Journal
ACS PHOTONICS
Volume 4, Issue 11, Pages 2676-2680Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acsphotonics.7b00870
Keywords
terahertz emission microscopy; near-field imaging; apertureless NSOM; nonlinear optics
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Funding
- Danish Council for Independent Research (FTP)
- U.S. National Science Foundation (NSF)
- NNSA's Kansas City National Security Campus [DE-NA0002839]
- Directorate For Engineering
- Div Of Electrical, Commun & Cyber Sys [1505536] Funding Source: National Science Foundation
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Laser terahertz emission microscopy (LTEM) has become a powerful tool for studying ultrafast dynamics and local fields in many different types of materials. This technique, which relies on acceleration of charge carriers in a material upon femtosecond excitation, can provide insight into the physics of charge transport, built-in fields, grain boundaries or surface states. We describe a new implementation of LTEM with a spatial resolution in the nanoscale regime based on a scattering-type near-field tip-based approach. We observe a spectral reshaping of the signal compared to conventional LTEM, which is analyzed using a resonant antenna model. Our experimental and computational results clarify the importance of the mechanisms for both the plasmonic in-coupling of the near-infrared pulses into the near field and the out-coupling of the generated terahertz pulses. We demonstrate a tip-size-limited spatial resolution of similar to 20 nm by imaging a gold nanorod using terahertz emission from the underlying substrate. This work enables for the first time the possibility of performing LTEM measurements on individual nanostructures.
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