APPARATUS FOR MEASURING DIAMETER OF LIGHT BEAM

PURPOSE:To measure the shapes and the diameters of light beams in the two directions on the same cross section at the same time by providing two slits which are not in parallel to each other on one plane that is orthogonal to the light axes of the light beams, moving the slits, and detecting the amount of transmitted light. CONSTITUTION:Slits 2a and 2b are provided so that the slits are intersected as a right angle. The amount of a light beam 1 to be measured which has passed through each slit is detected with a photodetector 3 and inputted into an amplifier circuit 6. A device 4 linearly moves the slits 2a and 2b so that each slit forms 45 deg. with respect to the longitudinal direction. A position detector 5 obtains the relative positions of the slits 2a and 2b. In this way, the light beam 1 is made to scan in the two orthogonally intersecting directions at the same cross section. Since the amount of each light beams passing through the slits 2a and 2b is sequentially changed, the shapes and the diameters of the light beam in the X and Y directions can be measured.