THz oscillations from optically anisotropic planar microcavities and organic microcavity lasers

摘要

We present a study of time-resolved transmission and emission properties of optically anisotropic planar micro-cavity structures. The structures consist of λ/4-layers of SiO_2 and TiO_2 for the dielectric mirrors and a cavity layer of either SiO_2 or the organic dye composite AlQ_3/DCM. For the SiO_2 cavity, we observe a polarization splitting at normal incidence leading to terahertz oscillations of transmitted coherent light. The polarization splitting is explained by an optical anisotropy of the dielectric layers caused by the fabrication process. We apply an up-conversion setup for temporally and spectrally resolved transmission measurements and obtain a corresponding beating of 1.25 THz. Time resolved measurements yield a Q-value of 1600, corresponding to a cavity photon lifetime of 0.65 ps. We explain our observations with a transfer-matrix model and introduce a Fourier-transform based analytical algorithm. The cavity filled with the organic dye composite can act as an organic microcavity laser. The birefringence of the distributed Bragg reflectors leads to lasing in two perpendicularly polarized modes. Investigations of the ultrafast dynamics of this laser system show a phase coupling of the two laser modes leading to the generation of a terahertz optical beat. The oscillation frequency can be widely tuned by variations in the fabrication process.