Nonlinear optical microscopy: Endogenous signals and exogenous probes

Nonlinear optical microscopy (NLOM) relies on nonlinear light–matter interactions to provide images from larger depths within biological structures compared to conventional confocal fluorescence microscopy. These nonlinear light–matter interactions include multiphoton excitation fluorescence (MPEF), second‐harmonic generation (SHG), coherent anti‐Stokes Raman scattering (CARS), and stimulated Raman scattering (SRS). This review discusses the theories of and instrumentation for various NLOM techniques, with a particular focus on endogenous signals and exogenous probes. These signals and probes expand the breadth of information that optical imaging can provide. We also discuss the application of NLOM in biomedical research, including tissue engineering, drug delivery and clinical diagnostics. Current technological limitations are also discussed.

     

Aider: Angle-of-incidence-derivative ellipsometry and reflectometry

A technique is proposed for the direct measurement of the derivatives ?ψ/??, ?Δ/?? and ?$\text{R}$/?? (or ? In $\text{R}$/? ?) of the ellipsometric (ψ, Δ) and reflectance ($\text{R}$) parameters of an optically isotropic surface with respect to the angle of incidence (?). A sinusoidal rotational oscillation of small amplitude

is applied to the sample around an axis in its surface perpendicular to the plane of incidence and the resulting ac/dc photoelectric signal-ratio η is measured in an ellipsometer with stationary polarizing and analyzing optics. From three such measurements η₁, η₂, η₃ at three different settings of the ellipsometer optics, the amplitudes of the sinusoidal perturbations

,

and

of the ellipsometric and reflectance parameters, caused by the angle-of-incidence oscillation

, can be determined. If

,

and

are divided by

, we get the desired derivatives ?ψ/??, ?Δ/?? and ? In $\text{R}$/??. This technique of Angle-of-Incidence-Derivative Ellipsometry and Reflectometry (given the acronym AIDER) promises to open up new possibilities in surface optics particularly for the measurement of the optical properties of film-substrate systems.     

Tailoring light with a digital micromirror device

A digital micromirror device (DMD) is a product of micromechanics. The DMD employs numerous micromirrors as the actuating components to switch small portions of light on and off. During the past few decades, such devices have been widely applied in digital light processing technology. The expanding range of applications makes the DMD increasingly important in various research aspects. Recent advances demonstrate that the DMD is potentially better than the traditional liquid crystal spatial light modulator in speed, spectrum sensitivity, and polarization modulation. These characteristics have been verified in a series of recently reported experiments. This review summarizes the related theory, experimental techniques, and applications for wavefront shaping with DMDs in both statically shaping various spatial modes and dynamically compensating for wavefront distortion caused by the scattering medium.

     

P‐type tin‐oxide thin film transistors for blue‐light detection application

We reported the characteristics of p‐type tin‐oxide (SnO) thin film transistors (TFTs) upon illumination with visible light. Our p‐type TFT device using the SnO film as the active channel layer exhibits high sensitivity toward the blue‐light with a high light/dark read current ratio (I_light/I_dark) of 8.2 × 10³ at a very low driven voltage of <3 V. Since sensing of blue‐light radiation is very critical to our eyes, the proposed p‐type SnO TFTs with high sensitivity toward the blue‐light show great potential for future blue‐light detection applications.

     

Background story of the invention of efficient blue InGaN light emitting diodes (Nobel Lecture)

Shuji Nakamura discovered p‐type doping in Gallium Nitride (GaN) and developed blue, green, and white InGaN based light emitting diodes (LEDs) and blue laser diodes (LDs). His inventions made possible energy efficient, solid‐state lighting systems and enabled the next generation of optical storage. Together with Isamu Akasaki and Hiroshi Amano, he is one of the three recipients of the 2014 Nobel Prize in Physics. In his Nobel lecture, Shuji Nakamura gives an overview of this research and the story of his inventions *** .

     

On the effective field theory of heterotic vacua

The effective field theory of heterotic vacua that realise Open image in new window preserving \(\mathcal {N}{=}1\) supersymmetry is studied. The vacua in question admit large radius limits taking the form Open image in new window , with Open image in new window a smooth threefold with vanishing first Chern class and a stable holomorphic gauge bundle Open image in new window . In a previous paper we calculated the kinetic terms for moduli, deducing the moduli metric and Kähler potential. In this paper, we compute the remaining couplings in the effective field theory, correct to first order in \({\alpha ^{\backprime }\,}\). In particular, we compute the contribution of the matter sector to the Kähler potential and derive the Yukawa couplings and other quadratic fermionic couplings. From this we write down a Kähler potential Open image in new window and superpotential Open image in new window .     

Fast‐response organic–inorganic hybrid light‐emitting diode

We demonstrated important changes produced on the modulation frequency of hybrid organic–inorganic light‐emitting diodes to examine the applicability as a light source for visible optical communications. The fabricated device structure was 4,4′‐bis[N ‐(1‐napthyl)‐N ‐phenyl‐amino]biphenyl/4,4′‐(bis(9‐ethyl‐3‐carbazovinylene)‐1,1′‐biphenyl:4,4′‐bis[9‐dicarbazolyl]‐2,2′‐biphenyl/ZnS/LiF/MgAg. This device showed an improvement in the modulation frequency using ZnS instead of an organic material, tris(8‐hydroxyquinoline)aluminum. A maximum cutoff frequency of 20.6 MHz was achieved.

