ABSTRACT
The ability to confine THz photons inside deep-subwavelength cavities promises a transformative impact for THz light engineering with metamaterials and for realizing ultrastrong light-matter coupling at the single emitter level. To that end, the most successful approach taken so far has relied on cavity architectures based on metals, for their ability to constrain the spread of electromagnetic fields and tailor geometrically their resonant behavior. Here, we experimentally demonstrate a comparatively high level of confinement by exploiting a plasmonic mechanism based on localized THz surface plasmon modes in bulk semiconductors. We achieve plasmonic confinement at around 1 THz into record breaking small footprint THz cavities exhibiting mode volumes as low as [Formula: see text], excellent coupling efficiencies and a large frequency tunability with temperature. Notably, we find that plasmonic-based THz cavities can operate until the emergence of electromagnetic nonlocality and Landau damping, which together constitute a fundamental limit to plasmonic confinement. This work discloses nonlocal plasmonic phenomena at unprecedentedly low frequencies and large spatial scales and opens the door to novel types of ultrastrong light-matter interaction experiments thanks to the plasmonic tunability.
ABSTRACT
The problem of protection of the front surface silver mirrors is a very important one for a number of applications. The atomic layer deposition (ALD) technique provides an efficient way to form a coating, protecting the sensitive surface of silver from a corrosive and oxidizing environment. Moreover, the ALD layer provides extremely high conformality (even when deposited over high aspect ratio features) and has high integrity, efficiently blocking foreign species diffusion to the silver-overcoat interface. We tested the efficiency of the protection of silver mirrors against oxygen plasma exposure by the ALD-deposited Al2O3 layers by combining spectroscopic ellipsometry, reflection measurements and pulsed glow-discharge optical emission spectroscopy (GD-OES) profiling. We have found that for optimal protection, the thickness of the ALD deposited layer should exceed at least 15 nm (about 150 ALD cycles at 150°C). We have also demonstrated that the deposition of 15 nm of a protective ALD-deposited Al2O3 layer does not affect the absolute reflectivity of a silver mirror in the spectral range 320 -2500 nm.
