Temporal femtosecond pulse tailoring for nanoscale laser processing of wide-bandgap materials

Abstract

Nanoscale laser processing of wide-bandgap materials with temporally shaped femtosecond laser pulses is investigated experimentally. Femtosecond pulse shaping in frequency domain is introduced and applied to two classes of shaped pulses relevant to laser nano structuring. The first class, characterized by a symmetric temporal pulse envelope but asymmetric instantaneous frequency allows us to examine the influence of the sweep of the photon energy. In contrast, asymmetric temporal pulse envelopes with a constant instantaneous frequency serve as a prototype for pulses with time-dependent energy flow but constant photon energy. In our experiment, we use a modified microscope set up to irradiate the surface of a fused silica sample with a single shaped pulse resulting in ablation structures. The topology of the laser generated structures is measured by Atomic Force Microscopy (AFM). Structure parameters are investigated as a function of the pulse energy and the modulation parameters. We find different thresholds for surface material modification with respect to an asymmetric pulse and its time reversed counterpart. However, we do not observe pronounced differences between up-and down-chirped radiation in the measured structure diameters and thresholds.

Morphology of nanoscale structures on fused silica surfaces from interaction with temporally tailored femtosecond pulses

“…Applying pure second order dispersion at threshold, also subdiffraction structures are created; however, no substructure being stable with respect to laser fluence variations was observed. 17 In Fig. 2, the observed morphologies for bandwidth limited pulses and TOD shaped pulses are summarized.…”

Ultrafast laser control of electron dynamics in atoms, molecules and solids

“…8). [116][117][118] The resulting nanometre scale structures were one order of magnitude below the diffraction limit. Recently we extended our studies to investigate the dynamics of free electron plasma created by femtosecond pulses in a thin water jet 119 to a direct observation of the free electron density after excitation with temporally shaped laser pulses by using spectral interference techniques.…”

High-performance laser processing using manipulated ultrafast laser pulses

“…[1][2][3] Since temporal manipulation of ultrafast laser pulses provides the possibility of controlling the transient free-electron density 4 , it has been used for realizing high-quality ablation and nanoscale ablation of transparent materials. [4][5][6] Additionally, the spatiotemporal manipulation provides a unique feature of reducing background excitation for internal modification of transparent materials by multiphoton absorption. 7 In this paper, we demonstrate two kinds of high-performance laser processing using the manipulated ultrafast laser pulses.…”