     

Synthesis and electrochemical characterization of olivine-type lithium iron phosphate cathode materials via different techniques

High-potential, eco-friendly LiFePO₄ cathode materials were synthesized by polyol, hydrothermal, and solid-state reaction methods. The polyol technique was carried out without any special atmosphere and postheat treatment. The synthesized samples were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM) with energy dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectrometry (XPS), and charge-discharge and cyclic voltammetry tests. The LiFePO₄ prepared via polyol technique exhibits good electrochemical performance than other method samples do.

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Graphical abstract?

     

Integrated fluorescence sensor based on ring‐shaped organic photodiodes

We demonstrate a novel sensor type, which is based on the monolithic integration of luminescent optical sensor spots together with ring‐shaped thin‐film organic photodiodes on one substrate. The organic photodiodes serve as integrated fluorescence detectors, simplifying the detection system by minimizing the number of required optical components. The proposed concept enables filter‐less discrimination between excitation light and generated fluorescence light. The functionality of the concept is demonstrated by an integrated oxygen sensor, exhibiting excellent performance. The sensor spots are excited by an assembled organic light emitting diode. The integrated optical sensor platform is suitable for the parallel detection of multiple parameters. Sensor schemes for the analytical parameters carbon dioxide, temperature and ammonia, are proposed.

     

Spectral dependence of light extraction efficiency of high‐power III‐nitride light‐emitting diodes

Using the recently suggested method of processing the data on external quantum efficiency as a function of output optical power, we have estimated the dependence of light extraction efficiency of high‐power light‐emitting diodes (LEDs) on their emission wavelength varied between 425 nm and 540 nm. The extraction efficiency is found to increase with the wavelength from ～80% to ～85% in this spectral range and to correlate with the wavelength dependence of reflectivity of the large‐area p‐electrode being the essential unit of the LED chip design. The correlation found identifies the incomplete reflection of emitted light from the electrode as the major mechanism eventually controlling the spectral dependence of the efficiency of light extraction from the LEDs.

     

Polarizing neutron by light‐irradiated graphene

We study the spin orientation of the neutron scattered by light‐irradiated graphene and calculate the average value of spin z‐component of the neutron in terms of a generating functional technique. Our calculation results indicate that there is a remarkable neutron polarization effect when a neutron penetrates graphene irradiated by a circularly polarized light. We analyse the dynamical source of generating this effect from the aspect of photon‐mediated interaction between the neutron spin and valley pseudospin. By comparing with the polarization induced by a magnetic field, we find that this polarization may be equivalent to the one led by a magnetic field of several hundred Teslas if the photon frequency is in the X‐ray frequency range. This provides an approach of polarizing neutrons.

     

Multi‐peak and chromaticity‐stable top‐emitting white organic light‐emitting diodes using single blue emitter

We have fabricated multi‐peak and chromaticity‐stable top‐emitting white organic light‐emitting diodes (TEWOLEDs) using single blue emitter. Besides the intrinsic emission of blue emitter, the additional emission can be well realized by simply adjusting the thickness of hole transporting layer (HTL), thus modifying the optical cavity length to obtain different resonant wavelengths. The detailed variation process for multi‐peak spectra with the increase of HTL thickness is studied, which provides a guidance for the design of microcavity TEWOLEDs.

     

White Light Emitting MZr<Subscript>4</Subscript>(PO<Subscript>4</Subscript>)<Subscript>6</Subscript>:Dy<Superscript>3+</Superscript> (M = Ca,Sr, Ba) Phosphors for WLEDs

A series of MZr₄(PO₄)₆:Dy³⁺ (M = Ca, Sr, Ba) phosphors were prepared by the solid state diffusion method. Confirmation of the phase formation and morphological studies were performed by X-ray powder diffraction (XRD) measurements and scanning electron microscopy, respectively. Photoluminescence (PL) properties of these phosphors were thoroughly analyzed and the characteristic emissions of Dy³⁺ ions were found to arise from them at an excitation wavelength of 351 nm. The PL emission spectra of the three phosphors were analyzed and compared. The CIE chromaticity coordinates assured that the phosphors produced cool white-light emission and hence, they are potential candidates for UV excited white-LEDs (WLEDs).

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Graphical Abstract ?

     

Pitowsky’s Kolmogorovian Models and Super-determinism

In an attempt to demonstrate that local hidden variables are mathematically possible, Pitowsky constructed “spin- Open image in new window functions” and later “Kolmogorovian models”, which employs a nonstandard notion of probability. We describe Pitowsky’s analysis and argue (with the benefit of hindsight) that his notion of hidden variables is in fact just super-determinism (and accordingly physically not relevant). Pitowsky’s first construction uses the Continuum Hypothesis. Farah and Magidor took this as an indication that at some stage physics might give arguments for or against adopting specific new axioms of set theory. We would rather argue that it supports the opposing view, i.e., the widespread intuition “if you need a non-measurable function, it is physically irrelevant”.     

