Laser beam spot shape detection method

A laser beam spot shape detection method for detecting a spot shape of a laser beam oscillated by laser beam oscillation means and collected by a condenser in a laser machining apparatus, the laser machining apparatus including:

• a chuck table operable to hold a workpiece;
• and
• a laser beam irradiation unit operable to irradiate a workpiece held by the chuck table with a laser beam,
• the laser beam irradiation unit having laser beam oscillation means adapted to oscillate a laser beam, and a condenser adapted to collect the laser beam oscillated by the laser beam oscillation means and irradiate the laser beam onto the workpiece held by the chuck table,
• the laser beam spot shape detection method comprising:
• a concave mirror holding step of holding a concave mirror having a spherical face forming a reflecting face with the chuck table;
• a beam splitting means positioning step of positioning beam splitting means at an acting position between the laser beam oscillation means and the condenser, the beam splitting means passing a laser beam from the laser beam oscillation means to the condenser and guiding reflected light, which is collected by the condenser and reflected by the reflecting face of the concave mirror held by the chuck table, into a reflected light detection path;
• a focal point positioning step of positioning a focal point of the condenser in a proximity including a center of the spherical face forming the reflecting face of the concave mirror held by the chuck table;
• a laser beam irradiation step of activating the laser beam oscillation means and irradiating a laser beam collected by the condenser onto the concave mirror held by the chuck table;
• and
• an imaging step of capturing, by imaging means, images of reflected light reflected by the reflecting face of the concave mirror held by the chuck table and guided into the detection path by the beam splitting means.