The three works used related approaches to confine the exposure patterns in lithography. Two of the papers use of a combination of photoactivation of the chemical reactions in the photoresist and, with a shaped beam that forms a ring around the photoactivating beam, photodeactivation such that the width of the patterned region is substantially narrowed. The other paper uses a photochromic film in contact with a photoresist and narrows the excitation pattern in the resist by controlling the transmission profile in the photochromic film using two pumping wavelengths with properly shaped patterns. The articles report feature sizes in the range of 10's of nm.

The Perry group has previously reported on nanolithography with a resolution of 65 nm using multiphoton excitation of photoresists. (“65 nm Feature Sizes using Visible Wavelength 3-D Multiphoton Lithography,” W. Haske, V. W. Chen, J. M. Hales, W. Dong, S. Barlow, S. R. Marder, J. W. Perry, Opt. Express, 15 (6), 3426-3436 (2007).)