Laser beam astigmatism evaluating method

A laser processing apparatus comprising:

• a holding unit configured to hold a workpiece;
• a laser beam irradiating unit including a laser oscillator and a condenser for condensing a laser beam emitted from the laser oscillator;
• a first moving mechanism configured to move the condenser and the holding unit relative to each other along a first direction as a direction of irradiation of the workpiece with the laser beam;
• a second moving mechanism configured to move the condenser and the holding unit relative to each other along a second direction intersecting the first direction;
• an imaging unit configured to image the workpiece held by the holding unit;
• and
• a controller including a processor and a memory, wherein
• the controller includes
• a processing control section configured to form a plurality of processing traces each having a spot shape by irradiating different positions of an exposed surface of the workpiece with the laser beam according to respective height positions of a condensing point of the laser beam by positioning the condensing point at a plurality of the height positions located between a first height position separated from a reference height position where the condensing point is located at the exposed surface of the workpiece by a predetermined distance in one direction of the first direction and a second height position separated from the reference height position by a predetermined distance in another direction opposite from the one direction in the first direction, and moving the condenser and the workpiece relative to each other along the second direction by operating the second moving mechanism, the condensing point being positioned at the plurality of height positions by moving the condenser and the workpiece relative to each other along the first direction by operating the first moving mechanism,
• an aspect ratio calculating section configured to calculate an aspect ratio of each of the processing traces from an image of each of the plurality of processing traces imaged by the imaging unit, and
• an astigmatism calculating section configured to calculate an index indicating a degree of astigmatism on a basis of the plurality of height positions of the condensing point and the aspect ratio of each of the processing traces.