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We focus on the normalized Stokes parameter s 3 of the specularly reflected light from a metal grating in a conical mounting in order to accurately and sensitively detect the occurrence of surface plasmon resonance (SPR). Experimental and theoretical investigations into the incident angle dependence of s 3 reveal a rapid change in s 3 around the resonance angle θ s p at which SPR occurs. The rapid change in s 3 has features that are successfully applied to SPR sensing: the zero-crossing point of s 3 determines θ s p , and s 3 in the vicinity of θ s p varies markedly in response to a small change in the refractive index of a sample. An experiment using gas samples demonstrates that SPR sensing that considers the rapid change in s 3 clearly detects a refractive index change on the order of 10 − 5 .

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We propose a system of highly efficient photoemitters comprising metal-molecule multilayered structures. In the proposed structure, the absorption in the molecular layer is greatly enhanced through quantum interference between the split modes arising from the coupling of the layered excitons and the plasmons sustained by the metal layer. Furthermore, the large interaction volume between surface plasmons and excitons causes exciton superradiance, which results in the extremely efficient photoemission. This finding indicates the possibility of designing highly efficient photoemitters based on simple layered structures.For the realization of high-efficiency solar cells, photo-emitting devices, and so forth, smart designs of the light-matter coupling are necessary 1-7 . In particular, the scheme of high-efficiency photon harvesting is crucial for the development of energy-saving technologies. For example, a high concentration of harvested light energy in the photoactive parts of devices is important for realizing efficient photonic functions. One approach to achieving the high concentration of harvested light energy is to utilize nanometallic structures sustaining surface plasmon (SP) resonance [8][9][10][11][12][13] . It has been proposed that the quantum interference between the split coupled modes comprising SPs and molecular excitons leads to strong energy concentration in molecules [11][12][13] , which has been discussed as a type of Fano resonance (FR) appearing through the interference between the sharp discrete resonance and much broader resonance 14 . However, such effects usually require highly sophisticated designs and the fabrication of nanometallic structures to ensure strict control of the system parameters. Thus, it is desirable to realize systems for efficient photon-harvesting with simpler designs such as those with layered structures. In studies on the control of the light-matter interaction, it was reported that metal-molecular composite layered structures easily induce large Rabi splitting (RS) due to the strong interaction between excitons and SPs 15-18 . Also, Hayashi et al. proposed highly sensitive sensors based on the interference between the SP mode and waveguide mode in multilayered structures 19 . However, such structures have received little interest for application to photon-harvesting through the mode interference effect (Fano resonance).On the other hand, to realize highly efficient photoemitters, not only an efficient photon-harvesting scheme but also an efficient photoemission scheme must be realized. It is known that highly efficient photoemission occurs through exciton superradiance. As the interaction volume (or coherence volume) between a) Electronic mail: matsuda@pe.osakafu-u.ac.jp excitons and the radiation field increases, the radiative decay rate increases (so-called exciton superradiance) 20-25 . For example, for very high quality CuCl thin films, the radiative decay time was observed to reach 100 fs order 26 , where excitons with a very high coherence volume over the entire...

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