Multi-soliton complexes in mode-locked fiber lasers

We numerically investigate the formation of soliton pairs (bound states) in mode-locked fiber ring lasers in the normal dispersion domain. In the distributed mathematical model (complex cubic-quintic Ginzburg–Landau equation), we observe a discrete family of soliton pairs with equidistantly increasing peak separation. We show that stabilization of previously unstable bound states can be achieved when the finite relaxation time of the saturable absorber is taken into account. The domain of stability can be controlled by varying this relaxation time. Furthermore, we investigate the parameter domain where the region of stable bound states does not shrink to zero for vanishing absorber recovery time corresponding to a laser with an instantaneous saturable absorber. For a certain domain of the small-signal gain, we obtain a robust first level bound state with almost constant separation where the phase of the two pulses evolves independently. Moreover, their phase difference can evolve either periodically or chaotically depending on the small signal gain. Interestingly, higher level bound states exhibit a fundamentally different dynamics. They represent oscillating solutions with a phase difference alternating between zero and π.     

Low-frequency and broad band metamaterial absorber: design, fabrication, and characterization

We report a metamaterial absorber (MA) with a broad absorption band in the frequency region of 2–4 GHz, whose thickness is not limited to the quarter-wavelength. Theoretical and experimental results show that the absorber has two adjacent absorption apexes at 2.24 and 3.46 GHz, respectively, which are both related to the electric and magnetic resonances of the metamaterial. The absorption is over 68% in the whole wave band of 2–4 GHz provided the thickness of 4 mm. The distributions of the surface currents and the power loss density indicate that the surface currents produced by the electric and magnetic resonances are strongly consumed by the resistive patches. This low-frequency absorber has potential applications in many scientific and martial fields.     

Characterization of InGaAs and InGaAsN semiconductor saturable absorber mirrors for high-power mode-locked thin-disk lasers

We report a comparative study of carrier dynamics in semiconductor saturable absorber mirrors (SESAMs) containing InGaAs quantum wells and InGaAsN quantum wells (QWs). The static and dynamic reflectivity spectra were measured with a Fourier-transform-infrared-spectrometer and a pump-probe setup, respectively. The influence of rapid thermal annealing (RTA) on carrier dynamics was studied. Due to the reduction of defect states by RTA we observed an increase of the static reflectivity and an increase of the electron–hole recombination time.     

Passive Q-switching of erbium glass laser by magnesium aluminosilicate sitall with cobalt ions

We have studied the radiation output parameters for an erbium glass laser, lasing at a wavelength of 1.54 μm, with passive Q-switching by means of a cobalt-containing magnesium aluminosilicate sitall compared with a saturable absorber based on a magnesium aluminum spinel crystal with cobalt ions. We have shown that the output characteristics of the laser emission when using sitall are not inferior to the analogous characteristics of a laser based on a spinel crystal, and are practically independent of the temperature of the saturable absorber in the range 0°C–80°C. The duration (energy) of the output pulses was 70 nsec (∼4 mJ), the energy dispersion of the radiation pulse relative to the average value was no greater than 3%, the beam divergence was 2.8 mrad, the laser beam quality factor was M² = 1.2. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 1, pp. 126–131, January–February, 2007.     

Filter for strangeness in J^{PC} exotic four-quark states

Symmetrization selection rules for the decay of four–quark states to two J=0 mesons are analysed in a non – field theoretic context with isospin symmetry. The OZI allowed decay of an isoscalar exotic state to or is only allowed for four–quark components of the state containing one pair, providing a filter for strangeness content in these states. Decays of four–quark states are narrower than otherwise expected. If the experimentally observed enhancement in is resonant, it is qualitatively in agreement with being a four–quark state. Received: 10 May 2001 / Revised version: 15 August 2001 / Published online: 21 September 2001     

