| abstract |
[PROBLEMS] To provide a retardation plate having small temperature dependence of refractive index anisotropy and small fluctuation of retardation, and an optical head device using the retardation plate capable of maintaining high diffraction efficiency in a wide temperature range. Offer. SOLUTION: CH 2 ＣＨCHCOO-Ph-OCO-Y- A retardation plate comprising a polymer liquid crystal obtained by polymerizing a liquid crystal composition containing a compound represented by Z (Y is a 1,4-phenylene group or the like, Z is an alkyl group having 1 to 8 carbon atoms). |