Abstract
Since the first realization of two-photon direct laser writing (DLW) in Maruo et al. (Opt Lett 22:132–134, 1997), the manufacturing using direct laser writing techniques spread out in many laboratories all over the world. Photosensitive materials with different material properties open a new field for micro- and nanofabrication. The achievable structuring resolution using this technique is reported to be sub-100 nm (Paz et al. in J. Laser Appl. 24:042004, 2012), while a smallest linewidth of 25 nm could be shown in Tan et al. (Appl Phys Lett 90:071106, 2007). In our approach, the combination of DLW with the nanopositioning and nanomeasuring machine NMM-1 offers an improvement of the technique from the engineering side regarding the ultra-precise positioning (Weidenfeller et al. in Adv Fabr Technol Micro/Nano Opt Photon XI 10544:105440E, 2018). One big benefit besides the high positioning resolution of 0.1 nm is offered by the positioning range of 25,hbox {mm} times 25,hbox {mm} times 5,hbox {mm} (Jäger et al. in Technisches Messen 67:319–323, 2000; Manske et al. in Meas Sci Technol 18:520–527, 2007). Thus, a trans-scale fabrication without any stitching or combination of different positioning systems is necessary. The immense synergy between the highly precise positioning and the DLW is demonstrated by the realization of resist lines and trenches whose center-to-center distance undergoes the modified diffraction limit for two-photon processes. The precise positioning accuracy enables a defined distance between illuminated lines. Hence, with a comparable huge width of the trenches of 1.655,upmu hbox {m} due to a low effective numerical aperture of 0.16, a resist line of 30 nm between two written trenches could be achieved. Although the interrelationships for achieving such narrow trenches have not yet been clarified, much smaller resist lines and trench widths are possible with this approach in the near future.
Highlights
In the last decades, two-photon absorption (2PA) has become a very promising tool for three-dimensional micro- and nanofabrication [2]
The distance between the focal spot and the sample with the photosensitive material is measured and controlled by a laser focus sensor that was developed for the use with nanopositioning and nanomeasuring machines [16]
This laser focus sensor works contact free with a wavelength of 650 nm to avoid an influence on the photosensitive material, which is typically designed for shorter wavelengths in the range of 400 nm or less
Summary
Two-photon absorption (2PA) has become a very promising tool for three-dimensional micro- and nanofabrication [2]. In this fabrication technique, a tightly focused ultrashort pulsed laser beam is used to induce energetic transitions in a photosensitive material [7]. In contrast to one-photon absorption, which follows the Beer–Lambert law, the 2PA processes only takes place in the focal region [7]. By a relative movement between the focal spot and the photosensitive material, a three-dimensional structure can be created [2, 4]. Super-resolution techniques like stimulated emission depletion STED-
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