Fermonic zero-norm states and enlarged supersymmetries of Type II string

We calculate the NS–R fermionic zero-norm states of the type II string spectrum. The massless and some possible massive zero-norm states are seen to be responsible for the space-time supersymmetry. The existence of other fermionic massive zero-norm states with higher spinor–tensor indices correspond to new enlarged boson–fermion symmetries of the theory at high energy. We also discuss the R–R charges and R–R zero-norm states and justify the idea that the perturbative string does not carry the massless R–R charges. Received: 12 July 1999 / Revised version: 16 September 1999 / Published online: 17 March 2000     

Correlated wave functions to approach the bound excited states of Li- and Be-

Explicitly correlated wave functions including a Jastrow factor to take into account the dynamical correlation effects, and a multi determinant model wave function to account for the non–dynamical correlations are used to study some metastable excited states of the negative ions Li^- and Be^-. A detailed analysis of one– and two–body properties has been carried out for these states. In particular the single–particle density as well as both the two–body inter electronic and center of mass densities have been obtained. All the calculations have been performed by using the variational Monte Carlo method.     

Electromagnetic and microwave absorption properties of carbonyl iron and carbon fiber filled epoxy/silicone resin coatings

The microwave electromagnetic properties of carbonyl-iron particles as magnetic absorber and carbon fiber as conductive absorber filled insulating epoxy/silicone resin coatings were investigated. The complex permittivity of the coatings increased while the complex permeability remained almost constant in the frequency range of 2–18 GHz, when the carbon fiber content was increased and the carbonyl-iron content kept constant. The minimum reflection loss of the coatings shifted to the lower frequency region by increasing the carbon fiber content or coating thickness. When the content of carbonyl iron was 65 wt% and carbon fiber was 2 wt%, the reflection loss below −10 dB can obtain in the frequency range of 8–18 GHz with coating thickness being 1 mm.     

Remarks on 2–q-bit states

We distinguish six classes of families of locally equivalent states in a straightforward scheme for classifying all 2–q-bit states; four of the classes consist of two subclasses each. The simple criteria that we stated recently for checking a given state’s positivity and separability are justified, and we discuss some important properties of Lewenstein–Sanpera decompositions. An upper bound is conjectured for the sum of the degree of separability of a 2–q-bit state and its concurrence. Received: 17 July 2000 / Published online: 6 December 2000     

Ferromagnetic Interaction between Copper and Terbium Ions in Pentanuclear Cluster [Cu3Tb2(ClCH2COO)12(H2O)8] · 2H2O

For the first time the exchange interaction between copper and non-Kramers Tb³⁺ ions was studied by means of electron paramagnetic resonance (EPR). Features of the manifestation of this interaction in the EPR spectra of dimer fragments Cu–Tb and pentanuclear fragments Cu–Tb–Cu–Tb–Cu are analyzed. The possibility to determine the sign and value of this interaction from EPR spectra for the case when the lowest states of Tb³⁺ are the states |0〉, | ± 1〉 is shown. The exchange interaction between copper and trivalent terbium ions in the studied pentanuclear complex is ferromagnetic. Authors' address: Violeta K. Voronkova, Kazan Physical-Technical Institute, Russian Academy of Sciences, Sibirsky trakt 10/7, Kazan 420029, Russian Federation     

Generation of sub-100-psec pulses by a continuous solid-state laser with a YAG:V3+ crystal-based saturable absorber

On the basis of the self-consistent laser field theory, the possibility of generation of ultrashort pulses (USP) with duration of the order of tens of picoseconds in a continuous forsterite laser with a YAG:V³⁺ crystal-based saturable absorber is shown. The conditions for the stabilization of pulses were determined, and the character of their self-modulation instability was investigated. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 2, pp. 172–175, March–April, 2000.     

