Experimental studies of high order soliton compression effect and gain characteristics in femtosecond laser pulses Er3+-doped fiber amplifier

Seed laser pulses with average power of 146 μW and pulse duration of 480 fs were amplified to 14.5 mW. The pulse duration was compressed to 260 fs using 6 m high concentration E³⁺ _r -doped fiber under forward pumping. The amplified signal pulse energy was 0.691 nJ (corresponding to a peak power of 2 657.7 W) and the repetition rate was 20.84 MHz. Spectrum breakup was observed simultaneously. The spectrum of pulses amplified by 3 m E³⁺ _r -doped fiber remains a single peak under different pump power. The amplified pulse duration was compressed abnormally with the increasing pump power using the backward pumping; that is, the amplified pulses were compressed with the increasing pump power under low pump power. When the pump power reached 38 mW, the shortest amplified pulse duration was 309 fs. With further increase in pump power, the amplified pulses began broadening, accompanied by a single peak spectrum under different pump power.     

Experimental studies of high order soliton compression effect and gain characteristics in femtosecond laser pulses E3+r-doped fiber amplifier

Seed laser pulses with average power of 146 μW and pulse duration of 480 fs were amplified to 14.5 mW. The pulse duration was compressed to 260 fs using 6 m high concentration E3+r-doped fiber under forward pumping. The amplified signal pulse energy was 0.691 nJ (corresponding to a peak power of 2 657.7 W) and the repetition rate was 20.84 MHz. Spectrum breakup was observed simultaneously. The spectrum of pulses amplified by 3 m E3+r-doped fiber remains a single peak under different pump power. The amplified pulse duration was compressed abnormally with the increasing pump power using the backward pumping; that is, the amplified pulses were compressed with the increasing pump power under low pump power. When the pump power reached 38 mW, the shortest amplified pulse duration was 309 fs. With further increase in pump power, the amplified pulses began broadening, accompanied by a single peak spectrum under different pump power.     

Experimental studies of high order soliton compression effect and gain characteristics in femtosecond laser pulses Er 3+-doped fiber amplifier

Seed laser pulses with average power of 146 μW and pulse duration of 480 fs were amplified to 14.5 mW. The pulse duration was compressed to 260 fs using 6 m high concentration E³⁺ _r -doped fiber under forward pumping. The amplified signal pulse energy was 0.691 nJ (corresponding to a peak power of 2 657.7 W) and the repetition rate was 20.84 MHz. Spectrum breakup was observed simultaneously. The spectrum of pulses amplified by 3 m E³⁺ _r -doped fiber remains a single peak under different pump power. The amplified pulse duration was compressed abnormally with the increasing pump power using the backward pumping; that is, the amplified pulses were compressed with the increasing pump power under low pump power. When the pump power reached 38 mW, the shortest amplified pulse duration was 309 fs. With further increase in pump power, the amplified pulses began broadening, accompanied by a single peak spectrum under different pump power.     

Amplification and compression of Ti:sapphire femtosecond pulses at high-repetition-rate

The experiment of the generation and amplification of femetosecond Ti:sapphire laser pulse at high repetition rate is reported. The laser pulses with minimum pulsewidth 15 fs, maximum spectrum width of 80 nm, average power of 200 mW are generated from a home-built self-mode-locked Ti:sapphire laser. As a seed pulse which is selected from the oscillator, the laser pulse is further amplified by using chirped-pulse-amplification technology in a Ti:sapphire amplifier from which a kind of pulses with single-pulse-energy of 100 uj, pulsewidth after compressing of 50 fs at 5 kHz repetition rate are produced. The system design and experimental results are discussed. Project supported by the National “Climbing Project” of China.     

