Reducing back-reflection in laser micromachining systems
View Patent ↗Systems and methods reduce or prevent back-reflections in a laser processing system. A system includes a laser source to generate an incident laser beam, a laser beam output to direct the incident laser beam toward a work surface along a beam path, and a spatial filter. The system further includes a beam expander to expand a diameter of the incident laser beam received through the spatial filter, and a scan lens to focus the expanded incident laser beam at a target location on a work surface. A reflected laser beam from the work surface returns through the scan lens to the beam expander, which reduces a diameter of the reflected beam and increases a divergence angle of the reflected laser beam. The spatial filter blocks a portion of the diverging reflected laser beam from passing through the aperture and returning to the laser beam output.
1. A method for processing a workpiece with a laser, the method comprising:
generating, with a laser, an incident laser beam;
determining a dead zone at a central location within a scan field of an f-theta lens, the determination based on a threshold power level of a portion of a reflected laser beam that returns to the laser;
selecting a scan angle of the incident laser beam with respect to an optical axis of the f-theta lens; and
propagating the incident laser beam along a beam path toward a work surface by passing the incident laser beam through the f-theta lens at the scan angle to produce an output beam incident the work surface at a target location that is not encompassed by the dead zone and at an angle of incidence that causes a reflected laser beam power level to be less than the threshold power level.
2. The method of claim 1 , wherein the angle of incidence is in a range from about zero degrees to about twelve degrees.
3. The method of claim 1 , wherein the angle of incidence is greater than ten degrees.
4. The method of claim 1 , wherein the angle of incidence is greater than twelve degrees.
5. The method of claim 1 , wherein the angle of incidence is sufficiently high such that the reflected laser beam power level is about zero power.
6. The method of claim 1 , wherein the central location corresponds to a circular region of the work surface defining a potential angle of incidence that is about zero.
7. The method of claim 1 , wherein the scan field has a diameter of about 20 mm.
8. The method of claim 1 , wherein the dead zone has a diameter of about 5 mm.
9. The method of claim 1 , further comprising controlling a secondary beam positioner to scan the incident laser beam across the f-theta lens such that the output beam is not incident the work surface within a circular region encompassed by the dead zone.
10. The method of claim 9 , wherein the secondary beam positioner comprises a pair of galvanometer-driven mirrors.