We present an experimental and theoretical study of the optical transmission of a thin metal screen perforated by two subwavelength slits, separated by many optical wavelengths. The total intensity of the far-field double-slit pattern is shown to be reduced or enhanced as a function of the wavelength of the incident light beam. This modulation is attributed to an interference phenomenon at each of the slits, instead of at the detector. The interference arises as a consequence of the excitation of surface plasmons propagating from one slit to the other. DOI: 10.1103/PhysRevLett.94.053901 PACS numbers: 42.79.Dj, 73.20.Mf, 78.66.Bz Recently, there has been a surge of interest in the phenomenon of light transmission through subwavelength apertures in metal plates. This followed the observation by Ebbesen et al. [1] that the transmission through a twodimensional hole array can be much larger than predicted by conventional diffraction theory [2]. This discovery has rekindled the interest in a similar but simpler problem, viz., the transmission of a one-dimensional array of subwavelength slits in a metal film, i.e., of a metal grating [1,[3][4][5][6][7][8][9][10][11][12][13][14][15][16]. In many cases the enhanced transmission of hole or slit arrays has been explained in terms of the excitation of (coupled) surface plasmons on the metal film [3][4][5][6], an explanation that has recently been challenged [16]. It has been shown that, for slit arrays, Fabry-Pérot-type waveguide resonances can also give rise to a considerably enhanced transmission [5,7,9,10,12].In the present Letter we study an even more fundamental system than the metallic grating, namely, a thin metal layer perforated by just two parallel subwavelength slits. In contrast to the systems that have recently attracted so much attention, our slits are separated by many optical wavelengths. Thus we study the light transmission of a setup that lies at the heart of wave physics, namely, that of Thomas Young. We do, however, not focus on the wellknown interference pattern named after him, but on the angle-integrated power transmission coefficient of the perforated screen, i.e., the transmission integrated over many interference orders. We show that this transmission coefficient is strongly modulated as a function of the wavelength of the incident light for the case that that light is TMpolarized, i.e., with the electric field aligned perpendicular to the slits. In contrast, there is no such modulation when the incident light is TE-polarized, or when the ''wrong'' metal is chosen. All our observations can be explained in terms of a model involving the coherent transport of electromagnetic energy between the slits by surface plasmons.Our samples consist of a 200 nm thick gold film, evaporated on top of a 0.5 mm thick fused quartz substrate with a 10 nm thick titanium adhesion layer between the gold and the glass. In such a sample a two-slit pattern is written using a focussed ion beam, each slit being 50 m long and 0:2 m wide. The slits are separated by a dis...

In this paper the phase singularities of the electromagnetic field near a sub-wavelength slit are studied. These phase singularities, such as optical vortices, are found in regular patterns, which can be created or annihilated under the conservation of certain topological quantities, when a parameter such as the slit width is changed. The connection between the phase singularities and the light transmission though the slit is considered.

The anomalous ͑i.e., more than 100%) light transmission through a subwavelength slit in a thin metal plate is accompanied by a combination of waveguiding and phase singularities of the field of power flow near the slit. The crucial role of these phase singularities ͑such as optical vortices and saddle points͒ in exciting the waveguide modes is systematically studied. We predict transmission efficiencies as high as 300% for certain configurations. DOI: 10.1103/PhysRevE.67.036608 PACS number͑s͒: 42.25.Bs, 42.25.Fx The analysis of light transmission through a slit with a subwavelength width in a thin plate is a subject with a venerable history ͓1-3͔, dating back to Lord Rayleigh. Because of its importance for near-field optics and semiconductor technology, it continues to attract attention. Recently Ebbesen et al. observed extraordinary light transmission ͑i.e., more than 100%) through an array of subwavelength holes ͓4,5͔, which led to a new wave of interest in the subject. Broadly speaking there are two mechanisms involved in extraordinary light transmission: the coupling of light with surface plasmons ͓4 -8͔, and Fabry-Pérot-like resonances inside the apertures ͓9-11͔.In this paper we study the light transmission for a different configuration, namely, a single subwavelength slit in a metal plate of finite conductivity for the TE-polarization case ͑i.e., with the electric field parallel to the slit͒. TE polarization differs from TM polarization in that no surface plasmons are excited ͓12͔. Furthermore, for TE polarization the first waveguide mode in a perfect conductor has a cutoff width of w cut-off ϭ/2, with being the wavelength. However, due to their finite conductivity, efficient energy transport may be possible at smaller slit widths in realistic metal plates. A rigorous computation of the field demonstrates that near these cutoff widths, there is an enhanced transmission through the slit. Transmission efficiencies as high as 300% are found for special configurations. We emphasize that these remarkable enhancement effects occur even though there is no coupling to surface plasmons.To elucidate why the field couples so effectively with the propagating waveguide modes, we have analyzed the field of power flow ͑i.e., the time-averaged Poynting vector͒ near the slit. It is found that this field exhibits optical vortices and other kinds of phase singularities ͓13-15͔, which are arranged in an arraylike pattern. We find that the location and annihilation or creation of these phase singularities are intimately connected with the phenomenon of enhanced transmission.The field around a single, infinitely long, slit in a metal plate was calculated using a rigorous scattering approach ͓16͔. The total electric field E is written as the sum of two parts, namely the incident field E (inc) and the scattered field E (sca) . The incident field is the field that would occur in the absence of the slit in the plate. The illuminating field is taken to be monochromatic and propagating perpendicular to the plate. We have suppre...

We analyze the coherence properties of a partially coherent field emerging from two pinholes in an opaque screen and show that the spectral degree of coherence possesses phase singularities on certain surfaces in the region of superposition. To our knowledge, this is the first illustration of the singular behavior of the spectral degree of coherence, and the results extend the field of singular optics to the study of phase singularities of correlation functions.

We analyze the coherence properties of a partially coherent field emerging from two pinholes in an opaque screen and show that the spectral degree of coherence possesses phase singularities on certain surfaces in the region of superposition. To our knowledge, this is the first illustration of the singular behavior of the spectral degree of coherence, and the results extend the field of singular optics to the study of phase singularities of correlation functions.