In 2024, Chengdu Miji Technology Co., Ltd. successfully delivered a terahertz near-field optical microscopy system to Henan University of Technology. The system performs reflection-mode terahertz near-field imaging. Its main body consists of a solid-state source (97.8 GHz, 80 mW), a detector and a dedicated near-field atomic force main unit.
Figure 1. Near-field imaging schematic
Figure 2. THz s-SNOM system
System Functions:
The system is a scattering-type terahertz near-field scanning imaging system, comprising a scattering near-field optimized AFM, a sample scanner with XY-axis closed-loop and Z-axis open-loop scanners, and an integrated parabolic mirror with a three-dimensional motorized translation stage for focusing external light sources onto the AFM tip. The system effectively extracts near-field signals and suppresses background noise: it supports simultaneous per-pixel signal demodulation at the 1st to 3rd harmonics of the tip frequency for two independent signals (mechanical/AFM and s-SNOM signals).
Terahertz Near-Field Imaging:
Terahertz near-field microscopy is a high-resolution imaging technique using terahertz waves (frequency range approximately 0.1–10 THz, wavelength 30 µm to 3 mm). Conventional terahertz imaging is limited by the optical diffraction limit, with resolution typically comparable to the wavelength. However, by exploiting the tip-enhancement effect, THz s-SNOM can break through this limit, confining terahertz waves into nanoscale volumes to achieve nanoscale super-resolution imaging while preserving the unique spectral characteristics of the terahertz band. Through surface plasmons, tip field enhancement and resonant structures, weak terahertz signals can be effectively enhanced. This technology has important application prospects in materials science, biomedicine, physical chemistry, semiconductor inspection and other fields.
The terahertz scattering-type near-field imaging system launched by Miji Technology adopts a high signal-to-noise-ratio terahertz system, enabling near-field imaging up to the 3rd order while simultaneously acquiring AFM topography data of the sample surface. Actual measurements show that the system achieves nanoscale resolution while maintaining excellent signal-to-noise ratios of 200 at the 1st order and 80 at the 2nd order.
Figure 3. Resolution and signal-to-noise ratio from actual system measurements
Figure 4. System user interface
While pursuing near-field imaging quality, the system also offers maximum user-friendliness in its software: a workflow-based system operation interface with a clean layout, allowing researchers or staff who are not yet familiar with near-field imaging to get started quickly.
The atomic force microscope (AFM) in the near-field system adopts an open structure, purpose-designed for near-field optical applications. Unlike most conventional AFMs on the market, an AFM for near-field optics must maintain spatial openness while offering multi-channel demodulation output. The open-structure design ensures that external light sources (such as visible light, infrared light and terahertz waves) can be precisely focused onto the tip position. Mainstream near-field AFM equipment on the market is dominated by German brands (such as the Nearspec series and Bruker IR series); while offering excellent performance, they are expensive and difficult to integrate efficiently with customers' own terahertz equipment. To address this, our near-field AFM, while maintaining an open structure, offers specially shaped off-axis focusing mirrors of various types and focal lengths, enabling broader compatibility with different types of terahertz sources and significantly improving the equipment's compatibility and practicality.
System specifications:
| Terahertz source frequency | 97.8 GHz |
| AFM near-field single scan range | 80 µm × 80 µm × 5 µm (XYZ) |
| AFM scanning accuracy | 0.2 nm × 0.2 nm × 0.6 nm (XYZ) |
| Optical CCD camera | 5 megapixels |
| Detector frequency band | 73.8 GHz–110 GHz |
| Near-field imaging resolution | 80 nm |
| Near-field resolution signal-to-noise ratio | 1st order: 200; 2nd order: 80 |
| Observable near-field demodulation orders | 4 |
| Maximum sample size accommodated by the sample stage | 40 mm × 50 mm × 15 mm |