Self-induced laser line sweeping in double-clad Yb-doped fiber-ring lasers

International audienceExperimental observation of the self-induced laser line sweeping (SLLS) in fiber ring lasers is presented. The SLLS with the same gain fiber is studied in Fabry-Perot cavity for comparison. The SLLS effect manifests itself as a laser wavelength drift with speed of the order of nanometer per second from shorter to longer wavelengths across several nanometers and fast backward jump. Recently, the dynamics of the SLLS in a Fabry-Perot cavity fiber laser was qualitatively described by a dynamic grating induced by spatial-hole-burning in the ytterbium doped fiber where the lifetime of the grating was related to the self-sustained relaxation oscillations. In this paper we address possible discrepancies between the published theoretical model and earlier observations of SLLS, particularly in fiber-ring lasers.We show that the qualitative theoretical model developed for explaining SLLS in the Fabry-Perot cavity can be used also to explain the SLLS effect we observed earlier in fiber-ring lasers

Sudesna mjerenja γγ-raspada stanja 166Ho nastalih reakcijom (n,γ)

Levels of 166Ho were studied using thermal and average resonance neutron capture and with the (d,p) and (d,3He) reactions. We have devoted a large effort to the measurements of the γγ-coincidence spectra in the broad energy region 50 - 6243 keV. Based on these data and those of earlier studies, the levels are grouped into 23 rotational bands. Among them are 6 new ones. The results are in good agreement with the semiempirical and quasiparticle-phonon model, where Coriolis and residual interactions are taken into account. Details of model interpretation have been presented in a previously published paper.Proučavali smo stanja 166Ho nastala termičkim i prosječnim rezonantnim uhvatom neutrona, te (d,p) i (d,3He) reakcijama. Uložili smo velik trud u mjerenjima sudesnih γγ-spektara u širokom energijskom području od 50 do 6243 keV. Na osnovi tih i ranijih podataka, stanja su grupirana u 23 rotacijske vrpce. Među njima je i 6 novih. Ishodi su u suglasju s poluempiričkim i kvazičestično-fononskim modelom, uzimajući u obzir Coriolisovo međudjelovanje i rezidualne interakcije. Podrobnosti modelskog tumačenja objavljene u u ranijem članku

Cooperative Binding

Molecular binding is an interaction between molecules that results in a stable association between those molecules. Cooperative binding occurs if the number of binding sites of a macromolecule that are occupied by a specific type of ligand is a nonlinear function of this ligand’s concentration. This can be due, for instance, to an affinity for the ligand that depends on the amount of ligand bound. Cooperativity can be positive (supralinear) or negative (infralinear). Cooperative binding is most often observed in proteins, but nucleic acids can also exhibit cooperative binding, for instance of transcription factors. Cooperative binding has been shown to be the mechanism underlying a large range of biochemical and physiological processes

Thulium-doped optical fibers for fiber lasers operating at around 2 μm

The paper deals with spectral and lasing characteristics of thulium-doped optical fibers fabricated by means of two doping techniques, i.e. via a conventional solution-doping method and via a nanoparticle-doping method. The difference in fabrication was the application of a suspension of aluminum oxide nanoparticles of defined size instead of a conventional chloride-containing solution. Samples of thulium-doped silica fibers having nearly identical chemical composition and wave guiding properties were fabricated. The sample fabricated by means of the nanoparticle-doping method exhibited longer lifetime, reflecting other observations and the trend already observed with the fibers doped with erbium and aluminum nanoparticles. The fiber fabricated by means of the nanoparticle-doping method exhibited a lower lasing threshold (by »20%) and higher slope efficiency (by »5% rel.). All these observed differences are not extensive and deserve more in-depth research; they may imply a positive influence of the nanoparticle approach on properties of rare-earth-doped fibers for fiber lasers

Erbium and Al2O3 nanocrystals-doped silica optical fibers

Fibre lasers and inherently rare-earth-doped optical fibers nowadays pass through a new period of their progress aiming at high efficiency of systems and their high power. In this paper, we deal with the preparation of silica fibers doped with erbium and Al2O3 nanocrystals and the characterization of their optical properties. The fibers were prepared by the extended Modified Chemical Vapor Deposition (MCVD) method from starting chlorides or oxide nanopowders. Conventional as well as modified approaches led to a nanocrystalline mullite phase formation in the fiber cores in which erbium is dissolved. The proposed modified approach based on starting nanopowders led to improved geometry of preforms and fibers and consequently to the improvement of their background attenuation. Such nanocrystal -doped fibers can be used for ASE sources. Further improvement of fiber optical properties can be expected

The mechanism of regulation of hexokinase: new insights from the crystal structure of recombinant human brain hexokinase complexed with glucose and glucose-6-phosphate

Hexokinase I is the pacemaker of glycolysis in brain tissue. The type I isozyme exhibits unique regulatory properties in that physiological levels of phosphate relieve potent inhibition by the product, glucose-6-phosphate (Gluc-6-P). The 100 kDa polypeptide chain of hexokinase I consists of a C-terminal (catalytic) domain and an N-terminal (regulatory) domain. Structures of ligated hexokinase I should provide a basis for understanding mechanisms of catalysis and regulation at an atomic level.The complex of human hexokinase I with glucose and Gluc-6-P (determined to 2.8 A resolution) is a dimer with twofold molecular symmetry. The N- and C-terminal domains of one monomer interact with the C- and N-terminal domains, respectively, of the symmetry-related monomer. The two domains of a monomer are connected by a single alpha helix and each have the fold of yeast hexokinase. Salt links between a possible cation-binding loop of the N-terminal domain and a loop of the C-terminal domain may be important to regulation. Each domain binds single glucose and Gluc-6-P molecules in proximity to each other. The 6-phosphoryl group of bound Gluc-6-P at the C-terminal domain occupies the putative binding site for ATP, whereas the 6-phosphoryl group at the N-terminal domain may overlap the binding site for phosphate.The binding synergism of glucose and Gluc-6-P probably arises out of the mutual stabilization of a common (glucose-bound) conformation of hexokinase I. Conformational changes in the N-terminal domain in response to glucose, phosphate, and/or Gluc-6-P may influence the binding of ATP to the C-terminal domain