Closed-loop corrective beam shaping for laser processing of curved surfaces

Laser processing is a widely used contactless machining technique, with ultrashort pulses affording the intensity to machine almost any material. However, micro-patterning over curved surfaces can be difficult, as a fixed beam shape will necessarily be skewed when directed at a non-orthogonal sample surface. Here, we show that this aberration can be compensated via closed-loop adaptive beam shaping, via the use of a MEMS device (Texas Instruments Digital Micromirror device) acting as an intensity spatial light modulator that is used to create a beam intensity profile transformation that takes into account the local surface gradient of the sample. The patterning of 18 μm diameter circular structures over a region of a 3.00 mm diameter titanium sphere has been demonstrated. Inclinations of the surface normal of up to π/2 from the vertical were tested, and the effective range was found to be up to π/5. The MEMs device is also shown to be capable of providing a real-time and precise laser beam repositioning that compensates for the errors in the movement stages.