Abstract

We have measured the enhanced transmission properties of periodic arrays of subwavelength apertures fabricated in thin metal films as a function of the metal film thickness. In doing so, we determine the minimum metal film thickness for an array that exhibits resonantly enhanced transmission and observe the transmission properties as the metal film thickness is increased. The thickness range explored extends from δ/15, where δ is the skin depth, to approximately 2δ. Using terahertz time-domain spectroscopy, we measure both the amplitude and phase of the transmitted broadband THz pulses. Experimentally, we find that there is negligible transmission enhancement for metal films as thin as δ/15. As the film thickness increases, there is a sublinear increase in the enhancement until the film thickness is equal to the skin depth. For metal films thicker than one skin depth, there appears to be little additional enhancement at the resonant frequencies. We also observe that as the thickness of metal films increases, there is a corresponding increase in the resonance frequencies.

© 2005 Optical Society of America

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References

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    [CrossRef]
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    [CrossRef] [PubMed]
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    [CrossRef] [PubMed]
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    [CrossRef] [PubMed]
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    [CrossRef]
  11. A. Degiron and T. W. Ebbesen, "Analysis of the transmission process through single apertures surrounded by periodic corrugations," Opt. Express 12, 3694-3700 (2004), <a href="http://www.opticsexpress.org/abstract.cfm?URI=OPEX-12-16-3694">http://www.opticsexpress.org/abstract.cfm?URI=OPEX-12-16-3694</a>.
    [CrossRef] [PubMed]
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    [CrossRef] [PubMed]
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    [CrossRef] [PubMed]
  14. D. Grischkowsky, in Frontiers in Nonlinear Optics, edited by H. Walther, N. Koroteev, and M.O. Scully (Institute of Physics Publishing, Philadelphia, 1992) and references therein.
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    [CrossRef] [PubMed]
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    [CrossRef] [PubMed]

Appl. Opt.

Appl. Phys. Lett.

D.E. Grupp, H.J. Lezec, T.W. Ebbesen, K.M. Pellerin, and T. Thio, “Crucial role of metal surface in enhanced transmission through subwavelength apertures,” Appl. Phys. Lett. 77, 1569-1571 (2000).
[CrossRef]

J. Opt. Soc. Am. B

Nature

T.W. Ebbesen, H.J. Lezec, H.F. Ghaemi, T. Thio, P.A. Wolff, “Extraordinary optical transmission through subwavelength hole arrays,” Nature 391, 667-669 (1998).
[CrossRef]

Opt. Express

H. Cao and A. Nahata, "Resonantly enhanced transmission of terahertz radiation through a periodic array of subwavelength apertures," Opt. Express 12, 1004-1010 (2004), <a href="http://www.opticsexpress.org/abstract.cfm?URI=OPEX-12-6-1004">http://www.opticsexpress.org/abstract.cfm?URI=OPEX-12-6-1004</a>.
[CrossRef] [PubMed]

H. Cao and A. Nahata, "Influence of aperture shape on the transmission properties of a periodic array of subwavelength apertures," Opt. Express 12, 3664-3672 (2004), <a href="http://www.opticsexpress.org/abstract.cfm?URI=OPEX-12-16-3664">http://www.opticsexpress.org/abstract.cfm?URI=OPEX-12-16-3664</a>.
[CrossRef] [PubMed]

A. Degiron and T. W. Ebbesen, "Analysis of the transmission process through single apertures surrounded by periodic corrugations," Opt. Express 12, 3694-3700 (2004), <a href="http://www.opticsexpress.org/abstract.cfm?URI=OPEX-12-16-3694">http://www.opticsexpress.org/abstract.cfm?URI=OPEX-12-16-3694</a>.
[CrossRef] [PubMed]

N. Bonod, S. Enoch, L. Li, P. Evgeny, and M. Neviere, "Resonant optical transmission through thin metallic films with and without holes," Opt. Express 11, 482-490 (2003), <a href="http://www.opticsexpress.org/abstract.cfm?URI=OPEX-11-5-482">http://www.opticsexpress.org/abstract.cfm?URI=OPEX-11-5-482</a>.
[CrossRef] [PubMed]

A. Agrawal, H. Cao, and A. Nahata, "Time-domain analysis of enhanced transmission through a single subwavelength aperture," Opt. Express 13, 3535-3542 (2005), <a href="http://www.opticsexpress.org/abstract.cfm?URI=OPEX-13-9-3535">http://www.opticsexpress.org/abstract.cfm?URI=OPEX-13-9-3535</a>.
[CrossRef] [PubMed]

Opt. Lett.

