Terahertz evanescent field microscopy of dielectric materials using on-chip waveguides

• Published in: Applied physics letters 2008-01, Vol.92 (3)
• Main Authors: Cunningham, J., Byrne, M., Upadhya, P., Lachab, M., Linfield, E. H., Davies, A. G.
• Format: Article
• Language: English
• ISSN: 0003-6951; 1077-3118
• DOI: 10.1063/1.2835705

We demonstrate an evanescent field modality for terahertz frequency time-domain measurements, based on the interaction between a sample and the evanescent field extending above lithographically defined terahertz waveguides. We quantify this interaction using freely positionable dielectric samples (GaAs) moved in close proximity to the waveguide (a terahertz microstrip line), finding a reduction in the microstrip-propagating pulse amplitude and an increase in its time delay when the dielectric is brought into the microstrip evanescent field. We also show that the frequency response of resonant passive circuit elements (stub band-stop filters), integrated into the microstrip line, can be used to determine the terahertz frequency properties of scanned samples, opening the way for a terahertz subwavelength imaging modality, the resolution of which is limited by lithographic constraints, rather than by free-space diffraction.