Signal Gain Coefficient Research Articles

万焦耳级激光主放大器增益空间分布计算研究

A model which can simulate the pump dynamics process of the main amplifiers in million joules laser facility is built based on Monte Carlo algorithm and a ASAP software. The model contains 3D airspace and 1D time domain, and the evolution of the distribution of the energy in light pass surface in different pumping time with complete absorption on cladding is calculated, which is the same with the results mentioned in previous articles proving the accuracy of the model. The comparisons of average small signal gain coefficient are made between the cases when the residual reflection in cladding is taken into consideration or not. The results show that there is no significant difference when residual reflectivity is below 0.05%. The value of calculated average small signal gain coefficient with residual reflection is 6 percentage smaller than the measured value(4.42/m), which results from the use of part approximation during the simulation, the unconsidered spectrum of spontaneous radiation,the subsurface damage in the actual Nd:phosphate glass and so on.

Comparative study of the small signal gain coefficient and the dissipative losses evaluation methods of three-level microchip lasers

The paper describes the study of three methods of evaluation of the small signal gain coefficient and the dissipative losses of three-level microchip lasers. Engaging optimization procedure for cw lasers a very simple way to compare these methods was proposed. On the basis of laser generation investigations and calculations the most accurate method was chosen.

SIMO channel performance evaluation on indoor environment at 2.4 GHz

This work presents an experimental study of single-input multiple-output (SIMO) channel performance in the indoor radio propagation environment. Indoor channel measurements at the 2.4-GHz ISM frequency band have been conducted using a versatile channel sounder test-bed platform. A single transmitting antenna, four receiving antennas with two proposed geometries and a four-branch receiver circuitry were used in order to achieve channel sounder measurements exploiting baseband signal-processing techniques. In-depth investigation of SIMO wireless channel performance was realised through three types of metrics: signal strength, gain coefficient and capacity. Performance results indicate SIMO channel capacity enhancement and illustrate differences between the two proposed geometries.

Output power enhancement of optical pumped gas waveguide terahertz laser by promoting vibrational de-excitation

Based on rate equation and vibration relaxation theory, the paper analyze theoretically the enhancement of THz laser output power due to vibration de-excite rate of the active gas considering buffer gas ratio and waveguide core diameter. The results show that the method of adding 1:1 buffer gas or appropriately reducing the waveguide core diameter can improve work material saturated absorption intensity, THz laser small signal gain coefficient, THz laser output power and decrease the THz absorption of excited work material at the same time. Considering the two factors at the same time, the above results are better than those with only one factor, and the output power improved by 18%.

Effect of Er+3 Concentration on the Small Signal Gain Coefficient and the Gain in the Erbium Doped Fiber Amplifier

The small signal gain coefficient and the gain of Erbium-Doped Fiber Amplifier (EDFA) in the wavelength range (1400-1700 nm) for different erbium concentrations and different amplifier lengths are calculated and studied. A core graded-index and erbium-doped concentration, are optimized for an EDFA in simplified two-level model. There is evidence to show that, the gain increases with the erbium concentration and the amplifier length. Where the relation between the gain and the amplifier length at different wavelengths is linear with the maximum gain at &lambda = 1530 nm. Also the temperature dependence of the small signal gain coefficient and the gain at the peak wavelength of EDFA was studied which shows, slightly increase in the values of both with temperature. The value of the signal wavelength was chosen in the gain window of EDFA at 1530 nm.

Bidirectional amplifying architecture with twin pulses for laser fusion facilities

A novel method to amplify laser pulses in inertial confinement fusion (ICF) facilities is presented, in which twin pulses are employed to propagate along the amplifier in opposite directions. The resulting bidirectional propagation provides a substantially higher extraction efficiency of the amplifier than the conventional multipass architecture for an equal B limit, while keeping the laser fluence at a low level that is beneficial to system reliability and stability. It is shown that an extraction efficiency of ∼61% is achievable under a laser fluence of 10 J cm−2 (1ω, one pulse) in an 18-slab amplifier with the bidirectional amplifying design (slab thickness: 4 cm, small signal gain coefficient: 0.0525 cm−1), while the extraction efficiency is only ∼40% under a fluence of 13 J cm−2 (1ω) for the conventional multipass architecture.

