A novel broadband probe for near-field imaging and spectroscopy from DC to THz

We have developed a broadband imaging technique for microwave-to-terahertz electromagnetic waves based on a metal-dielectric near-field antenna. In contrast to other near field approaches, a large portion of electromagnetic field energy is focused on a micron-sized spot. This technique allows for an almost frequency independent spatial resolution and a high sensitivity with respect to weak contrasts. Experimentally, a spatial resolution of about 20 μm was demonstrated for the frequency range between 80 GHz and 2 THz employing both continuous wave millimetre wave and picosecond time domain reflection experiments. Due to the broad band features of our near-field antenna, our approach has a strong potential to perform spatially resolved broad-band terahertz spectroscopy.