We demonstrate broadband non-resonant squeezing of terahertz (THz) waves through an isolated 2-nm-wide, 2-cm-long slit (aspect ratio of 107), representing a maximum intensity enhancement factor of one million. Unlike resonant nanogap structures, a single, effectively infinitely-long slit passes incident electromagnetic waves with no cutoff, enhances the electric field within the gap with a broad 1/f spectral response, and eliminates interference effects due to finite sample boundaries and adjacent elements. To construct such a uniform, isolated slit that is much longer than the millimeter-scale spot of a THz beam, we use atomic layer lithography to pattern vertical nanogaps in a metal film over an entire 4-inch wafer. We observe an increasing field enhancement as the slit width decreases from 20 nm to 2 nm, in agreement with numerical calculations.
Bibliographical noteFunding Information:
This work was supported by the U.S. Department of Defense (DARPA Young Faculty Award N66001-11-1-4152; X.S.C., H.R.P., J.S., S.-H.O.). Device fabrication was performed at the University of Minnesota, Nanofabrication Center, which receives support from the National Science Foundation (NSF) through the National Nanotechnology Infrastructure Network program, and the Characterization Facility, which has received capital equipment funding from NSF through the Materials Research Science and Engineering Center. S.-H.O. also acknowledges support from the Office of Naval Research Young Investigator Award. X.S.C. acknowledges support from the 3M Science and Technology Fellowship and the University of Minnesota Doctoral Dissertation Fellowship.