Structuring of photosensitive material below diffraction limit using far field irradiation

In this paper, we report on in-situ atomic force microscopy (AFM) studies of topographical changes in azobenzene-containing photosensitive polymer films that are irradiated with light interference patterns. We have developed an experimental setup consisting of an AFM combined with two-beam interferometry that permits us to switch between different polarization states of the two interfering beams while scanning the illuminated area of the polymer film, acquiring corresponding changes in topography in-situ. This way, we are able to analyze how the change in topography is related to the variation of the electrical field vector within the interference pattern. It is for the first time that with a rather simple experimental approach a rigorous assignment can be achieved. By performing in-situ measurements we found that for a certain polarization combination of two interfering beams [namely for the SP (?, ?) polarization pattern] the topography forms surface relief grating with only half the period of the interference patterns. Exploiting this phenomenon we are able to fabricate surface relief structures with characteristic features measuring only 140 nm, by using far field optics with a wavelength of 491 nm. We believe that this relatively simple method could be extremely valuable to, for instance, produce structural features below the diffraction limit at high-throughput, and this could significantly contribute to the search of new fabrication strategies in electronics and photonics industry.     

Overcoming the diffraction limit with a planar left-handed transmission-line lens

We report experimental results at 1.057 GHz that demonstrate the ability of a planar left-handed lens, with a relative refractive index of -1, to form images that overcome the diffraction limit. The left-handed lens is a planar slab consisting of a grid of printed metallic strips over a ground plane, loaded with series capacitors (C) and shunt inductors (L). The measured half-power beamwidth of the point-source image formed by the left-handed lens is 0.21 effective wavelengths, which is significantly narrower than that of the diffraction-limited image corresponding to 0.36 wavelengths.     

Manipulating near field polarization beyond the diffraction limit

We introduce a new optical nanoantenna structure with three-fold rotational symmetry. The proposed gold nanoantenna can produce a hot spot with circular polarization in the gap. The effect of the shape of the arms and geometrical imperfection on the optical response is examined. We introduce a figure of merit for practical applications that utilize the circular polarization. The figure of merit is more sensitive to changes of the geometry than the maximum near field amplitude or the maximum circular polarization. The relatively equivalent optical response of the proposed nanoantenna compared to its counterparts and its reasonable stability against small changes accompanied with its simpler structure design makes it more appropriate for experimentalists.     

A method for uniform demagnification imaging beyond the diffraction limit: cascaded planar hyperlens

Metamaterial composed of multistacked metal and dielectric films provides the access to ray tracing in subwavelength regions and to form a variety of transformation optical devices for manipulating light beyond the diffraction limit, such as hyperlens and cloak. In this paper, this method is employed to design planar hyperlens for demagnification imaging lithography. Variant ray route configurations are considered and compared for the sake of imaging quality as well as device structure complexity. It is found that specifically designed trajectory route from the object plane to the image plane help to yield imaging devices with uniform demagnification ratio and improved image quality. Then multiple similar imaging devices could be cascaded for further demagnification and reduce of structure complexity from the viewpoint of application. The imaging results with about 1/23 wavelength (16 nm) half-pitch resolution in the measure of electric field intensity are demonstrated with numerical simulations. Also presented are the imaging characteristic analyses including light intensity, demagnification ratio and resolution.     

Breaking the far-field diffraction limit in optical nanopatterning via repeated photochemical and electrochemical transitions in photochromic molecules

By saturating a photochromic transition with a nodal illumination (wavelength, λ), one isomeric form of a small molecule is spatially localized to a region smaller than the far-field diffraction limit. A selective oxidation step effectively locks this pattern allowing repeated patterning. Using this approach and a two-beam interferometer, we demonstrate isolated lines as narrow as λ/8 (78 nm) and spacing between features as narrow as λ/4 (153 nm). This is considerably smaller than the minimum far-field diffraction limit of λ/2. Most significantly, nanopatterning is achieved via single-photon reactions and at low light levels, which in turn allow for high throughput.     

Breaking the diffraction barrier in fluorescence microscopy by optical shelving

We report the breaking of the diffraction resolution barrier in far-field fluorescence microscopy by transiently shelving the fluorophore in a metastable dark state. Using a relatively modest light intensity of several kW/cm(2) in a focal distribution featuring a local zero, we confine the fluorescence emission to a spot whose diameter is a fraction of the wavelength of light. Nanoscale far-field optical resolution down to 50 nm is demonstrated by imaging microtubules in a mammalian cell and proteins on the plasma membrane of a neuron. The presence of dark states in virtually any fluorescent molecule opens up a new venue for far-field microscopy with resolution that is no longer limited by diffraction.     

The far field asymptotics in the problem of diffraction of an acoustic plane wave by an impedance cone

The work deals with the far field asymptotics of the classical solution for the problem of diffraction by an impedance cone. The incident acoustic plane wave completely illuminates the semi-infinite conical surface. The scattered field contains different components in the asymptotics, namely, the spherical wave from the vertex of the cone, the reflected waves, and, under some conditions, also the surface waves of Rayleigh type. We give integral representations for the scattering diagram of the spherical wave. The uniform (with respect to the observation direction) asymptotic expression for the wave field is also addressed and described by the parabolic cylinder ansatz. Dedicated to the memory of Vladimir Borovikov     

The quantum collective field method and its application to the planar limit

We formulate a general method of collective fields in quantum theory, which represents a direct generalization of the Bohm-Pines treatment of plasma oscillations. The present method provides a complete procedure for reformulating a given quantum system in terms of a most general (overcomplete) set of commuting operators. We point out and exemplify how this formalism offers a new powerful method for studying the large-N limit. For illustration we discuss the collective motions of N identical harmonic oscillators. As a much more important application, we show how, based on the present formalism, one solves the planar limit of a non-trivial SU(N) symmetric quantum theory.     

