Optical scattering imaging with sub-nanometer precision based on position-ultra-sensitive giant Lamb shift

The Lamb shift of a quantum emitter in close proximity to a plasmonic nanostructure can be three or more orders of magnitude larger than that in the free space and is ultra-sensitive to the emitter position and polarization.We demonstrate that this large Lamb shift can be sensitively observed from the scattering or absorption spectrum dip shift of the coupled system when the plasmonic nanoparticle or tip scans the emitter.Using these observations,we propose a scanning optical scattering imaging method based on the plasmonic-enhanced Lamb shift with achieves sub-nanometer resolution.Our method is based on the scattering or absorption spectrum of the plasmon-emitter coupling system,which is free of the fluorescence quenching problem and easier to implement in a plasmon-emitter coupling system.In addition,our scheme works even if the quantum emitter is slightly below the dielectric surface,which can bring about broader applications,such as detecting atoms and molecules or quantum dots above or under a surface.

Artificial intelligence assisted light control and computational imaging through scattering media

Coherent optical control within or through scattering media via wavefront shaping has seen broad applications since its invention around 2007.Wavefront shaping is aimed at overcoming the strong scattering,featured by random interference,namely speckle patterns.This randomness occurs due to the refractive index inhomogeneity in complex media like biological tissue or the modal dispersion in multimode fiber,yet this randomness is actually deterministic and potentially can be time reversal or precompensated.Various wavefront shaping approaches,such as optical phase conjugation,iterative optimization,and transmission matrix measurement,have been developed to generate tight and intense optical delivery or high-resolution image of an optical object behind or within a scattering medium.The performance of these modula-tions,however,is far from satisfaction.Most recently,artifcial intelligence has brought new inspirations to this field,providing exciting hopes to tackle the challenges by mapping the input and output optical patterns and building a neuron network that inherently links them.In this paper,we survey the developments to date on this topic and briefly discuss our views on how to harness machine learning(deep learning in particular)for further advancements in the field.

FRACTAL NATURE OF LIGHT SCATTERING IN TISSUES

Light scattering by a tissue has a wavelength dependence that depends on the size distribution of scatterers in the tissue.By measuring the wavelength dependence of scattering,one can deduce changes in the nanoscale architecture of cells and tissues.This report discusses the connection between nanoscale architecture and measurable light scattering.The significance of this work is to develop label-free optical imaging that describes tissue structure,to complement the absorption,fluorescence,and Raman scattering spectra that describe the chemical constituents of a tissue.

Angular-modulated spatial distribution of ultrahigh-order modes assisted by random scattering

In designing an optical waveguide with metallic films on a nanometer scale, the random scattering by the natural roughness of the thin film is always ignored. In this paper, we demonstrate that for the ultrahigh-order modes（UOMs） in the symmetric metal cladding waveguide, such a scattering leads to drastic variations in their spatial distribution at different incident angles. Owing to the high mode density of the UOMs, the random scattering induced coupling can be easily related to different modes with different propagation directions or wavenumbers. At small incident angles, the intra-mode coupling dominates, which results in a spatial distribution in the form of concentric rings. At large incident angles, the inter-mode coupling plays the most important role and leads to an array-like pattern. Experimental evidence via optically trapped nanoparticles support the theoretical hypothesis.

Iterative physical optics model for electromagnetic scattering and Doppler analysis

An iterative physical optics（IPO） model is proposed to solve extra large scale electric electromagnetic（EM） scattering from randomly rough surfaces. In order to accelerate the convergence of the IPO model, the forward-backward methodology and its modification with underrelaxation iteration are developed to simulate the rough surface scattering; the local iteration methodology and the fast far field approximation（Fa FFA） in the matrix-vector product are proposed to reduce greatly the computational complexity. These techniques make Monte Carlo simulations possible. Thus, the average Doppler spectra of backscattered signals obtained from the simulations are compared for different incident angles and sea states. In particular, the simulations show a broadening of the Doppler spectra for a more complicated sea state at a low grazing angle（LGA）.

A STUDY ON PENETRATION DEPTH OF POLARIZATION IMAGING

Optical clearing improves the penetration depth of optical measurements in turbid tissues.Polarization imaging has been demonstrated as a potentially promising tool for detecting cancers in superficial tissues,but its limited depth of detection is a major obstacle to the effective application in clinical diagnosis.In the present paper,detection depths of two polarization imaging methods,i.e.,rotating linear polarization imaging(RLPI)and degree of polarization imaging(DOPI),are examined quantitatively using both experiments and Monte Carlo simulations.The results show that the contrast curves of RLPI and DOPI are different.The characteristic depth of DOPI scales with transport mean free path length,and that of RLPI increases slightly with g.Both characteristic depths of RLPI and DOPI are on the order of transport mean free path length and the former is almost twice as large as the latter.It is expected that they should have different response to optical clearing process in tissues.

Influence of trap-assisted tunneling on trap-assisted tunneling current in double gate tunnel field-effect transistor

Trap-assisted tunneling（TAT） has attracted more and more attention, because it seriously affects the sub-threshold characteristic of tunnel field-effect transistor（TFET）. In this paper, we assess subthreshold performance of double gate TFET（DG-TFET） through a band-to-band tunneling（BTBT） model, including phonon-assisted scattering and acoustic surface phonons scattering. Interface state density profile（D_（it）） and the trap level are included in the simulation to analyze their effects on TAT current and the mechanism of gate leakage current.