High color rendering index and chromatic stability of top‐emitting white organic light‐emitting diodes capped with a supplementary green color conversion layer

We have demonstrated high color rendering index (CRI) and chromatic stability of top‐emitting white organic light‐emitting diodes (TEWOLEDs) by capping a supplementary green color conversion layer (CCL) on the cathode of single blue emitter based TEWOLEDs. By employing CCLs, blue photon energy is absorbed and converted to green emission efficiently, resulting in an improvement of CRI from 72 to 86. We attribute the increased high CRI to the broadening of the out‐coupled spectrum and an appropriate intensity match among the three primary colors. Meanwhile, the TEWOLEDs show extremely high chromatic stability. The results indicate that this method provides a new avenue to improve the CRI of TEWOLEDs.

     

Hierarchy of the non‐covalent interactions in the alanine‐based secondary structures. DFT study of the frequency shifts and electron‐density features

The alanine (Ala)‐based cluster models of C5, C7, and C10 H‐bonds are studied at the DFT/B3LYP level. CPMD/BLYP simulations of the infinite polyalanine α‐helix (C13 H‐bond) and the two‐stranded β‐sheets are performed. Combined use of frequency shifts and electron‐density features enable us to detect and describe quantitatively the non‐covalent interactions (H‐bonds) defining the intrinsic properties of Ala‐based secondary structures. The energies of the primary N? H O H‐bonds are decreasing in the following way: C13 > C5 ≥ C7 > C10. The energies of the secondary N? H O, N?H N, and H H interactions are comparable to those of the primary H‐bonds (～4.5 kcal/mol). Side chain–backbone C? H O interaction is found to be the weakest non‐covalent interaction in the considered species. Its energy is ～0.5 kcal/mol in the infinite polyalanine α‐helix. Quantum‐topological electron‐density analysis is found to be a powerful tool for the detection of secondary non‐covalent interactions (C?O H? C and H H) and bifurcated H‐bonds, while the frequency shift study is useful for the identification and characterization of primary or secondary H‐bonds of the N? H O type. Copyright © 2008 John Wiley & Sons, Ltd.     

Blue light emitting diode exceeding 100% quantum efficiency

InGaN/GaN light‐emitting diodes (LEDs) are known to exhibit a strongly non‐uniform vertical carrier distribution within the multi‐quantum well (MQW) active region. We propose to eliminate “dark” quantum wells by insertion of multiple tunnel junctions into the MQW which allow for the repeated use of electrons and holes for photon generation. In good agreement with available measurements, we demonstrate by self‐consistent numerical simulation that such tunnel junction LED design promises quantum efficiencies as high as 250% as well as a strongly enhanced output power at high input power, compared to conventional LED concepts.

     

Very thin,highly‐conductive ZnO:Al front electrode on textured glass as substrate for thin‐film silicon solar cells

A very thin (250 nm), highly conductive (annealed), non‐texturized DC‐sputtered aluminum‐doped zinc oxide layer (ZnO:Al) deposited on a textured glass is used as substrate for thin‐film silicon solar cells. Compared to the classical approach, where wet‐chemically texturized ZnO:Al on planar glass is used, this approach allows a reduction in the as‐deposited ZnO:Al thickness of almost 70% while at the same time, thanks to the good light trapping capability of the glass texture the efficiency of the cells was maintained at the high level of 10.9%.

     

Signatures and possible evidence for supersymmetry at the CERN collider

For certain ranges of masses of the supersymmetric partners of the gluons, quarks and W-bosons, it is expected that a few events of production and decay of the partners could be observed at the CERN pp? collider. The characteristic signatures are events with $\text{?±}\text{j}\textcolor{red}{}\text{, ?±}\text{jj}\textcolor{red}{}\text{,}\text{jjj}\textcolor{red}{}\text{,}\text{jj}\textcolor{red}{}\text{and j}\textcolor{red}{}$ where ?^± is an isolated charged lepton, j is a hadron jet and

stands for missing p_T. Some recently reported events are of this type.     

Superior electric storage in de‐alloyed and anodic oxidized Ti–Ni–Si glassy alloy ribbons

Ti–Ni–Si glassy alloy supercapacitors, devices that store electric charge on their TiO₂ surfaces that contain many nanometer‐sized cavities, display many advantages over other power‐source technologies. The use of de‐alloying and anodic oxidization methods has made possible the synthesis of a TiO₂ surface accessible to electron trapping. Until recently, no studies have addressed the “dry” electric storage in light glassy alloys. Our device realizes AC electric storage from 193 to 453 K with a voltage variation from 10 to 150 V, and DC capacitance of ～4.8 F (～52.8 kF/cm³), on the basis of electric double layers, deep electronic trapping sites and Shottky barriers. Further gains could be attained with surface optimization.