Direct writing of microlenses in polycarbonate with excimer laser ablation

Abstract

A method for fabricating microlenses in polycarbonate material is reported. Using a direct-write technique based on scanning excimer laser ablation with a circular beam, we can etch an arbitrary shape in the polymer material. The beam is obtained by imaging a circular aperture onto the polymer surface, and scanning is realized by the translation stage carrying the sample, which makes successive contours with well-chosen diameters and scan velocities. Afterward, to smooth the ablated surface and release it from debris, a large beam aperture covering the full lens area is used to ablate the lens deeper into the substrate. The fabrication process and the characterization method are described, including calculation of the contour set for a desired lens shape. The optical performance is evaluated by Mach-Zehnder interferometry, showing that aberrations below lambda/10 are possible for slow lenses.

Comparing glass and plastic refractive microlenses fabricated with different technologies

“…Several researchers have reported on fabrication methods for microlenses and lens arrays with these materials. They include techniques like photoresist reflow [8], laser beam shaping [9], deep lithography with protons [10], LIGA processing (German acronym for Lithographie, Galvanik und Abformung) [11], photopolymerization [12], microjet printing [13], laser ablation [14] and direct laser [15] or e-beam writing [16]. Some methods are relatively inexpensive and are based on existing technologies while others require dedicated processing tools and/or new materials with special properties.…”

“…Another asset of this approach is that a suitable choice of the photoresist material allows the use of well established, commercially available, semiconductor lithography equipment. Different types of direct writing techniques exist: direct laser writing [15], electron beam [16] and focused ion beam writing [37], and laser ablation [14]. For the sake of completeness, the fabrication by half-tone mask imaging [15,38]-although not strictly a direct writing technology-should also be mentioned.…”

Direct laser writing of Fresnel microlenses with use of the scanning contour ablation method

“…Given the need to design and prepare masks for each project individually, they have a limited application in the field of fast prototyping. A different group of solutions are methods based on the use of special algorithms that address the laser beam on a 2D plane, while working in the direct writing mode directly on the material [10,11], or automatically assembling the virtual mask image with the use of different discrete motives [12].…”

“…One particularly interesting method of producing 3D microstructures while working in the laser direct writing (LDW) mode using 'Top-Hat' beam profile is called 'scanning contour ablation' (SCA), which was proposed by Naessens et al [11]. This method, in its basic form, bears on the ablation of consequent trenches in the form of concentric circles, which makes it ideal for the preparation of the structures with axial symmetry such as spherical microlenses.…”

“…This method, in its basic form, bears on the ablation of consequent trenches in the form of concentric circles, which makes it ideal for the preparation of the structures with axial symmetry such as spherical microlenses. The development of the method was shown in [11], as well as the results for successful fabrication of the structures with absolutely monotonically changing cross-sectional profiles. In this paper, a few improvements on the already existing achievements are presented to create more complex structures, such as Fresnel microlenses.…”