Method and apparatus for measuring beam spot of scanning light

摘要

In order to measure a characteristics of a light beam which is repetitively deflected by a light scanning device within a first range in a first direction at a first velocity, there is provided a plate formed with at least one slit extending in a direction angled from the first direction and having a constant width. The plate is moved within the first range in the first direction at a second velocity which is sufficiently lower than the first velocity. A peak value of an optical power of light passing through the slit every time is detected when the deflected light beam crosses the slit being moved, thereby obtaining peak values at plural positions in the first direction. The peak values are displayed on a screen collectively in such a manner that positions on the screen correspond to the positions in the first direction.