Ultrafast photonic systems for FBG sensing in detonation and shock wave experiments

Ultrafast high speed photonics are shown to provide the necessary temporal and spectral information required for understanding FBG response under impulsive loading from either high explosive detonation or an inert shock wave interaction. Demonstration of both, chirped and uniform, silica based FBGs are presented for sensing under harsh conditions that vary from thermal ignition in high explosives to inert tracking of high pressure shock waves. Ultrafast laser based chirped pulse methods are used to time-stretch and streak the spectral response of the FBG sensor to provide information about material response under loading. Coherent broadband pulses from a femtosecond modelocked fiber laser at 1560 nm are used to illuminate and interrogate the FBG at a repetition rate of 100 MHz. After reflecting off the FBG, chromatic dispersion is applied to time stretch the pulse and separate spectral channels for detection with a 35 GHz photoreceiver and recording with a 25 GHz digitizing oscilloscope. Results include pressure wave tracking in weak inert shocks and pressure measurements in thermal ignition of high explosives detonation. The focus of the presentation is present the method and tools used for this approach to high speed FBG sensing.