Phys. Rev. B

H.F. Ghaemi, T. Thio, D.E. Grupp, T.W. Ebbesen, and H.J. Lezec, “Surface plasmons enhance optical transmission through subwavelength holes,” Phys. Rev. B 83, 6779-6782 (1998).
[CrossRef]

Phys. Rev. Lett.

R. Gordon, A.G. Brolo, A. McKinnon, A. Rajora, B. Leatham, and K.L. Kavanagh, “Strong polarization in the optical transmission through elliptical nanohole arrays,” Phys. Rev. Lett. 92, 037401 (2004).
[CrossRef] [PubMed]

K.J.K. Koerkamp, S. Enoch, F.B. Segerink, N.F. van Hulst, and L. Kuipers, “Strong influence of hole shape on extraordinary transmission through periodic arrays of subwavelength holes,” Phys. Rev. Lett. 92, 183901/1-4 (2004).
[CrossRef] [PubMed]

D. Qu, D. Grischkowsky, “Observation of a new type of THz resonance of surface plasmons propagating on metal-film hole arrays,” Phys. Rev. Lett. 93, 196804/1-4 (2004).
[CrossRef] [PubMed]

Other

D. Grischkowsky, in Frontiers in Nonlinear Optics, edited by H. Walther, N. Koroteev, and M.O. Scully (Institute of Physics Publishing, Philadelphia, 1992) and references therein.

H. Raether, Surface Plasmons on Smooth and Rough Surfaces and on Gratings, (Vol. 111 of Springer Tracts in Modern Physics, Springer-Verlag, Berlin, 1988).

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Figures (3)

Fig. 1.
Fig. 1.

Experimentally observed time-domain waveforms for an array fabricated in a 350 nm thick aluminum film vacuum deposited onto a high resistivity silicon wafer (red) and the reference waveform measured for a blank high resistivity silicon wafer (black). The time-domain waveforms for the other aperture arrays fabricated in thinner metal films look similar, although the amplitudes of the damped oscillations are progressively reduced with decreasing metal film thickness.

Fig. 2.
Fig. 2.

Amplitude and phase spectra for six different periodic aperture arrays fabricated in thin aluminum films deposited on high resistivity silicon wafers. The array consisted of 400 μm diameter circular apertures periodically spaced by 1 mm. The spectra correspond to a metal film thickness of 10 nm (dashed red traces), 25 nm (dashed black traces), 50 nm (green traces), 100 nm (blue traces), 150 nm nm (solid red traces), and 350 nm (solid black traces), respectively. (a) Amplitude spectra for the six aperture arrays. With increasing thickness, each spectrum has been successively incremented by 0.1 for clarity. (b) Phase spectra for the six aperture arrays. With increasing thickness, each spectrum has been successively incremented by 0.5 for clarity. The vertical dashed lines are located at the frequencies corresponding to transmission maxima for the array fabricated in the 350 nm thick metal film and clearly demonstrate a frequency shift in the resonance frequency with metal film thickness.

Fig. 3.
Fig. 3.

Quantitative determination of transmission enhancement based on the magnitude of the dip in the phase spectrum for the lowest order resonance (~0.29 THz). For each phase spectrum in Fig. 2(b), we perform a linear fit. At the location of the phase minimum for the lowest order resonance, we measure the difference between the numerical value of the linear fit at that frequency the resonance minimum the corresponding value at the resonance minimum.

Equations (3)

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ε m = ε ω p 2 ω 2 + iωω τ ,
t ( ν ) = E array ( ν ) ( 1 f AFF ) E metal ( ν ) E reference ( ν ) = t ( ν ) exp [ ( ν ) ] .
λ peak = P i 2 + j 2 n sp P i 2 + j 2 ε d ,

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