  Comparative study of thin film Cholesteric Liquid Crystal (CLC) lasers made
from different materials and optically pumped by external solid state laser
reveals a striking dependence of lasing behaviour (ranging from single mode at
the edge of the selective reflection band to multimode lasing) on the
morphology and microstructure of CLC films. The materials studied belong to two
groups: low molar mass liquid crystals and polymers. It is shown that the
orientation of individual chiral domains and fluctuations in helical pitch
contribute significantly to the type of lasing displayed by the material.
Different ways of preparing CLC cells that lead to predominantly one type of
lasing are discussed. The importance of variations of the helical pitch and
domain orientation in producing single and multimode lasing is justified by
optical simulations (4x4 matrix method) of lasing in multi-layered samples.
