FOCUS DETECTION EMITTER FOR A DATA STORAGE DEVICE, AN ELECTRON DATA STORAGE DEVICE AND A FOCUS CONTROLLING METHOD OF AN ELECTRON BEAM IN THE ELECTRON DATA STORAGE DEVICE, THEREBY EXACTLY MAINTAINING FOCUSES OF ELECTRON BEAMS TO GENERATE AND READ A SMALL RECORDING SPOT ON THE STORAGE MEDIUM

摘要

PURPOSE: A focus detection emitter for a data storage device, an electron data storage device and a focus controlling method of an electron beam in the electron data storage device are provided to generate the first spot on a storage medium by the first electron beam part while forming the second spot by the second electron beam part, thereby showing at least one focus state of the first and second electron beam parts in at least one of the first and second spots. CONSTITUTION: The first emitting section(158) selectively generates the first electron beam part(174). The second emitting section(160) selectively generates the second electron beam part(176). The first electron beam part(174) generates the first spot on a storage medium(106), while the second electron beam part(176) generates the second spot on the medium(106). A position of the first spot for the second spot shows focus states of the electron beam parts(174,176). At least one position of the first and second spots shows at least one focus state of the first and second electron beam parts(174,176).