Direct laser writing has become a versatile and routine tool for the mask-free fabrication of polymer structures with lateral linewidths down to less than 100 nm. In contrast to its planar counterpart, electron-beam lithography, direct laser writing also allows for the making of three-dimensional structures. However, its spatial resolution has been restricted by diffraction. Clearly, linewidths and resolutions on the scale of few tens of nanometers and below are highly desirable for various applications in nanotechnology. In visible-light far-field fluorescence microscopy, the concept of stimulated emission depletion (STED) introduced in 1994 has led to spectacular record resolutions down to 5.6 nm in 2009. This review addresses approaches aiming at translating this success in optical microscopy to optical lithography. After explaining basic principles and limitations, possible depletion mechanisms and recent lithography experiments by various groups are summarized. Today, Abbe's diffraction barrier as well as the generalized two-photon Sparrow criterion have been broken in far-field optical lithography. For further future progress in resolution, the development of novel tailored photoresists in combination with attractive laser sources is of utmost importance.

Three-dimensional direct laser writing has become a well established, versatile, widespread, and even readily commercially available "workhorse" of nano-and micro-technology. However, its lateral and axial spatial resolution is inherently governed by Abbe's diffraction limitation -analogous to optical microscopy. In microscopy, stimulated-emissiondepletion approaches have lately circumvented Abbe's barrier and lateral resolutions down to 5.6 nm using visible light have been achieved. In this paper, after very briefly reviewing our previous efforts with respect to translating this success in optical microscopy to optical lithography, we present our latest results regarding resolution improvement in the lateral as well as in the much more relevant axial direction. The structures presented in this paper set a new resolution-benchmark for next-generation direct-laser-writing optical lithography. In particular, we break the lateral and the axial Abbe criterion for the first time.

Sufficient progress towards redefining the International System of Units (SI) in terms of exact values of fundamental constants has been achieved. Exact values of the Planck constant h, elementary charge e, Boltzmann constant k, and Avogadro constant N A from the CODATA 2017 Special Adjustment of the Fundamental Constants are presented here. These values are recommended to the 26th General Conference on Weights and Measures to form the foundation of the revised SI.

Using a novel photoresist (composed of pentaerythritol triacrylate and isopropyl thioxanthone) that favors stimulated emission depletion by a π‐π* transition and using a two‐color two‐photon excitation scheme, 65‐nm wide lines are achieved. This value is limited by parasitic two‐photon absorption of the continuous‐wave depletion beam. It is estimated that, without this process, line widths of 30 nm are in reach.

At the request of the Consultative Committee for Thermometry (CCT), Working Group 4 (WG4) has critically reviewed all available measurements of the differences between thermodynamic and ITS-90 temperatures, (T − T 90 ), and documented the conversion of older data to the ITS-90. Particular attention has been given to the uncertainties. Based on this review, we provide consensus estimates of T − T 90 for selected measurements from 0.65 K to 1358 K. We provide two analytic functions for T − T 90 , one for use from 8 K to the triple point of water (T TPW ) and one for use above T TPW . The small discontinuity of the derivative dT 90 /dT at T TPW is discussed.J. Fischer (B) · L. Wolber PTB,We also identify temperature ranges where researchers are encouraged to undertake high-accuracy measurements of T − T 90 .