Physical processes in a laser-greenhouse target: Experimental results, theoretical models, and numerical calculations

The paper is devoted to recent results concerning investigation of physical processes occurring in a “laser greenhouse” target. Results of experimental and theoretical studies of laser-pulse interaction with a low-density absorber of the target, namely, with a porous substance having density close to the plasma critical density, are presented. On the basis of a vast cycle of experiments carried out in a number of laboratories, it is shown that the absorption of the laser radiation in porous media, including those with a density exceeding the critical one by at least a factor of 4 to 6, has a bulk nature and is distributed over the target depth. In particular, the laser-radiation absorption region in a porous substance with density 10⁻³–10⁻² g/cm³ is extended into the target 400–100 μm, respectively. The coefficient of absorption of laser radiation with intensity 10¹⁴–10¹⁵ W/cm² in porous substances, including those of the supercritical density, is 70–90%. Experiments have not shown enhanced (compared to a solid-state target) radiation intensity associated with a possible development of parametric instabilities in an extended laser plasma of low-density porous media, as well as noticeable contribution of fast electrons to the energy balance and their effect on the energy transfer. In this paper, theoretical models are developed explaining features of the laser-radiation absorption and energy transfer in porous media. These models are based on the phenomenon of laser-radiation interaction with solid components of a porous substance and plasma production inside pores and cells of the medium. The efficiency of energy conversion in the vicinity of the ignition threshold for the laser-greenhouse target is investigated in the case of an absorber having the above properties. Numerical calculations have shown that a thermonuclear-gain coefficient of 1 to 2 (with respect to the energy absorbed) is attained for a laser-radiation energy of 100 kJ. Translated from Preprint No. 58 of the P. N. Lebedev Physical Institute, Moscow (1999).     

SU(1,1) Lie Algebra Applied to the General Time-dependent Quadratic Hamiltonian System

Exact quantum states of the time-dependent quadratic Hamiltonian system are investigated using SU(1,1) Lie algebra. We realized SU(1,1) Lie algebra by defining appropriate SU(1,1) generators and derived exact wave functions using this algebra for the system. Raising and lowering operators of SU(1,1) Lie algebra expressed by multiplying a time-constant magnitude and a time-dependent phase factor. Two kinds of the SU(1,1) coherent states, i.e., even and odd coherent states and Perelomov coherent states are studied. We applied our result to the Caldirola–Kanai oscillator. The probability density of these coherent states for the Caldirola–Kanai oscillator converged to the center as time goes by, due to the damping constant γ. All the coherent state probability densities for the driven system are somewhat deformed. PACS Numbers: 02.20.Sv, 03.65.-w, 03.65.Fd     

Geometrothermodynamics of five dimensional black holes in Einstein–Gauss–Bonnet theory

We investigate the thermodynamic properties of 5D static and spherically symmetric black holes in (i) Einstein–Maxwell–Gauss–Bonnet theory, (ii) Einstein–Maxwell–Gauss–Bonnet theory with negative cosmological constant, and in (iii) Einstein–Yang–Mills–Gauss–Bonnet theory. To formulate the thermodynamics of these black holes we use the Bekenstein–Hawking entropy relation and, alternatively, a modified entropy formula which follows from the first law of thermodynamics of black holes. The results of both approaches are not equivalent. Using the formalism of geometrothermodynamics, we introduce in the manifold of equilibrium states a Legendre invariant metric for each black hole and for each thermodynamic approach, and show that the thermodynamic curvature diverges at those points where the temperature vanishes and the heat capacity diverges.     

A Partial Width Calculation of OZI-Allowed Charmonium Decays in a Coupled Channel Framework

Okubo–Zweig–Iizuka-allowed partial decay widths, masses, and total decay width of charmonium states are studied in a nonrelativistic coupled-channel framework based on microscopic effective quark interactions. With the help of the complex scale transformation, the coupled channel equation is easily solved under the proper boundary condition for resonances. The obtained result as a whole is very successful and encouraging for the traditional charmonium states including ψ(4040) whose features of mass and partial decay widths have been argued historically. The coupling mechanisms of these states are investigated by reducing artificially the channel coupling strengths little by little and finally turning the coupling off. The situations turn out to be quite different from what we would have naively supposed. Other solutions than the traditional charmonium states were obatined at the same time. Some of them are discussed in relation with new particles observed recently.     

