Continuous Detonation Velocity Measurement inside SEMTEX by using Mid-IR Photon Doppler Velocimeter

Our recent studies have demonstrated that Photon Doppler Velocimeter (PDV) operating in the 9–11 µm range (Mid-IR) offers a significant advantage in tracking shock velocities within non-transparent inert materials, such as High-Density Polyethylene (HDPE). It has higher time and spatial resolutions than a millimeter-wave interferometer. These properties have surged interest in tracking continuously the detonation wave profile inside an energetic material. The designed experiment used a plastic explosive SEMTEX with an expected detonation velocity around 6800 m/s. The explosive was placed within a 3D-printed housing and closed on the side by a 5-mm thick HDPE window. A 6-meter long hollow core fiber with 1dB/m losses was fixed perpendicular to the window that allows remote measurement. The beam has a limited divergence of 35 mrad inside the two materials. The laser wavelength was 9.25 µm and the probe output power was intentionally limited to 70 mW to prevent any laser ignition. The PDV measurements processed by spectrogram analysis successfully tracked the detonation within few mm of SEMTEX, with an apparent velocity (no index correction) of 8200 m/s, followed by a transmitted shockwave inside the HDPE at an apparent velocity of 3500 m/s. Additionally, the shockwave propagation inside the hollow core fiber at a velocity of 12 000 m/s was measured.