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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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Summary of the reflectivity measurements.(a) Contrast of the reflectivity resonances C as a function of the filling factor f for the gratings from data Figs. 2(b) and 2(c). (b) The respective quality factors Q (dotted curves), compared to the model (continuous curves). The shaded areas correspond to the standard mean deviations of the model, computed from the error bars of the contrast C and Eq.(2).
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f3: Summary of the reflectivity measurements.(a) Contrast of the reflectivity resonances C as a function of the filling factor f for the gratings from data Figs. 2(b) and 2(c). (b) The respective quality factors Q (dotted curves), compared to the model (continuous curves). The shaded areas correspond to the standard mean deviations of the model, computed from the error bars of the contrast C and Eq.(2).

Mentions: The experimental quantities that describe the ability of the structure to interact with the incoming radiation are the quality factor of the resonances Q and their reflectivity contrast C, defined as C = 1−Rmin, where Rmin is the reflectivity minimum at the resonant frequency. Both these values can be extracted from the data through Lorentzian fits (continuous lines in Fig. 2(b) and (c)) of the form: (In this work, the quality factors are defined as Q = ω0/Δν = 2πν0/Δν, where Δν is the FWHM of the reflectivity dip. Note that there is an additional 2π factor with respect to the definition used in Ref.19.) The contrast C is determined by the balance between the reflected photons and those absorbed by the array of resonators. The quality factor Q incorporates the radiation losses, 1/Qrad, and the ohmic losses of the metal layers, 1/Qohm, through 1/Q = 1/Qrad + 1/Qohm. The error bars indicated in Fig. 3 are estimated from the repeat measurements reported in Figs. 2(b),(c), which provide a standard mean deviation of 0.06 for the contrast C and 10% of uncertainties for the quality factors Q.


Strong near field enhancement in THz nano-antenna arrays.

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

Summary of the reflectivity measurements.(a) Contrast of the reflectivity resonances C as a function of the filling factor f for the gratings from data Figs. 2(b) and 2(c). (b) The respective quality factors Q (dotted curves), compared to the model (continuous curves). The shaded areas correspond to the standard mean deviations of the model, computed from the error bars of the contrast C and Eq.(2).
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f3: Summary of the reflectivity measurements.(a) Contrast of the reflectivity resonances C as a function of the filling factor f for the gratings from data Figs. 2(b) and 2(c). (b) The respective quality factors Q (dotted curves), compared to the model (continuous curves). The shaded areas correspond to the standard mean deviations of the model, computed from the error bars of the contrast C and Eq.(2).
Mentions: The experimental quantities that describe the ability of the structure to interact with the incoming radiation are the quality factor of the resonances Q and their reflectivity contrast C, defined as C = 1−Rmin, where Rmin is the reflectivity minimum at the resonant frequency. Both these values can be extracted from the data through Lorentzian fits (continuous lines in Fig. 2(b) and (c)) of the form: (In this work, the quality factors are defined as Q = ω0/Δν = 2πν0/Δν, where Δν is the FWHM of the reflectivity dip. Note that there is an additional 2π factor with respect to the definition used in Ref.19.) The contrast C is determined by the balance between the reflected photons and those absorbed by the array of resonators. The quality factor Q incorporates the radiation losses, 1/Qrad, and the ohmic losses of the metal layers, 1/Qohm, through 1/Q = 1/Qrad + 1/Qohm. The error bars indicated in Fig. 3 are estimated from the repeat measurements reported in Figs. 2(b),(c), which provide a standard mean deviation of 0.06 for the contrast C and 10% of uncertainties for the quality factors Q.

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