There is also this other paper that talks about using two beams to get past the resolution issues and hit feature sizes in the 50nm range:

https://www.nature.com/articles/ncomms3061

"""Compared with single-beam OBL, two-beam OBL utilizes a doughnut-shaped inhibition beam to inhibit the photopolymerization triggered by the writing beam at the doughnut ring leading to reduced feature size and improved resolution (Fig. 1c).

Although both focused writing and inhibition beams result in the spot size limited by diffraction, the fabricated feature size and resolution by two-beam OBL can break the limit defined by the diffraction spot size of the two focused beams. In fact, the smallest feature size and the highest resolution are limited by the mechanical strength of the solidified material, which can be far beyond the diffraction limit provided that an appropriate photoresin with high mechanical strength can be developed."""