Characteristics of pulsetrain-burst machining

Summary form only given, as follows. The discovery of ultrafast-laser pulsetrain-burst machining at the University of Toronto has prompted new research into the physics involved in this regime of laser-matter interactions. Using the oscillator output of the Toronto FCM-CPA laser system we have been able to explore the effects of machining with a train of up to 400 1.2 ps pulses at a repetition rate of 133MHz. Pulsetrain burst machining has advantages over single pulse and CW laser machining. These include that drilling of holes at fluencies that would cause cracking or other negative thermal effects seen when using the other sources. Since the original work on this topic, which included the characterization of morphology of the drilled holes, we have further examined the physics behind this and conventional ultrafast laser machining by varying different parameters of the micromachining system. The technique is particularly useful for laser-material processing of brittle materials, especially glasses. We will describe the optical and thermal mechanisms behind hole-depth saturation in metals; part of which we believe is due to a loss of coherence caused by the pulse propagating down a multimode wave guide. We also will describe the connection between these mechanisms and our measurements of differential etch-rates.