Implementation and assessment of a low-cost 3D laser platform controlled by open software for printing polymeric micro-structures

Abstract

A low-cost 3D opto-mechatronic platform controlled by free-source software with optical and mechanical resolutions of 120 m and 10 m, respectively, was developed to fabricate micro-pedestals in grid presentation and diffractive optical elements such as micro-square and micro-slits. Direct laser writing (DLW) and low-one photon absorption (LOPA) were employed as the fabrication protocol and the physical phenomena involved in the platform control and development of the micrometric structures. A laser pointer, one of the lowest-cost lasers in the market, centered at 532 nm with an intensity of 65 mW, was used to polymerize the SU8-2050 photoresist through the DLW procedures. The printing process was carried out by using 5X and 10X microscope objectives with numerical apertures of 0.13 and 0.25, respectively. The point spread function demonstrated the geometrical variations and the field intensity distribution about the focal plane, where the Debye–Wolf approximation is valid, which were used for comparison purposes. In addition, ray tracing simulations were presented to demonstrate how light interacts with the SU8-film and how out of focus condition plays a fundamental role in the final size of the printed micro-pattern. Finally, two optical diffractive elements and their diffraction patterns in the Fraunhofer regime were presented.

Microfluidic system manufacturing by direct laser writing for the generation and characterization of microdroplets

“…It is noticeable that the most popular case for the photon absorption mechanism is the TPA [29,43] for 3D microstructures fabrication. OPA has increased in number of publications and it is more commonly used for uni-dimensional or 2D micro fabrication, while LOPA is the newest explored photon absorption mechanism [29][30][31][32]43]. It has been explored due to some advantages over TPA, but same capability to produce 2D and 3D microstructures.…”

“…In the scenario of producing 2D structures by OPA, then it is possible to implement a DLW system using a continuous wave (CW) laser in the near UV region. The implementation of CW laser drops the cost of the laser sources and the specialized optics [31,32], but in this method the fabrication of microstructures is limited due to the surface optical absorption dependence [43].…”

“…The SU8-film is deposited on a conventional 1 mm-thickness soda-lime glass (SLG) via spin coating with final thicknesses ranging from ∼50 µm to ∼200 µm, which were measured by contact techniques, implementing a micrometer tool. In this way, the film thickness (the microfluidic channel height) is ensured under different rpm (revolutions per minute) values, while the width is adjusted by the optical parameters of the OL, such as the Rayleigh length and its work distance (WD) [31,45].…”

“…However, the high economical cost of the equipment and the maintenance to operate has limited its use. Novel fabrication techniques based on 'direct laser writing' (DLW) are nowadays increasingly used [28][29][30][31][32]. DLW is among the photopolymerization techniques, and it stands up from stereolithography [33,34] and selective laser sintering [35,36] due to superior resolution and it does not require re-coating or layer by layer fabrication, neither specialized and, most of the times, expensive equipment [37].…”

“…The increasing importance of LOPA method lies in the convenience of using a CW laser set up, which operates in an ultra-low optical absorption regime and allows the fabrication of 3D microstructures by a high light intensity at the tight focusing spot with few milliwatts [28]. Our research group previously demonstrated the capability and accuracy of the DLW technique by printing devices applied in microlasers and optical diffractive elements [30,31]. In these reports, the geometrical dimensions of the printed microstructures range from 50 µm to 120 µm, demonstrating the versatility of our technique and the scalability of the desired microstructures.…”