Gain performances of 980 nm-pumped erbium-doped fiber amplifiers

Through the introduction of the overlapping factors between the light (pump and signal) intensities and the erbium doping distributions inside the fiber core, analytical solutions of homogeneously broadened two-level systems for erbium-doped fiber amplifiers pumped in the 980 nm absorption band have been derived from EDFA rate equations and light propagation equations in steady-state case. By using these deduced expressions and numerical simulated methods, important features characterizing the amplifiers such as gain, pump threshold power, optimum fiber length have been analyzed and discussed. Project supported by the Chinese Academy of Sciences.     

The essential spectrum of periodically stationary pulses in lumped models of short-pulse fiber lasers

In modern short-pulse fiber lasers, there is significant pulse breathing over each round trip of the laser loop. Consequently, averaged models cannot be used for quantitative modeling and design. Instead, lumped models, which are obtained by concatenating models for the various components of the laser, are required. As the pulses in lumped models are periodic rather than stationary, their linear stability is evaluated with the aid of the monodromy operator obtained by linearizing the round-trip operator about the periodic pulse. Conditions are given on the smoothness and decay of the periodic pulse that ensure that the monodromy operator exists on an appropriate Lebesgue function space. A formula for the essential spectrum of the monodromy operator is given, which can be used to quantify the growth rate of continuous wave perturbations. This formula is established by showing that the essential spectrum of the monodromy operator equals that of an associated asymptotic operator. Since the asymptotic monodromy operator acts as a multiplication operator in the Fourier domain, it is possible to derive a formula for its spectrum. Although the main results are stated for a particular experimental stretched pulse laser, the analysis shows that they can be readily adapted to a wide range of lumped laser models.     

Modeling the optical nonlinear effects on DFB-RF laser based on the transfer matrix method

In this paper, the operation of π-phase shifted distributed feedback Raman fiber (DFB-RF) laser above threshold condition is analyzed theoretically. The nonlinear optical phenomena such as self phase modulation (SPM) and cross phase modulation (XPM) have significant effect on the performance of DFB-RF laser. The numerical results show that the nonlinear effects cause to the saturation of output power and the value of saturated power is dependent on the fiber length. It is found that, the operation wavelength of stokes modes of DFB-RF laser varies in above threshold condition as a result of nonlinear optical properties of the fiber. Simulation is performed by using transfer matrix method to solve three coupled nonlinear wave equations which describe the propagation of pump, forward and backward Stokes waves. The nonlinear SPM and XPM effects are considered in the presented theoretical model.     

Imaging through flesh tissue using fs electronic holographic gating method

The experimental results of imaging through flesh tissue using fs electronic holographic gating method is reported. In the experiment, Ti: sapphire mode-locked laser is used as light source, of which the repetition rate is 100 MHz, central wavelength 800 nm, duration of pulse 20 fs, output power 80 mW. Tissue is a 7 mm thick chicken slice, and the imaged object is a metal wire with diameter of 0.5 mm. A general CCD is used to record holograms and a clear image of metal wire is obtained. Several relevant problems are discussed.     

Mathematical simulation of light pulse propagating within a microring resonator system and applications

This paper presents the very fascinating simulation results of light pulse traveling within a ring resonator system that have shown the unexpected results with various applications. The design system consists of a nonlinear microring/nanoring resonator system incorporating an add/drop filter. The proposed fabricated material used is InGaAsP/InP, which can provide the required output behaviors. Three different forms of input light pulses are Gaussian pulse, dark and bright soliton, whereas the suitable simulation parameters are input power, pulse width, ring radii and the material refractive indices. Three different forms of the results have been interpreted, whereas the dominants behaviors are such as Gaussian soliton, multisoliton and tunable dark soliton are described, and the potential applications for new laser sources, new communication bands and dynamic optical tweezers have been discussed.     

