Density of photonic states in cholesteric liquid crystals

Density of photonic states ρ(ω), group vg, and phase vₚₕ velocity of light, and the dispersion relation between wave vector k, and frequency ω(k) were determined in a cholesteric photonic crystal. A highly sensitive method (measurement of rotation of the plane of polarization of light) was used to determine ρ(ω) in samples of different quality. In high-quality samples a drastic increase in ρ(ω) near the boundaries of the stop band and oscillations related to Pendell\"osung beatings are observed. In low-quality samples photonic properties are strongly modified. The maximal value of ρ(ω) is substantially smaller, and density of photonic states increases near the selective reflection band without oscillations in ρ(ω). Peculiarities of ρ(ω), vg, and ω(k) are discussed. Comparison of the experimental results with theory was performed.