Polarization state of transmitted and emitted light in homogeneous and inhomogeneous medium

The interaction of linearly polarized light with self-assembled photonic crystals (opals) grown from polymeric colloids is studied. The experimental work is carried out on opals with and without dye molecules. These active and passive opals influence the polarization state of transmitted light very differently and the role of photonic stop band is evident. The active opals, when excited within the absorption band of the dye, emit light at a longer wavelength and the polarization state of emitted light is also studied in them. For comparison of these inhomogeneous crystalline samples with fully or partially homogeneous medium, the polarization state of light is also investigated in an aqueous solution with dissolved powder dye, and an aqueous suspension of dye-doped colloids. When the incident light is linearly polarized, the transmitted light from the passive opal is fully linearly polarized and that from the active opal is slightly elliptically polarized. In the same experiment, the fully homogeneous solution gives linear polarization while the partially homogeneous solution gives elliptical polarization in transmission. On the other hand, the emitted light from the active opal as well as from the two solution samples is found to be mostly unpolarized. The polarization anisotropy value, which characterizes the extent of polarization in an arbitrary light, has been calculated for all the samples from the spatially and spectrally resolved experimental data. This value is close to unity in transmitted light, implying linear polarization, for the fully inhomogeneous passive opal and fully homogeneous solution sample, while it is less than unity in the fully inhomogeneous active opal and partially homogeneous colloidal solution. The polarization anisotropy of emitted light, in all samples containing the dye, is close to zero signifying predominantly unpolarized nature. But the extent and type of inhomogeneity is found to influence the sign of the polarization anisotropy parameter extracted from the angle-resolved polarization measurements.