mixed with glass bead spacers to find the weight concentration of the components c in a mixture of chiral additive and nematic liquid crystal with desired selective reflection wavelength u03bb o we used a well known relationship c n av u03bb o u00d7 htp where htp is the helical twisting power of the chiral additive in a nematic liquid crystal for cb15 in e7 htp u2248 7 3 u03bcm u2212 1 an e7 cb15 liquid crystal mixture with selected concentration was fed through a 0 45 u03bcm particle filter and a stainless steel syringe into the assembled cell parallel to the polymer alignment direction inscribed in the cell walls we prepared several tens of planar aligned cholesteric liquid crystal samples with band gaps in different spectral regions u03bb o varied from 430 nm to 2200 nm we used a perkin elmer lambda 900 spectrophotometer to measure the wavelength response of each prepared sample thereby determining the specific selective reflection photonic band gap for each sample a zero order quarter wave plates and a thin film linear polarizer were used in both spectrophotometer channels to create circularly polarized incident light of desired handedness samples were tested in unpolarized as well as in left handed and right handed circularly polarized incident light fig3 shows transmittance of wacker oligomer cholesteric liquid crystal samples versus wavelength in left handed circularly polarized light in these experiments we used both pure wacker oclcs with selective reflection bands centered around 450 nm 535 nm and 760 nm and mixtures of two oclcs possessing selective reflection closest.