Round-trip imaging through scattering media based on optical transmission matrix

Traditional one-way imaging methods become invalid when a target object is completely hidden behind scattering media. In this case, it has been much more challenging, since the light wave is distorted twice.To solve this problem, we propose an imaging method, so-called round-trip imaging, based on the optical transmission matrix of the scattering medium. We show that the object can be recovered directly from the distorted output wave, where no scanning is required during the imaging process. We predict that this method might improve the imaging speed and have potential application for real-time imaging.

Simple Raman scattering sensor integrated with a metallic planar optical waveguide: effective modulation via minor structural adjustment

We report experimental realization of Raman spectra enhancement of copper phthalocyanine, using an on-chip metallic planar waveguide of the sub-millimeter scale. The oscillating ultrahigh order modes excited by the direct coupling method yield high optical intensity at resonance, which is different from the conventional strategy to create localized ＂hot spots.＂ The observed excitation efficiency of the Raman signal is significantly enhanced,owing to the high Q factor of the resonant cavity. Furthermore, effective modulation of the Raman intensity is available by adjusting the polymethyl methacrylate（PMMA） thickness in the guiding layer, i.e., by tuning the light–matter interaction length. A large modulation depth is verified through the fact that 10 times variation in the enhancement factor is observed in the experiment as the PMMA thickness varies from 7 to 23 μm.

Optical tracking of picosecond coherent phonon pulse focusing inside a sub-micron object

By means of an ultrafast optical technique,we track focused gigahertz coherent phonon pulses in objects down to sub-micron in size.Infrared light pulses illuminating the surface of a single metal-coated silica fibre generate longitudinal-phonon wave packets.Reflection of visible probe light pulses from the fibre surface allows the vibrational modes of the fibre to be detected,and Brillouin optical scattering of partially transmitted light pulses allows the acoustic wavefronts inside the transparent fibre to be continuously monitored.We thereby probe acoustic focusing in the time domain resulting from generation at the curved fibre surface.An analytical model,supported by three-dimensional simulations,suggests that we have followed the focusing of the acoustic beam down to a~150-nm diameter waist inside the fibre.This work significantly narrows the lateral resolution for focusing of picosecond acoustic pulses,normally limited by the diffraction limit of focused optical pulses to~1μm,and thereby opens up a new range of possibilities including nanoscale acoustic microscopy and nanoscale computed tomography.

Passive inter-modulation scattering analysis of reflector considering contact nonlinearity

Passive inter-modulation （PIM） is a form of nonlinear distortion caused by the inherent nonlinearities of the passive devices and components in RF/microwave system. It will degenerate the performance of communication system with broad-band channel and high-sensitivity receiver. Therefore, it is necessary to construct a model to simulate this process in order to predict the level of PIM. This paper is aimed at constructing some plate models with one-dimensional and two-dimensional contact nonlinearity sections illuminated by two-tone waves, and calculating the scattered field at a fixed-point in space using time-domain physical optics method. By taking fast Fourier transform （FFT）, we get the spectrum of the scattered field and then analyze the generated PIM products. At the end of this paper, some numerical examples are presented to show the influence rules of the relative factors on PIM. The results indicate the variation of the level of PIM with the number of the nonlinear regions, the nonlinear spacing, and the incident power levels.

Folding model calculations for ~6He+^(12)C elastic scattering

In the framework of the double folding model, we used the α＋2n and di-triton configurations for the nuclear matter density of the ~6He nucleus to generate the real part of the optical potential for the system ~6He＋^（12）C. As an alternative, we also use the high energy approximation to generate the optical potential for the same system. The derived potentials are employed to analyze the elastic scattering differential cross section at energies of 38.3, 41.6 and 82.3 Me V/u. For the imaginary part of the potential we adopt the squared Woods-Saxon form. The obtained results are compared with the corresponding measured data as well as with available results in the literature. The calculated total reaction cross sections are investigated and compared with the optical limit Glauber model description.

Infrared nanoimaging of nanoscale sliding dislocation of collagen fibrils

Collagen,one of the major components in the mammalian connective tissues,plays an essential role in many vital physiological processes.Many common diseases,such as fibrosis,overuse injuries,and bone fracture,are associated with collagen arrangement defects.However,the underlying mechanism of collagen arrangement defects remains elusive.In this study,we applied infrared scattering-type scanning near-field optical microscopy to study collagen fibrils’structural properties.Experimentally,we observed two types of collagen fibrils’arrangement with different periodic characteristics.A crystal sliding model was employed to explain this observation qualitatively.Our results suggest that the collagen dislocation propagates in collagen fibrils,which may shed light on many collagen diseases’pathogenesis.These findings help to understand the regulation mechanism of hierarchical biological structure.

Model of Raman–Nath acousto-optic diffraction

In this Letter, we discuss Raman–Nath acousto-optic diffraction, and a new model of Raman–Nath acousto-optic diffraction is presented. The model is based on the individual and simultaneous occurrences of phase-grating diffraction and the Doppler effect and optical phase modulation and photon–phonon scattering. We find that the optical phase modulation can cause temporal and spatial fluctuations of the diffracted light power escaping from the acoustic field.