Abbe Barrier Research Articles

Terahertz solid immersion microscopy: Recent achievements and challenges

Unique effects of terahertz (THz)-wave–matter interaction push rapid progress in THz optoelectronics aimed at bridging the problematic THz gap. However, majority of modern methods of THz spectroscopy and imaging are still hampered by low spatial resolution. Common lens/mirror-based THz optics fails to overcome the Abbe barrier and usually provides resolution larger than a free-space wavelength λ (i.e., hundreds of micrometers or even few millimeters). To mitigate this difficulty, supperresolution THz imaging modalities were introduced recently, among which we particularly underline different methods of THz scanning-probe near-field microscopy. They not only rely on strong light confinement on sub-wavelength probes and provide resolution down to ∼10−1–10−3λ but also suffer from small energy efficiency or presume an interplay among imaging resolution, signal-to-noise ratio, and performance. In this paper, we consider reflection-mode THz solid immersion (SI) microscopy that offers some compromise between the high imaging resolution of 0.15λ and high energy efficiency, which is due to the absence of any subwavelength probe in an optical scheme. Recent achievements, challenging problems, and prospects of SI microscopy are overviewed with an emphasis on resolving the inverse problem and applications in THz biophotonics.

Experimental verification 3D subwavelength resolution beyond the diffraction limit with zone plate in millimeter wave

ABSTRACTThe results of experimental investigations of resolution power of millimeter‐wave phase reversal binary Fresnel zone plate with short focal distance are described. It has been experimentally shown that in the near‐field of single diffractive lens with subwavelength focal distance without the immersion medium a resolution of 0.3–0.4 were obtained. The “Abbe barrier” can be completely broken by such diffractive lenses with unique three‐dimensional super resolution. Also it was experimentally shown the focal spot in the high numerical aperture diffractive lenses is no longer an Airy pattern and focal intensity distribution is not circularly symmetric. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2436–2439, 2014

3D dif fractive lenses to overcome the 3D Abbe subwavelength dif fraction limit

The innovative radiating structures as a conical millimeter wave FZP lens are proposed for subwavelength focusing. The results of FDTD simulation and experimental verification are discussed. It has been shown that in contrast to the flat diffractive optics the curvilinear 3D diffractive conical optics is capable of overcoming 3D Abbe barrier with a focal distance F greater than 2λ. The focal intensity distribution for such type of lenses is not circularly symmetric and thus the focal spot in the high numerical aperture case is no longer an Airy pattern. These results may find useful applications in optical microscopes, including

Three-dimensional direct laser writing inspired by stimulated-emission-depletion microscopy [Invited

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-emission-depletion 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.

Focusing of millimeter-wave radiation beyond the Abbe barrier

A hemispherical focusing system for millimeter waves is presented. Focusing of the beam to a spot of ∼0.3λ was obtained in the frequency range from 100 to 200 GHz. Compared to the scanning near-field optical spectroscopy, the system allows simultaneous imaging of extensive subwavelength objects. As an example, a double slit of size d=1 mm was clearly resolved using a radiation with a wavelength λ=2 mm. Using future optically dense lenses, a resolution of the order λ/100 seems to become possible.