This antenna-based approach to near-field imaging and spectroscopy can be used for both continuous-wave and pulsed broadband electromagnetic radiation from microwave to terahertz frequencies. The model was constructed and simulated using CST MICROWAVE STUDIO® (CST MWS).
Figure 1: Picture of the near-field antenna
The near-field antenna consists of a rectangular-shaped block of low-loss dielectric material sharpened to a pyramidal tip which is partially metallized and terminated by a micron-sized plane facet.
Figure 2: Field distribution in near-field antenna
At this facet the entire energy of the incident wave is concentrated as a very high but strongly localized electric field, which can be used as a sensitive near-field microprobe for electromagnetic radiation. This is proven by the CST MWS simulation results shown in picture above .
Figure 3: Experimental Setup
Currently, experiments in reflection geometry with pulsed terahertz radiation and continuous-wave radiation near 80 GHz reveal a frequency-independent spatial resolution of about 20 µm corresponding to /200 at 80 GHz, which is only limited by the size of the facet terminating the tip.
Figure 4: 2D Scan of Water distribution in plant leafs at 80 GHz
Potential applications of this device are:
* Subcell resolution tissue imaging
* THz spectroscopy on single cells
* THz spectroscopy on single molecules
* Contact - free spectroscopic imaging of ferroelectric domains
* Fingerprint detection of very small amounts of hazardous substances
* Spatially resolved pump-probe experiments
* Detection of water inclusion in minerals
All results are published with the permission of the FZ Jülich, ISG, and have been published in Journal of Applied Physics 98 (2005), 14910.
No comments:
Post a Comment