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Strong near field enhancement in THz nano-antenna arrays.

Feuillet-Palma C, Todorov Y, Vasanelli A, Sirtori C - Sci Rep (2013)

Bottom Line: In the microwave domain, for many years this task has been successfully performed by antennas, built from metals that can be considered almost perfect at these frequencies.In this work we experimentally study the light coupling properties of dense arrays of subwavelength THz antenna microcavities.This effect is quantitatively described by an analytical model that can be applied for the optimization of any nanoantenna array.

View Article: PubMed Central - PubMed

Affiliation: Laboratoire "Matériaux et Phénomènes Quantiques", Sorbonne Paris Cité, Université Paris Diderot, CNRS-UMR 7162, FR-75013 Paris, France.

ABSTRACT
A key issue in modern photonics is the ability to concentrate light into very small volumes, thus enhancing its interaction with quantum objects of sizes much smaller than the wavelength. In the microwave domain, for many years this task has been successfully performed by antennas, built from metals that can be considered almost perfect at these frequencies. Antenna-like concepts have been recently extended into the THz and up to the visible, however metal losses increase and limit their performances. In this work we experimentally study the light coupling properties of dense arrays of subwavelength THz antenna microcavities. We demonstrate that the combination of array layout with subwavelength electromagnetic confinement allows for 10(4)-fold enhancement of the electromagnetic energy density inside the cavities, despite the low quality factor of a single element. This effect is quantitatively described by an analytical model that can be applied for the optimization of any nanoantenna array.

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Experimental characterization of the arrays.(a) Experimental configuration for reflectivity measurements performed at 10° incidence on arrays, with variable thickness L and lateral spacing dy. The electric field E of the incident wave has also been indicated. (b,c) Reflectivity spectra obtained with thickness L = 1 μm (b) and L = 300 nm (c). The corresponding spacings dy are indicated on the right. The experimental data is indicated by dotted curves, and the continuous lines are Lorentzian fits. The crossed curves indicate measurements from a repeat sample with the same parameters as the one indicated. The curves are shifted with a constant offset for clarity.
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f2: Experimental characterization of the arrays.(a) Experimental configuration for reflectivity measurements performed at 10° incidence on arrays, with variable thickness L and lateral spacing dy. The electric field E of the incident wave has also been indicated. (b,c) Reflectivity spectra obtained with thickness L = 1 μm (b) and L = 300 nm (c). The corresponding spacings dy are indicated on the right. The experimental data is indicated by dotted curves, and the continuous lines are Lorentzian fits. The crossed curves indicate measurements from a repeat sample with the same parameters as the one indicated. The curves are shifted with a constant offset for clarity.

Mentions: The structure studied in this work is depicted in Figure 1. Fig. 1(a) is a schematics of a single wire microcavity, Fig. 1(b) is a top view of a portion of the array, obtained by scanning electron microscope (SEM), and Fig. 1(c) is high resolution SEM scan along the red rectangle in Fig. 1(b). This structure is obtained by Au-Au bonding of a thin Gallium Arsenide (GaAs) layer on a host substrate. The gold bonding layer then plays the role of the metallic ground of the microcavity. An array of thin Au stripes is then deposited on the top of the GaAs layer. The microcavity operates on the fundamental TM100 mode, with a resonant wavelength λres = 2neffs, with s the length of the stripe, and neff ~ 4 the effective index17. For all structures reported here s = 12 μm, therefore the resonant frequencies span between 3 THz and 4 THz (Fig. 2), which corresponds to a wavelength range λ = 75 μm–100 μm. Both the width w of the stripe and the thickness L of the GaAs layer have very subwavelength dimensions. Two different thicknesses have been used in our experiments, L = 1 μm and L = 300 nm, and for all structures we have w = 1 μm.


Strong near field enhancement in THz nano-antenna arrays.

Feuillet-Palma C, Todorov Y, Vasanelli A, Sirtori C - Sci Rep (2013)

Experimental characterization of the arrays.(a) Experimental configuration for reflectivity measurements performed at 10° incidence on arrays, with variable thickness L and lateral spacing dy. The electric field E of the incident wave has also been indicated. (b,c) Reflectivity spectra obtained with thickness L = 1 μm (b) and L = 300 nm (c). The corresponding spacings dy are indicated on the right. The experimental data is indicated by dotted curves, and the continuous lines are Lorentzian fits. The crossed curves indicate measurements from a repeat sample with the same parameters as the one indicated. The curves are shifted with a constant offset for clarity.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3584925&req=5

f2: Experimental characterization of the arrays.(a) Experimental configuration for reflectivity measurements performed at 10° incidence on arrays, with variable thickness L and lateral spacing dy. The electric field E of the incident wave has also been indicated. (b,c) Reflectivity spectra obtained with thickness L = 1 μm (b) and L = 300 nm (c). The corresponding spacings dy are indicated on the right. The experimental data is indicated by dotted curves, and the continuous lines are Lorentzian fits. The crossed curves indicate measurements from a repeat sample with the same parameters as the one indicated. The curves are shifted with a constant offset for clarity.
Mentions: The structure studied in this work is depicted in Figure 1. Fig. 1(a) is a schematics of a single wire microcavity, Fig. 1(b) is a top view of a portion of the array, obtained by scanning electron microscope (SEM), and Fig. 1(c) is high resolution SEM scan along the red rectangle in Fig. 1(b). This structure is obtained by Au-Au bonding of a thin Gallium Arsenide (GaAs) layer on a host substrate. The gold bonding layer then plays the role of the metallic ground of the microcavity. An array of thin Au stripes is then deposited on the top of the GaAs layer. The microcavity operates on the fundamental TM100 mode, with a resonant wavelength λres = 2neffs, with s the length of the stripe, and neff ~ 4 the effective index17. For all structures reported here s = 12 μm, therefore the resonant frequencies span between 3 THz and 4 THz (Fig. 2), which corresponds to a wavelength range λ = 75 μm–100 μm. Both the width w of the stripe and the thickness L of the GaAs layer have very subwavelength dimensions. Two different thicknesses have been used in our experiments, L = 1 μm and L = 300 nm, and for all structures we have w = 1 μm.

Bottom Line: In the microwave domain, for many years this task has been successfully performed by antennas, built from metals that can be considered almost perfect at these frequencies.In this work we experimentally study the light coupling properties of dense arrays of subwavelength THz antenna microcavities.This effect is quantitatively described by an analytical model that can be applied for the optimization of any nanoantenna array.

View Article: PubMed Central - PubMed

Affiliation: Laboratoire "Matériaux et Phénomènes Quantiques", Sorbonne Paris Cité, Université Paris Diderot, CNRS-UMR 7162, FR-75013 Paris, France.

ABSTRACT
A key issue in modern photonics is the ability to concentrate light into very small volumes, thus enhancing its interaction with quantum objects of sizes much smaller than the wavelength. In the microwave domain, for many years this task has been successfully performed by antennas, built from metals that can be considered almost perfect at these frequencies. Antenna-like concepts have been recently extended into the THz and up to the visible, however metal losses increase and limit their performances. In this work we experimentally study the light coupling properties of dense arrays of subwavelength THz antenna microcavities. We demonstrate that the combination of array layout with subwavelength electromagnetic confinement allows for 10(4)-fold enhancement of the electromagnetic energy density inside the cavities, despite the low quality factor of a single element. This effect is quantitatively described by an analytical model that can be applied for the optimization of any nanoantenna array.

Show MeSH
Related in: MedlinePlus