M2 MEASURING DEVICE

PROBLEM TO BE SOLVED: To provide an M measuring device which measures the M value of a pulse laser and facilitates the adjustment of an optical axis. SOLUTION: An M measuring device is provided with a condensing lens 1 which condenses the laser of a light source 20 to be measured, a uniaxial stage 2 which moves the lens 1 in the optical axis direction of the beam, and objective lens 3 which is arranged rearward than the beam condensing position 4, a half mirror 12 which is arranged rearward than a rear-side focal point face 5 and divides the light into two directions, a relay lens 7 which is arranged on one of the divided optical axes and focuses the optical image of the rear-side focal point face 5, an image-pickup element 8 which picks up the focused picture, a magnifying lens 6 which is arranged on the other divided optical axis and magnifies and projects the beam image in a condensing position 4, an image pickup element 11 which picks up the projected image, and a control processing part which detects the expanded angle of the beam from the pickup picture of the pickup element 8, finds the beam west diameter from the pickup picture of the pickup element 11, while moving the condensing lens 1, and calculates the M value based on them.