Terahertz imaging for noninvasive measurements.

Surface plasmons limit the efficiency of organic light‐emitting diodes (OLEDs). Up to 40 % of the radiative power may be lost to surface plasmon (SP) modes associated with the metallic cathodes of OLEDs. Calculations show the importance of material selection and device geometry in this process. Experiments reveal the presence of the SP modes and suggest ways in which this power may be recovered using periodic nanostructure.

We report the experimental observation of strong exciton-photon coupling in a planar microcavity composed of an organic semiconductor positioned between two metallic ͑silver͒ mirrors. Via transmission and reflectivity measurements, we observe a very large, room temperature Rabi splitting in excess of 300 meV. We show that the Rabi-splitting is enhanced in all-metal microcavities by a factor of more than 2 compared to an organic film positioned between a silver mirror and a dielectric mirror. This enhancement results from the significantly larger optical fields that are confined within all-metal microcavities. © 2002 American Institute of Physics. ͓DOI: 10.1063/1.1517714͔Placing emitters of light such as excitons within microcavities is attractive for device applications and allows the study of new optical phenomena. The effect of the microcavity on the emission of light can be divided into two regimes. In the weak-coupling regime, the spatial and temporal distribution of the emitted radiation can be altered. This regime is employed in applications such as vertical cavity surface emitting lasers and resonant cavity light emitting diodes. 1,2In the strong-coupling regime, a mixing between optical and electronic ͑excitonic͒ states within the cavity occurs, leading to the appearance of new states termed cavity-polaritons. 3This effect is an intensive area of research due in part to the interest in coherent, stimulated effects in such systems that may lead to new optical devices. 4 The field has recently expanded to include Frenkel excitons supported by organic materials. [5][6][7] This has been important in that it has led to the observation of significantly larger, room temperature, strongcoupling effects, and opens the possibility of easily fabricated nonlinear optical devices.A key phenomenon associated with strong-coupling 8 is the anticrossing of the exciton and photon mode where, in the absence of a strong interaction, they would have crossed. Until now, investigations into strong-coupling in organic and inorganic materials have been conducted either using two Bragg reflectors ͑DBR͒ as microcavity mirrors or one Bragg reflector together with one optically thick metal mirror. In this letter we show that microcavities fabricated using just two metal mirrors can operate in the strong-coupling regime. All-metal cavities are characterized by relatively low Q-factors; 9 however we find that strong-coupling can still be achieved because the effective optical path length in an allmetal cavity is significantly shorter than that in microcavities based on one or more dielectric mirrors, providing a significant enhancement of the optical field within the organic semiconductor region of the cavity. Because of this enhancement we observe very large Rabi-splittings of over 300 meV.J-aggregates of organic dye molecules possess many features that make them particularly suitable to undergo strongcoupling in microcavities. 6 The narrow, inhomogeneous linewidths ͑40-50 meV͒ and very large oscillator strengths of molecular J-aggre...

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