Ultrathin Picoscale White Light Interferometer

White light interferometry is a well established technique with diverse precision applications, however, the conventional interferometers such as Michelson, Mach-Zehnder or Linnik are large in size, demand tedious alignment for obtaining white light fringes, require noise-isolation to achieve sub-nanometric stability and importantly, exhibit unbalanced dispersion causing uncertainty in absolute zero delay reference. Here, we demonstrate an ultrathin white light interferometer enabling picometer resolution by exploiting the wavefront division of a broadband incoherent light beam after transmission through a pair of micrometer thin identical glass plates. Spatial overlap between the two diffracted split wavefronts readily produce high-contrast and stable white light fringes, with unambiguous reference to absolute zero path-delay position. The colored fringes evolve when one of the ultrathin plates is rotated to tune the interferometer with picometric precision over tens of µm range. Our theoretical analysis validates formation of fringes and highlights self-calibration of the interferometer for picoscale measurements. We demonstrate measurement of coherence lengths of several broadband incoherent sources as small as a few micrometer with picoscale precision. Furthermore, we propose a versatile double-pass configuration using the ultrathin interferometer enabling a sample cavity for additional applications in probing dynamical properties of matter.

Study on the Sintering and Mg Composition Effect on MgB2 Superconducting Bulks and Wires Synthesized by Powder-in-Sealed-Tube Method

Numerous research efforts aimed at the MgB2 (Magnesium diboride) as a superconducting material due to its higher critical temperature than Nb-based superconductors such as NbTi, Nb3Sn. Nowadays MgB2 is becoming more popular as the candidate to be applied on medical devices and large-scale applications because of its full coherence lengths, improved critical current density and fields, and simple crystal structure. In this study, we fabricated the 4 mm MgB2 superconducting wires by mixing stoichiometric mole ratio of Mg: B with 1.0:2.0 and 1.1:2.0 through the Powder-In-Sealed-Tube (PIST) method to optimize high critical temperature (TC) than the conventional MgB2 bulk and wire. Furthermore, we decreased the diameter of 4 mm to 1.8 mm wire and analyze the effect of critical temperature. The specimens were sintered at a different temperature to investigate the sintering effect of MgB2 superconducting wire. The resistivity versus temperature relationship, surface morphology, and crystal phase was characterized using Cryogenic system, SEM (Scanning Electron Microscopy), and XRD (X-ray Diffractometer), respectively. We optimized the high Tc,onset for the bulk and 4 mm wire compared to other studies that are 42.1K and 40.3K respectively at 800°C sintered temperature. Finally, the results suggest that the stoichiometric ratio of MgB2 exhibited excellent feasibility to prepare conventional MgB2 superconducting wire.

Unraveling the Effect of Defects, Domain Size, and Chemical Doping on Photophysics and Charge Transport in Covalent Organic Frameworks

We present a novel theoretical approach to understanding the effect of electronic defects, domain size, and chemical dopants on the infrared spectral line shape and three-dimensional charge transport of positively charged polarons (“holes”) in doped (and undoped) Covalent Organic Frameworks (COFs). The simulated spectra are in excellent agreement with very recent measurements conducted on Iodine doped COF films. Through a detailed systematic analysis, we can also determine the polaron coherence lengths both along the 2D COF plane (intraframework) and through the molecular columns (interframework). The coherence lengths are important quantities in determining the anisotropic charge mobilities and conductivities in such films and are therefore of major interest in understanding the operation of organic electronic devices such as transistors and solar cells. By obtaining the first quantitative agreement with iodine doped TANG-COF, we identify well defined spectral signatures that provides conclusive evidence on why doped COFS have so far shown lower bulk conductivity compared to doped polythiophenes.

Unraveling the Effect of Defects, Domain Size, and Chemical Doping on Photophysics and Charge Transport in Covalent Organic Frameworks

We present a novel theoretical approach to understanding the effect of electronic defects, domain size, and chemical dopants on the infrared spectral line shape and three-dimensional charge transport of positively charged polarons (“holes”) in doped (and undoped) Covalent Organic Frameworks (COFs). The simulated spectra are in excellent agreement with very recent measurements conducted on Iodine doped COF films. Through a detailed systematic analysis, we can also determine the polaron coherence lengths both along the 2D COF plane (intraframework) and through the molecular columns (interframework). The coherence lengths are important quantities in determining the anisotropic charge mobilities and conductivities in such films and are therefore of major interest in understanding the operation of organic electronic devices such as transistors and solar cells. By obtaining the first quantitative agreement with iodine doped TANG-COF, we identify well defined spectral signatures that provides conclusive evidence on why doped COFS have so far shown lower bulk conductivity compared to doped polythiophenes.

