Micro-resonator Probe for THz Near-field Imaging Beyond the Diffraction Limit

太赫兹（THz）器件的研究和固体系统中太赫兹现象的研究需要在几微米尺度上探测太赫兹波和信号。这些测量提出了一个由太赫兹波衍射引起的主要技术问题。衍射极限阻止了使用最近开发的太赫兹光谱仪器来研究小于大约一个波长的物体。近场表面探测方法已经显示出克服衍射极限的潜在解决方案。然而，所有现有的太赫兹近场技术由于近场探测器引起的电场扰动而表现出另一个基本限制。探头的侵入性和跨太赫兹频谱的非均匀频率响应阻碍了现有近场探头在太赫兹器件中进行电场分布映射的使用。此外，空间分辨率优于~1/20波长的太赫兹近场成像系统的灵敏度会严重降低。为了缓解这些问题，并允许使用太赫兹波进行高空间分辨率的研究，我们建议开发一种具有新型近场探头的太赫兹成像和光谱系统。探头概念利用了电光检测方法的非侵入性，并利用光学微谐振器来提高检测灵敏度。所提出的电光微谐振器将集成到光纤耦合近场探头中。它将允许以~5微米（~波长的1/100）的空间分辨率探测太赫兹波和信号，并将在太赫兹范围（0.1-2.0太赫兹）提供全光谱功能。该方法的新颖之处在于利用极小的近场探头利用光学腔共振对太赫兹波进行电光探测。本课题的研究目标是开发和构建太赫兹近场探测系统，并将其应用于亚波长尺度的器件研究。提出的技术将把太赫兹研究的范围扩大到微米尺度的物体。它将有助于太赫兹器件研究的进展，并将促进物理学、材料科学和其他学科对太赫兹现象的研究。

Terahertz (THz) device research and studies of THz phenomena in solid state systems require detection of THz waves and signals on the scale of few microns. These measurements present a major technological problem caused by diffraction of THz waves. The diffraction limit prevents the use of the recently developed THz spectroscopic instrumentation for studies of objects smaller than approximately a wavelength. Near-field surface probing methods have shown potential solutions in overcoming the diffraction limit. However all the existing THz near-field techniques exhibit another fundamental limitation due to significant perturbations in the electric field caused by the near-field probe. The probe invasiveness and a non-uniform frequency response across the THz spectrum prevent the use of the existing near-field probes for mapping of electric field distribution in THz devices. In addition, THz near-field imaging systems with spatial resolution better than ~1/20 of a wavelength suffer from a severe reduction in sensitivity.To mitigate these problems and to allow high spatial resolution studies with THz waves we propose to develop a THz imaging and spectroscopy system with a novel near-field probe. The probe concept exploits the non-invasive nature of the electro-optic detection method and utilizes an optical micro-resonator to enhance the detection sensitivity. The proposed electro-optic micro-resonator will be integrated into a fibre-coupled near-field probe. It will allow THz wave and signal probing with a spatial resolution of ~5 microns (~1/100 of the wavelength) and it will offer full spectroscopic capabilities in the THz range (0.1-2.0 THz). The novelty of this approach is in exploiting the optical cavity resonance for electro-optic detection of THz waves by an extremely small near-field probe. The goal of this research programme is to develop and build the THz near-field probing system and apply it in device research on the sub-wavelength scale. The proposed technology will expand the spectrum of THz studies to micrometre-scale objects. It will aid in the progress of THz device research and will facilitate studies of THz phenomena in physics, materials science and other disciplines.