Lasing in imperfectly aligned cholesterics

Abstract

Optically pumped light emissions in imperfectly aligned dye-doped cholesteric cells with glance and frosted glass substrates of three different cell gap thicknesses are experimentally studied. Alignment imperfections show up in emission spectra by a broadening of the photonic bandgap (PhBG) lasing (allowed) lines at short- and long-wavelength PhBG edges and by an additional (forbidden) emission line inside the PhBG. Forbidden and allowed lines differ distinctively by their stability in the course of pumping. The origin of the forbidden line is discussed.

Lasing cholesteric capsules

“…The cavities in the plastic sheet were filled with a cholesteric mixture КЕТ90700+21%Е7+1%NR, which was studied in details in Ref. [3]. After filling the cavities, the plastic sheet was glued to a glass substrate.…”

“…2) and focal conical domains [5], as well as dislocations and disclinations. A densely defective cholesteric structure in the thick samples, including that of the capsules under test, produce strong light scattering and, consequently, the conditions necessary for the random lasing [3]. Fig.…”

“…[3], the 'allowed' PhBG lines are those located at the external sides of the PhBG edges, whereas the 'forbidden' lines fall inside the PhBG. One can see from Fig.…”

“…Our recent experiments [3] have revealed that cholesteric-alignment imperfections manifest themselves in the lasing spectra. Moreover, they have demonstrated that the laser generation in cholesterics can be obtained not only in well-aligned, thin planar cells -which is a common view in the current literature, -but also in thick defective cells with untreated though flat substrates.…”

Lasing in a hybrid-aligned cholesteric

“…Perfect enough planar alignment is hard to achieve for thick cells. Recently we have shown [6,7] that laser generation can also be obtained in thick imperfectly aligned cells with a large number of defects. In this study, we check whether this effect is possible in a dye-doped Ch cell with a hybrid surface alignment.…”