MOPA pulsed fiber laser with controlled peak power and pulse energy for micromachining of hard materials

A high brightness 1064nm MOPA pulsed fiber laser with controlled pulse width, peak power, and pulse energy is used to investigate the effects of changing the peak power and pulse width on the ablation process. Pulses of 10ns to 250ns are applied, with peak powers up to 10kW while maintaining average power. This corresponds to over 3 GW/cm2 fluence levels. The materials used in these experiments are mono and polycrystalline silicon, and aluminum coated silicon. Experimental results indicate that the material removal rates of a short pulse with high peak power is small, and that the material ablation benefits from a leading peak pulse shape at longer pulses of 100 to 150ns. These longer pulses accelerate the material removal by first heating and subsequently melting the substrate material. Material removal rate of about 13mm per scribe, single-pass, is obtained on mono silicon for 10W incident beam, 1m/s scan speed, 100 kHz rep rate and 20 m spot size with 50% spot overla p. Percussion drilled holes are also demonstrated for 200 mm thick polycrystalline silicon wafer. Through holes are drilled in 1msec using pulses of >50ns. Entry and exit diameters are typically 30 and 20m, respectively