| In the high sensitivity infrared weak and small target detection,such as target infrared radiation detection and infrared spectrum detection,the background infrared radiation is much larger than the target radiation,so the effective deduction of the background is one of the key technologies that the project must solve.Therefore,a realtime background subtraction scheme is proposed by using vibrating mirror(VM)in the system.The other two functions of the VM in the system are: modulating the target signal and providing the reference signal for the subsequent signal processing system to extract the target signal;The phase relation between the fundamental and the second harmonic is used to realize the precise infrared tracking.Therefore,the VM is the foundation of the whole large-scale system and the core of the core.The increase of the performance requirement of high-frequency VM not only brings great difficulty in improving the frequency,but also puts forward the urgent need for the study of the dynamic characteristics of high-frequency galvanometer.Because the high-frequency mirror only plays a modulation role when it vibrates,the dynamic surface shape and other dynamic characteristics of the high-frequency mirror will have a direct impact on the optical performance of the system,such as the imaging quality and the optical modulation effect,and then directly affect the performance of large-scale systems.However,the dynamic characteristics of the high-frequency VM are unknown,and the measurement of the dynamic shape of the high-frequency VM has not been published.Therefore,it is of great practical significance and application value to study the dynamic characteristics of the high frequency VM.This subject is guided by the high-frequency galvanometer and its dynamic characteristics,especially the measuring technology of dynamic surface,and makes a thorough study and analysis of the existing measuring methods,and makes full use of the advantages of high-precision real-time interferometric measurement,etc.,through the innovation of related key technologies,the dynamic surface measurement system of high-frequency VM is realized.The main work is as follows:First of all,according to the demand of large-caliber high-frequency VM,dualdynamic magnetic resonance driving mirror with double torsion bar structure(DDVM)is proposed.A complete mathematical model including free vibration model and excited vibration model is presented.According to the model,the conditions of obtaining high frequency and large amplitude are given.The scope of optical scanning is 0.58°and the frequency of vibration is 3033 Hz when the optical aperture of the mirror is Φ40×56.The measured frequency is less than 2.1% compared with the result of simulation and the result of analytical calculation according to the mathematical model,which verifies the correctness of the mathematical model and simulation analysis of DDVM.By measuring the gain curve,the bandwidth of DDVM is obtained,and the maximum gain coefficient,the damping coefficient and the differential equation of DDVM are obtained.Secondly,the technical route based on interferometry is established.A technique of generating multi-field interference(MFI)is proposed.The constraint conditions of MFI generation by pulse laser are given.Compared with the traditional method of producing one interference fringe at the same time,the proposed method can be simultaneously acquiring three interference patterns in the same frame image,the problem that it is difficult to measure the time series image in real time by traditional interference method is solved,and the interference pattern of MFI is obtained by experiment.In addition,this method is different from the traditional method in that a single frame is used to capture the MFI interference pattern instead of a continuous laser.This method can be used not only in pulse laser but also in continuous laser.This technique provides a basis for measuring the dynamic surface shape of VM.Then,the unwrapping algorithm of the MFI interference patten to understand the wavefront aberration of the measured surface is studied.Three-interferogram method,fringe scanning method,single interferogram method and wavelet transform method are investigated in detail.According to the characteristics of MFI images,an optimal phase difference unwrapping algorithm based on image correlation is proposed,which can calculate the phase distribution of the surface shape corresponding to the MFI interference pattern,the wavefront aberrations corresponding to the surface of VM are obtained.The effectiveness of the algorithm is verified by experiments.The numerical solution of phase difference optimization can be obtained by finite iteration,and the Algorithm is fast and stable.The RMS repeat error of the wave aberration calculated by this algorithm is less than λ/2000,and the wave aberration is insensitive to the time noise and the instability of the laser source.In addition,the technique of capturing the MFI interference pattern with dynamic surface information is studied when the VM vibrates.According to the dynamic characteristics of VM,a Long Exposure Short Pulse Synchronous Phase Lock(LSPL)technique is proposed,the position synchronization signals form a lock-phase relation of tens of nanoseconds between VM vibration phase,laser pulse and camera exposure.Compared with the high-speed projective camera,the high-frequency camera is used to acquire the dynamic image.The method in this paper uses the low-cost commercial camera to acquire the 3033 Hz vibrating surface interference pattern at 10 fps.Compared with the traditional interference method,this method can measure the dynamic surface shape of vibration,but the traditional interference method has been invalid.Finally,On the basis of the above key technologies,the data acquisition,analysis and verification experiments of each key link are carried out respectively.A dynamic surface measurement system is established,and the dynamic surface is obtained by calculating the capured MFI interference pattern with the method of phase calculation.A complete technical route from mathematical model to design simulation and development,as well as dynamic surface shape and other dynamic characteristics measurement of high frequency VM is formed. |
