Development And Applications Of 532 Nm Fiber-optic Displacement Interferometer

Dynamic response,mechanical and physical properties of condensed matter subjected to fast shock loading configure a main body of shock wave physics researches.Shock wave physic-s is widely used in aerospace,geological exploration,defense industry,transportation and other fields.Basic methodology of shock wave physics research concerns wave propagation in con-densed matter and its analysis.Speed of a shock wave is generally on the order of acoustic velocity in a condensed matter(10 km/s).Hence,a fast photo-electronic diagnostics with nano-second resolution is required for measurement of the waves.Because of its advantages of non-contact,broad scope,good temporal and speed resolutions,interferometer velocimetry had became the working horse device in the field of shock wave physics research after it had been invented.And it is under progressive development for new systems with better performance and wider applications to meet new diagnostic requirements of shock wave physics research which is also under development.In this paper,laser interferometer velocimetry is systematically studied including theo-retical principles,technical requirements,data processing methods,limiting factors,applicable conditions and so on.We designed and built a 532 ns wavelength laser displacement interfer-ometry system.Static and dynamic validation experiments had been designed and performed for checking performance of the new system in comparison with traditional instruments.The main work of this paper includes the followings:1:Development history and application range of laser interferometer velocimetry are sim-ply introduced.Its basic structure and principle are briefly described.We analyse the influence of various factors on interference fringe.The factors include spectral width of light source,initial phase,Modulation Depth of Signal.When the optical path of signal and reference is not equal,single frequency laser is used to ensure small spectral width and stable phase difference for signal and reference respectively.In this way,high quality interference fringes can been obtained.When the light intensity of signal is equal to reference,the modulation degree of interference signal is maximum.2:Short time Fourier transform is the most common way in fringe signal.We analysed the advantages and disadvantages of several widely used window functions.In the further analysis of STFT,we find that there is a prescribed minimum for the product of time resolution and velocity resolution.Time window can't been changed as the frequency change and must more than a stripe cycle.To overcome these shortcomings and reduce economic cost,we propose a fiber-optic displacement interferometer operated at short wavelength for low-velocity impact experiments in the case of only one laser.3:We establish the short wavelength interferometer with a 2*2 SM optical fiber coupler replacing optical fiber circulator and design contrastive experiment in dynamic state and static state respectively.Through static contrast experiment,the instrument with single fiber-optic path for transmitting both signal and reference light is less sensitive to external disturbance compared to those systems with two separate fiber-optic paths.532 nm fiber-optic displacement interferometer can get higher time resolution and more accurate HEL(Hugoniot Elastic Limit)in low-velocity impact.Besides,in order to eliminate the influence of intermodal dispersion in multimode fiber,multimode fiber is replaced by single-mode...