E-Mail IMAGE: Realization of far-field, label-free super-resolution imaging based on evanescent waves excited by nonlinear four-wave mixing. view more Credit: Zhou et al., doi 10.1117/1.AP.3.2.025001 The diffraction limit, also known as Abbe diffraction limit in optics, poses a great challenge in many systems that involve wave dynamics, such as imaging, astronomy, and photolithography. For example, the best optical microscope only possesses resolution around 200 nm, but the physical size of the photolithography process with an excimer laser is around tens of nanometers. Meanwhile, physical sizes in current research and applications in biology and the semiconductor industry have scaled down to several nanometers, which is far beyond the ability of optical waves. According to the Abbe theory, subwavelength features are usually associated with evanescent waves, which decay exponentially with distance from the target. In response to this problem, researchers have developed many ways to bypass the Abbe limit, showing success in different applications. In one instance, the 2014 Nobel Prize in Chemistry was awarded to Eric Betzig, Stefan W. Hell, and William E. Moerner, for their contributions to the development of super-resolved fluorescence microscopy for life-sciences research.