Ultrafast Fiber Bragg Grating Interrogation for Sensing in Detonation and Shock Wave Experiments

Abstract

Abstract:Chirped fiber Bragg grating (CFBG) sensors coupled to high speed interrogation systems are described as robust diagnostic approaches to monitoring shock wave and detonation front propagation tracking events for use in high energy density shock physics applications. Taking advantage of the linear distributed spatial encoding of the spectral band in single-mode CFBGs, embedded fiber systems and associated photonic interrogation methodologies are shown as an effective approach to sensing shock and detonation-driven loading processes along the CFBG length. Two approaches, one that detects spectral changes in the integrated spectrum of the CFBG and another coherent pulse interrogation approach that fully resolves its spectral response, shows that 100-MHz-1-GHz interrogation rates are possible with spatial resolution along the CFBG in the 50 µm to sub-millimeter range depending on the combination of CFBG parameters (i.e., length, chirp rate, spectrum) and interrogator design specifics. Results from several dynamic tests are used to demonstrate the performance of these high speed systems for shock and detonation propagation tracking under strong and weak shock pressure loading: (1) linear detonation front tracking in the plastic bonded explosive (PBX) PBX-9501; (2) tracking of radial decaying shock with crossover to non-destructive CFBG response; (3) shock wave tracking along an aluminum cylinder wall under weak loading accompanied by dynamic strain effects in the CFBG sensor.

Extreme Environment Sensing Using Femtosecond Laser-Inscribed Fiber Bragg Gratings

“…From a sensing perspective, such structures allow for truly continuous high spatial resolution measurements of, for example, strain and crack formation in a composite laminate [ 125 ], or temperature and strain distributions within photonic lightwave circuit packages [ 126 ]. For harsh environments, CFBGs when coupled to high speed interrogation systems are a robust approach for continuous spatial measurements of shock wave and detonation front propagation within energetic materials or explosives [ 127 , 128 ]. The propagation distance over which the shock wave can be measured is limited by the length of the CFBG.…”

Development of a Shock and Detonation Velocity Measurement System Using Chirped Fiber Bragg Gratings

“…Their integration needs to be improved and better understood to increase the sensitivity. Therefore, new experiments were recently carried out using a dynamic dispersive spectrometer [36,37] in order to dynamically measure the entire reflected spectrum of the CFBG. Such a system was developed to measure pressure levels in inert and HE materials using monochromatic FBGs, but it can also detect any defect or delay in the shortening process of a CFBG during an SDT, for instance.…”

High Speed, Localized Multi-Point Strain Measurements on a Containment Vessel at 1.7 MHz Using Swept-Wavelength Laser-Interrogated Fiber Bragg Gratings

“…These have been demonstrated at 100 MHz repetition rates for measuring the detonation wavefront and even some strain in the detonation process [ 13 , 14 ]. These experiments are often very fast (few 10s of microseconds) while also having such high pressures that the gratings are sometimes cleanly destroyed in the experiment with no measurable strain behavior.While the technology for this work is well developed, it is cost prohibitive to many labs interested in non-destructive testing.Indeed, the high bandwidth scopes alone cost well over $100K while only providing recording times of up to 2 ms. Additionally, such high repetition rates in the light source limit the number of samples that can be made in a single measurement.For example, a 50 GS/s scope measuring data from a grating interrogated by a 100 MHz laser will only have 500 points in each measurement [ 13 ]. This is a sacrifice of fine resolution for fast recording speeds in order to achieve these state-of-the-art measurements.…”