acoustic phonon pulses. The generated periodic surface displacement is detected by the atomic force microscopy. We considered this method theoretically and did actual experiments. In addition, we did related studies of the technique to estimate the local elasticity with nanometer spatial resolution by the ultrasonic force microscope and of the ultra high frequency phonon generation by a semiconductor quantum well structure.