Dynamics of Bessel beam induced graphitization of diamond: exploring the role of in-bulk plasma

In this work, we study the graphitic wire formation by means of a pulsed Bessel beam focused across a 500 mu m thick monocrystalline synthetic diamond sample. Thanks to interferometric pump-probe diagnostics, we show that while pulse energies above the material optical breakdown (and thus the presence of plasma) are necessary for the creation of an initial graphitic seed and for the initiation of the graphitization process, the graphitization wave propagates throughout the material even in the absence of in-bulk critical plasma density. The holography and shadowgraphy experiments suggest that the non-diffracting focal zone of the beam, covering the whole sample thickness, might be the hot channel able to deliver the energy for the material transformation, acting thus as a guide for the in-bulk graphitization.