Machining of micrometer-scale high aspect ratio features with single femtosecond laser pulses

Abstract

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.

Areal Surface Texture Parameters for Copper/Glass Plating Adhesion Characteristics

“…The use of lasers for the machining of traditional circuit board substrates such as FR-4 with features such as microvias are now being offered as commercial equipment solutions. In addition, there has been a significant increase of research into the application of lasers for ablative machining of various substrates with the advent of controllable materials processing picosecond and femtosecond lasers [25], [26].…”

Intensity distribution on cylindrical surfaces in ultrashort pulse laser turning

“…The focusing of ultrashort laser pulses allows the machining of a large variety of materials down to a microscopic scale [1][2][3]. Non-contact, cold ablation enables the processing and manufacturing of work pieces without altering the surrounding material through excessive energy input, either through heat or through mechanical influences.…”

Fundamental Considerations and Analysis of the Energy Distribution in Laser Turning with Ultrashort Laser Pulses

“…Laser ablation using ultrashort laser pulses offers the possibility of machining a large variety of materials, some of which are hard to machine using conventional approaches because of their material properties, for instance, the brittleness of fused silica [1][2][3], sapphire [4][5][6][7] or tungsten alloys [8][9][10]. This capability enables, for example, the manufacturing of high-precision microtools via the tangential processing of cylindrical work pieces [11,12].…”