Influence of the modal composition of the radiation on the oscillation dynamics of a CO2-laser with a saturable absorber

The influence of the modal composition (transverse modes of a single longitudinal mode) of the laser radiation on the oscillation dynamics of a CO₂-laser with a saturable absorber in the cavity is investigated. Passive Q-switching in initiation of the fundamental mode TEM₀₀ and the modes of the first family TEM₀₁ and TEM₁₀ is considered. It is established that in the case of multimode oscillations sequences of single pulses with an irregular change in their amplitude can be observed. The multimode oscillations obtained are compared with similar single-mode oscillations, and their special features and differences are discussed. Reported at the Second International Scientific and Technical Conference on Quantum Electronics, Minsk, November 23–25, 1998. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 5, pp. 681–687, September–October, 1999.     

Colliding-pulse harmonically mode-locked fiber laser

A Fabry–Perot semiconductor saturable absorber has been implemented in a colliding pulse configuration for stabilizing a harmonically mode-locked fiber laser. An environmentally stable CPM design is shown to enhance supermode suppression. Received: 24 October 2000 / Revised version: 28 November 2000 / Published online: 9 February 2001     

The Nambu–Jona–Lasinio model of light nuclei

The Nambu–Jona–Lasinio model of the deuteron suggested by Nambu and Jona–Lasinio (Phys. Rev. 124 (1961) 246) is formulated from the first principles of QCD. The deuteron appears as a neutron–proton collective excitation, i.e. a Cooper np–pair, induced by a phenomenological local four–nucleon interaction in the nuclear phase of QCD. The model describes the deuteron coupled to itself, nucleons and other particles through one–nucleon loop exchanges providing a minimal transfer of nucleon flavours from initial to final nuclear states and accounting for contributions of nucleon–loop anomalies which are completely determined by one–nucleon loop diagrams. The dominance of contributions of nucleon–loop anomalies to effective Lagrangians of low–energy nuclear interactions is justified in the large N _C expansion, where N _C is the number of quark colours. Received: 10 March 2000     

Vibrational states in odd deformed nuclei

The energies and wave functions of the nonrotational states in odd deformed nuclei are calculated in the quasiparticle-phonon model of the nucleus. It is shown that the number of vibrational states in odd nuclei is many times larger than the number of vibrational states in even-even nuclei. The wave functions of the overwhelming majority of these states with excitation energies in the range 1.5–2.5 MeV possess a dominant term of the type quasiparticle⊗phonon. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 8, 575–578 (25 April 1996)     

RETRACTED ARTICLE: Hydrogenated nanocrystalline silicon germanium thin films

Hydrogenated nanocrystalline silicon germanium thin films (nc-SiGe:H) is an interesting alternative material to replace hydrogenated nanocrystalline silicon (nc-Si:H) as the narrow bandgap absorber in an a-Si/a-SiGe/nc-SiGe(nc-Si) triple-junction solar cell due to its higher optical absorption in the wavelength range of interest. In this paper, we present results of optical, structural investigations and electrical characterization of nc-SiGe:H thin films made by hot-wire chemical vapor deposition (HW-CVD) with a coil-shaped tungsten filament and with a disilane/germane/hydrogen gas mixture. The optical band gaps of a-SiGe:H and nc-SiGe:H thin-films, which are deposited with the same disilane/germane/hydrogen gas mixture ratio of 3.4 : 1.7 : 7, are about 1.58 eV and 2.1 eV, respectively. The nc-SiGe:H thin film exhibits a larger optical absorption coefficient of about 2–4 in the 600–900 nm range when compared to nc-Si:H thin film. Therefore, a thinner nc-SiGe:H layer of ∼500 nm thickness may be sufficient for the narrow bandgap absorber in an a-Si based multiple-junction solar cell. We enhanced the transport properties as measured by the photoconductivity frequency mixing technique. These improved alloys do not necessarily show an improvement in the degree of structural heterogeneity on the nanometer scale as measured by smallangle X-ray scattering. Decreasing both the filament temperature and substrate temperature produced a film with relatively low structural heterogeneity while photoluminescence showed an order of magnitude increase in defect density for a similar change in the process.