Recent results for flexible manufacturing of fused silica micro-optics using a surface optimization process are presented. Selective laser-induced etching technology (SLE) is used to fabricate highly precise microstructured glass components while thermal annealing is used to smoothen the optical surfaces. An optimization process for SLE printing and thermal annealing is investigated using a response surface methodology. Fabrication parameters such as laser power, writing velocity in the SLE process, as well as annealing temperature and thermal anneal time are varied to minimize the average surface roughness of the glass components. The optimization results show that the average surface roughness of printed glass is reduced from >500nm to ∼ 10nm in an area with a diameter of 250 μm, allowing the process to be used for optical applications.
High-resolution microfabrication techniques such as two-photon polymerization have been extensively developed in response to the increasing demand for non-spherical optical surfaces. However, these fabrication processes are limited to polymer materials. On the other hand, glass freeform optics fabrication relies on complex and expensive processes, with strong limits on accessible dimensions, particularly for micro-optics. We present here a flexible, time-efficient and potentially low-cost fabrication process for freeform optics fabricated in fused silica. The process starts from a three-dimensional (3D) CAD model of a freeform surface which is precisely printed into a block of fused silica using tightly focused ultrashort laser pulses, with the precision up to 1 µm. The exposed volumes of the glass part are then removed in a KOH etch to reveal the freeform surface, which is still topically rough. In a subsequent step, the sample is subjected to a smoothening process using thermal annealing, where the sample is placed in an oven at 1350°C for 1 hour, followed by a slow cooling at a rate of 0.5°K/min. The roughness of the sample is then reduced from µm to sub nm, and is thus of optical quality. The results demonstrate the possibility of a novel micro fabrication process for glass freeform optics.
Mid-Infrared (MIR) spectroscopy is a powerful method to identify different molecular species due to the fact that molecular vibrations exhibit strong responses in this spectral range. In order to control and optimize the chemistry process, as well as enhance the chemical output, an in-situ measurement is necessary. However traditional MIR spectrometers are usually bulky and expensive, and are difficult to use for a spatially distributed, real-time detection, especially in a micro-reactor.
We present here a highly-miniaturized continuously tunable optical bandpass filter in the MIR range for chemical detection in microreactors. Similar to a Fabry-Perot interferometer, the micro filter consists of two parallel multi-thin-film Bragg mirrors and an air gap, spaced by Liquid Crystal Elastomers (LCEs). The LCE is a novel actuator material composed of crosslinked polymer chains exhibiting strong macroscopic contraction as temperature is raised. We will show that the LCE can provide an extremely precise yet large mechanical movement of the two parallel mirrors leading to large freedom in the wavelength tuning range. Design, fabrication and measurements will be shown, demonstrating the functionality of the filter.
Mid-infrared (IR) spectroscopy, typically 3 to 5 µm, is often the technology of choice to monitor the interaction between and concentration of molecules during photochemical reactions. However, classical mid-IR spectrometers are bulky, complex and expensive, making them unsuitable for use in the miniaturized microreactors increasingly being employed for chemical synthesis. We present here the concept for an ultra-miniaturized mid-IR spectrometer directly integrated onto a chemical microreactor to monitor the chemical reaction. The spectrometer is based on micro-machined Fabry-Perot resonator filters realized using pairs of Bragg mirrors to achieve a high spectral resolution. The fabrication of the optical filters is outlined and the measurement of transmittance spectra in the mid-IR range show a good agreement with theory and are thus promising candidates for a fully integrated system.
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