Optimization of laser ablation for silver and nickel removal from piezoceramic discs in bimorph deformable mirror fabrication

The development of bimorph deformable mirrors with high spatial resolution of control elements requires the precise removal of conductive electrode layers—typically silver and nickel —from specific regions of a piezoceramic disc. This selective ablation is critical to isolate individual piezo-actuators while maintaining electrical continuity across the rear surface. Optimizing this laser micromachining process involves balancing thermal load, material ejection efficiency, and substrate integrity.

The primary challenge lies in the disparate physical properties of the metals and the ceramic base. Silver possesses high thermal and electrical conductivity, often leading to heat dissipation into the underlying lead zirconate titanate (PZT). Conversely, nickel has lower reflectivity but higher melting thresholds. To prevent micro-cracking of the brittle piezoceramic due to rapid thermal expansion, nanosecond or picosecond pulsed fiber lasers operating at wavelengths of 1064 nm or 532 nm are preferred over continuous-wave sources.

To remove nickel from the surface of the piezoelectric plates, Nd:YAG laser radiation with a wavelength of 1.06 µm was used. Compared to silver coatings, nickel has a significantly lower reflectivity at this wavelength (98% versus 76%, respectively), so different parameters were chosen for removing nickel from the surface of the piezoelectric plates. Thereby, for nickel coating following parameters was used: pulse duration – 100 ns, laser frequency – 20 kHz, power – 20 W, and operation speed – 250 mm/s. For silver film removal the parameters were slighlty different: silver was removed using radiation with an average power of 4 W and a pulse repetition rate of 20 kHz. The processing speed was 150 mm/s. The resulting track width was 300 µm. The material removal quality was observed with optical microscope. The verification of the proposed technique was investigated under high-voltage control signal, it was shown that the maximal voltage is in the range from -300 to +300 V