The seamless integration of customized micro-optical components into light-sensitive devices remains a challenging task toward enhancing the performance of solar cells and photodetectors. In this talk, I will show how laser additive processes can help ease this problem. We use laser pulses for depositing microdroplets and microdisks at targeted positions on a substrate. Following a photocuring or thermal reflow process, these elements are converted into microlenses and microlens arrays whose geometry, size, and optical properties solely depend on the laser parameters and substrate used. The excellent optical quality of the so-fabricated micro-optics offers a promising route for next-generation optoelectronic systems.
Bessel and annular laser beams offer intriguing possibilities for material processing. However, current beam shaping methods can be limited in tunability, speed, or parallelization possibilities. Here, we show how ultrasounds in liquids enable generating user-selectable arrays of Gaussian, Bessel-like, or annular beams. By cascading two liquid-filled acoustic cavities, each with a different geometry, light control can be achieved at microsecond time scales. Such an acousto-optic technology is easy to implement in current laser-direct writing workstations, providing an unprecedented ability to tune light fields based on application.
Laser-based systems are fundamental tools in several research and industrial fields as important as optical imaging and material processing. They grant high precision and flexibility, though, the throughput of these processes is constrained by their inherent point-scanning nature. An effective solution to this problem is beam parallelization, though, current implementations suffer from lack of flexibility, long response time or optical aberrations. In order to overcome these issues, we propose an original acousto-optofludic (AOF) device that exploits mechanical vibrations in a liquid to diffract light in a comb of multiple beams. In this work, we detail design, implementation, and optical characterization of AOF-based multi-focal laser system. In particular, we show that the main features of the acoustically generated beamlets can be tuned by properly varying frequency, amplitude, and phase of the mechanical oscillations. The application of this device to laser direct writing will enable high throughput processes of various materials in an highly tunable way.
Micro-optics have emerged as a cost-effective solution for increasing the photon collection efficiency of optoelectronic systems. By placing a microlens or microlens array (MLA) on top of the active area of a solar cell or photodetector, sustained improvements of up to 50% in the quantum efficiency of these devices have been demonstrated. However, current fabrication technologies for micro-optics can be limited in throughput, attainable geometries, fill-factor (FF) or range of suitable substrates. In this talk, I will present laser catapulting (LCP), a novel maskless laser additive manufacturing technique capable of customized and in-situ fabrication of polymeric micro-lenses over planar, curved and flexible substrates. LCP is based on a two-step process. First, a single laser shot is used to transfer a microdisk from a solid donor film directly to the area of interest on the optoelectronic device. Second, a thermal reflow process converts the disks into high-quality microlenses that exhibit almost perfect smoothness. Notably, closely packed MLA with a 100% FF can be obtained, not possible with standard direct-write methods such as inkjet printing or microdispensing. Furthermore, precise, accurate and high-throughput fabrication of lenses with different focusing power and geometries –spherical, cylindrical or even triangular – can be realized by simply adjusting laser parameters such as laser fluence or beam shape. I will present an in-depth experimental characterization of LCP, discuss the advantages and pitfalls of this technology and illustrate them with several applications, including enhancing the performance of single-photon avalanche diode (SPAD) arrays for super-resolution microscopy.
The inherent flexibility of laser direct writing (LDW) systems is compromised by its sequential nature and consequent sacrifice in throughput. Efforts to address this use include simultaneous multi-spot processing or the generation of multi-beam interference patterns. However, these approaches are normally limited to patterning arrayed features or uniformly distributed aperiodic patterns. Even if changing the number of beams or the angles between them enables to control the distribution and periodicity of the patterns, this task typically involves the mechanical displacement of a focusing lens or the displacement of several optical elements. Other beam shaping methods, such as a spatial light modulator, offer unparalleled flexibility, but their limited refresh rate precludes the fast control of patterns. Here, we explore the unique interactions between sound, liquids, and light to split a laser beam at microsecond timescales. By using the acoustic standing waves generated in a resonant cavity filled with a liquid, we are able to split a beam into multiple spots along two orthogonal directions, namely the X and Y axis. Notably, no Doppler shifting occurs between the diffracted beams. Thus, blocking the zeroth diffraction order can be used to generate multi-beam interference patterns, with a geometry that can be user-selected by adjusting the frequency of the acoustic wave. We provide a theoretical foundation of the working principle of our acousto-optic approach, which is in good agreement with experiments, and demonstrate the myriad of possibilities it offers by laser fabrication of patterns in both subtractive as well as additive modalities.
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