Abstract: Provided are a biodegradable aliphatic-aromatic polyester copolymer having excellent hydrolysis resistance and high viscosity which has a carboxyl end group (CEG) content of 15 mg KOH/g or less, a ratio (Mz/Mn) of a z-average molecular weight (Mz) to a number average molecular weight (Mn) of 3 to 15, and a melt index (MI) of 5 g/10 min or less as measured under conditions of a temperature of 190° C. and a load of 2.16 kg in accordance with ASTM D 1238. A method of preparing a biodegradable aliphatic-aromatic polyester copolymer is provided, including adding a chain extender and an anti-hydrolysis agent to an aliphatic-aromatic polyester pre-copolymer over time, whereby a significant viscosity rise and improvement of hydrolysis resistance may be implemented simultaneously.

Abstract: Provided is an operating method of a measuring apparatus measuring a wavefront of a target. The operating method includes measuring a measurement wavefront on the basis of the wavefront of the target, measuring reference slope information and first to third slope information respectively corresponding to a reference direction and first to third directions on the basis of the measurement wavefront, obtaining first to third rotation angles on the basis of the measured reference slope information and first to third slope information, and outputting a wavefront of which an error is corrected, which is generated by rotation errors on the basis of the obtained first to third rotation angles, wherein the first to third rotation angles are differences in angle between the reference direction and the first to third directions.

Abstract: Provided is an operating method of a measuring apparatus measuring a wavefront of a target. The operating method includes measuring a measurement wavefront on the basis of the wavefront of the target, measuring reference slope information and first to third slope information respectively corresponding to a reference direction and first to third directions on the basis of the measurement wavefront, obtaining first to third rotation angles on the basis of the measured reference slope information and first to third slope information, and outputting a wavefront of which an error is corrected, which is generated by rotation errors on the basis of the obtained first to third rotation angles, wherein the first to third rotation angles are differences in angle between the reference direction and the first to third directions.