Синтез тонких пленок ниобия на кремнии и исследование их сверхпроводящих свойств в области размерного кроссовера

Niobium films of 4–100 nm thickness were synthesized on a silicon substrate under ultrahigh vacuum conditions. Measurements of electrical resistance showed a high temperature of the superconducting transition Tc, in the range of 4.7–9.1 K, and extremely small transition widths ΔTc in the range of 260–11 mK. The dependences of Tc and ΔTc on the magnetic field were studied, and superconducting coherence lengths and mean free paths of the conduction electrons were determined for different thicknesses of the synthesized films. A specific effect of the magnetic field on ΔTc was found, which reveals a transition from three-dimensional to two-dimensional superconductivity at thicknesses below 10 nm. The dependences of Tc and ΔTc on the films thickness and the magnitude of the magnetic field are discussed in the framework of existing concepts of superconductivity in thin films of superconducting metals.

Temporal coherence properties of laser modules used in headlamps determined by a Michelson interferometer

In this work, an investigation of the temporal coherence properties of radiation which is emitted by laser modules integrated in headlamps is presented. The motivation for these measurements was difficulties concerning the field of classification for laser products which function as conventional headlamps. Based on an experimental setup including a Michelson interferometer, a goniophotometer and a spectrometer, coherence lengths of 92.5 and 147.0 μm are obtained for two different laser modules. The results show that the temporal coherence of the examined radiation is appreciably higher than the temporal coherence of conventionally produced white light. Therefore, at this point in time, laser modules used in headlamps cannot be considered as customary white light sources.

The LPM effect in sequential bremsstrahlung: nearly complete results for QCD

The splitting processes of bremsstrahlung and pair production in a medium are coherent over large distances in the very high energy limit, which leads to a suppression known as the Landau-Pomeranchuk-Migdal (LPM) effect. We continue study of the case when the coherence lengths of two consecutive splitting processes overlap (which is important for understanding corrections to standard treatments of the LPM effect in QCD), avoiding soft-emission approximations. Previous work has computed overlap effects for double splitting g → gg → ggg. To make use of those results, one also needs calculations of related virtual loop corrections to single splitting g → gg in order to cancel severe (power-law) infrared (IR) divergences. This paper provides calculations of nearly all such processes involving gluons and discusses how to organize the results to demonstrate the cancellation. In the soft emission limit, our results reproduce the known double-log behavior of earlier authors who worked in leading-log approximation. We also present a first (albeit numerical and not yet analytic) investigation of sub-leading, single IR logarithms. Ultraviolet divergences appearing in our calculations correctly renormalize the coupling αs in the usual LPM result for leading-order g → gg.

h/e oscillations in interlayer transport of delafossites

Microstructures can be carefully designed to reveal the quantum phase of the wave-like nature of electrons in a metal. Here, we report phase-coherent oscillations of out-of-plane magnetoresistance in the layered delafossites PdCoO2 and PtCoO2. The oscillation period is equivalent to that determined by the magnetic flux quantum, h/e, threading an area defined by the atomic interlayer separation and the sample width, where h is Planck’s constant and e is the charge of an electron. The phase of the electron wave function appears robust over length scales exceeding 10 micrometers and persisting up to temperatures of T > 50 kelvin. We show that the experimental signal stems from a periodic field modulation of the out-of-plane hopping. These results demonstrate extraordinary single-particle quantum coherence lengths in delafossites.

Differential Study of Projectile Coherence Effects on Double Capture Processes in p + Ar Collisions

We have measured differential yields for double capture and double capture accompanied by ionization in 75 keV p + Ar collisions. Data were taken for two different transverse projectile coherence lengths. A small effect of the projectile coherence properties on the yields were found for double capture, but not for double capture plus ionization. The results suggest that multiple projectile–target interactions can lead to a significant weakening of projectile coherence effects.