Spectral filtering for ultra-fast mode-locking in the normal dispersive regime

A theoretical model is developed which characterizes the physical process responsible for generating ultra-short, high-energy, mode-locked pulses in a normal GVD laser cavity with spectral filtering. Two physical parameters are critical to achieving optimal performance: the ratio of the filter bandwidth to the gain bandwidth and the placement of the output coupler in the laser cavity. The spectral filtering allows for the high-energy of typical normal GVD laser cavities to be maintained while the pulse intensity doubles and the FWHM reduces by an order of magnitude. This phenomenon is generic and ubiquitous to normal GVD mode-locking. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Beyond the Mean-Field Model of the Ring Cavity

The ring cavity device with large diffraction path in the free-space of the cavity cannotbe described within the mean-field model. It is shown to generate a large variety of monoconicaland multiconical patterns with wave and/or Türing modes, for anonlinear medium either made of two-level atoms or with a χ ⁽²⁾ crystal.Even in the limit of a single-longitudinal mode operation, monoconical structures can be differentfrom those predicted by the mean-field model. For instance, chaotic localized structures with anatomic medium and square patterns with a DOPO are presented.     

Optimising prediction model of centrifugal pump as turbine with viscosity effects

Performance conversion of a centrifugal pump as turbine from the known performance curves in pump mode is vital important in pump selection, power generation and investment assessment, especially under low Reynolds number operation conditions. Effects of Reynolds number on such a performance conversion have not been taken into account so far. In the paper, flow rate, head and output power and hydraulic efficiency conversion factors at zero efficiency/power, 0.8 part-load, best efficiency, 1.2 over-load and maximum flow rate points are defined and extracted from the performance curves of a centrifugal pump as turbine at five viscosities obtained by using CFD simulations. The conversion factors are correlated to impeller Reynolds number and a performance conversion model is proposed by employing 3rd and 4th order polynomials for the output power and head curves. New correlations of flow rate, head and efficiency conversion factors are also attempted in terms of specific speed and efficiency as well as impeller Reynolds number based on the data found in literature. The conversion model is a framework and can be useful for design of pump as turbine and its performance prediction, especially under variable liquid viscosity conditions.     

Angle- and time-resolved mass spectrometric study on pulsed laser ablation of an La-Ca-Mn-O target

Pulsed laser ablation (PLA) of an La₂O₃-CaO-MnO₂ target at 532 nm has been investigated by angle- and time-resolved quadrupole mass spectrometry. The results show that different kinds of metal oxides as well as metal ions and atoms are produced during the ablation at high laser fluence. The measured TOF spectra are fitted by multicomponent Maxwell-Boltzmann distribution with a stream velocity, which gives the translational energy of 6.34 and 0.43 eV for Mn⁺ ions and Mn atoms, respectively. It implies that ablated ions are mainly formed via a nonthermal process, while the neutral atoms mainly via a thermal one. The angular distributions of Mn + ions and Mn atoms can be described by a cos ⁿ θ and a bicosine function a cosθ+ (1-a)cos ⁿ θ, respectively. Possible mechanisms of laser ablation of La-Ca-Mn-0 are discussed. Project supported by the National Natural Science Foundation of China (Grant No. 29683001).     

Changes in the mechanical properties of polycarbonate produced by a powerful light flux

The effects of a laser beam on PC are examined in relation to the power and duration of the light pulse. In uniaxial tension there is a sharp change in the relative elongation of the irradiated specimens (pulse length 10^–3 sec); the elastic modulus and the molecular weight remain unchanged. Irradiation of PC with a giant pulse does not affect its mechanical properties.Mekhanika Polimerov, Vol. 4, No. 2, pp. 288–292, 1968     

Schliereneffekte bei organischen Farbstofflasern

The pump energy absorbed by the active molecules of flashlamp pumped dye lasers causes thermal inhomogeneities in the solvent, which alter the quality factor of the laser cavity. By means of a Schlieren method, the time dependent optical quality of the active medium has been investigated. Slowly varying Schlieren occur due to the nonuniformly heated flowing liquid and hence depend on the flow velocity. Rapidly varying Schlieren (sec time scale), give, rise to a modulation of the optical quality of the dye cell, which leads under certain conditions to a modulation of the laser output intensity (spiking).     

