Laser processing apparatus and laser processing method

A laser processing apparatus for surface treatment of a target member by supplying liquid to a surface of the target member and irradiating pulsed laser light to the surface via the liquid, the apparatus comprising:

• an optical window;
• a laser oscillator configured to irradiate the laser light to the surface through the liquid through the optical window;
• a liquid supply configured to supply the liquid to the surface through a flow path passing on an outer surface of the optical window,
• a laser light sampler configured to sample part of the laser light, the sampler being disposed on an optical path;
• and
• a sampling laser light energy detector configured to measure energy of the sampled laser light, wherein
• when the liquid is in contact with a laser light emission surface of the optical window, the laser light emission surface transmits the laser light, and
• when the liquid is not in contact with the laser light emission surface, the laser light emission surface reflects the laser light.

A laser processing method for surface treatment of a target member in a gaseous atmosphere by supplying liquid to a surface of the target member and irradiating pulsed laser light to the surface via the liquid, the method comprising:

• preparing a laser oscillator configured to irradiate the laser light to the surface through the liquid via an optical window and a liquid supply configured to supply the liquid to the surface via a flow path passing on an outer surface of the optical window, and a beam dump to which the laser light reflected by the laser light emission surface is guided;
• and
• changing an optical path of the laser light from a first optical path to a second optical path due to a difference in refractive index between the liquid and the gaseous atmosphere, wherein
• when the liquid is supplied to an outer side of the optical window from the liquid supply, the laser light passes through the first optical path to reach the surface, and
• when the liquid is not supplied to the outer side of the optical window from the liquid supply, the laser light passes through the second optical path not to reach the surface.