Predicting the Linear Optical Response of J-Aggregate Microcavity Exciton-Polariton Devices M. Scott Bradley, Jonathan R. Tischler, Yasuhiro Shirasaki, Gleb Akselrod, Vladimir Bulović Laboratory of Organic Optics and Electronics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA USA 02139 We use the transfer matrix numerical formalism to accurately predict the linear optical properties of strongly-coupled microcavity exciton-polariton devices containing thin films of J-aggregated cyanine dyes. Thin films of cyanine dye J-aggregates enable the observation of strong coupling between light and matter at room temperature due to their high absorption constant and narrow linewidth, which allowed for the first demonstration of exciton-polariton electroluminescence at room temperature [1-4]. Our model uses the spectrally-resolved complex index of refraction of the TDBC (5,6-dichloro-2-[3-[5,6-dichloro-1-ethyl-3-(3- sulfopropyl)-2(3H)-benzimidazolidene]-1-propenyl]-1-ethyl-3-(3-sulfopropyl) benzimidazolium hydroxide, inner salt, sodium salt) J-aggregate films [5]. The index of refraction is calculated by model-free quasi-Kramers- Kronig regression performed on the reflectance measurements of neat J-aggregate films on glass, enabling us to numerically engineer the properties of the complete microcavity devices (see Figure A) prior to fabrication. We demonstrate robustness of this numerical method by matching the experimentally obtained angular dispersion of light reflected from the strongly-coupled microcavity to the predictions of our model. Both numerically and experimentally we demonstrate that the Rabi splitting of exciton-polariton modes of strongly-coupled microcavities can be finely tuned by modifying the J-aggregate film thickness (see Figure B). SiO 2 Substrate TiO 2 SiO 2 SiO 2 Spacer Alq 3 Spacer DBR Mirror Ag Mirror Probe J-Aggregate Thin Film 1.6 1.8 2.0 2.2 2.4 2.6 0.0 0.2 0.4 0.6 0.8 1.0 700 600 500 Measured Predicted d=5.1 nm Reflectance Energy (eV) Wavelength (nm) 1.6 1.8 2.0 2.2 2.4 2.6 0.0 0.2 0.4 0.6 0.8 1.0 700 600 500 d=8.5 nm Energy (eV) Wavelength (nm) 1.6 1.8 2.0 2.2 2.4 2.6 0.0 0.2 0.4 0.6 0.8 1.0 700 600 500 d=11.9 nm Energy (eV) Wavelength (nm) LB UB LB UB LB UB  R =120 meV  R =200 meV  R =240 meV (A) J-aggregate microcavity exciton-polariton device structure. (B) Comparison of measured and predicted reflectance spectra for device shown. Upper and lower branch (UB and LB) polaritons are indicated. Finally, we apply the model to estimate the linewidth of the lower branch exciton-polaritons in J- aggregate-based structures to be 8.4 meV. This is a key parameter in theoretical modeling of exciton-polariton dynamics and more than a factor of two smaller than linewidths assumed in previous studies [6-8]. References [1] D. G. Lidzey, D. D. C. Bradley, M. S. Skolnick, T. Virgili, S. Walker, and D. M. Whittaker, "Strong exciton-photon coupling in an organic semiconductor microcavity," Nature, vol. 395, pp. 53-55, 1998. [2] D. G. Lidzey, D. D. C. Bradley, T. Virgili, A. Armitage, M. S. Skolnick, and S. Walker, "Room Temperature Polariton Emission from Strongly Coupled Organic Semiconductor Microcavities," Physical Review Letters, vol. 82, pp. 3316-3319, 1999. [3] J. R. Tischler, M. S. Bradley, V. Bulovic, J. H. Song, and A. Nurmikko, "Strong Coupling in a Microcavity LED," Physical Review Letters, vol. 95, pp. 036401-4, 2005. [4] J. R. Tischler, M. S. Bradley, Q. Zhang, T. Atay, A. Nurmikko, and V. Bulovic, "Solid state cavity QED: Strong coupling in organic thin films," Organic Electronics, vol. 8, pp. 94-113, 2007. [5] M. S. Bradley, J. R. Tischler, and V. Bulovic, "Layer-by-layer J-aggregate thin films with a peak absorption constant of 10(6) cm(-1)," Advanced Materials, vol. 17, pp. 1881-1886, 2005. [6] V. M. Agranovich, M. Litinskaia, and D. G. Lidzey, "Cavity polaritons in microcavities containing disordered organic semiconductors," Physical Review B (Condensed Matter and Materials Physics), vol. 67, pp. 085311-10, 2003. [7] P. Michetti and G. C. La Rocca, "Polariton states in disordered organic microcavities," Physical Review B, vol. 71, 2005. [8] M. Litinskaya and P. Reineker, "Loss of coherence of exciton polaritons in inhomogeneous organic microcavities," Physical Review B, vol. 74, 2006. A) B)