Tailoring submicrometer periodic surface structures via ultrashort pulsed direct laser interference patterning

Direct laser interference patterning (DLIP) with ultrashort laser pulses (ULPs) represents a precise and fast technique to produce tailored periodic submicrometer structures on various materials. In this work, an experimental and theoretical approach is presented to investigate the fundamental mechanisms for the formation of unprecedented laser-induced topographies on stainless steel following proper combinations of DLIP with ULPs. The combined spatial and temporal shaping of the pulse increases the level of control over the structure while it brings insights into the structure formation process. The aim of DLIP is to determine the initial conditions of the laser-matter interaction by defining an ablated region while double ULPs are used to control the reorganization of the self-assembled laser-induced submicrometer sized structures by exploiting the interplay of different absorption and excitation levels coupled with the melt hydrodynamics induced by the first of the double pulses. A multiscale physical model is presented to correlate the interference period, polarization orientation, and number of incident pulses with the induced morphologies. Special emphasis is given to electron excitation, relaxation processes, and hydrodynamical effects that are crucial to the production of complex morphologies. Results are expected to derive knowledge of laser-matter interaction in combined DLIP and ULP conditions and enable enhanced fabrication capabilities of complex hierarchical submicrometer sized structures for a variety of applications.

Figure 1

(a) Experimental setup of combined DLIP and DP. Abbreviations: Half-wave plate (HWP), linear polarizing cube (LPC), beam splitter (BS), spatial light modulator (SLM), focusing lens (f). (b) Surface processed with four beams with ${\theta }_n=19\pm 0.5^{\circ },\mathit{NP}=50$, and 42 μJ per pulse.

Figure 2

Normalized intensity distribution for (a) two- and (b) four- beam interference. Periodicities equal to ${\mathrm{\Lambda }}_{\mathrm{DLIP}}=1650\mathrm{nm}$ along the $x$ axis [for (a)] and $x$ and $y$ axes [for (b)] have been selected.

Figure 3

Surface pattern upon single pulse irradiation with ${\mathrm{\Lambda }}_{\mathrm{DLIP}}\sim 1650$ nm. SEM images of stainless steel surface for $\mathit{NP}=10$ (a) and $\mathit{NP}=50$ (b). (c) Cross section from (b). (d) FFT of (b) in a $30\times 30\mu {\mathrm{m}}^2$ region (e) Cross section of (d). (f) Modeling of the temperature profile and the flow vectors 450 ps after irradiation with first pulse. (g) Calculated surface profile after $\mathit{NP}=10$. (h) Depth profile along white dashed line in (g) for $\mathit{NP}=5$, 10, 15, 20. Red double-ended arrow in [(a),(b)] indicates polarization direction.

Figure 4

Surface pattern upon double pulse irradiation with ${\mathrm{\Lambda }}_{\mathrm{DLIP}}\sim 1650$ nm. SEM images of stainless steel surface for $\mathit{NP}=10$ (a) and $\mathit{NP}=50$ (b). (c) Cross section from b. (d) FFT of (b) in a $30\times 30\mu {\mathrm{m}}^2$ region. (e) Cross section of (d.) (f) Modeling of the temperature profile and the flow vectors 505 ps after irradiation with first pulse. (g) Calculated surface profile after $\mathit{NP}=10$. (h). Depth profile along white dashed line in (g) for $\mathit{NP}=5$, 10, 15, 20. Red double-ended arrow in [(a),(b)] indicates polarization direction.

Figure 5

Surface pattern upon single pulse irradiation with ${\mathrm{\Lambda }}_{\mathrm{DLIP}}\sim 5500$ nm. SEM images of stainless steel surface for $\mathit{NP}=10$ (a) and $\mathit{NP}=50$ (b). (c) Modeling of the temperature profile and the flow vectors 450 ps after $\mathit{NP}=9$. (d) Calculated surface profile after $\mathit{NP}=10$. (e) Depth profile along white dashed line in (d) for $\mathit{NP}=5$, 10, 15, 20. Red double-ended arrow in [(a),(b)] indicates polarization direction.

Figure 6

Surface pattern upon double pulse irradiation with ${\mathrm{\Lambda }}_{\mathrm{DLIP}}\sim 5500$ nm. SEM images of stainless steel surface for $\mathit{NP}=10$ (a) and $\mathit{NP}=50$ (b). (c) Modeling of the temperature profile and the flow vectors 505 ps after $\mathit{NP}=9$. (d) Calculated surface profile after $\mathit{NP}=10$. (e) Depth profile along white dashed line in (d) for $\mathit{NP}=5$, 10, 15, 20. Red double-ended arrow in (a) and (b) indicates polarization direction.

Figure 7

SEM images of stainless steel surface irradiated with ${\mathrm{\Lambda }}_{\mathrm{DLIP}}\sim 2262$ nm with single (a), (c) and double pulses (b), (d) with $\mathit{NP}=10$ and 50, respectively. Simulation results of the surface profile obtained with $\mathit{NP}=10$ are shown for SP (e) and DP. Depth profile along white dashed lines in (e), (f) for $\mathit{NP}=5$, 10, 15, 20 are shown in (g), (h).

Figure 8

SEM images of stainless steel surface irradiated with ${\mathrm{\Lambda }}_{\mathrm{DLIP}}\sim 7600$ nm with single (a), (c) and double pulses (b), (d) with $\mathit{NP}=10$ and 50, respectively. Simulation results of the surface profile obtained with $\mathit{NP}=10$ are shown for SP (e) and DP (f). Depth profile along white dashed lines in (e), (f) for $\mathit{NP}=5$, 10, 15, 20 are shown in (g), (h).