Reducing of birefringence of [111]-cut crystal rod using side-pumping and suitable crystal rotation

The beam quality and output power of high power solid-state lasers is influenced by birefringence. Inhomogeneous distribution of the thermal field inside the laser crystal rod occurs due to non-uniform absorption of the pump light inside the crystal and a heat sink only at boundaries. Due to the photoelastic effect, this distribution leads to inhomogeneous thermal strains and birefringence inside the rod. Plane stress and plane strain assumptions for an axially symmetric pumped crystal have been used formerly for analytical models for calculating the birefringence. This model leads in case of an [111]-cut crystal to an axially symmetric birefringence pattern. However, the shear strains in the axial-radial plane are neglected in this former models using plane stress and plane strain assumptions. This shear strains are taken into account by full 3D numerical calculations. A threefold symmetry pattern due to the anisotropic behaviour of the photoelastic tensor, which is contradictory to the ideal use of a radial or azimuthal polarized beam, is shown by results of the birefringence simulation. A laser rod pumped at three sides with threefold symmetry is analysed in order to reduce the effect of birefringence. In this case the absorption is not axially symmetric anymore. Within the crystal in regions where pumping is stronger, the pump light absorption and consequently the temperature, the strains and birefringence are higher. The degree of three-fold symmetry of birefringence will be reduced, if the region having a low birefringence due to the photoelastic effect is more strongly pumped than the rest of domain. This means the birefringence is affected by the rotation of crystal around its [111]-axis. By an optimal rotation with respect to the edges of the crystal, smallest birefringence can be obtained. For generating radial or azimuthal polarizations, the output beam of this laser device is therefore more suitable. (© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Fluorescence of YA103∶Er excited withns pulses of λ=377.6 nm

YA10₃Er (1.25 at %) is excited with the =377.6 nm emission of a Thallium laser. Upon absorption of this wavelength the⁴ G _11/2 levels of Er³⁺ are selectively populated. Fluorescence spectra in the wavelength range of 400 nm to 675 nm and the temperature dependence of the corresponding lifetimes are measured.

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Zusammenfassung YAlO₃Er (1.25 at %) wurde mit der =377.6 nm Emission eines Thalliumlasers angeregt. Durch Absorption dieser Wellenlänge werden selektiv die⁴ G _11/2 Niveaus von Er³⁺ bevölkert. Fluoreszenz-Spektren im Wellenlängenbereich von 400 nm bis 675 nm und die Temperaturabhängigkeit der entsprechenden Fluoreszenz-Lebensdauer wurden gemessen.

     

A generalization of anti-commutative rings arising from 2-varieties

Let R be a non-associative ring of characteristic not 2 or 3 which satisfies the identities (ab+ba)c = (ac+ca)b, a(bc+cb) = b(ac+ca), and a².a = a.a². It is proved that R is power asso-ciative, that if R is simple, then R is either anti-commutative or else commutative and associative. It is shown that if R is nil and semiprime, then R is anti-commutative, and an example of a prime ring of this type which is neither commutative nor anti-commu-tative is given.     

Research of processing techniques used in fabrication of solid oxide fuel cells and study of their selected properties

The processing techniques used in the fabrication of solid oxide fuel cells (SOFC) were studied. A fast, simple and convenient method of studying and fabricating SOFC was found. The properties of the single cell and the series stack of the SOFC were measured and studied. The maximum open voltage and short current density of the single cell are 1.18V and 360 mA/cm², respectively. And the maximum open voltage and short current density of the series stack of 7 cells are 7.30 and 400 mA/cm² respectively and the output power is about 2.0 w. Some simple applications were tried by using the SOFC series stack. Project supported by the National Plan Committee, Jilin Province Plan Committee, the National Natural Science Youth Fund Committee, Jilin Province Youth Science Fund Committee and the General Company of Transport and Energy of Jilin Province.