This letter presents a novel strategy for template synthesis of polymer structures with laser machined substrates. User-designed patterns of submicrometer holes with aspect ratios >10:1 and depths >10 μm were produced by focusing 160 fs, 5.2 μJ laser pulses on the surface of fused silica with a high numerical aperture microscope objective. Some holes were enlarged by chemical etching. Polymer solutions were cast into the templates to create high-aspect-ratio polymer structures using replication. Engineered polymer structures prepared by this unique method are useful for a number of applications such as high surface area electrodes and biological substrates.

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In this paper we report on the fabrication of regular arrays of silica nanoneedles by deposition of a thin layer of silica on patterned arrays of polymer nanowires (or polymer nanohair). An array of high-aspect-ratio nanoscale diameter holes of depths greater than 10 µm was produced at the surface of a fused silica wafer by an amplified femtosecond laser system operated in single-pulse mode. Cellulose acetate (CA) film was imprinted into the nanoholes and peeled off to form a patterned array of standing CA nanowires, a negative replica of the laser machined nanoholes. The cellulose acetate replica was then coated with silica in a chemical vapor deposition process using silicon tetrachloride vapor at 65 °C. Field emission scanning electron microscopy, focused ion beam sectioning, energy dispersive x-ray analysis and Fourier-transform infrared spectroscopy were used to characterize the silica nanoneedles. Precisely patterned, functionalized arrays of standing silica nanoneedles are useful for a number of applications.

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The authors characterize femtosecond laser single-pulse machining of deep, micrometer-diameter holes and long, micrometer-width channels in fused silica by the use of spherical, cylindrical, and aspheric singlet lenses. Repositionable spherical lenses form an adjustable beam expander that also provides a means of minimizing—or deliberately introducing—spherical aberration (SA) in the focal region by controlling the beam divergence at the asphere. Inserting cylindrical lenses creates a line focus for machining channel patterns parallel to the sample surface and at any depth within the bulk of the sample. The effects of controlled SA and pulse energy on the depth of round-focus holes and line-focus channels are studied. Holes less than 1 μm in diameter but with depths exceeding 30 μm are observed in the case of strong positive SA. Channel patterns from ∼1 to 3 μm wide, up to 2000 μm long, and with depths of 6–40 μm can also be machined with a single pulse, depending on the lens configuration and pulse energy. For the highest pulse energies studied, channel features exhibit phenomena such as bifurcations and multiple, separated focal regions along the beam path, indicating a possible complex interplay between SA, self-focusing, and filamentation. The authors also present experiments on attempting to form arrays of closely spaced, parallel microfluidic channels in fused silica by KOH etching of line-focus features for highly parallelized microfluidic applications.