Abstract
This article reviews recent advances in terahertz science and technology that rely on confining the energy of incident terahertz radiation to small, very sub-wavelength sized regions. We focus on two broad areas of application for such field confinement: metamaterial-based nonlinear terahertz devices and terahertz near-field microscopy and spectroscopy techniques. In particular, we focus on field confinement in: terahertz nonlinear absorbers, metamaterial enhanced nonlinear terahertz spectroscopy, and in sub-wavelength terahertz imaging systems.
Highlights
The terahertz (THz) frequency potion of the electromagnetic spectrum consists of light frequencies between 100 GHz and 10 THz, and uniquely bridges the worlds of ultrahigh frequency (UHF)electronics and photonics
Intense THz pulses directed onto a sharp metal tip have shown the ability to induce field emission of electrons [11] or even tunnel electrons across an scanning tunneling microscopy (STM) junction [12], adding time-resolution to STM techniques where spatial resolutions of down to the sub-nm scale can be achieved in ultra-high vacuum conditions [13,14]
We review recent advances in the methods of THz field confinement (FC), focusing on these two broad areas of application: nonlinear THz devices based on MMs and THz near-field imaging techniques
Summary
The terahertz (THz) frequency potion of the electromagnetic spectrum consists of light frequencies between 100 GHz and 10 THz, and uniquely bridges the worlds of ultrahigh frequency (UHF). THz devices based on MMs or other plasmonic structures implement the nonlinear response by using subwavelength resonator inclusions to confine incident fields, coupling to and amplifying an underlying nonlinearity in either a substrate or material inclusion Such enhanced THz nonlinearities have applications not just in nonlinear optics [9], but in enhanced sensing and nonlinear pump-probe spectroscopy as well [10]. Intense THz pulses directed onto a sharp metal tip have shown the ability to induce field emission of electrons [11] or even tunnel electrons across an STM junction [12], adding time-resolution to STM techniques where spatial resolutions of down to the sub-nm scale can be achieved in ultra-high vacuum conditions [13,14] Staying below this extreme tunneling regime with less intense THz pulses, the field confinement of THz light at the apex of a tip has been used to image samples with a spatial resolution much better than the diffraction-limit of a THz beam.
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