Nondegenerate four-wave-mixing-based radio frequency up/downconversion using a parametric loop mirror

We propose a method of reconfigurable radio frequency up/downconversion using a parametric optical loop mirror. The baseband optical signal can be unconverted to a carrier-suppressed radio-over-fiber signal at a wide range of frequencies without the help of optical filters to remove the optical carrier. Upconversion of up to 60 GHz and downconversion from 40 GHz for both single-channel and wavelength-division-multiplexing signals using the same setup are demonstrated.     

Nonlinear interactions with an ultrahigh flux of broadband entangled photons

We experimentally demonstrate sum-frequency generation with entangled photon pairs, generating as many as 40,000 photons per second, visible even to the naked eye. The nonclassical nature of the interaction is exhibited by a linear intensity dependence of the nonlinear process. The key element in our scheme is the generation of an ultrahigh flux of entangled photons while maintaining their nonclassical properties. This is made possible by generating the down-converted photons as broadband as possible, orders of magnitude wider than the pump. This approach can be applied to other nonlinear interactions, and may become useful for various quantum-measurement tasks.     

Jump inversions of algebraic structures and Σ‐definability

It is proved that for every countable structure and a computable successor ordinal α there is a countable structure which is ‐least among all countable structures such that is Σ‐definable in the αth jump . We also show that this result does not hold for the limit ordinal . Moreover, we prove that there is no countable structure with the degree spectrum for .     

Heavy Heparin: A Stable Isotope‐Enriched,Chemoenzymatically‐Synthesized,Poly‐Component Drug

Heparin is a highly sulfated, complex polysaccharide and widely used anticoagulant pharmaceutical. In this work, we chemoenzymatically synthesized perdeuteroheparin from biosynthetically enriched heparosan precursor obtained from microbial culture in deuterated medium. Chemical de‐N‐acetylation, chemical N‐sulfation, enzymatic epimerization, and enzymatic sulfation with recombinant heparin biosynthetic enzymes afforded perdeuteroheparin comparable to pharmaceutical heparin. A series of applications for heavy heparin and its heavy biosynthetic intermediates are demonstrated, including generation of stable isotope labeled disaccharide standards, development of a non‐radioactive NMR assay for glucuronosyl‐C5‐epimerase, and background‐free quantification of in vivo half‐life following administration to rabbits. We anticipate that this approach can be extended to produce other isotope‐enriched glycosaminoglycans.     

Coherent addition of two dimensional array of fiber lasers

Configurations for efficient free space coherent addition of four separate fiber lasers arranged in two dimensional array are presented. They include compact and robust interferometric combiners that can be inserted either inside or outside the cavity of the combined lasers system. The results reveal that over 85% combining efficiency can be obtained.     

Phase locking and coherent combining of high-order-mode fiber lasers

Efficient free-space configurations for phase locking and coherent addition of two fiber lasers, each operating with a high-order mode, are presented. Experimental results reveal that when the two fiber lasers are coupled, the polarization and modal distribution of one are imposed on the other. Coherent addition with a combining efficiency larger than 90% was achieved.     

Dirac-Schwinger commutation relations on a lattice

Low-frequency excitations of a one-dimensional chain of oscillators propagate like waves with a uniform velocity. Therefore this lattice is Lorentz invariant on a macroscopic scale. The Dirac-Schwinger commutation relations are constructed explicitly and shown to have the correct limit for long wavelengths. A similar test could be used to check the Lorentz invariance of lattice field theories.     

Measurement of the fine structure separation in the 42 D term of lithium by the method of electric field induced level anti-crossing

An electric field is employed to convert lithium 4² D Zeeman level crossings into anti-crossings. The lithium atoms are excited by electron impact. The anti-crossings are detected by the change in polarization of the light emitted in the 4² D-2² P transition. From the corresponding values of the magnetic field, we obtain 400 (10) MHz for the zero field fine structure energy separationE(4² D _5/2)-E(4² D _3/2).     

A measurement of the ground state hyperfine splitting for Li-like fluorine ions by nuclear quantum beats

The technique of nuclear quantum beats (perturbed angular correlations) has been applied to the investigation of the hyperfine splitting of the²S_1/2 ground state in Li-like fluorine ions. Using the 197 keV state in¹⁹F as a probe, a value of 73.1 (1.5) GHz was found for the hf splitting. This result is compared with theoretical predictions.