In this study, a digital mask-based STED lithography technique was proposed, and the effective resolution of the proposed system was calculated analytically. The proposed STED lithography system uses two spatial light modulators to modulate the phase of an excitation beam and a depletion beam, respectively. The excitation spatial light modulator acts as a digital mask to form the patterning image, while the depletion spatial light modulator creates an image surrounding the projected excitation image. Thus, photopolymerization is suppressed by stimulated emission occurring in the depletion focus region surrounding the excitation focus, thereby improving lithographic resolution. Electromagnetic field and intensity distribution were calculated, and the resolution of the proposed STED lithography was simulated based on vectorial diffraction theory. An effective resolution of 72 nm was calculated under the condition of I_s 0.1, which is similar to the resolution of conventional STED lithography at 70 nm. These results analytically confirmed that the proposed STED lithography system could pattern a two-dimensional region simultaneously without the loss of resolution compared to conventional STED lithography.

Optical dimensional metrology has playing a long-term key role from high-precision engineering to large-scale industrial manufacturing. Various methods of optical dimensional metrology have been proposed and demonstrated to respond to the ever-growing industrial demands as well as fundamental science demands for the measurement precision and range. However, most of them demonstrated under laboratory conditions have a long way to go outside the laboratory. Here, we present a progress review on optical modulation technique-based dimensional metrology, which has already been used in real applications and has been commercialized. Amplitude modulation (AM) and frequency modulation (FM) based dimensional measurement techniques are described with their operating principles, and recent progresses and applications in 3D imaging are presented in this review.