Study On Transmission Of Energy And Driving Characteristics In Optical Fiber Laser Flyer

Laser Initiating explosive devices use optical fibers instead of wires,so as to realize the isolation of energetic materials and electrical systems,and be insensitive to interference such as electrostatic discharge and electromagnetic radiation.Therefore,Laser Initiating explosive devices can adapt to complex electromagnetic environment,which is an important development direction of safe initiation technology in the future.As an important laser initiation technology,laser flyer initiation technology has its unique advantages in initiation safety and instantaneity.However,at present,the split design is still used in the aspect of flyer energy exchange element and optical fiber in China.This method has some problems,such as low energy coupling coefficient between flyer energy exchange element and optical fiber end,poor reliability and so on.The integrated optical fiber flyer energy exchange element,which integrates optical fiber and flyer film,is very beneficial to improve the flyer energy exchange efficiency.Aiming at the coupling transmission of laser energy by optical fiber and the energy conversion between laser and flyer in the integrated optical fiber flyer energy conversion element,this paper focuses on the influence of alignment error and other factors on the coupling transmission efficiency of optical fiber,the design and preparation of optical fiber flyer energy conversion element,the laser driving characteristics of optical fiber flyer,and the interaction between laser and flyer film.The main conclusions are as follows:The influence of alignment error,i.e.axial error and radial error,on the coupling transmission characteristics of optical fiber is studied by ZEMAX software.The simulation results show that the coupling transmission efficiency decreases with the increase of axial error;when the radial error increases to a certain value,the coupling transmission efficiency decreases in a cliff jumping manner.On this basis,it is verified by experiments,and it is measured that the axial error adjustment range of 1.0mm and 0.8mm core diameter fiber is 0～4.5mm and 0～2mm,and the radial error adjustment range of 1.0mm and 0.8mm core diameter fiber is 0～0.45mm and 0～0.4mm.The effects of different laser energy on1.0mm The research shows that the maximum injection energy of 1.0mm and 0.8mm core diameter fibers is 109.8m J,the maximum output energy is 85.4m J and 69.4m J respectively,and the maximum coupling efficiency is 85.7%and 83.6%respectively.The coupling transmission efficiency of conical fiber is between 23.3%and 39.0%under the laser injection energy of 46.4m J.Based on Gurney theory,the thickness of laser flyer energy exchange element is deduced.The results show that the total thickness of optical fiber laser flyer film layer should not be less than 4μm.The thickness of laser ablation layer film shall be 2.2μm.Al-Al₂O₃-Al（preset thickness 0.6μm-1μm-4.4μm）was prepared on the end face of quartz fiber by magnetron sputtering.The composite film is characterized by SEM and EDS.The results show that the interface of different material layers of the composite film is clear,has obvious layered structure,and the film thickness is consistent with the preset.The driving speed of the optical fiber flyer energy exchange element is measured by PDV velocity measurement system.The average speeds of the 0.8mm and 1.0mm core diameter split optical fiber flyer are 1417m/s and 1036m/s respectively when the laser injection energy is 79.4m J,and the average speeds of the 0.8mm and 1.0mm core diameter integrated optical fiber flyer are 2200m/s and 1910m/s respectively when the laser injection energy is 46.4m J,when the laser injection energy is 79.4m J,the average speeds of 0.8mm and 1.0mm core diameter integrated optical fiber flyer are 1727m/s and 1287m/s respectively.The velocity curve of flyer and the impact morphology of flyer on PMMA sheet are analyzed.It shows that the driving speed of integrated optical fiber flyer energy converter is higher under the same conditions.The flyer is easy to split and disperse in the process of movement.In the process of integrated optical fiber flyer velocity measurement,the damage inside the optical fiber is analyzed and considered to be due to the"secondary focusing"inside the optical fiber and the reflection of Al film.The energy conversion mechanism between optical fiber output laser and optical fiber flyer energy exchange element is analyzed,and the energy conversion efficiency constant is calculated by flyer speed and optical fiber output laser energy.The calculation results show that the efficiency constant of integrated flyer energy exchange element with 1.0mm core diameter is 60%,which has high energy conversion efficiency of laser driven flyer movement.The plasma plume generated by the laser driven integrated optical fiber flyer film is photographed and recorded by the ultra-high speed camera.The research shows that when the laser drives the integrated optical fiber flyer film,there is obvious plasma generation in 0～210ns and plasma annihilation in 330ns～680ns,according to the PDV velocity measurement curve,it is inferred that the growth period of the plasma plume plays a role in driving and accelerating the flyer,while the plasma plume shock wave in the attenuation period can not overcome the air pressure on the outer surface of the flyer and accelerate the flyer,which will reduce the velocity of the flyer.The impact characteristic parameters of optical fiber flyer are calculated by the critical initiation energy criterion of heterogeneous explosives.The results show that with the increase of laser energy,the velocity of flyer increases,the impact pressure and the value of²τalso increases,the value of²τis only related to the final velocity of flyer,not to the selection of optical fiber core diameter.