Fused filament fabrication (FFF) is an inexpensive way of producing objects through a programmed layer-by-layer deposition. For multi-layer, macro-scaled prints, acceptable printing is achieved provided, amongst other factors, first layer adhesion is sufficient to fix a part to the surface during printing. However, in the deposition of structures with a single or few layers, first layer consistency is significantly more important and is an issue that has been previously overlooked. As layer-to-bed adhesion is prioritised in first layer printing, thin layer structures are difficult to remove without damage. The deposition of controllable thin structures has potential in tissue engineering through the use of bioactive filaments and incorporation of microfeatures into complex, patient-specific scaffolds. This paper presents techniques to progress the deposition of thin, reproducible structures. The linear thickness variation of 3D-printed single PVA and PLLA layers is presented as a function of extrusion factor and the programmed vertical distance moved by the nozzle between layers (the layer separation). A sacrificial PVA layer is shown to significantly improve first layer consistency, reducing the onus on fine printer calibration in the deposition of single layers. In this way, the linear variation in printed single PLLA layers with bed deviation is drastically reduced. Further, this technique is used to demonstrate the printing of freestanding thin layers of ~25 µm in thickness.

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The nonlinear interactions of femtosecond lasers are driving multiple new application directions for nanopatterning and structuring of thin transparent dielectric films that serve in range of technological fields. Fresnel reflections generated by film interfaces were recently shown to confine strong nonlinear interactions at the Fabry-Perot fringe maxima to generate thin nanoscale plasma disks of 20 to 40 nm thickness stacked on half wavelength spacing, λ/2nfilm, inside a film (refractive index, nfilm). The following phase-explosion and ablation dynamics have resulted in a novel means for intrafilm processing that includes 'quantized' half-wavelength machining steps and formation of blisters with embedded nanocavities. This paper presents an extension in the control of interferometric laser processing around our past study of Si3N4 and SiOx thin films at 515 nm, 800 nm, and 1044 nm laser wavelengths. The role of laser polarization and incident angle is explored on fringe visibility and improving interferometric processing inside the film to dominate over interface and / or surface ablation. SiOx thin films of 1 µm thickness on silicon substrates were irradiated with a 515 nm wavelength, 280 fs duration laser pulses at 0° to 65° incident angles. A significant transition in ablation region from complete film removal to structured quantized ejection is reported for p-and s-polarised light that is promising to improve control and expand the versatility of the technique to a wider range of applications and materials. The research is aimed at creating novel bio-engineered surfaces for cell culture, bacterial studies and regenerative medicine, and nanofluidic structures that underpin lab-in-a-film. Similarly, the formation of intrafilm blisters and nanocavities offers new opportunities in structuring existing thin film devices, such as CMOS microelectronics, LED, lab-on-chips, and MEMS.

interactions, electronic phenomena, and mechanical responses. With a preference, for top-down patterning, optical lithography or direct laser writing offers flexible interaction controls to structure multiple types of thin to thick film materials.In the case of transparent films, femtosecond lasers drive nonlinear optical interactions that further localize modification into the third dimension. For example, for focusing into the volume of photoresist, multilevel diffractive optic elements have been constructed that, in turn, enabled large volume formation of 3D photonic crystal templates. [6,7] In non-photosensitive film, the laser interaction can be selectively guided into a buried interface to drive full film mechanical ejection. This can permit the patterning of conductive coatings on display glass [8] through to new means of biological or electronic printing such as laser-induced forward transfer. [9][10][11] At reduced exposure, thin-film delamination enables the formation of interface micro-and nanochannels, and blisters in silica-silicon systems. [12,13] Thin-film optical interference has offered a promising means for confining nonlinear interactions, for example, to enable step-wise ablation of organic films. [14] However, directing energetic laser processes to physically structure internally in transparent film has been more challenging. By moving to dielectric materials, Kumar et al. introduced a controllable quantized intrafilm modification in sub-micrometer thick Si 3 N 4 -coated silicon. [15,16] By confining nonlinear interactions to fringe maxima, spaced by λ/2n film through thin-film interference, periodic stacks of plasma disks were formed above critical density that enable a novel intrafilm cleaving geometry. Expanding plasma disks in the film can override interface interactions to open nanocavities and lead to blister formation or quantized segment ejection for SiO x and Si 3 N 4 thin films on silicon substrates, for thicknesses in the range of 400 nm [15] to 3.5 µm [17] at multiple laser wavelengths. [18] However, this method is limited to a narrow range of thin-film and substrate combinations, wherein sufficient refractive index contrast is necessary to generate strong interference fringes. Fringe visibility is a key underlying factor that has not been previously examined in facilitating quantized processing of thin films. In particular, The combination of optical interference and ultrafast laser interaction within microscale transparent films offers novel high resolution means for nonlinear confinement of dissipated energy to facilitate 3D nanostructuring. This approach relies on the formation of nanoscale (≈40 nm) plasma disks stacked on halfwavelength spacings, λ/2n film (film refractive index, n film ), opening directions for intrafilm cleaving and nanostructuring of free-standing blisters or embedded nanocavities with controllable surface topography. Given a limited number of film-substrate systems suitable for generating high contrast interference fringes, this paper introduces angle and...