Tunable time delay in active fiber Bragg grating coupler

Slowing down velocity and controlling time delay of optical pulses in fiber have many potential applications in optical communication systems, and a number of theoretical and experimental studies have been done. In this paper, the transmission spectrum and reflective spectrum of active fiber Bragg grating (FBG) couplers are studied, and the analytic expressions of dispersion and time delay are obtained. By changing the detuning and gain coefficient, different dispersions and time delays in active fiber Bragg grating coupler are obtained. The results show that different detunings and gain coefficients can result in various time delays, and thus tunable time delay could be achieved by changing signal frequency or gain coefficient.

Amplified Spontaneous Emission in Discharge-Driven HF Chemical Lasers

An amplified spontaneous emission (ASE) calculation model is established for the discharge-driven CW HF chemical gain module. By using a small signal gain coefficient and upper state population density, the ASE propagated outside the amplifier is calculated, where after, it is measured by experiment. The result of theory and experiment shows that the experimental results are consistent with the calculations from the simplified model. The difference between them is less than 15%. This simple model can effectively calculate the ASE in the amplifier of master oscillator-power amplifier configuration.

环形HYLTE喷管耦合段及光腔区流场的数值模拟

Heat energy loss fraction and corresponding equilibrium temperature of combustor are roughly estimated according to the heat transfer theory on condition that input fuels' mass flow rates, compositions pro- portioning and relevant configuration parameters of combustor are known. Entrance boundary parameters of primary nozzle are then determined. The flow field in coupling region and optical cavity of annular hypersonic low temperature (HYLTE) nozzle is numerically simulated using 3D computational fluid dynamics method. Spatial distributions of F atom mass fraction, static temperature and pressure are described. Small signal gain coefficient distributions for spectral lines in optical cavity are calculated by post processing of the flow field data. The experiments of measuring output spectrum and moving optical axis demonstrate the rationality of the computational model considering heat energy loss of combustor walls.

Amplification properties of vacuum ultraviolet Ar_2* produced by infrared high-intensity laser

We report optical amplification of Ar(2)* at 126 nm, pumped by optical-field-induced ionization (OFI) created by an infrared high-intensity laser. A gain-length product of 0.84 was obtained by using multipass amplification with a vacuum ultraviolet (VUV) cavity. The gain-length product was increased up to 4.3 through the use of single-pass amplification with a VUV reflector and a hollow 5.0 cm-long fiber. Similar small signal gain coefficients of 0.84 and 0.86 cm(-1) were obtained in two different experiments, in which OFI Ar plasma gain media were produced in free space filled with Ar and inside an Ar-filled hollow fiber.

掺钕磷酸盐玻璃的小信号增益性能

掺钕磷酸盐玻璃的小信号增益性能

Nonlinear Operation of a 2-D Triangular Lattice Photonic Crystal Laser

In this paper, an approximate method is presented for the analysis of 2-D triangular lattice photonic crystal laser operation above the threshold. Our approach is based on coupled wave equations, including gain saturation and spatial hole burning effects, and energy theorem. An expression is derived for the small signal gain coefficient for transverse magnetic modes as a function of the output power, losses, coupling strength depending on the shape of the primitive cell of a photonic crystal as well as the index contrast. The laser characteristics obtained reveals optimal coupling strength, for given structure parameters, for which maximal power efficiency of the laser structure is obtained.

掺钕磷酸盐玻璃的小信号增益性能

掺钕磷酸盐玻璃的小信号增益性能

掺钕磷酸盐玻璃的小信号增益性能

掺钕磷酸盐玻璃的小信号增益性能

Approximate Analysis of Nonlinear Operation of Square Lattice Photonic Crystal Laser

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> In this paper, an approximate method for the analysis of 2-D square lattice photonic crystal laser operation above the threshold is presented. Our approach is based on coupled wave equations, including gain saturation effect, and energy theorem. An expression for the small signal gain coefficient as a function of the output power, losses, coupling strength depending on the shape of the primitive cell of photonic crystal as well as index contrast, and active medium dimension is derived. Laser characteristics obtained reveal optimal coupling strength, for given structure parameters, for which maximal power efficiency of the laser structure is obtained. </para>

