Understanding and overcoming proximity effects in multi-spot two-photon direct laser writing

Abstract

Although additive manufacturing using multi-photon direct laser writing is nowadays considered as a major tool in the fabrication of future nano/micro-objects and optical components, it is currently limited by the low throughput of the writing process. To circumvent this issue, massive parallelization of the write process is a very promising avenue. However, simultaneous writing of structures in close spatial proximity generates fabrication artefacts, collectively referred to as "proximity effects", which strongly limit the accessible structure resolution. In this work, we systematically investigate the experimental parameters that influence these effects using specifically designed N×N spot diffractive optical elements. Through computer simulations, we show that these effects can be modeled remarkably successfully simply by taking Point Spread Function overlap and diffusion processes into account. We illustrate the usefulness of the concept by designing a parallel write approach giving access to periodic structures with short inter-object distances while very largely overcoming proximity effects.

Ultrafast 3D nanofabrication via digital holography

“…8a ). Similar phenomenon has been observed and studied by Arnoux, C. et al 35 , which agrees with our observation. Further experimental investigation shows that the bulk solidification effect can be entirely eliminated, achieving high-quality printing results, for up to 2000 laser foci when the smallest distance between any two scanning foci is larger than 3 µm (Supplementary Fig.…”

Two‐Photon Polymerization Lithography for Optics and Photonics: Fundamentals, Materials, Technologies, and Applications

“…The choice of dose parameters determine the minimum achievable 3D feature called "voxel", [252][253][254][255] and dependent on the scan algorithm and can distort the intended geometry. [256,257] The difficulty arises in the fact even there is lack of standardization on how to set each combination of viable parameters for each desired practical outcome. Depending on the application compromise might not be allowed.…”

“…[366] The proximity effect of voxel arrays can be calibrated by considering the point spread function overlap and diffusion processes. [256] When multiple voxels form into lines, the dimensions of width and height can be estimated, [265,367] thus we can predict the optical damage threshold with the proximity effect of lines (Figure 5c). [368,369] A lumped TPL parametric model with parameters of beam scan speed, laser power, slicing distance, and hatching distance based on single-photon absorption model was built to realize near-perfect 3D printing (Figure 5d-h), [370] in which, the effect of employed microscope objective, printing configuration, substrate, and resin also should be included.…”

Search for Alternative Two‐Step‐Absorption Photoinitiators for 3D Laser Nanoprinting

“…The resin inherently requires an effective nonlinearity to suppress the tails of the laser focus that otherwise accumulate ("proximity effect") and prevent one from printing truly 3D objects. [1,2] In early experiments, [3] this nonlinearity has been provided in optical form by two-photon absorption, [4] which is determined by the imaginary part of the third-order nonlinear optical susceptibility. [5][6][7] Later, it has become clear that chemical nonlinearities can contribute as well, with [8] or without [9][10][11][12] optical nonlinearities.…”