Laser processing machine and method of correcting spot diameter of laser processing machine

A laser processing machine comprising:

• a lens for condensing a laser beam;
• an actuator changing a relative position between the lens and a workpiece to change a focal position of the laser beam with respect to the workpiece;
• a protective glass disposed between the lens and the workpiece;
• a detector detecting the focal position of the laser beam;
• and
• a controller comprising a processor and a memory, wherein the memory stores a relationship data, wherein the relationship data indicates a relationship between a deviation amount of the focal position from a target position and a spot diameter of the laser beam on a surface of the workpiece when contaminant adheres to the protective glass,
• wherein the processor is configured to:
• obtain a current deviation amount of the focal position from the target position using the detector,
• obtain the relationship data stored in the memory,
• estimate a current spot diameter of the laser beam on the surface of the workpiece based on the current deviation amount and the relationship data,
• correct the current spot diameter by controlling the actuator so that the focal position moves a total distance of a first distance and a second distance, wherein the first distance is a distance for moving the focal position so that the current deviation amount becomes zero, and wherein the second distance is a distance for moving the focal position from a position in which the current deviation amount is zero to a position in which the spot diameter on the surface becomes a target diameter.