Collaborative Research: Nanoprobes for mapping the spatiotemporal evolution of ultrafast optical vector near field

光学纳米技术的进步已经实现了广泛的应用，例如提高了用等离子体纳米颗粒检测几个分子的灵敏度。为了量化光学器件的性能并开发新的功能，必须测量具有纳米级空间分辨率和飞秒级时间分辨率的超快光场的行为。为了应对这一挑战，该计划产生了一种新型的纳米探针，与定制的近场扫描显微镜系统集成，用于超快光学近场的全面表征。该研究计划将通过结合三所大学不同研究领域的三名研究人员的专业知识来增进理解。在超快光学和纳米光学令人兴奋的领域将提供研究生和本科生以及K-12学生在实验室，在课堂上，并通过推广活动的良好教育机会。研究生和本科生将通过研究活动进行培训，如纳米探针制造，近场扫描光学显微镜系统的应用，光学测量，以及三所大学合作设置的数值模拟和检索。结果将纳入课程。为了与研究人员之前的项目保持一致，将鼓励和期望女性和代表性不足的群体参与该计划。该计划的目标是开发一种基于纳米探针的表征方法，可以映射纳米-飞秒尺度下超快光学矢量近场的时空演化。纳米探针由位于纳米线上的二阶非线性微扰器或近场扫描光学显微镜（NSOM）探针组成，将与定制的NSOM系统集成，以实现样品-探针距离控制和纳米级空间分辨率。非线性响应（即，二次谐波产生（SHG）可以用来表征局部超快场的振幅和相位分布以及通过共线SHG频率分辨光学选通（FROG）全息术的时空演化。由于存在强大的“本地振荡器”和依赖零差检测，FROG全息术还将提高测量灵敏度。最后，利用纳米探针的偏振二次谐波探测局部超快光场的偏振。由于二次谐波信号具有不同的波长，因此它对由基波场的反射或散射产生的任何背景噪声不敏感。此外，二阶非线性张量由诸如晶体结构的材料性质确定，并且在很大程度上与颗粒形态无关，从而导致更可控的纳米探针传感器。当地时空领域的知识提高了能力，从等离子体结构，在纳米光谱学的一个长期的挑战，量化光谱信号。

Advances in optical nanotechnology have enabled a wide range of applications, such as increased sensitivity for the detection of just a few molecules with plasmonic nanoparticles. To quantify the performance of optical devices and develop new capabilities, it is essential to measure the behaviors of ultrafast optical fields with nanoscale spatial resolution and femtosecond scale temporal resolution. To address the challenge, this program engenders a novel type of nanoprobe, integrated with a custom near-field scanning microscope system, for comprehensive characterization of the ultrafast optical near field. The research program will enhance understanding by combining the expertise of three researchers in different research areas at three universities. The exciting areas in ultrafast optics and nano-optics will provide excellent education opportunities for graduate and undergraduate as well as K-12 students in the lab, in the classroom, and through outreach activities. Graduate and undergraduate students will be trained through the research activities such as nanoprobe fabrication, application of near-field scanning optical microscope system, optical measurements, and numerical simulation and retrieval in a collaborative setting across the three universities. Results will be incorporated into courses. In keeping with prior projects of the researchers, women and underrepresented groups will be encouraged and expected to participate in the program.The goal of this program is to develop a nanoprobe based characterization method that can map the spatiotemporal evolution of ultrafast optical vector near field in nanometer-femtosecond scale. A nanoprobe, which consists of a second order nonlinear nanocrystal perched on a nanowire or a near-field scanning optical microscope (NSOM) probe, will be integrated with a custom-built NSOM system to achieve sample-probe distance control and nanoscale spatial resolution. The nonlinear response of the nanocrystal (i.e., second harmonic generation -SHG) can be exploited to characterize both the amplitude and the phase profiles of the local ultrafast field as well as the spatiotemporal evolution through the collinear SHG frequency resolved optical gating (FROG) holography. Due to the presence of a strong "local oscillator" and the reliance on homodyne detection, FROG holography will also improve the measurement sensitivity. Finally, polarized SHG from the nanoprobe is utilized to probe the polarization of the local ultrafast optical field. Since the second harmonic signal has a distinct wavelength, it is insensitive to any background noise generated by the reflection or scattering of the fundamental field. Further, the second order nonlinear tensor is determined by the material properties such as the crystal structure and is largely independent of the particle morphology, leading to a more controllable nanoprobe sensor. Knowledge of the local spatiotemporal fields enhances the capability to quantify spectroscopic signals from plasmonic structures, a long-standing challenge in nanospectroscopy.