Laser surface texturing using a single diffractive optical element as an alternative for direct laser interference patterning

Abstract

In this work, we introduce a simple and universal optical setup design for laser surface texturing (LST) that provides functionality superior than direct laser interference patterning (DLIP). The method requires only a single periodic diffractive optical element and a focusing lens while enabling unlimited freedom for spatial shaping and amplitude variations. The concept is based on the special behavior of diffraction gratings when illuminating an area on the grating that is close in size to a single period rather than effectively infinite periods as is usually discussed in fundamental grating studies. Empirical optimization for a specific ratio value of grating period and incident laser beam size was done on a two-dimensional intensity distribution by fitting the one-dimensional intensity profile to a periodical squared cosine function. We investigate the design characteristics and tolerance sensitivity for this work regime and discuss some application ideas including practical example suggestion of optical design, and some tailored patterning capabilities allowed by the method. A detailed comparison was made between DLIP setup and the proposed alternative method for LST.

LIPSS-based functional surfaces produced by multi-beam nanostructuring with 2601 beams and real-time thermal processes measurement

“…DLITe DOE is working in a regime where the splitter period is approximately X0.65 the laser input beam size. This texturing concept was introduced in previous theoretical work by the authors 33 , and this work is an experimental validation of this concept.…”

“…As shown in previous works 33 , a beam splitter DOE was designed to have a period equal to 0.65 times the input beam size, to achieve a dense pattern of intensity with a distance between maxima equal to the size of a diffraction limited spot. Input beam size was selected as 8 mm, to account for the optics clear aperture of 14 mm, resulting in a diffraction limited spot size of ~ 20 µm and a DOE period of 5150 µm which are typical values for tribology and hydrophobic applications 48 – 50 .…”

“…While all orders of the DOE are designed to have identical power (within standard deviation of 2%) mutual interference effects create a non-uniformity of the spots, calculated to have standard deviation of 28%. This results directly from the optimal ratio of beam size to DOE period for statistical area processing, defined in reference 33 as 0.65.…”

Towards Rapid Fabrication of Superhydrophobic Surfaces by Multi-Beam Nanostructuring with 40,401 Beams

“…The operating principle of the DLITe patterning method used in this work was described by a previous article of the authors [ 31 ]. The DLITe splitter MS-835-J-Y-X (Holo/Or LTD, Ness Ziona, Israel) was designed to generate 201 × 201 diffractive orders with an order separation angle of 0.136 mrad.…”

“…The splitter had a period of 7800 µm, and was designed to operate with a special custom-built wide-field focusing lens giving an order separation of 5 µm at EFL = 40 mm. Accordingly, beam size was set to be 12 mm, to achieve the desirable 0.65 ratio of period to beam size described in reference [ 31 ]. Under these operating conditions, the diffraction-limited spot size of the focuser was calculated to be 4.9 µm, resulting in dense patterning of the entire field covered by the splitter.…”