ABSTRACT
The maximum value of the electromagnetic field of an SP just lies at the metal-dielectric interface. In both the metal and the dielectric, the modal field decays exponentially. The penetration
depth ∧z, which represents the field decay from the metal-dielectric interface [1], is given by /ˆ 1 2dm 2+= 2z e el ¢ e¢ (4.5) /ˆ 1 2dd 2d+= 2z e¢ el e (4.6) 4.1.2 Enhanced TransmissionAccording to classical aperture theory, the transmission through a subwavelength pinhole in metal is very low [3, 4]. Therefore, it appears that there is no need to investigate the transmission through a single pinhole in metal. However, it was found in 1998 that the transmission through an array of subwavelength pinholes in metal is much higher than that predicted by the classical aperture theory [5]. This surprising finding has attracted a lot of research interest [6-29].In the same year of 1998, it was numerically shown by Schröter and Heitmann [8] that the enhanced transmission also exists for a one-dimensional subwavelength slit array in metal for the case of transverse magnetic field. One year later, Porto et al. [9] further numerically investigated the enhanced transmission of the 1D structure in detail. It was shown that the transmittance can be more than 80% in the near infrared region. At that time, people generally thought that the SPs play a crucial positive role in the enhanced transmission for both the 2D and 1D structures. Only Treacy did not agree this explanation [6]. He though that the enhanced transmission results not from SP but from dynamic diffraction.
