Dependence of lasing threshold power on excitation wavelength in dye-doped cholesteric liquid crystals

Relationship between threshold power and excitation wavelength has been investigated in distributed feedback (DFB) lasers using dye-doped cholesteric liquid crystals (CLCs). We found that the threshold shows strong dependence on the excitation wavelength. The excitation wavelength was varied over the whole absorption band of a commercial DCM dye, resulting in almost one-order of magnitude lower threshold power by the excitation at the higher energy tail than at the lower energy tail of the absorption band. We confirmed the existence of an optimum wavelength giving the lowest threshold power due to the competition between this effect and decreasing absorption at the higer-energy tail of the absorption band using a different dye, pyromethene 580.