Study of Optimal Cavity Parameter in Optically Pumped D2O Gas Terahertz Laser

Heavy water gas (D2O gas) which owns special structure property, can generate terahertz radiation by optically pumping technology, and its 385 μm wavelength radiation can be widely used. In this research, on the base of semi-classical density matrix theory, we set up a three-level energy system as its theoretical model, a TEA-CO2 laser 9R (22) output line (λ = 9.26 μm) acted as pumping source, D2O gas molecules were operating medium, the expressions of pumping absorption coefficient G p and Terahertz signal gain coefficient G s were deduced. It was shown that the gain of Terahertz signal was related with the energy-level parameters of operating molecules and some operating parameters of the Terahertz laser cavity, mainly including cavity length. By means of iteration method, the output power density of Terahertz pulse signal was calculated numerically. Changing the parameter of cavity length and keeping others steady, the relationship curve between the output power intensity (Is) of Terahertz pulse laser and the operating cavity length (L) was obtained. The curve showed that the power intensity (Is) increased with cavity length (L) in a certain range, but decreased when the length (L) exceeded some value because of the absorption effect, and there was an optimal cavity length for the highest output power. We used a grating tuned TEA-CO2 laser as pumping power and a sample tube of variable length in 70–160 cm as terahertz laser operating cavity to experiment. The results of theoretical calculation and experiment matched with each other, and it is helpful for miniaturizing terahertz laser volume to make it practical.

High gain oscillators: Pulse propagation and saturation

Semianalytical formulas have been used to model the pulse propagation dynamics of low gain free electron laser oscillators. Most of the scaling relations, including pulse propagation effects, are limited to the low gain regime. We discuss the problem of oscillator devices operating with small signal gain coefficients larger than 1. We comment on the relevant physical aspects and show that gain and saturated power can be reproduced by a set of simple formulas, analogous to those employed for the low gain case.

Semiclassical theory of optically pumped D2O gas tera-Hz laser

By solving the density matrix equation of three-level molecular system, the pulsed laser pumped D2O gas terahertz laser was theoretically studied, the expression of terahertz signal gain coefficient(Gs)and the pumping signal absorption coefficient (Gp) were obtained, the output power density of terahertz laser was calculated numerically by iteration method. The calculation shows that the spectral characteristics of terahertz laser was in full accordance with the stimulated Raman emission. The signal frequency detuning obviously affects the amplification process, and there exists splitting in the curve because of the dipole of D2O gas molecule being disturbed by the field of pumping pulse. The theoretical spectrum is in good agreement with reported experimental results.

高マッハ数ランプノズルを用いた超音速流ヨウ素レーザーの数値シミュレーション

The adoption of three types of nozzle contours, the ramp nozzle, symmetric ramp nozzle, and symmetric swept-ramp nozzle, in chemical oxygen-iodine lasers with supersonic ejector-nozzle banks is examined by simulating the mixing and reacting flow fields numerically. The compressible Navier-Stokes equations with a detailed chemical kinetic model are solved using a full-implicit finite volume method. The numerical results show that streamwise vortices induced downstream of the base region of the nozzle array are enhanced with decreasing the length ls of diverging region in I2 nozzle. However, the optimum ls which results in a high small signal gain coefficient exists for each nozzle contour, since the mixing depends also on the size and location of the streamwise vortex. Therefore, the symmetric swept-ramp nozzle which produces strong streamwise vortices even with rather large ls is most preferable among the proposed nozzle contours. The pitot pressure in the mixing region obtained in the present calculation is approximately 10kPa which is ten times higher than that of conventional supersonic flow chemical oxygen-iodine lasers.

Estimation of molecular parameters in laser grade dyes: Coumarin 450 and Coumarin 460

Optical gain spectroscopy is exploited to examine photo-physical parameters viz. absorption and emission cross-sections, threshold pump rate, excited to ground state rate constant in two important molecules of Coumarin class of laser grade dyes. The results for the intensity dependent gain coefficient for ethanolic solutions of Coumarin 450 (C-450) and Coumarin 460 (C-460) have been presented in the concentration range from ∼1 × 10 −5 to ∼1 × 10 −2 mol/l under nitrogen laser excitation. The concentration dependent threshold pump rate, small signal gain coefficient and saturation parameter have also been investigated. The results have been explained in terms of variation of fluorescence lifetime with concentration that originates due to excited state absorption.