Magnetic anomaly detection based on magnetic gradient tensor has become more and more important in civil and military applications. Compared with methods based on magnetic total field or components measurement, magnetic gradient tensor has some unique advantages. Usually, a magnetic gradient tensor measurement array is constituted by four three-axis magnetometers. The prominent problem of magnetic gradient tensor measurement array is the misalignment of sensors. In order to measure the magnetic gradient tensor accurately, it is quite essential to calibrate the measurement array. The calibration method, which is proposed in this paper, is divided into two steps. In the first step, each sensor of the measurement array should be calibrated, whose error is mainly caused by constant biases, scale factor deviations and nonorthogonality of sensor axes. The error of measurement array is mainly caused by the misalignment of sensors, so that triplets’ deviation in sensors array coordinates is calibrated in the second step. In order to verify the effectiveness of the proposed method, simulation was taken and the result shows that the proposed method improves the measurement accuracy of magnetic gradient tensor greatly.
A 100 W-class all-fiber linearly-polarized single-mode fiber laser at 1120 nm with an optical pump efficiency of 50% was demonstrated. Linearly polarized output with a polarization extinction ratio of 15 dB is achieved by a cavity that selects both wavelength and polarization. Macro pulse operations with square shaped pulses from 100 μs to 1 ms are achieved without relaxation oscillation. The exact wavelength of pump diode is found to be crucial for amplified spontaneous emission and parasitic oscillation in high power 1120 nm fiber laser. Effects of inhomogeneous spectral broadening and temperature dependent absorption are proposed to explain experimental observations.
KEYWORDS: Control systems, Control systems design, Fiber amplifiers, Optical amplifiers, Optical fibers, Fiber lasers, Phase measurement, Negative feedback, Oscillators, High power fiber amplifiers
Combining fiber laser beams are of current interest for scaling lasers to high average output power. The Master
Oscillator Power Amplifier (MOPA) configuration is important in fiber laser beam combination. The efficiency of
coherent beam combining is depended on the phase control precision of the system mostly, which is equivalent to the
closed loop output phase noise. In this paper, a simplified negative feedback model of the phase control system is
constructed to study the optimum design of the system. The effects of the transfer function of the system on the phase
noise of the optical fiber amplifier, the measured noise and the stability of the system are analyzed. The relationship
between the closed loop output noise and the system parameters is analyzed and calculated. The results show that there is
a set of system parameters to minimize the closed loop output noise for different phase noise of the optical fiber amplifier,
and for a fixed set of system parameters, the closed loop output noise of the system almost changes linearly with the
change of the input noise. The effective means to achieve optimal system parameters for higher degree of control
precision are obtained.
A two-dimensional program is applied to simulate the chemical dynamic process,gas dynamic process and lasing process of a combustion-driven CW HF overtone chemical lasers.Some important parameters in the cavity are obtained.The calculated results include averaged pressure and temperature,zero power gain coefficient, laser spectrum, output power, chemical efficiency and overtone efficiency.Based on the numerical simulation,the influence of entering gas flow parameter,nozzle structure and nozzle array length on the performance of HF overtone lasers are investigated separately.Because of small zero power gain coefficient of each HF overtone spectral line,the saturation degree of gain medium in the cavity is the most important parameter to influence the overtone efficiency of HF lasers.
A two-dimensional program was applied to simulate the chemical dynamic process, gas dynamic process and lasing process of a combustion-driven CW HF overtone chemical lasers. Some important parameters in the cavity were obtained. The calculated results included HF molecule concentration on each vibration energy level while lasing, averaged pressure and temperature, zero power gain coefficient of each spectral line, laser spectrum, the averaged laser intensity, output power, chemical efficiency and the length of lasing zone.
The performance change of photovoltaic (PV) indium stibium (InSb) detector illuminated by continuous wave (CW) chemical oxygen iodine laser (COIL) with different power density was measured and the damage threshold interval of the detector was achieved to be 26(0.89S) approximately 113(1.4S)W/cm2. Using the integrating sphere technology, the thermal coupling coefficient of InSb crystal material to CW COIL was measured to be 0.664 +/- 0.004. Compared with the theoretical result, the thermal coupling coefficient measured was a little bigger due to the effect of the surface defect of InSb material. The principle and damage mechanism of PV InSb detector was reviewed. The temperature rise and performance change of PV InSb detector illuminated by CW COIL were calculated with 1D thermal model. The calculated results was consistent with the experimental results.
The He is usually used as diluent in combustion cw hydrogen/deuterium fluoride (HF/DF) chemical lasers. Sometimes, the N2 is also used as diluent in cw HF/DF chemical laser, because N2 is more cheaper than the He. It was thought that the efficiency of cw HF/DF laser with N2 diluent was lower than that of HF/DF laser with He diluent since the molecular weight of N2 is heavier than that of He. In this paper, the performance of cw DF chemical lasers with He and N2 diluent was investigated. The small signal gain, power spectral distributions, cavity pressure, power and efficiency of DF lasers with these two diluents have been calculated using a finite-difference technique for the numerical integration of the steady and unsteady Navier-Stokes equation with reactive flow (compressibility scaling method-CSM), which was developed in the chemical gas dynamic laboratory of the state institute of applied chemistry in Russia. The numerical results show that the efficiency of DF lasers with N2 diluent is not lower than that of the lasers with He diluent.
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