Real-time in situ study of femtosecond-laser-induced periodic structures on metals by linear and nonlinear optics

Abstract

Femtosecond-laser surface structuring on metals is investigated in real time by both fundamental and second harmonic generation (SHG) signals. The onset of surface modification and its progress can be monitored by both the fundamental and SHG probes. However, the dynamics of femtosecond-laser-induced periodic surface structures (FLIPSSs) formation can only be revealed by SHG but not fundamental because of the higher sensitivity of SHG to structural geometry on metal. Our technique provides a simple and effective way to monitor the surface modification and FLIPSS formation thresholds and allows us to obtain the optimal FLIPSS for SHG enhancement.

Femtosecond laser-induced herringbone patterns

“…First observed by Birnbaum in 1965 on Ge [7], LIPSS have since been extensively studied using both continuous and relatively long-pulsed lasers [8][9][10][11][12]. More recently, LIPSS have been investigated using femtosecond lasers on a variety of materials, including semiconductors and dielectrics by others [13][14][15][16][17], and on metals by us [18][19][20][21][22]. Several theories exist, and the generally accepted means by which these structures are formed is by the interference of incident laser light with surface scattered electromagnetic waves, causing periodic modulation of the laser's deposited energy, resulting in inhomogeneous ablation of material [23][24][25].…”

Emission from silicon as a real-time figure of merit for laser-induced periodic surface structure formation

“…Although the SHG signal during LIPSS formation has been recognized by many authors [8,11] as an important indicator of modification of surface morphology, we emphasize that the ratio of SHG to PL (or SHG to EL) is more informative, as this ratio characterizes the quality rather than the quantity of the structuring process.…”

Monitoring of Evolving Laser Induced Periodic Surface Structures

“…In order to study the formation process and to gain information on the underlying principles, different monitoring processes have been developed, for example, in situ diffraction [24], in situ imaging deploying a microscope [25] and in situ surface second harmonic generation [26]. In situ imaging and diffraction requires a pump probe setup, that is, a probe beam at lower wavelength in addition to the patterning beam.…”