The intermediate regime of light diffraction by ultrasound in planar gyrotropic optical waveguides in an external electric field

A theoretical investigation is carried out for an intermediate regime of optoacoustic interaction, close to the Bragg one, by ultasonic Rayleigh surface waves in gyrotropic planar waveguides in an external electric field. A system of equations of associated waves is presented which describes the planar optoacoustic interaction in intermediate, Raman—Nath, and Bragg regimes of diffraction by ultrasonic surface waves in gyrotropic crystals with electrically induced anisotropy. It is shown that the intermediate (transition) regime of optoacoustic interaction, which is characterized by an angular selectivity and by the presence of several diffraction maxima, is the basic regime of diffraction. In this case diffracted light is generally elliptically polarized with an ellipticity and polarization azimuth that depend on the external electric field intensity. Translated from Zhurrnal Prikladnoi Spektroskopii, Vol. 66, No. 1, pp. 30–35, January–February, 1999.     

衍射极限尺度下的亚波长电磁学

作为波的本性之一,衍射是现代物理学的重要研究内容.衍射导致自由空间中波的能量不能被无限小地聚集,从而为成像、光刻、光存储、光波导等技术设定了一个原理性的障碍——衍射极限.对于电磁波和光波而言,尽管通过提高介质的折射率可以压缩衍射效应,但由于自然界中材料的折射率有限,该方法存在很大限制.近年来,随着表面等离子体光学的兴起,表面等离子体在超越传统衍射极限方面的能力和应用前景受到了学术界的关注.本文从亚波长电磁学的角度出发,介绍衍射极限研究的历史,综述了突破衍射极限的理论方法.首先,利用金属介质表面等离子体激元的短波长特性,可将等效波长压缩一个数量级以上,在纳米尺度实现光波的聚焦或定向传输;更进一步,通过人为设计超构材料和超构表面,利用结构化金属和介质中的局域谐振、耦合等特殊电磁响应,可实现亚波长局域相位调制、超宽带色散调控、近完美吸收、光子自旋轨道耦合等,从而突破传统理论的诸多局限,为下一代电磁学和光学功能器件奠定重要基础.     

Calculation of laser-beam diffraction in the near and far zones

The article investigates the possibility of using the method of expanding the field of a diffracted wave in free-space TEM _pl modes in order to compute the diffraction of laser radiation. The calculation algorithm for the diffraction in both the near and far zones reduces to two operations: determination of the expansion coefficients and summation of the amplitudes of the TEM _pl modes in the observation plane. A comparison is made between the theoretical curves characterizing the field distribution of the diffracted-wave field, as calculated by the proposed method, and the experimental dependences for the near and far zones.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 21, No. 11, pp. 1644–1647, November, 1978.The authors are grateful to F. A. Korolev, A. I. Kostienko, and A. I. Odintsov for discussions.     

Nonanalyticity in scale in the planar limit of QCD

Using methods of numerical lattice gauge theory we show that, in the limit of a large number of colors, properly regularized Wilson loops have an eigenvalue distribution which changes nonanalytically as the overall size of the loop is increased. This establishes a large-N phase transition in continuum planar gauge theory, a fact whose precise implications remain to be worked out.     

Far-field photothermal microscopy beyond the diffraction limit

The principles of laser photothermal (PT) imaging beyond the diffraction limit are discussed. Algorithms for obtaining information on the sizes and the shapes of nanotargets are analyzed. Spectral PT lifetime imaging is suggested to provide spatial localization of nanotargets overlapping inside the diffraction volume.     

Resonant interferometric lithography beyond the diffraction limit

A novel approach for the generation of subwavelength structures in interferometric optical lithography is described. Our scheme relies on the preparation of the system in a position dependent trapping state via phase shifted standing wave patterns. Since this process only comprises resonant atom-field interactions, a multiphoton absorption medium is not required. The contrast of the induced pattern does only depend on the ratios of the applied field strengths such that our method in principle works at very low laser intensities.     

平面超透镜的远场超衍射极限聚焦和成像研究进展

突破瑞利衍射极限,实现纯光学的远场超衍射极限聚焦和成像在科学和工程的各个领域都有重要意义.现有光学超分辨技术都存在一些固有的限制因素,如工作距离短、适用领域窄、不利于集成等问题.平面超透镜由于理论上的创新、设计灵活、效率高、方便集成等优势,成为实现超衍射极限的有效途径.本文综述了平面超透镜的物理原理及其在超衍射极限聚焦和成像方面近年来的研究进展,并讨论了该领域面临的问题和未来的研究重点和方向.     

Emergence of chaos in quantum systems far from the classical limit

The dynamical status of isolated quantum systems is unclear as conventional measures fail to detect chaos in such systems. However, when quantum systems are subjected to observation--as all experimental systems must be--their dynamics is no longer linear and, in the appropriate limit(s), the evolution of expectation values, conditioned on the observations, closely approaches the behavior of classical trajectories. Here we show, by analyzing a specific example, that microscopic continuously observed quantum systems, even far from any classical limit, can have a positive Lyapunov exponent, and thus be truly chaotic.     

The problem of superresolution in reconstructing the dielectric-constant profile in a planar optical waveguide using the far field of the emission mode

An algorithm for analytical continuation of the Fourier transform for the mode field in a planar optical waveguide is suggested; this algorithm makes it possible to reconstruct the dielectric-constant profile in the waveguide using the far field of the mode emission with subwavelength resolution. The reconstruction errors were studied. Examples illustrating the efficiency of this approach are given.