Time Divided Laser Interfence Velocimetry

With the advantages of non contact measuring, high time resolution (～ns), high precision (<2%) and wide dynamic range (>10 km/s), laser interferometer velocimetry has become one of the standard techniques in the experimental research of shock wave physics and explosion physics, and has extensively been applied to many fields such as conventional weapons, detonator testing, interior ballistics, and electrical gun. Therefore, exploring and studying the new technique of laser interferometer velocimetry, enhancing its performance and expanding its applications have important academically value and favorable applicable potentials.Based on the traditional laser interferometer, and the tools of theoretical analysis, experiments, computational simulation, the dissertation studies the laser beat frequency interference comprehensively based on the two-beam interference. Then system design scheme, key techniques and technical implementation are explored.Finally the time-dividied laser interference velocimetry is proposed and the demonstrational experiments are done. The main points of this dissertation are listed as follows:1. The influencing factors and applicable conditions of two-beam laser beat frequency interference are analyzed.The principle of laser Doppler interferometer is deduced, the frequency range, modulation degree and phase components of Doppler sign that affects the interference and the applicable conditions are analyzed. The results show that the effect of initial phase,that is brought about by the temperature and vibration ,on the measuring results in the process of measuring and testing,can be ignored, while the intensity ratio of two beams can bring about a great effect to the measured signal's contrast.2. The feasibility of applying the single-mode fiber displacement interference system to diffuse reflection plane is analyzed.Combined with the structure of Michelson interferometer and Doppler interferometer, the mirror requirements for the plane to be measured and the bottleneck of this technique that is only applicable to lower velocity are analyzed theoretically and elucidated. By using the Fresnel approximation, the feasible of applying this technique to the diffuse reflection plane and single mode interferometer system is deduced, and the upper bound of velocity measuring for the displacement interference technique is explained theoretically. The study shows by using of single mode fiber, the measuring system can be used to measure the diffuse reflector. A single mode fiber displacement measuring system is designed and implemented, and verified respectively by a lower velocity vibration speaker and a higher velocity explosion targets. The experiment results show the consistency with the theory.3. The key techniques of laser beat frequency interference for velocity measuring are explored and the computational simulation and experiments design are carried out.The laser Doppler interferometer technique is analyzed theoretically. Combined with laser interferometer structure and the properties of measuring system, key techniques and development potentials are analyzed and some relative research work is unfolded. The multi-reflection etalon is designed that greatly improves the interferometer's sensitivity. The long-pulsed electro-optic switch outside the laser cavity is manufactured that expands the multiplier phototube's dynamic range and greatly improves the signal quality(noses to signals ratio).The methods of measuring distance, measuring time interval, and comparing velocity are explored for demarcating the velocity-per-fringe. This work provides a better base for evaluating the uncertainty of velocity interferometer. A computational simulation is also done for the factors of precision of VISAR, velocity resolution and integer streaking losing. All the theoretically analysis above are supported well by the corresponding dynamical experiments.4.The fiber VISAR and fiber velocity interferometer measuring system is designed.The principle of fiber VISAR is analyzed. Combined with the working property of single-mode fiber and fiber coupler's structure, a fiber VISAR system is designed and a dynamical experiment is done. Good results are obtained in the low velocity (Hopkins rod) experiment. A full single-mode fiber interferometer system that can be applied to diffuse reflector is designed, in which the contrast of the interference signals can reach 1. The results obtained in both at the low velocity Hopkins bar experiment and at the highvelocity laser-driven flyer experiments validate its effectiveness.5. The time-divided laser Doppler velocimetry is proposed and researched.A novel time-dividied laser Doppler velocimetry is analyzed theoretically and proposed. The applicable base and developmental potential of this technique is analyzed. The key techniques related are discussed and analyzed. Combined with the property of the explosion process, the appropriate interference measuring parameters is selected with respect to its key techniques. A primary experimental result is obtained with this technique. It effectively solves the bottleneck problem presented in the current technique. The data processing method is studied for the time-dividied laser Doppler velocimetry. By combination of the data processing method used in the laser beat frequency distance interference system and laser beat frequency velocity interference system, the dynamical experimental data is processed.