Patent ID: 7443900
Filing Date: 2008-10-28
Classification: C09K,H01S

Abstract:
1. A laser gain medium, comprising: at least one active species adapted to be stimulated to emit laser light within a predetermined wavelength range, optical feedback means defining a resonator for said laser light, said feedback means comprising at least one substantially solid cholesteric layer having a substantially planar texture exhibiting selective reflection of light defined by a reflection band tuned to said predetermined wavelength range, said cholesteric layer being obtained from reactive cholesteric mixtures selected from mixtures comprising: a) at least one cholesteric, polymerizable monomer; or b) at least one achiral, nematic, polymerizable monomer and one chiral compound in an inert diluent; or c) at least one cholesteric, crosslinkable oligomer or polymer selected from the group comprising cholesteric cellulose derivatives, propargyl-terminated cholesteric polyesters or polycarbonates, crosslinkable oligo- or polyorgano-siloxanes; or d) crosslinkable cholesteric copolyisocyanates in a polymerizable diluent; or e) chiral nematic polyesters having flexible chains whose cholesteric phase can be frozen in by rapid cooling to below the glass transition temperature, werein said mixtures b) do not comprise mixtures of an achiral, nematic, polymerizable monomer having a mesogenic group comprising and a chiral cholesterylcarbonate and a crosslinking agent; wherein said monomer of mixture a) is a chiral, liquid-crystalline, polymerizable monomer of the formula I where Z Y A M X is an n-valent chiral radical, R is hydrogen or C n is 1 to 6, and Z wherein said cholesteric mixture b) comprises at least one achiral, nematic, polymerizable monomer of the formula II where Z n is 0 or 1 Y A M