# Fabrication of Smart Materials Using Laser Processing: Analysis and Prospects
## 4 Laser Surface Modification by Direct Laser Interference Patterning (DLIP)
The potential of DLIP has been enhanced by utilizing two beams, enabling the production of surfaces with two-dimensional periodicity and multiple symmetry axes [128]. This technique involved picosecond laser writing of a consistent one-dimensional pattern for different sample orientations, offering versatility in creating diverse two-dimensional periodic structures with varying rotation angles and number of scans. The picosecond laser, operating at a wavelength of 1064 nm and a spectral bandwidth of \(<\)0.3 nm, was chosen for  
Figure 8: SEM images of (**a**) untreated ITO surface and (**b**) patterned surface at \(F\) = 250 mJ cm\({}^{-2}\). The electrical field’s polarization direction is indicated by the double arrow. (**c**) Tilted view of the ablated area of the sample. (**d**) Absolute value of the two-dimensional Fast Fourier Transform (2D-FFT) applied to (**b**) with a zoomed view of the center frequencies. The double-lobes shapes corresponding to High Spatial Frequency LIPSS are marked by dotted circles [124]. its narrow bandwidth, ensuring high-contrast interference patterns throughout the entire spot size. In [129], surface structures on 4H-SiC were generated using ultrashort pulsed DLIP (USP-DLIP) and a single Gaussian beam process. Through the utilization of a DOE to split a single beam into two, the interfered beams produced hierarchical structures, encompassing high spatial frequency LIPSS (HSFL) and low spatial frequency LIPSS (LSFL). The aspect ratio control capability of USP-DLIP was demonstrated through experimental results and Raman analysis, indicating a reduction in crystalline SiC peak intensity following USP-DLIP irradiation. The study employed a femtosecond laser with linear polarization, a wavelength of 1030 nm, a pulse duration of 420 fs, a frequency of 100 kHz, a maximum output power of 2 W, and a beam diameter of 2.4 mm (at 1/e\({}^{2}\)). In [130], a single-step method for creating porous photocatalytic surfaces on titanium substrates was introduced by DLIP with picosecond-range pulses. The study showcased the tunability of composition and morphology in the resulting surfaces, allowing customization for applications like antimicrobial surfaces, implant materials, or water treatment, utilizing a DLIP setup with a DOE and prism for versatile beam manipulation. The laser patterning was executed using a picosecond laser with a pulse width of 12 ps, a wavelength of 532 nm, a frequency of 100 kHz, and a maximum average power of 10 W.  
In [131], the focus was on integrating a diffractive fundamental beam-mode shaper element, or DOE, into a DLIP optical setup to create a square-shaped top-hat intensity distribution. The research involved measuring and characterizing interference patterns, identifying the system's sensitivity to optical misalignments, and elaborating an optical system for generating square-shaped interference distributions of energy with a flat-top intensity profile. The goal was to enhance the homogeneity of surface patterns in applications involving functionalized surfaces, emphasizing the application of the DOE. In [132], a diffractive beam-shaping element, or DOE, was integrated into a four-beam DLIP setup, demonstrating advantages over using a standard Gaussian beam configuration, including increased structure height, improved pattern uniformity, and enhanced productivity for specific patterns. The experimental investigations utilized a laser four-beam interference setup, resulting in the formation of dot-like interference patterns. This setup included a nanosecond-pulsed laser system operating at a wavelength of 1053 nm, with a maximum average output power of 4 W, a frequency of 4 kHz, and a pulse duration of 6 ns. Figure 10 illustrates the schematic of the experimental setup, along with the interference intensity patterns for the setup with and without a DOE. Figure 9: Illustration of the DLIP process. \(\Lambda\) indicates the period of the interference structure formed on the processed material’s surface, aligning with the structure’s period.