Abstract
High pressure shock profiles are monitored using a long Fiber Bragg Grating (FBG). Such thin probe, with a diameter of
typically 150 μm, can be inserted directly into targets for shock plate experiments. The shocked FBG’s portion is
stressed under compression, which increases its optical group index and shortens its grating period. Placed along the 2D
symmetrical axis of the cylindrical target, the second effect is stronger and the reflected spectrum shifts towards the
shorter wavelengths. The dynamic evolution of FBG spectra is recorded with a customized Arrayed Waveguide Grating
(AWG) spectrometer covering the C+L band. The AWG provides 40 channels of 200-GHz spacing with a special flattop
design. The output channels are fiber-connected to photoreceivers (bandwidth: DC - 400 MHz or 10 kHz – 2 GHz).
The experimental setup was a symmetric impact, completed in a 110-mm diameter single-stage gas gun with Aluminum
(6061T6) impactors and targets. The FBG’s central wavelength was 1605 nm to cover the pressure range of 0 – 8 GPa.
The FBG was 50-mm long as well as the target’s thickness. The 20-mm thick impactor maintains a shock within the
target over a distance of 30 mm. For the impact at 522 m/s, the sustained pressure of 3.6 GPa, which resulted in a Bragg
shift of (26.2 ± 1.5) nm, is measured and retrieved with respectively thin-film gauges and the hydrodynamic code
Ouranos. The shock sensitivity of the FBG is about 7 nm/GPa, but it decreases with the pressure level. The overall
spectra evolution is in good agreement with the numerical simulations.
