We present a beyond-mean-field approach to predict the nature of organic polariton lasing, accounting for all relevant photon modes in a planar microcavity. Starting from a microscopic picture, we show how lasing can switch between polaritonic states resonant with the maximal gain, and those at the bottom of the polariton dispersion. We show how the population of nonlasing modes can be found, and by using two-time correlations, we show how the photoluminescence spectrum (of both lasing and nonlasing modes) evolves with pumping and coupling strength, confirming recent experimental work on the origin of blueshift for polariton lasing.

Strong coupling between cavity photons and molecular vibrations can lead to the formation of vibron-polaritons. In a recent experiment with PVAc molecules in a metal-metal microcavity [A. Shalabney et al., Ang. Chem. Int. Ed. 54 7971 (2015)], such a coupling was observed to enhance the Raman scattering probability by several orders of magnitude. Inspired by this, we theoretically analyze the effect of strong photon-vibron coupling on the Raman scattering amplitude of organic molecules. This problem has recently been addressed in [J. del Pino, J. Feist and F. J. GarciaVidal; J. Phys. Chem. C 119 29132 (2015)] using exact numerics for a small number of molecules. In this paper we derive compact analytic results for any number of molecules, also including the ultra-strong coupling regime. Our calculations predict a division of the Raman signal into upper and lower polariton modes, with some enhancement to the lower polariton Raman amplitude due to the mode softening under strong coupling.

Following experimental realizations of room temperature polariton lasing with organic molecules, we present a microscopic model that allows us to explore the crossover from weak to strong matterlight coupling. We consider a non-equilibrium Dicke-Holstein model, including both strong coupling to vibrational modes and strong matter-light coupling, providing the phase diagram of this model in the thermodynamic limit. We discuss the mechanism of polariton lasing, uncovering a process of self-tuning, and identify the relation and distinction between regular dye lasers and organic polariton lasers.Bose-Einstein statistics underpin both the thermal equilibrium phenomenon of Bose-Einstein condensation, and the non-equilibrium phenomenon of lasing. Lying between these two extremes, there now exist several experimental platforms; in particular exciton-polaritons (quasiparticles resulting from strong coupling between photons and excitons) in semiconductor microcavities at cryogenic temperatures [1][2][3], and photons in dye-filled microcavities at room temperature [4]. Since these microcavities are imperfect, they are sources of coherent light (as is a laser), but differ in mechanism from photon lasing [5,6]. Indeed, polariton lasing does not need electronic inversion, and so it is often stated that it can provide coherent light sources with ultra-low thresholds. Polariton lasing can also occur at room temperature in appropriate materials: inorganic materials such as wide bandgap semiconductors [7-9] and two-dimensional materials [10], and the focus of this Letter, organic materials [11][12][13].Polariton condensation in organic materials prompts interesting questions regarding the mechanisms of polariton relaxation and lasing. Excitons in organic materials are Frenkel excitons -electronic excitations of a molecule or chromaphore delocalized by hopping [14]. Excitons in organic materials typically show complex absorption and emission spectra, due to strong coupling between the electronic state and the nuclear configuration, leading to rovibrational dressing. This causes a Stokes shift, so that emission is at longer wavelengths than absorption. Spectral separation of emission and absorption underpins the operation of dye lasers [15], allowing gain without electronic inversion. Since both strong matterlight coupling and large Stokes shifts are expected to reduce the lasing threshold, how they act in concert is of both fundamental interest and practical relevance.Theoretical modeling of polariton condensates can follow a number of approaches. To describe the macroscopic pattern formation and superfluid hydrodynamics it mostly suffices to use the phenomenological complex Gross-Pitaevskii equation [6,16]. However, such order parameter equations are ubiquitous in non-equilibrium systems breaking U (1) symmetry, so similar equations also apply for a photon laser [17,18]. Such approaches are thus not well suited to understanding the relation between polariton and photon lasing, or the particular properties of organic polaritons. To...

We study two-dimensional charge-imbalanced electron-hole systems embedded in an optical microcavity. We find that strong coupling to photons favors states with pairing at zero or small center-of-mass momentum, leading to a condensed state with spontaneously broken time-reversal and rotational symmetry and unpaired carriers that occupy an anisotropic crescent-shaped sliver of momentum space. The crescent state is favored at moderate charge imbalance, while a Fulde-Ferrel-Larkin-Ovchinnikov-like state-with pairing at large center-of-mass momentum-occurs instead at strong imbalance. The crescent state stability results from long-range Coulomb interactions in combination with extremely long-range photon-mediated interactions.

In this paper, the reflection of light from a metal surface covered with thin film comprising resonant materials (for example, atoms, molecules, molecular aggregates, and quantum dots) is considered. It was found that dips appear in the reflection spectrum. In the case of atoms or molecules, two dips appear. In the particular case of molecular J-aggregates (when dielectric permittivity is not isotropic), the dip corresponds to the frequency of the dielectric permittivity resonance of the thin transition layer for S-and P-polarization of incident light. For molecular Haggregates, the dip corresponds to the frequency where the dielectric permittivity of the transition layer becomes zero (only for P-polarization of incident light). The origin of such an effect is also discussed.