Abstract: A phase difference detecting device includes a splitter for splitting laser beams into a first group which will travel along a first path and a second group which will travel along a second path, a beam selection/extraction unit for selecting, as reference light, one beam from the first group to allow it to pass therethrough, a path length changing unit for changing the length of the first path, a combining unit for combining the reference light and beams which construct the second group to produce interference light, and a detector for detecting the intensity of the interference light. The device changes the length of the first path using the path length changing unit to detect a path length which maximizes the intensity of the interference light for each of the beams which construct the second group, and determines a phase difference among the beams from the detected path length.

Abstract: A phase difference detecting device includes a splitter for splitting laser beams into a first group which will travel along a first path and a second group which will travel along a second path, a beam selection/extraction unit for selecting, as reference light, one beam from the first group to allow it to pass therethrough, a path length changing unit for changing the length of the first path, a combining unit for combining the reference light and beams which construct the second group to produce interference light, and a detector for detecting the intensity of the interference light. The device changes the length of the first path using the path length changing unit to detect a path length which maximizes the intensity of the interference light for each of the beams which construct the second group, and determines a phase difference among the beams from the detected path length.

Abstract: A grating alignment device performs alignment of two or more plane gratings so as to eliminate an angular misalignment and a phase misalignment which are caused between respective diffracted light beams generated when incident light is diffracted by the plane gratings. Specifically, alignment is performed by appropriately adjusting an angle A, an angle B, an angle C, a coordinate Z, and a coordinate X of the second plane grating so as to eliminate at least one of the angular misalignment and the phase misalignment which are caused between the respective diffracted light beams generated when incident light is diffracted by the first plane grating and the second plane grating.